Steven Declerck

Dr. Steven Declerck

Senior Researcher
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Visiting Address

Droevendaalsesteeg 10
6708 PB Wageningen

+31 (0) 317 47 34 00

The Netherlands



I am an ecologist interested in the mechanisms through which populations and communities respond to human-induced changes in their environment


Steven Declerck is an aquatic ecologist who addresses a broad range of ecological and microevolutionary questions, with a focus on freshwater zooplankton. In 2001, he received his PhD-thesis at Ghent University (Belgium) with greatest distinction. After having worked at the University of Leuven (KULeuven, Belgium) as researcher on several research projects, he was awarded two consecutive postdoctoral fellowships from FWO-Vlaanderen (2004-2007 and 2007-2010). During this period (2008), he was also awarded an FWO travel grant for a one-year stay as a guest researcher at the University of British Colombia (UBC, Vancouver, Canada). In 2010, he started a tenure track at the Department of Aquatic Ecology (NIOO-KNAW) where he became tenured as a senior scientist in 2015. In 2018, he was appointed guest professor and in 2019 he received the position of associate professor at KULeuven.

Research groups



  • 2015–Present
    Tenured senior scientist at NIOO-KNAW
  • 2019–Present
    Associate professor "Community Ecology and Aquatic Foodwebs" at the University of Leuven (KULeuven), Belgium
  • 2018–2019
    Guest professor at the University of Leuven (KULeuven). Belgium
  • 2010–2015
    Tenure track at NIOO-KNAW
  • 2007–2010
    Postdoctoral fellow FWO
  • 2004–2007
    Postdoctoral fellow FWO

Editorial board memberships

  • 2022–Present
    Freshwater Biology
  • 2016–Present
  • 2011–Present
    Journal of Plankton Research
  • 2006–2009

PhD students

  • 2019–Present
    Shuwen Han
    Promotors and Copromotors: Paul van den Brink (copromotor: Steven Declerck)
  • 2015–2021
    Wei Zhang
    NIOO-KNAW; Utrecht University
    Promotors and Copromotors: Ellen van Donk (copromotor: Steven Declerck)
  • 2014–2021
    Kimberley D. Lemmen
    NIOO-KNAW; Utrecht University
    Promotors and Copromotors: Ellen van Donk (copromotor: Steven Declerck)
  • 2015–2019
    Libin Zhou
    NIOO-KNAW; Utrecht University
    Promotors and Copromotors: Ellen van Donk (copromotor: Steven Declerck)
  • 2012–2019
    Sven Teurlincx
    NIOO-KNAW; Utrecht University
    Promotors and Copromotors: Ellen van Donk (copromotor: Steven Declerck
  • 2007–2014
    Pieter Lemmens
    Promotors and Copromotors: Luc De Meester (copromotor: Steven Declerck)
  • 2009–2013
    Mekonen Teferi
    KULeuven; Mekelle University
    Promotors and Copromotors: Luc De Meester (copromotors: Jos Snoeks and Steven Declerck)
  • 2006–2011
    Sarah Rousseaux
    Promotors and Copromotors: Luc De Meester (copromotor: Steven Declerck)
  • 2007–2011
    Maarten Vanderstukken
    Promotors and Copromotors: Koenraad Muylaert (copromotor: Steven Declerck)
  • 2005–2009
    Jorge Coronel
    KULeuven; Universidad de San Simon
    Promotors and Copromotors: Luc Brenkdonck (copromotor: Steven Declerck)
  • 2004–2008
    Tadesse Dejenie
    KULeuven; Mekelle University
    Promotors and Copromotors: Luc De Meester (copromotor: Steven Declerck)
  • 2002–2006
    Ximena Aguilera
    KULeuven; Mekelle University
    Promotors and Copromotors: Luc De Meester (copromotor: Steven Declerck)

Ancillary activities


Peer-reviewed publications

  • Limnology and Oceanography

    Rapidly evolving zooplankton in a salinizing world

    Shuaiying Zhao, Libin Zhou, Guangjie Chen, Steven A.J. Declerck
    Salinization is a worldwide emerging threat to freshwater systems. It can be caused by various salts with different toxicity to freshwater organisms. Populations of freshwater organisms have been shown to rapidly evolve adaptations to salinity, yet it remains unclear whether adaptation to one salt increases tolerance or, conversely, susceptibility to other salts. Using an experimental evolution approach, we subjected replicate populations of a planktonic monogonont rotifer species (Brachionus calyciflorus Pallas) to non-saline and NaCl-enriched environments. A subsequent multigenerational common garden (CG) transplant experiment demonstrated rapid microevolutionary adaptation to salinity. A second CG experiment provided evidence that adaptation to NaCl increases tolerance mainly to CaCl2 but to a much lesser extent to Na2SO4. Increased tolerance to CaCl2 was associated with increased tolerance to Ca2+ ion toxicity. In contrast, acquired tolerance to Na2SO4 could not be shown to involve an improved ability to cope with
    ion toxicity. Our results highlight that the evolution of cross-tolerance may expand the temporal and spatial dimensions under which the ecological consequences of salt adaptation apply.
  • Ecology Letters

    SEED: A framework for integrating ecological stoichiometry and eco‐evolutionary dynamics

    Rana W. El‐Sabaawi, Kimberley Lemmen, Punidan D. Jeyasingh, Steven A.J. Declerck
    Characterising the extent and sources of intraspecific variation and their ecological consequences is a central challenge in the study of eco-evolutionary dynamics. Ecological stoichiometry, which uses elemental variation of organisms and their environment to understand ecosystem patterns and processes, can be a powerful framework for characterising eco-evolutionary dynamics. However, the current emphasis on the relative content of elements in the body (i.e. organismal stoichiometry) has constrained its application. Intraspecific variation in the rates at which elements are acquired, assimilated, allocated or lost is often greater than the variation in organismal stoichiometry. There is much to gain from studying these traits together as components of an ‘elemental phenotype’. Furthermore, each of these traits can have distinct ecological effects that are underappreciated in the current literature. We propose a conceptual framework that explores how microevolutionary change in the elemental phenotype occurs, how its components interact with each other and with other traits, and how its changes can affect a wide range of ecological processes. We demonstrate how the framework can be used to generate novel hypotheses and outline pathways for future research that enhance our ability to explain, analyse and predict eco-evolutionary dynamics.
  • Ecology of Freshwater Fish

    The introduced Arapaima gigas in the Bolivian Amazon: Trophic position and isotopic niche overlap with native species

    Danny Rejas, Thierry Oberdorff, Steven A.J. Declerck, Monika Winder
    Non-native fish species may generate major ecological impacts on native assemblages. This study aims to assess the potential impact of the introduced Arapaima gigas on native fish assemblages in two oxbow lakes of the Bolivian Amazon. Stable isotope data were used to determine trophic position (TP) and isotopic niche overlap, to evaluate potential predation and competition interactions, respectively. Results suggest that A. gigas is more an omnivore than a top predator, as often claimed. Arapaima gigas occupied an intermediate TP between detritivore/herbivore and piscivore fish species and showed broader isotopic niche compared to most native species analysed. The isotopic niche of A. gigas significantly overlapped with most native fish species in one lake (i.e. Lake Mentiroso), while there was low niche overlap in the second (i.e. Lake Miraflores). Given its omnivorous tendencies, the predation impact of A. gigas on other fish species is likely less than currently claimed and likely varies with the food web structure of the ecosystem. More precise data on resource availability and use are necessary to infer whether niche overlap will have negative impacts on native fish species through potential competitive interactions. Increasing our understanding on the processes generating impact of these introductions on resident communities through food web ecology will pave the way for better resource management and conservation efforts.
  • Oikos

    How sharp is the knife? Herbivore and carnivore sensitivity to resource stoichiometric quality

    Cédric L. Meunier, Maarten Boersma, Steven A.J. Declerck, Cecilia Laspoumaderes

    While understanding feeding preferences of herbivores and carnivores is of major importance in ecology, we still know very little on the sensitivity of different functional groups to suboptimal stoichiometric resource quality. Here, we apply concepts of ecological stoichiometry to shed light on differences in the nutritional requirements of herbivores and carnivores, and to make predictions on the influence of suboptimal resource stoichiometric quality on the fitness of these different consumers to. Herbivores generally experience more variation in the quality of their resource than carnivores do, and these differences have likely shaped the extent to which coping mechanisms have evolved. Consequently, we expect 1) herbivores to maintain their stoichiometric homeostasis over a broader range of resource stoichiometry than carnivores, 2) the threshold elemental ratio (TER), i.e. the dietary carbon to nutrient ratio which maximizes fitness, of herbivores to be higher than that of carnivores, 3) a narrower and sharper knife-edge response in carnivores than herbivores and 4) asymmetric knife-edge responses indicating a higher sensitivity to the diet quality that consumers are not used to dealing with, namely nutrient limitation in carnivores and nutrient excess in herbivores. Our study poses that documenting the ranges of resource quality where consumer fitness declines in diverse organisms is a very promising avenue to increase our understanding of community composition and food web functioning.
  • Water Research

    Restoring gradual land-water transitions in a shallow lake improved phytoplankton quantity and quality with cascading effects on zooplankton production

    Land-water transition areas play a significant role in the functioning of aquatic ecosystems. However, anthropogenic pressures are posing severe threats on land-water transition areas, which leads to degradation of the ecological integrity of many lakes worldwide. Enhancing habitat complexity and heterogeneity by restoring land-water transition areas in lake systems is deemed a suitable method to restore lakes bottom-up by stimulating lower trophic levels. Stimulating productivity of lower trophic levels (phytoplankton, zooplankton) generates important food sources for declining higher trophic levels (fish, birds). Here, we study ecosystem restoration project Marker Wadden in Lake Markermeer, The Netherlands. This project involved the construction of a 700-ha archipelago of five islands in a degrading shallow lake, aiming to create additional sheltered land-water transition areas to stimulate food web development from its base by improving phytoplankton quantity and quality. We found that phytoplankton quantity (chlorophyll-a concentration) and quality (inversed carbon:nutrient ratio) in the shallow waters inside the Marker Wadden archipelago were significantly improved, likely due to higher nutrient availabilities, while light availability remained sufficient, compared to the surrounding lake. Higher phytoplankton quantity and quality was positively correlated with zooplankton biomass, which was higher inside the archipelago than in the surrounding lake due to improved trophic transfer efficiency between phytoplankton and zooplankton. We conclude that creating new land-water transition areas can be used to increase light and nutrient availabilities and thereby enhancing primary productivity, which in turn can stimulate higher trophic levels in degrading aquatic ecosystems.
  • Hydrobiologia

    Beyond Daphnia: a plea for a more inclusive and unifying approach to freshwater zooplankton ecology

    Luc De Meester, Steven A.J. Declerck, Kemal Ali Ger
    Zooplankton plays a pivotal role in lentic water bodies, linking planktonic primary producers to higher trophic levels and being a cornerstone of the planktonic food web of ponds and lakes. Because of its ease of culture, large size, rich ecology, abundance in northern temperate lakes where limnology is rooted, and the ability to work with clones, Daphnia has, in the last centuries grown to become a key model system in ecology, evolution, and ecotoxicology. Consequently, a vast majority of freshwater zooplankton ecology focuses on the role of Daphnia. While generating essential insights, this has also deviated attention from the broad ecological impact of other zooplankton. Here, we emphasize how other zooplankton taxa have an important impact in nature - often in qualitatively different ways than Daphnia. We illustrate this point by focusing on two key zooplankton functions (herbivory and stoichiometry) and suggest research to capitalize on the success story of mechanistic ecological, eco-evolutionary, and genomic Daphnia work to develop a richer set of model organisms. We currently have the tools to do so and integrating mechanistic insights in multispecies settings would foster a better understanding of the rich diversity and ecology of freshwater zooplankton.
  • Ecology

    An experimental test of the growth rate hypothesis as a predictive framework for microevolutionary adaptation

    Kimberley Lemmen, Libin Zhou, Spiros Papakostas, Steven A.J. Declerck

    The growth rate hypothesis (GRH) posits that the relative body phosphorus content of an organism is positively related to somatic growth rate, as protein synthesis, which is necessary for growth, requires P-rich rRNA. This hypothesis has strong support at the interspecific level. Here, we explore the use of the GRH to predict microevolutionary responses in consumer body stoichiometry. For this, we subjected populations of the rotifer Brachionus calyciflorus to selection for fast population growth rate (PGR) in P-rich (HPF) and P-poor (LPF) food environments. With common garden transplant experiments, we demonstrate that in HP populations evolution toward increased PGR was concomitant with an increase in relative phosphorus content. In contrast, LP populations evolved higher PGR without an increase in relative phosphorus content. We conclude that the GRH has the potential to predict microevolutionary change, but that its application is contingent on the environmental context. Our results highlight the potential of cryptic evolution in determining the performance response of populations to elemental limitation of their food resources.
  • Freshwater Biology

    Intrinsic postzygotic barriers constrain cross-fertilisation between two hybridising sibling rotifer species of the Brachionus calyciflorus species complex

    Brachionus calyciflorus is a recently described monogonont rotifer species complex that comprises four species. The observation of hybridisation between two of these species challenges this species delimitation. The mechanisms of reproductive isolation essential to the maintenance of species integrity remain unclear. Here, we conducted upscaled hybridisation experiments to obtain large numbers of hybrid and non-hybrid dormant propagules. Through hatching assays, we compared the zygote viability of hybrid with non-hybrid dormant propagules. Furthermore, we investigated populations of F1 hybrid clones and assessed their clonal growth rate and the ability to reproduce sexually. Our results demonstrated higher rates of morphological abnormality and associated mortality in dormant propagules of hybrids compared to non-hybrids yet hatching rates of healthy-looking propagules proved similar. F1 hybrids exhibited high clonal population growth rates, nevertheless, we also observed strong differences between clones and a strong influence of parental genotype identity. Two-thirds of the F1 hybrid clones showed a low incidence of sexual reproduction and almost never produced dormant propagules. Clones with high population growth rates seemed to invest less in sexual reproduction. Our results clearly demonstrate the existence of intrinsic postzygotic barriers caused by relatively high mortality of dormant propagules. Furthermore, the low ability of most hybrid clones to engage in sexual reproduction may reduce the long-term fitness of hybrid clones. These postzygotic barriers probably impede genetic exchange between parental species and contribute to the maintenance of their integrity.
  • Ecosphere

    Phytoplankton functional composition determines limitation by nutrients and grazers across a lake productivity gradient

    M. Schulhof, Dedmer Van de Waal, Steven A.J. Declerck, J.B. Shurin
    Functional trade-offs among ecologically important traits govern the diversity of communities and changes in species composition along environmental gradients. A trade-off between predator defense and resource competitive ability has been invoked as a mechanism that may maintain diversity in lake phytoplankton. Trade-offs may promote diversity in communities where grazing- and resource-limited taxa coexist, which determines the extent to which communities are resource- or consumer-controlled. In addition, changes in temperature may alter nutrient demands and grazing pressure, changing the balance between the two regulating factors. Our study aims to understand whether a trade-off between grazer vulnerability and nutrient limitation promotes coexistence of phytoplankton functional groups in communities that differ in trophic status, and how this trade-off may shift with warming. We conducted multifactorial experiments manipulating grazing, nutrients, and temperature in phytoplankton communities from three Dutch lakes varying in trophic status, and used a trait-based approach to classify functional groups based on grazing susceptibility. We found no associations between susceptibility to grazing and response to nutrient additions in any of the communities or temperature regimes, indicating that a competition–defense trade-off is unlikely to explain diversity within the tested communities. Instead, we observed a tendency toward both a higher grazing resistance and weaker nutrient limitation along with a shift in the functional composition of phytoplankton in communities across a gradient from low to high productivity.
  • Functional Ecology

    Experimental evidence of rapid heritable adaptation in the absence of initial standing genetic variation

    The success of genetically depauperate populations in the face of environmental change is contrary to the expectation that high genetic diversity is required for rapid adaptation. Alternative pathways such as environmentally induced genetic modifications and non-genetic heritable phenotypes have been proposed mechanisms for heritable adaptation within an ecologically relevant time frame. However, experimental evidence is currently lacking to establish if, and to what extent, these sources of phenotypic variation can produce a response.
    To test if adaptation can rapidly occur in the absence of initial standing genetic variation and recombination in small populations, we (a) exposed replicate monoclonal populations of the microzooplankton Brachionus calyciflorus to a culturing regime that selected for phenotypic variants with elevated population growth with either high or low phosphorus food for a period of 55 days and (b) examined population level response in two fully factorial common garden experiments at day 15 and 35 of the exposure experiment.
    Within six generations, we observed heritable local adaptation to nutrient limitation. More specifically, populations with a history of exposure to low P food exhibited higher population growth rates under low P food conditions than populations with a high P exposure history. However, the capacity for such a response was found to vary among clones.
    Our study finds that although standing genetic variation is considered essential for rapid heritable adaptation, the rapid emergence of de novo genetic variation or alternative sources of phenotypic variation could aid in the establishment and persistence of low-diversity populations.
  • Hydrobiologia

    A combination of host ecology and habitat but not evolutionary history explains differences in the microbiomes associated with rotifers

    Ester M. Eckert, Tommaso Cancellario, Paul Bodelier, Steven A.J. Declerck, Liang Diwen, Sainur Samad, Monika Winder, Libin Zhou, Diego Fontaneto
    The holobiont concept places emphasis on the strict relationship between a host and its associated microbiome, with several studies supporting a strong effect of the quality of the microbiome on the host fitness. The generalities of the holobiont have been questioned for several invertebrates, including zooplankton. Here we assess the role of host ecology, habitat, and evolutionary history to explain the differences in the microbiomes associated with rotifers, across a broad taxonomic spectrum and from different habitats. The analyses of 93 rotifer-associated microbiomes from 23 rotifer host species revealed that a combination of effects from the host ecology and its habitat seem to be stronger than host phylogenetic distances in explaining differences in microbial composition of the microbiomes. This pattern is in line with the idea of habitat filtering being a stronger explanation than co-evolution in shaping the relationship between a microbiome and its rotifer host.
  • Hydrobiologia

    Reduced fertilization constitutes an important prezygotic reproductive barrier between two sibling species of the hybridizing Brachionus calyciflorus species complex

    Brachionus calyciflorus is a species complex consisting of four recently described species. Although several lines of evidence support their species status, hybridization between two of the sibling species B. calyciflorus s.s. and B. elevatus has been inferred from both field and laboratory studies. In this study, we tested for the existence of prezygotic barriers between these species by performing two types of cross-fertilization experiments. In a ‘mate competition’ experiment we exposed mictic females to equal numbers of conspecific and allospecific males and demonstrate that intraspecific fertilizations occur at much higher frequencies than interspecific fertilizations, providing evidence for a strong prezygotic reproductive barrier. This result was consistent across numerous combinations of parental genotypes. In addition, by creating interspecific combinations of mictic females and males in a ‘no choice’ experiment, we found that interspecific fertilization success is independent of fertilization direction while it does seem to depend on maternal genotype. Our results demonstrate the existence of a strong prezygotic barrier that may play an important role in the maintenance of species boundaries. Yet, the observation of hybrids also shows a potential for gene flow between the species through hybridization.
  • Oikos

    Measuring the contribution of evolution to community trait structure in freshwater zooplankton

    Lynn Govaert, Luc De Meester, S. Rousseaux, Steven A.J. Declerck, Jelena Pantel
    There are currently few predictions about when evolutionary processes are likely to play an important role in structuring community features. Determining predictors that indicate when evolution is expected to impact ecological processes in natural landscapes can help researchers identify eco-evolutionary ‘hotspots', where eco-evolutionary interactions are more likely to occur. Using data collected from a survey in freshwater cladoceran communities, landscape population genetic data and phenotypic trait data measured in a common garden, we applied a Bayesian linear model to assess whether the impact of local trait evolution in the keystone species Daphnia magna on cladoceran community trait values could be predicted by population genetic properties (within-population genetic diversity, genetic distance among populations), ecological properties (Simpson's diversity, phenotypic divergence) or environmental divergence. We found that the impact of local trait evolution varied among communities. Moreover, community diversity and phenotypic divergence were found to be better predictors of the contribution of evolution to community trait values than environmental features or genetic properties of the evolving species. Our results thus indicate the importance of ecological context for the impact of evolution on community features. Our study also demonstrates one way to detect signatures of eco-evolutionary interactions in communities inhabiting heterogeneous landscapes using survey data of contemporary ecological and evolutionary structure.
  • Genes

    The role of microbiome and genotype in Daphnia magna upon parasite re-exposure

    L. Bulteel, S. Houwenhuyse, Steven A.J. Declerck, E. Decaestecker
    Recently, it has been shown that the community of gut microorganisms plays a crucial role in host performance with respect to parasite tolerance. Knowledge, however, is lacking on the role of the gut microbiome in mediating host tolerance after parasite re-exposure, especially considering multiple parasite infections. We here aimed to fill this knowledge gap by studying the role of the gut microbiome on tolerance in Daphnia magna upon multiple parasite species re-exposure. Additionally, we investigated the role of the host genotype in the interaction between the gut microbiome and the host phenotypic performance. A microbiome transplant experiment was performed in which three germ-free D. magna genotypes were exposed to a gut microbial inoculum and a parasite community treatment. The gut microbiome inocula were pre-exposed to the same parasite communities or a control treatment. Daphnia performance was monitored, and amplicon sequencing was performed to characterize the gut microbial community. Our experimental results showed that the gut microbiome plays no role in Daphnia tolerance upon parasite re-exposure. We did, however, find a main effect of the gut microbiome on Daphnia body size reflecting parasite specific responses. Our results also showed that it is rather the Daphnia genotype, and not the gut microbiome, that affected parasite-induced host mortality. Additionally, we found a role of the genotype in structuring the gut microbial community, both in alpha diversity as in the microbial composition.
  • RIO

    Securing Biodiversity, Functional Integrity, and Ecosystem Services in Drying River Networks (DRYvER)

    Thibault Datry, Daniel Allen, Roger Argelich, Jose Barquin, Nuria Bonada, Andrew Boulton, Flora Branger, Yongjiu Cai, Miguel Cañedo-Argüelles, Núria Cid, Zoltán Csabai, Martin Dallimer, José Carlos de Araújo, Steven A.J. Declerck, Thijs Dekker, Petra Döll, Andrea Encalada, Maxence Forcellini, Arnaud Foulquier, Jani Heino, Franck Jabot, Patrícia Keszler, Leena Kopperoinen, Sven Kralisch, Annika Künne, Nicolas Lamouroux, Claire Lauvernet, Virpi Lehtoranta, Barbora Loskotová, Rafael Marcé, Julia Martin Ortega, Christine Matauschek, Marko Miliša, Szilárd Mogyorósi, Nabor Moya, Hannes Müller Schmied, Antoni Munné, François Munoz, Heikki Mykrä, Irina Pal, Riikka Paloniemi, Petr Pařil, Polona Pengal, Bálint Pernecker, Marek Polášek, Carla Rezende, Sergi Sabater, Romain Sarremejane, Guido Schmidt, Lisette de Senerpont Domis, Gabriel Singer, Esteban Suárez, Matthew V. Talluto, Sven Teurlincx, Tim Trautmann, Amélie Truchy, Emmanouil Tyllianakis, Sari Väisänen, Liisa Varumo, Jean-Philippe Vidal, Annika Vilmi, Dolors Vinyoles
    River networks are among Earth’s most threatened hot-spots of biodiversity and provide key ecosystem services (e.g., supply drinking water and food, climate regulation) essential to sustaining human well-being. Climate change and increased human water use are causing more rivers and streams to dry, with devastating impacts on biodiversity and ecosystem services. Currently, more than a half of the global river networks consist of drying channels, and these are expanding dramatically. However, drying river networks (DRNs) have received little attention from scientists and policy makers, and the public is unaware of their importance. Consequently, there is no effective integrated biodiversity conservation or ecosystem management strategy of DRNs.A multidisciplinary team of 25 experts from 11 countries in Europe, South America, China and the USA will build on EU efforts to assess the cascading effects of climate change on biodiversity, ecosystem functions and ecosystem services of DRNs through changes in flow regimes and water use. DRYvER (DRYing riVER networks) will gather and upscale empirical and modelling data from nine focal DRNs (case studies) in Europe (EU) and Community of Latin American and Caribbean States (CELAC) to develop a meta-system framework applicable to Europe and worldwide. It will also generate crucial knowledge-based strategies, tools and guidelines for economically-efficient adaptive management of DRNs. Working closely with stakeholders and end-users, DRYvER will co-develop strategies to mitigate and adapt to climate change impacts in DRNs, integrating hydrological, ecological (including nature-based solutions), socio-economic and policy perspectives. The end results of DRYvER will contribute to reaching the objectives of the Paris Agreement and placing Europe at the forefront of research on climate change.
  • Aquaculture Nutrition

    In situ fatty acid production supports shrimp yields in diets lacking fish oil and fishmeal

    D. Hermsen, Dedmer Van de Waal, Steven A.J. Declerck, J. A. J. Verreth, M. C.J. Verdegem

    Using capture fishery-derived fish oil and fishmeal in aquafeeds is unsustainable. This study mimicked semi-intensive shrimp ponds, including primary producers, in mesocosm tanks. Fatty acid mass balances were computed to distinguish between diet-based and primary production-based LC-PUFA contributions to shrimp (Litopenaeus vannamei) production and meat quality. Performance and body fatty acid composition were compared of shrimp fed a commercial diet containing fish oil and fishmeal (control), with a fishmeal- and fish oil-free diet (low LC-PUFA diet: LOW). Six mesocosms were each stocked with 60 juvenile shrimp and randomly assigned to the two diets. After an 8-week grow-out period, biomass production, survival and proximate body composition were similar between diets. Control shrimp contained twice as much LC-PUFA and omega-3 fatty acids than LOW shrimp. Large quantitative losses (85%) were found in both treatments of the LC-PUFA-precursors alpha-linolenic acid (ALA) and linoleic acid (LA) that were being used as energy source by the shrimp instead for LC-PUFA synthesis. Whereas losses were also observed for eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the control group, there was a gain for these components in the LOW tanks. LOW shrimp sourced at least 32% of their total EPA gain and 15% of their total DHA gain from the algal-based food web. This quantitative analysis of the fate of major dietary fatty acids strongly suggests that the pond's primary production can provide shrimp additional LC-PUFA. Finding a balance between LC-PUFA contribution through formulated feed and natural production seems possible and deserves further research.
  • Aquatic Ecology

    A critical assessment of the stoichiometric knife-edge: no evidence for artefacts caused by the experimental P-supplementation

    Libin Zhou, Steven A.J. Declerck
    The stoichiometric knife-edge refers to the reduced performance of consumers encountering food with excess phosphorus (P) relative to carbon (C) or nitrogen (N). Studies that provide evidence for such knife-edge in aquatic systems often apply phosphate supplementation to create P-rich food treatments. However, this method may suffer from artifacts, because after uptake algae may store P in a form different from the P-rich biomolecules typically consumed by zooplankton. Our aim was to test if P supplementation results in potential biases. We experimentally exposed populations of the herbivore rotifer species, Brachionus calyciflorus (Pallas), to four different food quality treatments: algae grown under P-saturating (HPchem, molar C:P ratio = 59.7 ± 2.7) and P-sufficient (MPchem, molar C:P = 116.3 ± 5.2) conditions in chemostats, and algae grown under P-limiting conditions, but with molar C:P ratios equal to HPchem and MPchem treatments, respectively (HPLP+P, molar C:P = 59.8 ± 0.14; MPLP+P, molar C:P = 121.0 ± 4.3). The latter two treatments were achieved through P-supplementation of P-limited algae. Results show that for rotifers fed algae with either excess or intermediate P content, population growth rates were consistently higher on algae grown in chemostats than algae treated with the P supplementation method. Importantly, growth rates were also consistently lower in HP than in MP treatments and the magnitude of this negative impact was independent on algal growth history. The latter result confirms the existence of a stoichiometric knife-edge and indicates that P supplementation is a reliable method to study the relative effect of excess P on zooplankton performance in a standardized way.
  • Limnology and Oceanography

    Food nutrient availability affects epibiont prevalence and richness in natural Daphnia populations

    L. Reyershove, J. Bulteel, Jing Liu, Caroline Souffreau, K.I. Brans, J.M.T. Engelen, Luc De Meester, F. Hendrickx, K. Muylaert, Steven A.J. Declerck, Ellen Decaestecker
    The increased input of nutrients into biological systems has been shown to result in altered biotic interactions through changes in food availability. The aim of this study was to test for an association between phytoplankton nutrient content and epibiont variables in natural zooplankton populations. Via a field survey, we studied how a gradient in food quantity and quality impacted host population density and epibiont variables in Daphnia pulex . We found a significant decrease in epibiont prevalence and infracommunity richness, which could mainly be attributed to a changing phytoplankton N : P ratio (caused by P‐limitation). We performed a lab experiment in which we exposed Daphnia magna to different algal nutrient ratios and the epibionts detected in the field study. P‐limitation in the algae affected D. magna performance and resulted in similar trends of food quality effects in the epibiont variables. The experiment, however, also reflected subtle differences between different epibiont species.
  • Global Ecology and Conservation

    Key management rules for agricultural alpine newt breeding ponds based on habitat suitability models

    N. de Troyer, M.A.E. Forio, K. Roels, Luc De Meester, Pieter Lemmens, Steven A.J. Declerck, K. Martens, P. Goethals
    The alpine newt, Ichthyosaura alpestris, is very sensitive to habitat destruction and alteration which has led to declining populations across Europe. As this species is protected through the Bern Convention, it is essential to have a comprehensive understanding of its habitat requirements to ensure proper conservation measures. We trained, validated and optimized classification tree models based on data on local aquatic habitat conditions from 125 farmland ponds scattered over Belgium and Luxembourg where the alpine newt commonly occurs. To obtain user-friendly and representative models, data was pre-processed and stratified after which different degrees of pruning were applied for model optimization. In order to check the model’s applicability for management, we predicted alpine newt occurrence with an independent dataset. The most robust and reliable model revealed that fish absence was the major driving factor followed by the thickness of the sludge layer. We found that fish presence established alpine newt absence and that fishless ponds with a sludge layer of 15 cm or more were predicted to host no alpine newts. The latter provides quantitative information for decision makers. Moreover, our results indicated that the amount of sludge could be associated with eutrophication and erosion. Regarding management practices, it is advised to assure the absence of fish and reduce sludge accumulation in ponds designated for the conservation of alpine newts, for example by designing temporary ponds not fed through fish-containing surface waters. Furthermore, we recommend to install buffer strips around a pond to reduce nutrient and soil run-off from the terrestrial environment.
  • Oikos

    Maternal effects in zooplankton consumers are not only mediated by direct but also by indirect effects of phosphorus limitation

    Libin Zhou, Steven A.J. Declerck
    Nutrient limitation of primary producers has repeatedly been shown to negatively affect consumers, directly through stoichiometric mismatch and indirectly via alterations in the producer's biochemical quality or palatability. In this study, we assessed whether direct and indirect impacts of phosphorus‐limitation on a planktonic consumer are transferred to the next generation via maternal effects and whether these effects reflect an anticipatory adaptive strategy. For this, we subjected cultures of the algivorous monogonont rotifer Brachionus calyciflorus to three food quality treatments, i.e. P‐limited (LP), P‐replete (HP) and P‐enriched LP algae (i.e. algae with an LP‐growth history but with molar C:P ratios equal to those of HP‐algae). After two generations, we subjected offspring of these cultures to each of the three food quality treatments and monitored life history traits. In addition, we tested starvation resistance. Our results showed very strong negative maternal effects of low P food on offspring performance. These negative effects prevailed irrespective of contemporary diets, suggesting transmissive and selfish maternal effects rather than anticipatory adaptive effects. The relative strength of direct and indirect maternal P‐limitation effects varied among different traits. Adult body size was predominantly determined by direct effects of P‐shortage in maternal as well as contemporary food (LP < LP + P and LP + P = HP). In contrast, whereas egg size was negatively affected by direct effects of P‐limitation in the maternal diet, a contemporary diet of LP and LP + P algae resulted in larger eggs than HP algae. Animals born from such larger eggs showed no higher growth rates, but they were more resistant to starvation, likely as the result of higher maternal allocation of energy rich molecules to the eggs. The present study shows that maternal food conditions represent an important factor that should be taken into account in studies of stoichiometric mismatch between producers and consumers.
  • Freshwater Biology

    Patterns of differentiation in the life history and demography of four recently described species of the Brachionus calyciflorus cryptic species complex

    Wei Zhang, Kimberley Lemmen, Libin Zhou, S. Papakostas, Steven A.J. Declerck
    Brachionus calyciflorus is arguably the most studied freshwater monogonont rotifer. Although it has been recognised as a cryptic species complex for more than a decade, a formal (re‐)description of the four species known so far (B. calyciflorus, Brachionus dorcas, Brachionus elevatus, and Brachionus fernandoi) has only recently been made. Information on the ecology of these species is very scant and fragmented. The aim of this study was to test for ecological divergence between these four species, specifically their life history strategy and population demography.
    We conducted a life history experiment using 12–16 genotypes per species. For each species, genotypes were extracted from at least three different natural populations. In addition, we performed population‐level culture experiments with the aim to compare population growth rates and demographic structure of experimental populations among species. Finally, we searched the literature for life history studies with molecular data allowing retrospective species identification.
    We found pronounced differences in life history traits between B. fernandoi and the other three species. B. fernandoi had higher egg and juvenile development times and a lower egg production rate and mictic ratio. We detected no significant life history differences among B. calyciflorus, B. elevatus, and B. dorcas.
    Population growth rates of B. fernandoi and B. calyciflorus were higher than those of B. elevatus and B. dorcas. Life history divergence resulted in marked differences in the demographic structure of populations. Populations of B. fernandoi contained larger fractions of pre‐reproductive females and lower fractions of adult females with sexual eggs than populations of B. calyciflorus, B. elevatus, and B. dorcas. Mortality was found to be highest in B. elevatus and lowest in B. calyciflorus populations.
    Our results show that a reverse taxonomy approach is powerful in revealing sources of variation in ecologically relevant traits of cryptic species, such as life history and demographic structure. Explicit consideration of this variation is crucial for future studies of their dynamics in natural communities.
  • Global Change Biology

    Phytoplankton growth and stoichiometric responses to warming, nutrient addition and grazing depend on lake productivity and cell size

    M. Schulhof, Jonathan B. Shurin, Steven A.J. Declerck, Dedmer Van de Waal
    Abstract Global change involves shifts in multiple environmental factors that act in concert to shape ecological systems in ways that depend on local biotic and abiotic conditions. Little is known about the effects of combined global change stressors on phytoplankton communities, and particularly how these are mediated by distinct community properties such as productivity, grazing pressure and size distribution. Here, we tested for the effects of warming and eutrophication on phytoplankton net growth rate and C:N:P stoichiometry in two phytoplankton cell size fractions (30?m) in the presence and absence of grazing in microcosm experiments. Because effects may also depend on lake productivity, we used phytoplankton communities from three Dutch lakes spanning a trophic gradient. We measured the response of each community to multifactorial combinations of temperature, nutrient, and grazing treatments and found that nutrients elevated net growth rates and reduced carbon:nutrient ratios of all three phytoplankton communities. Warming effects on growth and stoichiometry depended on nutrient supply and lake productivity, with enhanced growth in the most productive community dominated by cyanobacteria, and strongest stoichiometric responses in the most oligotrophic community at ambient nutrient levels. Grazing effects were also most evident in the most oligotrophic community, with reduced net growth rates and phytoplankton C:P stoichiometry that suggests consumer-driven nutrient recycling. Our experiments indicate that stoichiometric responses to warming and interactions with nutrient addition and grazing are not universal but depend on lake productivity and cell size distribution. This article is protected by copyright. All rights reserved.
  • Ecology Letters

    Herbivore consumers face different challenges along opposite sides of the stoichiometric knife-edge

    Libin Zhou, Steven A.J. Declerck
    Anthropogenic activities have reshaped the relative supply rates of essential elements to organisms. Recent studies suggested that consumer performance is strongly reduced by food that is either very high or very low in relative phosphorus content. However, the generality of such ‘stoichiometric knife‐edge’ and its underlying mechanisms are poorly understood. We studied the response of a planktonic rotifer to a 10‐fold food carbon : phosphorus (C : P) gradient and confirmed the existence of the stoichiometric knife‐edge. Interestingly, we observed a complete homeostatic breakdown associated with strong growth reductions at high food C : P. In contrast, at low food C : P, animals maintained homeostasis despite pronounced performance reductions. Our results suggest that the mechanisms underlying adverse effects of stoichiometric imbalance are determined by both the identity of elements that are limiting and those that are present in excess. Negative effects of excess P reveal an additional way of how eutrophication may affect consumers.
  • Molecular Ecology Resources

    The genome of the freshwater monogonont rotifer Brachionus calyciflorus

    Hui-Su Kim, Bo-Young Lee, Jeonghoon Han, Chang-Bum Jeong, Dae-Sik Hwang, Min-Chul Lee, Hye-Min Kang, Duck-Hyun Kim, Hee-Jin Kim, S. Papakostas, Steven A.J. Declerck, Ik-Young Choi, Atsushi Hagiwara, Heum Gi Park, Jae-Seong Lee
    Monogononta is the most speciose class of rotifers, with more than 2,000 species. The monogonont genus Brachionus is widely distributed at a global scale, and a few of its species are commonly used as ecological and evolutionary models to address questions related to aquatic ecology, cryptic speciation, evolutionary ecology, the evolution of sex and ecotoxicology. With the importance of Brachionus species in many areas of research, it is remarkable that the genome has not been characterized. This study aims to address this lacuna by presenting, for the first time, the whole‐genome assembly of the freshwater species Brachionus calyciflorus. The total length of the assembled genome was 129.6 Mb, with 1,041 scaffolds. The N50 value was 786.6 kb, and the GC content was 24%. A total of 16,114 genes were annotated with repeat sequences, accounting for 21% of the assembled genome. This assembled genome may form a basis for future studies addressing key questions on the evolution of monogonont rotifers. It will also provide the necessary molecular resources to mechanistically investigate ecophysiological and ecotoxicological responses.
  • Ecosystems

    Bottom-up effects on biomass versus top-down effects on identity: a multiple-lake fish community manipulation experiment

    Pieter Lemmens, Steven A.J. Declerck, K. Tuytens, M. Vanderstukken, Luc De Meester
    The extent to which ecosystems are regulated by top-down relative to bottom-up control has been a dominant paradigm in ecology for many decades. For lakes, it has been shown that predation by fish is an important determinant of variation in zooplankton and phytoplankton community characteristics. Effects of fish are expected to not only be a function of total fish biomass, but also of functional composition of the fish community. Previous research on the importance of trophic cascades in lakes has largely focused on the role of zooplanktivorous and piscivorous fish. We conducted a large-scale multiple-lake fish community manipulation experiment to test for the effect of differences in fish functional community composition on the trophic structure of lakes. We examine the effect of top-down and bottom-up factors on phytoplankton and zooplankton biomass as well as on their community composition. We put our data in a broader perspective by comparing our results to data of a survey that also included ponds with low fish densities as well as ponds with very high densities of fish. Our results indicate that the overall food web structure under relative high fish densities is primarily structured by bottom-up factors, whereas community characteristics seem to be primarily regulated by top-down factors. Our results suggest a subtle interplay between bottom-up and top-down factors, in which bottom-up factors dominate in determining quantities while top-down effects are important in determining identities of the communities.
  • Comparative Biochemistry and Physiology - Part D: Genomics and Proteomics

    Genome-wide identification of 31 cytochrome P450 (CYP) genes in the freshwater rotifer Brachionus calyciflorus and analysis of their benzo[alpha]pyrene-induced expression patterns

    Jeonghoon Han, Duck-Hyun Kim, Hui-Su Kim, Hee-Jin Kim, Steven A.J. Declerck, Atsushi Hagiwara, Jae-Seong Lee
    While marine invertebrate cytochrome P450 (CYP) genes and their roles in detoxification mechanisms have been studied, little information is available regarding freshwater rotifer CYPs and their functions. Here, we used genomic sequences and RNA-seq databases to identify 31 CYP genes in the freshwater rotifer Brachionus calyciflorus. The 31 Bc-CYP genes with a few tandem duplications were clustered into CYP 2, 3, 4, mitochondrial, and 46 clans with two marine rotifers Brachionus plicatilis and Brachionus koreanus. To understand the molecular responses of these 31 Bc-CYP genes, we also examined their expression patterns in response to benzo[α]pyrene (B[α]P). Three Bc-CYP genes (Bc-CYP3044B3, Bc-CYP3049B4, Bc-CYP3049B6) were significantly upregulated (P < 0.05) in response to B[α]P, suggesting that these CYP genes can be involved in detoxification in response to B[α]P exposure. These genes might be useful as biomarkers of B[α]P exposure in B. calyciflorus. Overall, our findings expand the repertoire of known CYPs and shed light on their potential roles in xenobiotic detoxification in rotifers.
  • Ecology Letters

    Integrating community assembly and biodiversity to better understand ecosystem function: the Community Assembly and the Functioning of Ecosystems (CAFE) approach

    K. Bannar-Martin, C. Kremer, M. Ernest, M. Leibold, H. Auge, Jonathan M. Chase, Steven A.J. Declerck, Nico Eisenhauer, W.S. Harpole, H. Hillebrand, F. Isbell, T. Koffel, S. Larsen, A. Narwani, Jana S. Petermann, Christiane Roscher, J. Sarmento Cabral, S. Supp
    The research of a generation of ecologists was catalysed by the recognition that the number and identity of species in communities influences the functioning of ecosystems. The relationship between biodiversity and ecosystem functioning (BEF) is most often examined by controlling species richness and randomising community composition. In natural systems, biodiversity changes are often part of a bigger community assembly dynamic. Therefore, focusing on community assembly and the functioning of ecosystems (CAFE), by integrating both species richness and composition through species gains, losses and changes in abundance, will better reveal how community changes affect ecosystem function. We synthesise the BEF and CAFE perspectives using an ecological application of the Price equation, which partitions the contributions of richness and composition to function. Using empirical examples, we show how the CAFE approach reveals important contributions of composition to function. These examples show how changes in species richness and composition driven by environmental perturbations can work in concert or antagonistically to influence ecosystem function. Considering how communities change in an integrative fashion, rather than focusing on one axis of community structure at a time, will improve our ability to anticipate and predict changes in ecosystem function.
  • Limnology and Oceanography

    Fungal parasites of a toxic inedible cyanobacterium provide food to zooplankton

    Thijs Frenken, Joren Wierenga, Ellen Van Donk, Steven A.J. Declerck, Lisette de Senerpont Domis, Thomas Rohrlack, Dedmer Van de Waal
    During the end of spring and throughout summer, large‐sized phytoplankton taxa often proliferate and form dense blooms in freshwater ecosystems. In many cases, they are inedible to zooplankton and prevent efficient transfer of energy and elements to higher trophic levels. Such a constraint may be alleviated by fungal parasite infections on large‐sized phytoplankton taxa like diatoms and filamentous cyanobacteria, as infections may provide zooplankton with a complementary food source in the form of fungal zoospores. Zoospores have been shown to support somatic growth of large filter feeding zooplankton species. Here, we tested if selectively feeding zooplankton, more specifically rotifers, also can use fungal zoospores as a food source. Our results show that chytrid fungal parasites can indeed support population growth of rotifers (Keratella sp.). Specifically, in cultures of an inedible filamentous cyanobacterium (Planktothrix rubescens), Keratella populations rapidly declined, while in Planktothrix cultures infected with chytrids, Keratella population growth rate equaled the growth observed for populations fed with a more suitable green algal diet (Chlorella sorokiniana). Feeding of Keratella on zoospores was furthermore indicated by a reduced number of zoospores during the last sampling day. These findings not only imply that rotifers may survive on zoospores, but also that the zoospores can support high rotifer population growth rates. We thus show that fungal parasites of inedible cyanobacteria can facilitate grazers by providing them alternative food sources. Together, these results highlight the important role that parasites may play in the aquatic plankton food web.
  • Frontiers in Microbiology

    Local functioning, landscape structuring: drivers of soil microbial community structure and function in peatlands

    Sven Teurlincx, Amber Heijboer, Annelies Veraart, George Kowalchuk, Steven A.J. Declerck
    Agricultural peatlands are essential for a myriad of ecosystem functions and play an important role in the global carbon (C) cycle through C sequestration. Management of these agricultural peatlands takes place at different spatial scales, ranging from local to landscape management, and drivers of soil microbial community structure and function may be scale-dependent. Effective management for an optimal biogeochemical functioning thus requires knowledge of the drivers on soil microbial community structure and functioning, as well as the spatial scales upon which they are influenced. During two field campaigns, we examined the importance of different drivers (i.e., soil characteristics, nutrient management, vegetation composition) at two spatial scales (local vs. landscape) for, respectively, the soil microbial community structure (determined by PLFA) and soil microbial community functional capacity (as assessed by CLPP) in agricultural peatlands. First, we show by an analysis of PLFA profiles that the total microbial biomass changes with soil moisture and relative C:P nutrient availability. Secondly, we showed that soil communities are controlled by a distinct set of drivers at the local, as opposed to landscape, scale. Community structure was found to be markedly different between areas, in contrast to community function which showed high variability within areas. We further found that microbial structure appears to be controlled more at a landscape scale by nutrient-related variables, whereas microbial functional capacity is driven locally through plant community feedbacks. Optimal management strategies within such peatlands should therefore consider the scale-dependent action of soil microbial community drivers, for example by first optimizing microbial structure at the landscape scale by targeted areal management, and then optimizing soil microbial function by local vegetation management.
  • Frontiers in Microbiology

    Direct and indirect effects of resource P-limitation differentially impact population growth, life history and body elemental composition of a zooplankton consumer

    Libin Zhou, Kimberley Lemmen, Wei Zhang, Steven A.J. Declerck
    One of the central tenets of ecological stoichiometry is that consumer growth rate is strongly determined by food phosphorus (P) content. In planktonic organisms population growth rates of zooplankton have repeatedly been shown to be reduced when fed with P-limited algal food sources. However, P-limitation may also affect other quality-related aspects of algae, such as biochemical composition or palatability. We studied the population growth, detailed life history and body elemental composition of the herbivorous rotifer, Brachionus calyciflorus, in response to three different food quality treatments: algae cultured in high phosphorus conditions (average algal molar C:P ≈112,‘HP’), algae cultured in low P conditions (molar C:P ≈ 631, ‘LP’) and low-P cultured algae spiked with P just before feeding (molar C:P ≈113, ‘LP+P’). LP+P algae thus combined high P content with a history of growth under P-limited conditions. Total P content and the C:P ratio of rotifers in the LP+P treatment equaled those of rotifers in the HP treatment. Rotifer population growth rates were higher in HP than in LP and intermediate in the LP+P treatment. Similarly, many life history traits observed for animals in the LP+P treatment, such as somatic growth rate, age at maturity, and egg production rate were also intermediate to those observed in the LP and HP treatments. However, there were important deviations from this pattern: size at first reproduction and egg mortality in the LP+P treatment equaled the HP treatment, whereas size and development time of the first eggs equaled those of the LP treatment. Our results indicate that elemental limitation cannot fully explain reduced performance of consumers fed with P-limited algae and strongly suggest that indirect, non-stoichiometric effects of P-limitation, e.g. via changes in biochemical composition or morphology of the algae also play a major role. Furthermore, our study highlights that such indirect effects have a differential impact on major fitness components and may as such also determine the population dynamics and demographic structure of consumer populations.
  • Freshwater Biology

    Compositional and functional consequences of environmental change in Belgian farmland ponds.

    L. Verbeek, M. Vanhamel, E. van den Berg, F.T.T. Hanashiro, Andros T. Gianuca, Maren Striebel, Pieter Lemmens, Steven A.J. Declerck, Helmut Hillebrand, Luc De Meester
    A resampling of 38 small farmland ponds in Belgium after 10 years revealed a high temporal species turnover for both phytoplankton and zooplankton communities, associated with substantial changes in abiotic factors, especially a reduction in total phosphorus concentration.
    Across ponds, phytoplankton biomass decreased while evenness and richness increased between the samplings in 2003 and 2013. By contrast, the zooplankton assemblage was characterised by lower biomass, richness and evenness in 2013. Ponds experiencing larger environmental change showed stronger changes in phytoplankton richness and evenness.
    Resource use efficiency (RUE) of zooplankton increased with greater environmental change and zooplankton evenness, which points to a switch towards species with higher RUE or greater variety in food sources in higher trophic levels.
    As ponds are important habitats for freshwater biodiversity and ecosystems services, the strong but predictable species turnover and the opposing effects of environmental change on different trophic levels need to be embedded in conservation and management plans.
  • Oikos

    After-life effects: living and dead invertebrates differentially affect plants and their associated above- and belowground multitrophic communities

    Martine Kos, Jingying Jing, Ivor Keesmaat, Steven A.J. Declerck, Roel Wagenaar, T. Martijn Bezemer
    Above-belowground (AG-BG) studies typically focus on plant-mediated effects inflicted by living organisms. However, animal cadavers may also play an important role in AG-BG interactions. Here, we explore whether living and dead foliar-feeding and soil-dwelling invertebrates differentially affect plants and their associated AG and BG multitrophic communities.

    In a mesocosm study we separated effects of living and dead locusts (AG herbivores) and earthworms (BG detritivores) on experimental multitrophic communities consisting of eight plant species, an AG aphid and parasitoid community and a BG nematode community. We measured root and shoot biomass and determined plant community composition and densities of aphids, parasitoids and nematodes.

    Living locusts decreased total shoot and root biomass in the mesocosms, whereas living earthworms enhanced total root biomass. Cadavers of both invertebrates strongly increased total root and shoot biomass, and changed the plant community composition mainly via enhanced growth of grasses. Earthworm cadavers affected plant biomass and community composition more strongly than their living counterparts, while this was reversed for locusts. Structural equation models showed that aphids and parasitoids were influenced via changes in plant community composition. Nematode densities in the soil, especially those of bacterivorous and entomopathogenic nematodes, were strongly increased by dead invertebrates, but unaffected by living ones.

    We conclude that effects of invertebrates on plant growth and densities of AG and BG organisms strongly depend on whether the invertebrates are dead or alive. Remarkably, invertebrate cadavers may inflict even stronger effects than their living counterparts. Hence, our study reveals an important, but often neglected, role of animal cadavers in AG-BG studies.
  • Hydrobiologia

    Monogonont rotifers as model systems for the study of micro-evolutionary adaptation and its eco-evolutionary implications

    Steven A.J. Declerck, S. Papakostas
    A better understanding of the ability of organisms to adapt to local selection conditions is essential for a better insight in their ecological dynamics. The study of micro-evolutionary adaptation and its eco-evolutionary consequences is challenging for many reasons and the choice of a suitable model organism is particularly important. In this paper, we explain why monogonont rotifers, through their unique combination of traits, are ideal study organisms for this purpose. With a literature review, we demonstrate the capacity of monogonont populations to adapt to a variety of selection conditions (e.g., salinity, food shortage, elemental limitation, and disturbance regimes) within very short-time frames and highlight some potential eco-evolutionary implications. Although monogononts are increasingly used in eco-evolution-oriented studies, their potential is still underappreciated compared to other model organisms. No doubt the high prevalence of cryptic species complexes and the lack of genomic tools form important obstacles that may discourage researchers to work with this group. Here, we argue that none of these difficulties should prevent monogonont rotifers from becoming commonly used model organisms in micro-evolutionary studies and make suggestions for future research.
  • Ecology

    Effects of dispersal and environmental heterogeneity on the replacement and nestedness components of β-diversity

    Andros T. Gianuca, Steven A.J. Declerck, Pieter Lemmens, Luc De Meester
    Traditionally metacommunity studies have quantified the relative importance of dispersal and environmental processes on observed β-diversity. Separating β-diversity into its replacement and nestedness components and linking such patterns to metacommunity drivers can provide richer insights into biodiversity organization across spatial scales. It is often very difficult to measure actual dispersal rates in the field and to define the boundaries of natural metacommunities. To overcome those limitations, we revisited an experimental metacommunity dataset to test the independent and interacting effects of environmental heterogeneity and dispersal on each component of β-diversity. We show that the balance between the replacement and nestedness components of β-diversity resulting from eutrophication changes completely depending on dispersal rates. Nutrient enrichment negatively affected local zooplankton diversity and generated a pattern of β-diversity derived from nestedness in unconnected, environmentally heterogeneous landscapes. Increasing dispersal erased the pattern of nestedness, whereas the replacement component gained importance. In environmentally homogeneous metacommunities, dispersal limitation created community dissimilarity via species replacement whereas the nestedness component remained low and unchanged across dispersal levels. Our study provides novel insights into how environmental heterogeneity and dispersal interact and shape metacommunity structure.
  • Ecology Letters

    Species sorting and stoichiometric plasticity control community C:P ratio of first-order aquatic consumers

    Sven Teurlincx, Mandy Velthuis, D. Seroka, Lynn Govaert, Ellen Van Donk, Dedmer Van de Waal, Steven A.J. Declerck
    Ecological stoichiometry has proven to be invaluable for understanding consumer response to changes in resource quality. Although interactions between trophic levels occur at the community level, most studies focus on single consumer species. In contrast to individual species, communities may deal with trophic mismatch not only through elemental plasticity but also through changes in species composition. Here, we show that a community of first-order consumers (e.g. zooplankton) is able to adjust its stoichiometry (C:P) in response to experimentally induced changes in resource quality, but only to a limited extent. Furthermore, using the Price equation framework we show the importance of both elemental plasticity and species sorting. These results illustrate the need for a community perspective in ecological stoichiometry, requiring consideration of species-specific elemental composition, intraspecific elemental plasticity and species turnover.
  • Philosophical Transactions of the Royal Society B: Biological Sciences

    The influence of balanced and imbalanced resource supply on biodiversity–functioning relationship across ecosystems

    Aleksandra M. Lewandowska, Antje Biermann, Elizabeth T. Borer, Miguel A. Cebrián-Piqueras, Steven A.J. Declerck, Luc De Meester, Ellen Van Donk, Lars Gamfeldt, Daniel S. Gruner, Nicole Hagenah, W. Stanley Harpole, Kevin P. Kirkman, Christopher A. Klausmeier, Michael Kleyer, Johannes M. H. Knops, Pieter Lemmens, Eric M. Lind, Elena Litchman, Jasmin Mantilla-Contreras, Koen Martens, Sandra Meier, Vanessa Minden, Joslin L. Moore, Harry Olde Venterink, Eric W. Seabloom, Ulrich Sommer, Maren Striebel, Anastasia Trenkamp, Juliane Trinogga, Jotaro Urabe, Wim Vyverman, Dedmer Van de Waal, Claire E. Widdicombe, Helmut Hillebrand
    Numerous studies show that increasing species richness leads to higher ecosystem productivity. This effect is often attributed to more efficient portioning of multiple resources in communities with higher numbers of competing species, indicating the role of resource supply and stoichiometry for biodiversity–ecosystem functioning relationships. Here, we merged theory on ecological stoichiometry with a framework of biodiversity–ecosystem functioning to understand how resource use transfers into primary production. We applied a structural equation model to define patterns of diversity–productivity relationships with respect to available resources. Meta-analysis was used to summarize the findings across ecosystem types ranging from aquatic ecosystems to grasslands and forests. As hypothesized, resource supply increased realized productivity and richness, but we found significant differences between ecosystems and study types. Increased richness was associated with increased productivity, although this effect was not seen in experiments. More even communities had lower productivity, indicating that biomass production is often maintained by a few dominant species, and reduced dominance generally reduced ecosystem productivity. This synthesis, which integrates observational and experimental studies in a variety of ecosystems and geographical regions, exposes common patterns and differences in biodiversity–functioning relationships, and increases the mechanistic understanding of changes in ecosystems productivity.
  • Oecologia

    A naturally heterogeneous landscape can effectively slow down dispersal of aquatic microcrustaceans

    P.J. Juračka, Steven A.J. Declerck, D. Vondrák, L. Beran, M. Černý, A. Petrusek
    dispersers in a variety of landscapes, whereas others have indicated dispersal
    limitation at large spatial scales or under specific circumstances. Based on a survey of
    a set of recently created ponds in an area of approximately 18×25 km, we found
    multiple indications of dispersal limitation affecting the community assembly of
    microcrustacean communities. Spatial patterns in the community composition were
    better explained by the geomorphological structure of the landscape than by mere
    geographic distances. This suggests that ridges separating the network of valleys act
    as dispersal barriers, and as such may channel the dispersal routes of the studied taxa
    and, likely, of their animal vectors as well. Dispersal limitation was further supported by
    a strong positive relationship between species richness and the abundance of
    neighbouring water bodies, suggesting that isolation affects colonization rates. Finally,
    the apparent dispersal limitation of microcrustaceans is further corroborated by the
    observation of low colonization rates in newly dug experimental ponds in the study
  • Freshwater Biology

    Contributions of airborne dispersal and dormant propagule recruitment to the assembly of rotifer and crustacean zooplankton communities in temporary ponds.

    P.M. Lopes, R.L. Bozelli, Luis M. Bini, J. M. Santangelo, Steven A.J. Declerck
    Metacommunity theory assumes that communities are not only affected by local processes but also interact with each other through dispersal. It is generally assumed that zooplankton can quickly recolonise water bodies after droughts, via both dormant egg banks and dispersal of resting eggs. Hitherto, few studies have evaluated the relative importance of resting egg bank recruitment and airborne dispersal in the re-establishment of zooplankton communities.
    As zooplankton communities of temporary ponds are frequently confronted by dry phases and have the potential to build up large resting egg banks, we expected the contribution of such resting egg bank to be more important than airborne dispersal for community re-establishment after drought. We also expected that the relative importance of airborne dispersal would be higher for rotifers than for microcrustaceans, as the former group has key traits (e.g. smaller body sizes, shorter generation times and higher reproductive potential) that are thought to enhance the dispersal to and colonisation of vacant habitat.
    We performed an enclosure experiment in the vicinity of seven temporary ponds, simulating the colonisation by zooplankton exclusively via the resting egg bank, exclusively via airborne dispersal and via both pathways simultaneously. The enclosures were sampled five times during a period of 53 days.
    Our results show that zooplankton organisms were able to rapidly colonise the experimental enclosures, either through their resting egg bank or by airborne dispersal of resting eggs. However, microcrustaceans tended to rely more on recolonisation from the resting egg banks than rotifers, at least for the spatial and temporal scales considered in our study.
  • Fisheries Management and Ecology

    Can underwater refuges protect fish populations against cormorant predation? Evidence from a large-scale multiple pond experiment

    Pieter Lemmens, Luc De Meester, Steven A.J. Declerck
    Artificial structures can protect fish against predation by cormorants (Phalacocorax spp.). However, their effectiveness in larger water bodies with different fish communities in the presence of natural vegetation still needs to be explored. Using a large-scale field experiment with 24 ponds stocked with differently composed fish communities, the present study investigates the extent to which the effect of artificial refuges on fish is species-specific and determined by the characteristics of the fish community. This study provides strong experimental evidence for artificial refuges protecting fish against predation from cormorants, even in the presence of submerged vegetation. The effect of refuges was, however, highly species-specific and depended on the composition of the fish community. Strong positive effects of refuges on rudd, Scardinius erythrophthalmus (L.), and roach, Rutilus rutilus (L.), populations were observed, especially in ponds where these species dominated. Overall, the total biomass of young-of-the-year, 1-year-old and adult rudd and roach was on average 500, 7 and 15 times lower in ponds without than in ponds with refuges, respectively. No effect of artificial refuges on other fish species was found. This study indicates that artificial refuges can facilitate the coexistence of predation vulnerable fish populations with cormorants in lakes and ponds.
  • Systematic Biology

    Integrative Taxonomy Recognizes Evolutionary Units Despite Widespread Mitonuclear Discordance: Evidence from a Rotifer Cryptic Species Complex

    S. Papakostas, Evangelia Michaloudi, Konstantinos Proios, Michaela Brehm, Laurens Verhage, Jadranka Rota, Carlos Peña, Georgia Stamou, Victoria L. Pritchard, Diego Fontaneto, Steven A.J. Declerck
    Mitonuclear discordance across taxa is increasingly recognized as posing a major challenge to species delimitation based on DNA sequence data. Integrative taxonomy has been proposed as a promising framework to help address this problem. However, we still lack compelling empirical evidence scrutinizing the efficacy of integrative taxonomy in relation to, for instance, complex introgression scenarios involving many species. Here, we report remarkably widespread mitonuclear discordance between about 15 mitochondrial and four nuclear Brachionus calyciflorus groups identified using different species delimitation approaches. Using coalescent-, Bayesian admixture-, and allele sharing-based methods with DNA sequence or microsatellite data, we provide strong evidence in support of hybridization as a driver of the observed discordance. We then describe our combined molecular, morphological, and ecological approaches to resolving phylogenetic conflict and inferring species boundaries. Species delimitations based on the ITS1 and 28S nuclear DNA markers proved a more reliable predictor of morphological variation than delimitations using the mitochondrial COI gene. A short-term competition experiment further revealed systematic differences in the competitive ability between two of the nuclear-delimited species under six different growth conditions, independent of COI delimitations; hybrids were also observed. In light of these findings, we discuss the failure of the COI marker to estimate morphological stasis and morphological plasticity in the B. calyciflorus complex. By using B. calyciflorus as a representative case, we demonstrate the potential of integrative taxonomy to guide species delimitation in the presence of mitonuclear phylogenetic conflicts.
  • Ecology

    Parasite and nutrient enrichment effects on Daphnia interspecific competition

    Ellen Decaestecker, Dino Verreydt, Luc De Meester, Steven A.J. Declerck
    Increased productivity due to nutrient enrichment is hypothesized to affect density-dependent processes, such as transmission success of horizontally transmitting parasites. Changes in nutrient availability can also modify the stoichiometry and condition of individual hosts, which may affect their susceptibility for parasites as well as the growth conditions for parasites within the host. Consequently, if not balanced by increased host immuno-competence or life history responses, changes in the magnitude of parasite effects with increasing nutrient availability are expected. If these parasite effects are host species specific, this may lead to shifts in the host community structure. We here used the Daphnia-parasite model system to study the effect of nutrient enrichment on parasite-mediated competition in experimental mesocosms. In the absence of parasites, D. magna was competitively dominant to D. pulex at both low and high nutrient levels. Introduction of parasites resulted in infections of D. magna, but not of D. pulex and as such reversed the competitive hierarchy between these two species. Nutrient addition resulted in an increased prevalence and infection intensity of some of the parasites on D. magna. However, there was no evidence that high nutrient levels enhanced negative effects of parasites on the hosts. Costs associated with parasite infections may have been compensated by better growth conditions for D. magna in the presence of high nutrient levels.
  • Ecology Letters

    Rapid adaptation of herbivore consumers to nutrient limitation: eco-evolutionary feedbacks to population demography and resource

    Steven A.J. Declerck, Andrea Malo, S. Diehl, Dennis Waasdorp, Kimberley Lemmen, Konstantinos Proios, S. Papakostas
    Humans alter biogeochemical cycles of essential elements such as phosphorus (P). Prediction of ecosystem consequences of altered elemental cycles requires integration of ecology, evolutionary biology and the framework of ecological stoichiometry. We studied micro-evolutionary responses of a herbivorous rotifer to P-limited food and the potential consequences for its population demography and for ecosystem properties. We subjected field-derived, replicate rotifer populations to P-deficient and P-replete algal food, and studied adaptation in common garden transplant experiments after 103 and 209 days of selection. When fed P-limited food, populations with a P-limitation selection history suffered 37% lower mortality, reached twice the steady state biomass, and reduced algae by 40% compared to populations with a P-replete selection history. Adaptation involved no change in rotifer elemental composition but reduced investment in sex. This study demonstrates potentially strong eco-evolutionary feedbacks from shifting elemental balances to ecosystem properties, including grazing pressure and the ratio of grazer:producer biomass.
  • PLoS One

    The impact of conservation management on the community composition of multiple organism groups in eutrophic interconnected man-made ponds

    Pieter Lemmens, J. Mergeay, J. Van Wichelen, Luc De Meester, Steven A.J. Declerck
    Ponds throughout the world are subjected to a variety of management measures for purposes of biodiversity conservation. Current conservation efforts typically comprise a combination of multiple measures that directly and indirectly impact a wide range of organism groups. Knowledge of the relative impact of individual measures on different taxonomic groups is important for the development of effective conservation programs. We conducted a field study of 28 man-made ponds, representing four management types differing in the frequency of periodic pond drainage and the intensity of fish stock management. We disentangled the relative importance of direct and indirect effects of pond management measures on the community composition of phytoplankton, zooplankton, aquatic macro-invertebrates, submerged and emergent vascular plants. With the exception of phytoplankton, pond management had strong effects on the community composition of all investigated biota. Whether management affected communities directly or indirectly through its impact on fish communities or local environmental conditions in the pond varied between organism groups. Overall, the impact of pond drainage regime and fish community characteristics on the community composition of target organism groups were more important than local environmental conditions. The majority of taxa were negatively associated with fish density, whereas multiple emergent plant species and several taxa of aquatic macro-invertebrates were positively affected by increased drainage frequency. The effects of fish community and drainage tended to be largely independent. The present study indicates that pond drainage is an important element for biodiversity conservation in eutrophicated shallow and interconnected man-made ponds.
  • Aquatic Conservation: Marine and Freshwater Ecosystems

    Suppression of invasive topmouth gudgeon Pseudorasbora parva by native pike Esox lucius in ponds

    Pieter Lemmens, J. Mergeay, T. Vanhove, Luc De Meester, Steven A.J. Declerck
    1. Asian topmouth gudgeon Pseudorasbora parva has been recognized as a highly invasive cyprinid fish species in Europe that can present risk to native fish communities. 2. The present study aimed to investigate whether a native piscivorous fish, pike Esox lucius, is able to reduce the establishment success and invasiveness of topmouth gudgeon Pseudorasbora parva in shallow ponds. We performed a large scale, replicated whole-pond experiment in which ponds were spontaneously colonized by topmouth gudgeon and exposed to experimental native fish communities with and without pike. 3. Our results provide evidence for strong negative effects of pike stocking on the abundance and biomass of topmouth gudgeon, while we found no effects on native fish species. The present study suggests that the presence of native pike can considerably enhance the biotic resistance of fish communities against invasion by topmouth gudgeon. 4. We argue that the resistance of fish communities against invasion by exotic species may in some cases be enhanced by management strategies that reinforce the presence and abundance of naturally occurring and indigenous pike.
  • Ecological Engineering

    Fighting internal phosphorus loading: An evaluation of the large scale application of gradual Fe-addition to a shallow peat lake

    Anne Immers, (Liesbeth) E.S. Bakker, Ellen Van Donk, G. Ter Heerdt, Jeroen Geurts, Steven A.J. Declerck
    Abatement of external phosphorus (P) loading and biomanipulation are measures that are often applied with the aim to restore a macrophyte dominated clearwater state in turbid, anthropogenically eutrophied lakes. The recovery of such lakes, however, is often hampered by ‘internal eutrophication’, as a result of the release of historically accumulated P from the sediment into the water column. One way to combat this internal P loading is by adding iron (Fe) into the lake, which naturally binds to phosphate. Although studied in the laboratory or mesocosms, the effects of iron addition on a whole-lake scale are largely
    unknown. In this study we therefore compiled lake monitoring data to evaluate the effect of a gradual dose of 33 g Fe m2 on the water quality and biotic communities (phytoplankton, zooplankton and macrophytes) of Lake Terra Nova. During and after the Fe-addition, we also carried out assays to evaluate the effect of the Fe-addition on sediment P-release rates. Lake Terra Nova is a eutrophied, shallow peaty lake that has been subjected to biomanipulation measures for 10 years.
    The large scale addition of iron during 2010 and 2011 resulted in a substantial reduction of dissolved P, suspended matter (SM), phytoplankton biomass and relative Cyanobacterial biomass, whereas macrophytes reappeared. Fe-addition also resulted in strongly reduced sediment P-mobilisation rates.
    Nevertheless, reductions of water column TP in response to the Fe-addition were short-lived. This discrepancy between the observed TP-levels in the water column and sediment P-release rates could indicate that sustained loading with external P and interactions of chemical compounds with Fe may jeopardize long term restoration success by depleting the water column reservoir of reactive Fe. Ecological processes can in addition enhance this process by shunting P from the sediment to the water column.
  • Freshwater Biology

    Long-term allelopathic control of phytoplankton by the submerged macrophyte Elodea nuttallii

    M. Vanderstukken, Steven A.J. Declerck, E. Decaestecker, K. Muylaert
    Keywords: allelochemicals; chemical ecology; competition; nutrient limitation; shallow lakes Summary 1.It is well known that submerged macrophytes can suppress phytoplankton blooms in lakes and thus promote water quality and biodiversity. One of the possible mechanisms through which submerged macrophytes control phytoplankton is by producing allelochemicals that suppress phytoplankton growth rates. The in situ importance of allelopathy, however, is often questioned because it is assumed that phytoplankton communities can rapidly evolve resistance to allelochemicals. 2.Here, we present the results of two mesocosm experiments in which we evaluated whether the submerged macrophyte Elodea nuttallii is capable of controlling phytoplankton biomass over periods of 4 to 8 weeks. Such a timescale is long relative to the generation time of phytoplankton and is therefore expected to allow the development of resistance through compositional shifts at both population and community levels. 3.Although the mesocosms were inoculated with a diverse phytoplankton inoculum including species that had previously been exposed to Elodea, phytoplankton biomass remained consistently low during the course of the experiments in the treatments with Elodea. As zooplankton grazing and competition for nutrients and light by macrophytes were excluded in our experiments, this suggests that phytoplankton was controlled by allelopathy. 4.Dialysis bag assays, performed at the end of each mesocosm experiment, showed that phytoplankton communities from mesocosms with Elodea were equally sensitive to exudates from Elodea than phytoplankton communities from mesocosms without Elodea. 5.These results suggest that phytoplankton communities do not evolve resistance to allelochemicals from Elodea. This may allow Elodea to control phytoplankton in natural ecosystems over prolonged time periods through allelopathy.
  • Freshwater Biology

    Strong effects of occasional drying on subsequrnt water clarity and cyanobacterial blooms in cool tropical reservoirs

    M. Teferi, Steven A.J. Declerck, T. De Bie, Pieter Lemmens, A. Gebrekidan, T. Asmelash, T. Dejenie, K. Gebrehiwot, H. Bauer, J.A. Deckers, J. Snoeks, Luc De Meester
    Keywords: Ethiopia; fish biomass; Microcystis; reservoir ecology; water clarity Summary 1.In semi-arid regions, the construction of small reservoirs is important in alleviating water shortage, although many have poor water quality with high turbidity and dense blooms of algae and cyanobacteria, and there are large differences in the ecology of such reservoirs. 2.We took advantage of two exceptionally dry years in northern Ethiopia to study the effect of a dry period and the associated fish kills on reservoir ecology and water quality. We studied 13 reservoirs, seven of which dried up in 2009. Four of the latter dried up again in 2010. We monitored the ecology of these reservoirs from 2009 to 2011, hypothesising that the pattern of reservoir drying would explain ecological differences among them. 3.Reservoirs that refilled after drying had a significantly lower fish biomass, lower biomass of phytoplankton (expressed as chlorophyll-a) and cyanobacteria (Microcystis), clearer water, greater macrophyte cover and lower nutrient concentrations than reservoirs that did not dry. Although the differences in water quality were most striking in the wet season after a drying event, there were persistent effects on reservoir ecology. The three categories of reservoirs we distinguished, based on their behaviour in 2009 and 2010, also showed differences in 2004, a year during which none of the reservoirs dried out. While drying evidently results in better water quality, we could not disentangle the effects of drying per se from that of reductions in fish biomass. The total combined effect was highly significant in all 3 years, whereas the separate effects of drying and loss of fish were only significant in 2004. 4.Our results suggest that differences in water quality and ecology among reservoirs depend on their propensity to dry out. Drying might be used as a restoration measure to reduce potentially harmful cyanobacterial blooms in reservoirs.
  • PLoS One

    Dispersal Ability Determines the Role of Environmental, Spatial and Temporal Drivers of Metacommunity Structure

    André A. Padial, Fernanda Ceschin, Steven A.J. Declerck, Luc De Meester, Cláudia C. Bonecker, Fabio A. Lansac-Tôha, Liliana Rodrigues, Luzia C. Rodrigues, Sueli Train, Luiz F. M. Velho, Luis M. Bini

    Recently, community ecologists are focusing on the relative importance of local environmental factors and proxies to dispersal limitation to explain spatial variation in community structure. Albeit less explored, temporal processes may also be important in explaining species composition variation in metacommunities occupying dynamic systems. We aimed to evaluate the relative role of environmental, spatial and temporal variables on the metacommunity structure of different organism groups in the Upper Paraná River floodplain (Brazil). We used data on macrophytes, fish, benthic macroinvertebrates, zooplankton, periphyton, and phytoplankton collected in up to 36 habitats during a total of eight sampling campaigns over two years. According to variation partitioning results, the importance of predictors varied among biological groups. Spatial predictors were particularly important for organisms with comparatively lower dispersal ability, such as aquatic macrophytes and fish. On the other hand, environmental predictors were particularly important for organisms with high dispersal ability, such as microalgae, indicating the importance of species sorting processes in shaping the community structure of these organisms. The importance of watercourse distances increased when spatial variables were the main predictors of metacommunity structure. The contribution of temporal predictors was low. Our results emphasize the strength of a trait-based analysis and of better defining spatial variables. More importantly, they supported the view that “all-or- nothing” interpretations on the mechanisms structuring metacommunities are rather the exception than the rule.
  • Ecology Letters

    Stoichiometric regulation of phytoplankton toxins

    Dedmer Van de Waal, V.H. Smith, Steven A.J. Declerck, E.C.M. Stam, J.J. Elser
    Ecological Stoichiometry theory predicts that the production, elemental structure and cellular content of biomolecules should depend on the relative availability of resources and the elemental composition of their producer organism. We review the extent to which carbon- and nitrogen-rich phytoplankton toxins are regulated by nutrient limitation and cellular stoichiometry. Consistent with theory, we show that nitrogen limitation causes a reduction in the cellular quota of nitrogen-rich toxins, while phosphorus limitation causes an increase in the most nitrogen-rich paralytic shellfish poisoning toxin. In addition, we show that the cellular content of nitrogen-rich toxins increases with increasing cellular N : P ratios. Also consistent with theory, limitation by either nitrogen or phosphorus promotes the C-rich toxin cell quota or toxicity of phytoplankton cells. These observed relationships may assist in predicting and managing toxin-producing phytoplankton blooms. Such a stoichiometric regulation of toxins is likely not restricted to phytoplankton, and may well apply to carbon- and nitrogen-rich secondary metabolites produced by bacteria, fungi and plants.
  • PLoS One

    Correlates of zooplankton beta diversity in tropical lake systems

    P.M. Lopes, Luis M. Bini, Steven A.J. Declerck, V.F. Farjalla, L.C.G. Vieira, C.C. Bonecker, F.A. Lansac-Tôha, Francisco de Assis Esteves, R.L. Bozelli
    The changes in species composition between habitat patches (beta diversity) are likely related to a number of factors, including environmental heterogeneity, connectivity, disturbance and productivity. Here, we used data from aquatic environments in five Brazilian regions over two years and two seasons (rainy and dry seasons or high and low water level periods in floodplain lakes) in each year to test hypotheses underlying zooplankton beta diversity variation. The regions present different levels of hydrological connectivity, where three regions present lakes that are permanent and connected with the main river, while the water bodies of the other two regions consist of permanent lakes and temporary ponds, with no hydrological connections between them. We tested for relationships between zooplankton beta diversity and environmental heterogeneity, spatial extent, hydrological connectivity, seasonality, disturbance and productivity. Negative relationships were detected between zooplankton beta diversity and both hydrological connectivity and disturbance (periodic dry-outs). Hydrological connectivity is likely to affect beta diversity by facilitating dispersal between habitats. In addition, the harsh environmental filter imposed by disturbance selected for only a small portion of the species from the regional pool that were able to cope with periodic dry-outs (e.g., those with a high production of resting eggs). In summary, this study suggests that faunal exchange and disturbance play important roles in structuring local zooplankton communities
  • Hydrobiologia

    Effect of land use on pollution status and risk of fish endocrine disruption in small farmland ponds

    S.N.M. Mandiki, V. Gillardin, K. Martens, D. Ercken, E. De Roeck, T. De Bie, Steven A.J. Declerck, Luc De Meester, C. Brasseur, E. Van der Heiden, M. Schippo, M. Kestemont
    To study whether the intensity of agricultural activities affects pesticides loads in pond environment, a large number of Belgian farmland ponds were surveyed in spring 2004. Temporal distribution of pollutants was also investigated over restricted survey ponds sampled three times round year 2007. Sedentary pond Prussian carp juveniles were also captured to determine their brain aromatase activity (AA) and plasma vitellogenin (VTG) levels. Heavy metal distribution was also examined in various pond matrices. Amongst the pesticides analysed, only herbicides were detected. Contamination of pond water by atrazine was frequently observed during spring 2004, while isoproturon and glyphosate were detected round year 2007. Levels of herbicides were inversely related to the distance of ponds to crop field, and values peaked in April or October. Absence of endocrine disruptors in pond water was confirmed by lack of modulation in VTG and AA in male fish. Heavy metals were present in all the pond matrices, but overall contamination levels were low. The results demonstrated that Belgian ponds were mainly contaminated by herbicides and that pond sedentary fish were not affected by endocrine disruptors. They also demonstrated a marked effect of land-use intensity on herbicide pollution which can be mitigated by an adjustment of the buffer zones.
  • Journal of Environmental Management

    An ecosystem service approach to support integrated pond management: A case study using Bayesian belief networks – Highlighting opportunities and risks

    D. Landuyt, Pieter Lemmens, R. D'Hondt, S. Broekx, I. Liekens, T. De Bie, Steven A.J. Declerck, Luc De Meester, P. Goethals
    Freshwater ponds deliver a broad range of ecosystem services (ESS). Taking into account this broad range of services to attain cost-effective ESS delivery is an important challenge facing integrated pond management. To assess the strengths and weaknesses of an ESS approach to support decisions in integrated pond management, we applied it on a small case study in Flanders, Belgium. A Bayesian belief network model was developed to assess ESS delivery under three alternative pond management scenarios: intensive fish farming (IFF), extensive fish farming (EFF) and nature conservation management (NCM). A probabilistic cost-benefit analysis was performed that includes both costs associated with pond management practices and benefits associated with ESS delivery. Whether or not a particular ESS is included in the analysis affects the identification of the most preferable management scenario by the model. Assessing the delivery of a more complete set of ecosystem services tends to shift the results away from intensive management to more biodiversity-oriented management scenarios. The proposed methodology illustrates the potential of Bayesian belief networks. BBNs facilitate knowledge integration and their modular nature encourages future model expansion to more encompassing sets of services. Yet, we also illustrate the key weaknesses of such exercises, being that the choice whether or not to include a particular ecosystem service may determine the suggested optimal management practice.
  • Inland Waters

    Food quality dominates the impact of food quantity on Daphnia life history: possible implications for re-oligotrophication

    The elemental composition of phytoplankton is highly variable compared to the relatively narrow stoichiometry of zooplankton grazers. Using a full factorial design, we tested the effects of alterations in algal elemental composition (i.e., food quality) combined with food quantity on the life history of a Daphnia galeata clone from Lake IJsselmeer. Lower food quality reduced survival, growth, and reproduction. Food quantity became important at high food quality only. The strong effect of food quality indicates the potential for a stoichiometric bottleneck in Lake IJsselmeer, resulting in less high quality food for higher trophic levels as a result of re-oligotrophication.
  • European Journal of Protistology

    Planktonic ciliate community structure in shallow lakes of lowland Western Europe

    J. Van Wichelen, L. Johansson, P. Vanormelingen, Steven A.J. Declerck, T. Lauridsen, Luc De Meester, Erik Jeppesen, W. Vyverman
    Temperate shallow meso- to eutrophic lakes can exist in one of two alternative states with contrasting foodwebs, referred to as the clear-water and the turbid state. We describe the planktonic ciliate communities of such lakes based on a survey of 66 northwestern European lakes. Ciliates were enumerated and identified to species level according to the quantitative protargol staining technique. Ciliate biomass was on average twice as high in the turbid than in the clear-water lakes. The ciliate communities were dominated by oligotrichs and protostomatids, and no differences in functional composition or α-diversity could be detected between turbid and clear-water lakes, although β-diversity tended to be higher in the latter. At the species level, however, community structure strongly differed between turbid and clear-water lakes, and several indicator species could be identified for the different lake categories. Variation partitioning showed that nutrient status did not explain ciliate community structure independent of the alternative states, while lake area was identified as an additional structuring factor for the ciliate communities. These results stress the importance of the ecosystem structure in shaping ciliate communities in temperate shallow lakes and suggest that nutrient status has little direct effect on ciliate community structure in such lakes.
  • PLoS One

    How to Maximally Support Local and Regional Biodiversity in Applied Conservation? Insights from Pond Management

    Pieter Lemmens, J. Mergeay, T. De Bie, J. Van Wichelen, Luc De Meester, Steven A.J. Declerck
    Biodiversity and nature values in anthropogenic landscapes often depend on land use practices and management. Evaluations of the association between management and biodiversity remain, however, comparatively scarce, especially in aquatic systems. Furthermore, studies also tend to focus on a limited set of organism groups at the local scale, whereas a multi-group approach at the landscape scale is to be preferred. This study aims to investigate the effect of pond management on the diversity of multiple aquatic organism groups (e.g. phytoplankton, zooplankton, several groups of macro-invertebrates, submerged and emergent macrophytes) at local and regional spatial scales. For this purpose, we performed a field study of 39 shallow man-made ponds representing five different management types. Our results indicate that fish stock management and periodic pond drainage are crucial drivers of pond biodiversity. Furthermore, this study provides insight in how the management of eutrophied ponds can contribute to aquatic biodiversity. A combination of regular draining of ponds with efforts to keep ponds free of fish seems to be highly beneficial for the biodiversity of many groups of aquatic organisms at local and regional scales. Regular draining combined with a stocking of fish at low biomass is also preferable to infrequent draining and lack of fish stock control. These insights are essential for the development of conservation programs that aim long-term maintenance of regional biodiversity in pond areas across Europe.
  • Journal of Biogeography

    Effects of connectivity, dispersal directionality and functional traits on the metacommunity structure of river benthic diatoms

    Jing Liu, J. Soininen, B.P. Han, Steven A.J. Declerck
    Aim Dendritic ecological networks (DENs), such as river systems, combine features that challenge the traditional conceptual views and empirical approaches applied to metacommunities. As a result of their dendritic branching geometry and stream flow directionality, they are strongly hierarchical and asymmetrical. We analysed the metacommunity structure of benthic diatoms in a large-scale river system with the aim of evaluating the importance of potential causal influences. Furthermore, we hypothesized that metacommunities of diatoms that are strongly attached to their substrata show a different spatial structure than metacommunities of other, more weakly attached diatoms. Location The study was carried out in the Dong River, a 32,275 km2 subtropical river network located in southern China. Methods We surveyed benthic diatom communities during three seasons (dry, intermediate and wet). Using partial redundancy analysis, we partitioned community variation among environmental models and different spatial eigenfunction models to evaluate the influence of alternative dispersal pathways (overland versus water course dispersal), stream directionality, man-made dams and diatom functional traits on diatom metacommunity structure. Results Models based on hydrological connections and water directionality represent spatial patterns better than overland distances, suggesting that the dynamics of benthic diatom metacommunities are mainly confined to the river network and influenced by the prevailing water flow. We found significant effects of man-made dams on the spatial structure of important limnological variables and diatom metacommunity structure. The metacommunity of strongly attached diatoms also showed a weaker signature of flow directionality than that of other growth forms, especially in seasons with high water levels. Main conclusions We conclude that the consideration of among-site connectivity, flow directionality and species traits is key to a better understanding of the spatial ecology of passively dispersing microbial organisms in river systems.
  • ISME Journal

    Effects of patch connectivity and heterogeneity on metacommunity structure of planktonic bacteria and viruses

    Steven A.J. Declerck, C. Winter, J.B. Shurin, C.A. Suttle, B. Matthews
    Dispersal limitation is generally considered to have little influence on the spatial structure of biodiversity in microbial metacommunities. This notion derives mainly from the analysis of spatial patterns in the field, but experimental tests of dispersal limitation using natural communities are rare for prokaryotes and, to our knowledge, non-existent for viruses. We studied the effects of dispersal intensity (three levels) and patch heterogeneity (two levels) on the structure of replicate experimental metacommunities of bacteria and viruses using outdoor mesocosms with plankton communities from natural ponds and lakes. Low levels of dispersal resulted in a decrease in the compositional differences (beta diversity) among the communities of both bacteria and viruses, but we found no effects of patch heterogeneity. The reductions in beta diversity are unlikely to be a result of mass effects and only partly explained by indirect dispersal-mediated interactions with phytoplankton and zooplankton. Our results suggest that even a very limited exchange among local communities can alter the trajectory of bacterial and viral communities at small temporal and spatial scales.
  • Inland Waters

    The ecology of the riverine Garra species (Teleostei, Cypriniformes) in reservoirs of the semi-arid highlands of northern Ethiopia: temporal dynamics of feeding activity

    M. Teferi, Steven A.J. Declerck, T. De Bie, A. Gebrekidan, J. Snoeks, T. Asmelash, T. Dejenie, H. Bauer, J.A. Deckers, Luc De Meester
    Garra species are among the most abundant fish in small rivers of northern Ethiopia. Many manmade reservoirs in the region have been colonized by Garra, which often are the only fish species present and have become very abundant. Little is known about the ecology of these reservoir populations of riverine species. In this study we investigated the distribution patterns and gut fullness of 2 dominant species, G. blanfordii and G. geba, in 3 recently created reservoirs (Gereb Awso, Tsinkanet, and Mai Gassa I) in Tigray, northern Ethiopia. Species composition differed among reservoirs. Our data on fish catch densities and the fullness of the foregut suggest that the ecology of the Garra populations in the reservoirs is likely influenced by the avoidance of predation by birds. G. blanfordii, and to a lesser extent G. geba, foraged most actively after sunset.
  • Limnologica

    Cladoceran community composition in tropical semi-arid highland reservoirs in Tigray (Northern Ethiopia): a metacommunity perspective applied to young reservoirs

    T. Dejenie, Steven A.J. Declerck, T. Asmelash, S. Risch, J. Mergeay, T. De Bie, Luc De Meester
    A field survey of zooplankton communities was carried out in 32 recently established tropical semi-arid reservoirs in the highlands of Northern Ethiopia with the aim to identify to what extent environmental factors determine species composition of the cladoceran community in such isolated and young reservoirs. To address seasonal variation, the survey was carried out both at the beginning and the end of the dry season. A total of 15 species of cladocerans were identified. Daphnia was the most abundant cladoceran genus, and was present in all reservoirs. Using presence–absence data, no association between cladoceran community composition and geographic distance was found. RDA results indicate that the set of environmental variables that explained cladoceran community composition differed among seasons. Depth, altitude and fish biomass showed a significant association with cladoceran community composition during the wet season, whereas variation in cladoceran community structure was associated with phytoplankton biomass in the dry season. The relative abundance of Daphnia was much higher in the pelagic than in the littoral zone of our study systems. Two key groups of pelagic filter-feeding cladocerans, Diaphanosoma and Daphnia, showed a clear pattern, in which one or the other tended to strongly dominate the community. In addition, we observed a negative association between dominance of Daphnia in the zooplankton community and dominance of cyanobacteria in the phytoplankton community.
  • Ecology Letters

    Body size and dispersal mode as key traits determining metacommunity structure of aquatic organisms

    T. De Bie, Luc De Meester, L. Brendonck, K. Martens, B. Goddeeris, D. Ercken, H. Hampel, L. Denys, L. Vanhecke, K. van der Gucht, J. Van Wichelen, W. Vyverman, Steven A.J. Declerck
    Relationships between traits of organisms and the structure of their metacommunities have so far mainly been explored with meta-analyses. We compared metacommunities of a wide variety of aquatic organism groups (12 groups, ranging from bacteria to fish) in the same set of 99 ponds to minimise biases inherent to meta-analyses. In the category of passive dispersers, large-bodied groups showed stronger spatial patterning than small-bodied groups suggesting an increasing impact of dispersal limitation with increasing body size. Metacommunities of organisms with the ability to fly (i.e. insect groups) showed a weaker imprint of dispersal limitation than passive dispersers with similar body size. In contrast, dispersal movements of vertebrate groups (fish and amphibians) seemed to be mainly confined to local connectivity patterns. Our results reveal that body size and dispersal mode are important drivers of metacommunity structure and these traits should therefore be considered when developing a predictive framework for metacommunity dynamics.
  • Freshwater Biology

    Evidence against the use of surrogates for biomonitoring of Neotropical floodplains

    A.A. Padial, Steven A.J. Declerck, Luc De Meester, C.C. Bonecker, F.A. Lansac-Toha, L.C. Rodrigues, A. Takeda, S. Train, L.F.M. Velho, Luis M. Bini
    1. Community concordance measures the level of association between the compositional patterns shown by two groups of organisms. If strong community concordance occurs, one group could be used as a surrogate for another in conservation planning and biodiversity monitoring. In this study, we evaluated the variability in the strength of community concordance, the likely mechanisms underlying community concordance and the degree to which one community can predict another in a set of Neotropical floodplain lakes (Upper Parana´ River floodplain, Brazil). 2. We used a data set including six aquatic communities: fish, macrophytes, benthic macroinvertebrates, zooplankton, phytoplankton and periphyton. We used Mantel and PROTEST approaches to evaluate the levels of community concordance in up to four sampling periods. Also, we used partial Mantel test and information about biotic interactions to investigate reasons for observed patterns of concordance. Finally, we used co-correspondence analysis to evaluate the performance of one taxonomic group in predicting the structures of other communities. 3. The levels of community concordance varied over time for almost all cross-taxa comparisons. Concordance between phytoplankton and periphyton probably resulted from similar responses to environmental gradients, whereas other patterns of concordance were likely generated by interactions among groups. However, the levels of predictability were low, and no particular taxonomic group significantly predicted all other groups. 4. The low and temporally variable levels of community concordance cast doubts on the use of surrogate groups for biodiversity management in Neotropical floodplains.
  • Ecology Letters

    Dispersal-mediated trophic interactions can generate apparent patterns of dispersal limitation in aquatic metacommunities

    D. Verreydt, Luc De Meester, E. Decaestecker, M.J. Villena, K. van der Gucht, P. Vannormelingen, W. Vyverman, Steven A.J. Declerck
    Dispersal is a major organising force in metacommunities, which may facilitate compositional responses of local communities to environmental change and affect ecosystem function. Organism groups differ widely in their dispersal abilities and their communities are therefore expected to have different adaptive abilities. In mesocosms, we studied the simultaneous compositional response of three plankton communities (zoo-, phyto- and bacterioplankton) to a primary productivity gradient and evaluated how this response was mediated by dispersal intensity. Dispersal enhanced responses in all three planktonic groups, which also affected ecosystem functioning. Yet, variation partitioning analyses indicated that responses in phytoplankton and bacterial communities were not only controlled by dispersal directly but also indirectly through complex trophic interactions. Our results indicate that metacommunity patterns emerging from dispersal can cascade through the food web and generate patterns of apparent dispersal limitation in organisms at other trophic levels.
  • Basic and Applied Ecology

    Effects of nutrient additions and macrophyte composition on invertebrate community assembly and diversity in experimental ponds.

    Steven A.J. Declerck, (Liesbeth) E.S. Bakker, Bart van Lith, A.P. Kersbergen, Ellen Van Donk
    Macrophytes and nutrient loading are two factors that can strongly determine the diversity and composition of aquatic invertebrate communities. Both factors may also interact, because macrophyte species may be differentially affected by nutrients. Macrophyte community characteristics, such as species composition, morphotype and biomass have the potential to mediate the response of invertebrate communities to nutrient loading. In 36 newly constructed experimental ponds,weorthogonally combined three macrophyte community types (Chara-, Potamogeton- and Elodea-dominated) with two levels of nutrient additions (no addition and an addition of 0.5 mg P and 3mg N/L per week) and studied community assembly in three functional groups of invertebrates (epiphytic macroinvertebrates, littoral and pelagic crustacean zooplankton). Macrophyte biomass was negatively affected by nutrient addition. General linear models indicated negative responses of species richness in the zooplankton functional groups to nutrient addition and phytoplankton chlorophyll-a, but demonstrated no effects of macrophyte community type. Conversely, macroinvertebrate taxon richness differed among macrophyte community types but showed no response to nutrient enrichment. Macrophyte biomass correlated positively with the richness of littoral zooplankton and macroinvertebrates and was a better predictor of these diversity variables than macrophyte community type. Overall, our results indicate that lake management practices that aim at obtaining a nutrient poor and macrophyte dominated clear water state contribute also to the maintenance of aquatic invertebrate diversity.
  • Freshwater Biology

    Biological control of phytoplankton by the subtropical submerged macrophytes Egeria densa and Potamogeton illinoensis: a mesocosm study

    M. Vanderstukken, N. Mazzeo, W. Colen, Steven A.J. Declerck, K. Muylaert
    1. In temperate regions, submerged macrophytes can hamper phytoplankton blooms. Such an effect could arise directly, for instance via allelopathy, or indirectly, via competition for nutrients or the positive interaction between submerged macrophytes and zooplankton grazing. However, there is some evidence that the positive interaction between submerged macrophytes and zooplankton grazing is less marked in warmer regions, where the interaction is less well studied, and that negative effects of higher water plants on phytoplankton biomass are weaker. 2. We carried out two consecutive mesocosm experiments in Uruguay (subtropical South America) to study the effects of two common submerged macrophytes from this region (Egeria densa and Potamogeton illinoensis) on phytoplankton biomass, in the absence of zooplankton grazing. We compared phytoplankton development between different macrophyte treatments (no macrophytes, artificial macrophytes, real Egeria and real Potamogeton). We used artificial macrophytes to differentiate between physical effects (i.e. shading, sedimentation and competition with periphyton) and biological effects (i.e. nutrient competition and allelopathy). 3. In Experiment 1, we found no evidence for physical effects of macrophytes on phytoplankton biomass, but both macrophyte species seemed to exert strong biological effects on phytoplankton biomass. Only Egeria affected phytoplankton community structure, particularly tempering the dominance of Scenedesmus. Nutrient addition assays revealed that only Egeria suppressed phytoplankton through nutrient competition. 4. We performed a second mesocosm experiment with the same design, but applying saturating nutrient conditions as a way of excluding the effects of competition for nutrients. This experiment showed that both macrophytes were still able to suppress phytoplankton through biological mechanisms, providing evidence for allelopathic effects. Our results indicate that both common macrophytes are able to keep phytoplankton biomass low, even in the absence of zooplankton grazing.
  • Ecography

    Scale dependency of processes structuring metacommunities of cladocerans in temporary pools of High-Andes wetlands

    Steven A.J. Declerck, J.S. Coronel, P. Legendre, L. Brendonck
    Metacommunity structure can be shaped by a variety of processes operating at different spatial scales. With increasing scale, the compositional variation among local communities (beta diversity) may reflect stronger environmental heterogeneity, but may also reflect reduced exchange of organisms between habitat patches. We analyzed the spatial architecture of a metacommunity of cladoceran zooplankton in temporary pools of High Andes wetlands, with the objective of explaining the spatial dependency of its structure. The spatial distribution of the pools is hierarchical and highly discontinuous: pools are clustered within small wetlands, which lay scattered over valleys that are separated from each other by mountain ridges. We studied a total of 59 pools, belonging to six different wetlands in four different valleys. We assessed pool environmental heterogeneity and sampled active communities and dormant propagule banks of cladoceran zooplankton. Environmental heterogeneity proved very high within wetlands and showed almost no increase with increasing spatial scale. Conversely, diversity partitioning analyses indicated an increase in beta diversity with spatial scale, especially among valleys. Variation partitioning on environmental data and spatial RDA models suggested environmental heterogeneity as the most important generator of beta diversity within wetlands. At the largest spatial scale, beta diversity manifested itself mainly as a differentiation of species occurrence patterns among valleys, which could not be entirely explained by environmental variables. Our study thus presents a case where environmental control seems to be the dominant metacommunity structuring process at the smallest spatial scale, whereas neutral processes and dispersal limitation are the most likely generators of beta diversity at the largest spatial scale.
  • Aquatic Ecology

    Genetic diversity of Microcystis blooms (Cyanobacteria) in recently constructed reservoirs in Tigray (Northern Ethiopia) assessed by rDNA ITS

    I. van Gremberghe, K. van der Gucht, P. Vanormelingen, T. Asmelash, T. Dejenie, S. D'Hondt, Steven A.J. Declerck, Luc De Meester, W. Vyverman
    The cyanobacterium Microcystis is notorious for forming extensive and potentially toxic blooms in nutrient-rich freshwater bodies worldwide. However, little is known about the factors underlying the genetic diversity and structure of natural Microcystis populations, despite the fact that this knowledge is essential to understand the build-up of blooms. Microcystis blooms are common and occur year-round in Africa, but are underinvestigated in this continent. We studied the genetic diversity and structure of Microcystis populations in 30 man-made reservoirs in Tigray (Northern Ethiopia) using Denaturing Gradient Gel Electrophoresis of the 16S-23S rDNA internal transcribed spacer (ITS) region and assessed the importance of local environmental conditions and geographic position of the reservoirs for the observed patterns. The analyses showed that both regional and local Microcystis ITS diversity in these recently constructed reservoirs was relatively low, with several dense blooms containing only a single ITS type. Especially one non-toxic ITS type dominated a considerable fraction of Microcystis blooms, but appeared restricted in its geographic distribution. The relationship between Microcystis ITS population structure and abiotic variables (water clarity, pH) and with zooplankton (Daphnia biomass) indicates a (limited) influence of environmental conditions on Microcystis population structure in the reservoirs of Tigray.
  • Hydrobiologia

    Variation in ostracod (Crustacea, Ostracoda) communities in the alluvial valley of the upper Paraná River (Brazil) in relation to substrate

    J. Higuti, Steven A.J. Declerck, F.A. Lansac-Tôha, L.F.M. Velho, K. Martens
    Large river floodplains are convenient model systems to test for variation in animal and plant community structure, as they have a variety of habitats and substrates and are generally dynamic systems through the occurrence of flood pulses with varying intensity. South American floodplain systems furthermore have unique types of substrates, in the form of root systems of floating macrophytes. Here, we investigate the variation in ostracod (small, bivalved crustaceans) communities in relation to substrates and related environmental variables. Sampling was effected in 2004 in the alluvial valley of the upper Paraná River, Brazil, in the wet and dry seasons. Five different substrates, including littoral sediment and four macrophyte species root and leaf systems, in four hydrological systems and a variety of habitat types, were sampled. Fifty-four species of Ostracoda were found. Variation partitioning analysis (RDA) showed that ostracod communities significantly differed between different substrates, mainly between the littoral and plants with small root systems (Eichhornia azurea) on the one hand, and plants with large and complex root systems on the other hand (Eichhornia crassipes and Pistia stratiotes). RDA analyses indicated that the pleuston (biotic communities associated with root systems of floating plants) of E. crassipes comprised more non-swimming species than the pleuston of the smaller roots of P. stratiotes, but species-level Kruskal–Wallis analyses could not detect significant differences between both macrophyte species. Also habitat type and hydrological systems contributed to variation amongst ostracod communities, but less so than the factor substrate. Abiotic factors also contributed to variation, but the ranges of all measured water chemistry variables were narrow. This uniformity in abiotic factors, which might be owing to the occurrence of large flooding events, unites all water bodies, even those that are generally separated.
  • Hydrobiologia

    Effects of medium renewal and handling stress on life history traits in Daphnia

    S. Rousseaux, J. Vanoverbeke, J. Aerts, Steven A.J. Declerck
    The zooplankton genus Daphnia is used as a model organism in ecological, ecotoxicological and evolutionary research. It is often used in experimental laboratory setups to examine life history traits under a variety of factors inducing stress. One type of stress, handling stress because of manipulation during the experiments, however, is often neglected. In a standard life history experiment, we found that several kinds of experimental manipulation may have a significant impact on the life history response of test animals. Especially renewal of the medium may reduce the reproductive output of the individuals significantly. In every experiment where the reproduction of Daphnia is an important trait under study, the negative effects of medium renewal and handling stress should be considered and care should be taken to keep handling of the individuals to a minimum.
  • Applied Microbiology and Biotechnology

    Bacterial community analysis of activated sludge: an evaluation of four commonly used DNA extraction methods

    L. Vanysacker, Steven A.J. Declerck, B. Hellemans, Luc De Meester, I. Vankelecom, P. Declerck
    The effectiveness of three commercially available direct DNA isolation kits (Mobio, Fast, Qiagen) and one published direct DNA extraction protocol (Bead) for extracting bacterial DNA from different types of activated sludge was investigated and mutually compared. The DNA quantity and purity were determined using real-time PCR targeting the bacterial 16S rDNA gene. Microbial community fingerprints were assessed by automated ribosomal intergenic spacer analysis. The resulting community profiles were analyzed with canonical correspondence analysis. Our results clearly demonstrate that direct DNA extraction methods can significantly influence the DNA quantity, purity, and observed community patterns of microbiota in activated sludge. Fast and Mobio generated high amounts of good quality DNA compared to Bead and Qiagen. Mobio also resulted in the detection of the highest number of species while Fast scored the best in discriminating between the community patterns of different activated sludge types. With respect to the characterization of community profiles, our analyses demonstrated a strong sludge type dependent variability among methods. Taking into account our results, we recommend Fast as the most suitable DNA extraction method for activated sludge samples used for bacterial community studies.
  • Hydrobiologia

    Influence of nutrients, submerged macrophytes and zooplankton grazing on phytoplankton biomass and diversity along a latitudinal gradient in Europe

    K. Muylaert, C. Pérez-Martínez, P. Sánchez-Castillo, T. Lauridsen, M. Vanderstukken, Steven A.J. Declerck, K. van der Gucht, J-M. Conde-Porcuna, Erik Jeppesen, Luc De Meester, W. Vyverman
    In order to evaluate latitudinal differences in the relationship of phytoplankton biomass and diversity with environmental conditions in shallow lakes, we sampled 98 shallow lakes from three European regions: Denmark (DK), Belgium/The Netherlands (BNL) and southern Spain (SP). Phytoplankton biomass increased with total phosphorus (TP) concentrations and decreased with submerged macrophyte cover across the three regions. Generic richness was significantly negatively related to submerged macrophyte cover and related environmental variables. Zooplankton:phytoplankton biomass ratios were positively related to submerged macrophyte cover and negatively to phytoplankton generic richness in DK and BNL, suggesting that the low generic richness in lakes with submerged macrophytes was due to a higher zooplankton grazing pressure in these regions. In SP, phytoplankton generic richness was not influenced by zooplankton grazing pressure but related to conductivity. We observed no relationship between phytoplankton generic richness and TP concentration in any of the three regions. The three regions differed significantly with respect to mean local and regional generic richness, with BNL being more diverse than the other two regions. Our observations suggest that phytoplankton diversity in European shallow lakes is influenced by submerged macrophyte cover indirectly by modulating zooplankton grazing. This influence of submerged macrophytes and zooplankton grazing on phytoplankton diversity decreases from north to south.
  • Hydrobiologia

    The influence of plant-associated filter feeders on phytoplankton biomass: a mesocosm study

    M. Vanderstukken, Steven A.J. Declerck, A. Pals, Luc De Meester, K. Muylaert
    Low phytoplankton biomass usually occurs in the presence of submerged macrophytes, possibly because submerged macrophytes enhance top-down control of phytoplankton by offering a refuge for efficient grazers like Daphnia against fish predation. However, other field studies also suggest that submerged macrophytes suppress phytoplankton in the absence of Daphnia. In order to investigate these mechanisms further, we conducted an outdoor mesocosm experiment to study the effect of submerged macrophytes (Elodea nuttallii) on phytoplankton and zooplankton biomass. The experiment combined four nutrient addition levels (0, 10, 100, and 1000 lg P l-1; N/P ratio: 16) with three macrophyte levels (no macrophytes, artificial macrophytes, and real macrophytes). We inoculated the tanks with species-rich inocula of phytoplankton and zooplank macrophyte treatment combinations. Compared to the treatment combinations without macrophytes, lower phytoplankton biomass occurred in the treatment combinations with real macrophytes at all the nutrient addition levels and in those with artificial macrophytes at all the nutrient levels except the highest. Significantly, higher abundances of plant-associated filter feeders (Simocephalus vetulus and Ceriodaphnia spp.) occurred in the treatment combinations with real and artificial macrophytes. Th
  • Basic and Applied Ecology

    Effect of macrophyte community composition and nutrient enrichment on plant biomass and algal blooms.

    Submerged freshwater macrophytes decline with increasing eutrophication. This has consequences for ecosystem processes in shallow lakes and ponds as macrophytes can reduce algal blooms under eutrophic conditions. We hypothesize that the productivity of submerged vegetation, biomass change under eutrophication and the suppression of algal blooms may be affected by macrophyte community composition. To test our hypothesis, we established three macrophyte community types in 36 fishless experimental ponds: one dominated by the oligotrophic species Chara globularis, one dominated by the eutrophic species Potamogeton pectinatus and a diverse vegetation which became co-dominated by Elodea nuttallii and C. globularis, and we fertilized half of the ponds. The macrophyte communities produced different amounts of biomass and they responded differently to fertilization. The community dominated by Potamogeton produced the lowest overall biomass, but was not affected by nutrient addition. The communities dominated by Chara and co-dominated by Elodea and Chara produced more than four-fold the amount of biomass produced in Potamogeton communities under oligotrophic conditions, but were strongly negatively affected by nutrient addition. Phytoplankton abundance did not differ significantly among the plant community types, but showed large variation within community types. There was a significant negative relationship between spring macrophyte biomass and the probability of summer algal blooms. The occurrence of algal blooms coincided with low daphnid densities and high pH (>10). We conclude that the macrophyte community composition, characterized by the dominant species, strongly affected the amount of biomass production as well as the short-term response of the vegetation to nutrient enrichment. Macrophyte community composition had no direct effect on algal blooms, but can affect the occurrence of algal blooms indirectly as these occurred only in ponds with low (
  • Hydrobiologia

    Impacts of climate warming on lake fish community structure and potential effects on ecosystem function

    Erik Jeppesen, M. Meerhoff, K. Holmgren, I. González-Bergonzoni, F. Teixeira-de Mello, Steven A.J. Declerck, Luc De Meester, M. Søndergaard, T. Lauridsen, R. Bjerring, J-M. Conde-Porcuna, N. Mazzeo, C. Iglesias, M. Reizenstein, H.J. Malmquist, Z. Liu, D. Balayla, X. Lazzaro
    Fish play a key role in the trophic dynamics of lakes, not least in shallow systems. With climate warming, complex changes in fish community structure may be expected owing to the direct and indirect effects of temperature, and indirect effects of eutrophication, water-level changes and salinisation on fish metabolism, biotic interactions and geographical distribution. We review published and new data supporting the hypotheses that, with a warming climate, there will be changes in: fish community structure (e.g. higher or lower richness depending on local conditions); life history traits (e.g. smaller body size, shorter life span, earlier and less synchronised reproduction); feeding mode (i.e. increased omnivory and herbivory); behaviour (i.e. stronger association with littoral areas and a greater proportion of benthivores); and winter survival. All these changes imply higher predation on zooplankton and macroinvertebrates with increasing temperatures, suggesting that the changes in the fish communities partly resemble, and may intensify, the effects triggered by eutrophication. Modulating factors identified in cold and temperate systems, such as the presence of submerged plants and winter ice cover, seem to be weaker or non-existent in warm(ing) lakes. Consequently, in the future lower nutrient thresholds may be needed to obtain clear-water conditions and good ecological status in the future in currently cold or temperate lakes. Although examples are still scarce and more research is needed, we foresee biomanipulation to be a less successful restoration tool in warm(ing) lakes without a strong reduction of the nutrient load.
  • Freshwater Reviews

    Climate change and the future of freshwater biodiversity in Europe: a primer for policy-makers

    B. Moss, Daniel Hering, Andy J. Green, A. Adoud, E. Becares, Meryem Beklioğlu, H. Bennion, D. Boix, S. Brucet, L. Carvalho, B. Clement, Thomas A. Davidson, Steven A.J. Declerck, M. Dobson, Ellen Van Donk, B. Dudley, H. Feuchtmayr, N. Friberg, G. Grenouillet, H. Hillebrand, A. Hobaek, K. Irvine, Erik Jeppesen, R. Johnson, I. Jones, M. Kernan, T. Lauridsen, M. Manca, M. Meerhof, J. Olafsson, S. Ormerod, E. Papastergiadou, W.E. Penning, R. Ptacnik, X. Quintana, L. Sandin, M. Seferlis, G. Simpson, C. Trigal, P.F.M. Verdonschot, Anthony M. Verschoor, G. Weyhenmeyer
    Earth’s climate is changing, and by the end of the 21st century in Europe, average temperatures are likely to have risen by at least 2 °C, and more likely 4 °C, with associated effects on patterns of precipitation and the frequency of extreme weather events. Attention among policy-makers is divided about how to minimise the change, how to mitigate its effects, how to maintain the natural resources on which societies depend and how to adapt human societies to the changes. Natural systems are still seen, through a long tradition of conservation management that is largely species-based, as amenable to adaptive management, and biodiversity, mostly perceived as the richness of plant and vertebrate communities, often forms a focus for planning. We argue that prediction of particular species changes will be possible only in a minority of cases but that prediction of trends in general structure and operation of four generic freshwater ecosystems (erosive rivers, depositional floodplain rivers, shallow lakes and deep lakes) in three broad zones of Europe (Mediterranean, Central and Arctic-Boreal) is practicable. Maintenance and rehabilitation of ecological structures and operations will inevitably and incidentally embrace restoration of appropriate levels of species biodiversity. Using expert judgement, based on an extensive literature, we have outlined, primarily for lay policy makers, the pristine features of these systems, their states under current human impacts, how these states are likely to alter with a warming of 2 °C to 4 °C and what might be done to mitigate this. We have avoided technical terms in the interests of communication, and although we have included full referencing as in academic papers, we have eliminated degrees of detail that could confuse broad policy-making.
  • Freshwater Biology

    Impact of the fish Garra on the ecology of reservoirs and the occurrence of Microcystis blooms in semi-arid tropical highlands: an experimental assessment using enclosures

    T. Dejenie, T. Asmelash, S. Rousseaux, T. Gebregiorgis, A. Gebrekidan, M. Teferi, J. Nyssen, J. Deckers, K. van der Gucht, W. Vyverman, Luc De Meester, Steven A.J. Declerck
    1. Many man-made reservoirs in the semi-arid highlands of Northern Ethiopia (Tigray) are characterised by the occurrence of intensive blooms of cyanobacteria and a dominance of small riverine fishes belonging to the genus Garra. 2. We carried out enclosure experiments to test for the effect of these small fish on abiotic characteristics, phytoplankton biomass and zooplankton community structure in the pelagic of two reservoirs (Gereb Awso and Tsinkanet). Two experiments were carried out in each of the reservoirs, one at the end of the rainy season (highest water level) and one at the end of the dry season (lowest water level). 3. The presence of Garra in general increased the amount of suspended matter, nutrient concentrations (total nitrogen and total phosphorus), phytoplankton and Microcystis biomass (including the proportion of Microcystis in the phytoplankton community), and reduced water transparency. The positive effect of the presence of Garra on nutrient concentrations and phytoplankton productivity indicate that Garra has the potential to affect food web functioning indirectly through bottom-up effects, by enhancing nutrient concentrations through sediment resuspension and excretion of nutrients. Indeed, population densities of the cladoceran zooplankton taxa Ceriodaphnia and Diaphanosoma also showed an overall increase in enclosures with Garra. 4. However, our data also provide some evidence for a potential of Garra to exert top-down control on large bodied daphnids (Daphnia carinata, D. barbata), although such effect varied among experiments. The limited capability of Garra to control zooplankton communities mainly reflects the low efficiency of these small, riverine and benthos-oriented fish in foraging on zooplankton and suggests the existence of an unoccupied niche for zooplanktivorous fish in the majority of the reservoirs. 5. Although the main effects of Garra on the pelagic food web seemed to be mediated by bottom-up mechanisms, our results also indicate that one of the key variables, the relative abundance of Microcystis, was impacted by Daphnia-mediated trophic cascade effects.
  • Freshwater Biology

    Subfossil Cladocera in relation to contemporary environmental variables in 54 Pan-European lakes

    R. Bjerring, E. Becares, Steven A.J. Declerck, Elisabeth M. Gross, L-A. Hansson, T. Kairesalo, M. Nykänen, A. Halkiewicz, R. Kornijow, J-M. Conde-Porcuna, M. Seferlis, Tiina Nõges, B. Moss, S. L. Amsinck, Bent V. Odgaard, Erik Jeppesen
    P>1. Changes in cladoceran subfossils in the surface sediments of 54 shallow lakes were studied along a European latitude gradient (36-68 degrees N). Multivariate methods, such as regression trees and ordination, were applied to explore the relationships between cladoceran taxa distribution and contemporary environmental variables, with special focus on the impact of climate. 2. Multivariate regression tree analysis showed distinct differences in cladoceran community structure and lake characteristics along the latitude gradient, identifying three groups: (i) northern lakes characterised by low annual mean temperature, conductivity, nutrient concentrations and fish abundance, (ii) southern, macrophyte rich, warm water lakes with high conductivity and high fish abundance and (iii) Mid-European lakes at intermediate latitudes with intermediate conductivities, trophic state and temperatures. 3. Large-sized, pelagic species dominated a group of seven northern lakes with low conductivity, where acid-tolerant species were also occasionally abundant. Small-sized, benthic-associated species dominated a group of five warm water lakes with high conductivity. Cladoceran communities generally showed low species-specific preferences for habitat and environmental conditions in the Mid-European group of lakes. Taxon richness was low in the southern-most, high-conductivity lakes as well as in the two northern-most sub-arctic lakes. 4. The proportion of cladoceran resting eggs relative to body shields was high in the northern lakes, and linearly (negatively) related to both temperature and Chl a, indicating that both cold climate (short growing season) and low food availability induce high ephippia production. 5. Latitude and, implicitly, temperature were strongly correlated with conductivity and nutrient concentrations, highlighting the difficulties of disentangling a direct climate signal from indirect effects of climate, such as changes in fish community structure and human-related impacts, when a latitude gradient is used as a climate proxy. Future studies should focus on the interrelationships between latitude and gradients in nutrient concentration and conductivity.
  • Restoration Ecology

    Evaluation of Restoration Measures in a Shallow Lake through a Comparison of Present Day Zooplankton Communities with Historical Samples

    G. Louette, Steven A.J. Declerck, J. Vandekerkhove, Luc De Meester
    Many shallow lakes have lost a large part of their ecological value during the past decades. Human-induced factors such as eutrophication and inappropriate fish stock management are generally the main causes for this loss. To restore such degraded habitats, several measures are taken, typically involving a reduction of nutrient loading and interventions in the aquatic food web functioning (biomanipulation). In this study, we report on the joint effects of a series of restoration measures in a shallow lake (Lake Kraenepoel, Belgium, 22 ha) and evaluate these effects via three different criteria. The first criterion is that the target condition, being a clearwater phase with submerged macrophytes, was successfully achieved and persisted for a period of at least 5 years after restoration. Second, we detected a substantial change in community structure of cladoceran zooplankton and an associated increase in species richness and conservation value following restoration measures. Finally, we observed that the general structure of the present day cladoceran zooplankton community resembles well that of the preeutrophication period (1929-1931). Current species richness, however, tends to be lower than in the reference period, and some rare species are still lacking. It is conceivable that, when submerged macrophytes develop further, a subset of specialist species may reappear. Overall, the use of historical habitat-specific samples offers a major opportunity for evaluating restoration success in great detail. Community structures may directly be compared, the gain or loss of specific species can accurately be documented, and more insights in the observed patterns be obtained.
  • Molecular Ecology

    The genetic legacy of polyploid Bolivian Daphnia: the tropical Andes as a source for the North and South American D-pulicaria complex

    J. Mergeay, X. Aguilera, Steven A.J. Declerck, A. Petrusek, T. Huyse, Luc De Meester
    We investigated genetic variation in asexual polyploid members of the water flea Daphnia pulex complex from a set of 12 Bolivian high-altitude lakes. We used nuclear microsatellite markers to study genetic relationships among all encountered multilocus genotypes, and combined this with a phylogenetic approach using DNA sequence data of three mitochondrial genes. Analyses of mitochondrial gene sequence divergence showed the presence of three very distinct clades that likely represent cryptic undescribed species. Our phylogenetic results suggest that the Daphnia pulicaria group, a complex of predominantly North American species that has diversified rapidly since the Pleistocene, has its origin in South America, as specific tests of topology indicated that all three South American lineages are ancestral to the North American members of this species group. A comparison between variation of nuclear and mitochondrial markers revealed that closely related polyploid nuclear genotypes sometimes belonged to very divergent mitochondrial lineages, while distantly related nuclear genotypes often belonged to the same mitochondrial lineage. This discrepancy suggests that these South American water fleas originated through reciprocal hybridization between different endemic, sexually reproducing parental lineages. It is also likely that polyploidy of the investigated lineages resulted from this hybridization. Nevertheless, no putative diploid parental lineages were found in the studied region.
  • Freshwater Biology

    Assembly of zooplankton communities in newly created ponds

    G. Louette, Luc De Meester, Steven A.J. Declerck
    1. The creation or severe disturbance of habitat patches is generally followed by a phase of community (re)assembly. After such an event, the trajectory of community assembly in habitat patches may be highly variable because of stochasticity during the dispersal and colonization process. Conversely, assembly patterns may also be deterministic if communities are shaped by prevalent environmental conditions in the habitat patches (species sorting), or by systematic differences in the dispersal capacities of species. 2. In this study, we investigated the pattern of community assembly of zooplankton species in 25 newly created ponds at 13 different sites in Flanders (Belgium). Over a period of three consecutive years, we assessed at what rate and with what frequency species of the regional species pool colonized the newly created ponds. We also studied the development of community structure over time and tested whether the dynamics were consistent across different ponds at the different locations. In addition, we characterized the dynamics of metacommunity features, such as alpha, beta and gamma diversity in clusters of ponds. 3. Even within the first year after their creation, the new ponds were rapidly colonized by a small subset of species from the regional species pool (Daphnia obtusa, Chydorus sphaericus and Simocephalus vetulus). These species dominated the cladoceran assemblages during the subsequent years. Other species in the regional species pools were only sporadically able to colonize ponds. 4. During the entire study period, we observed no significant shifts in species lists or in the occurrences of species among years. The low incidence of the majority of species may be the result of dispersal limitation or the failure of immigrants to establish due to priority effects exerted by the first colonizers. There was, nevertheless, a consistent change in the relative abundance of species, which was most probably mediated by differences in the hatching time among species influencing species composition in the first year. 5. In contrast to expectations, we observed no increase in average alpha diversity (local species richness) and gamma diversity (total richness of entire pond clusters) during the course of the study period. Beta diversity was relatively low from the beginning and remained constant throughout the study period. These deterministic patterns can mainly be attributed to the dominance of the three first colonizing species and the low success rate of other species in colonizing the ponds.
  • Hydrobiologia

    A comparative analysis of cladoceran communities from different water body types: patterns in community composition and diversity

    T. De Bie, Steven A.J. Declerck, K. Martens, Luc De Meester, L. Brendonck
    To develop strategies for the management and protection of aquatic biodiversity in water bodies at the landscape scale, there is a need for information on the spatial organization of diversity in different types of aquatic habitats. In this study, we compared the cladoceran composition and diversity between wheel tracks, pools, ponds, lakes, ditches, and streams, in 18 different areas of Flanders (Belgium). Multivariate analysis revealed significant differences in the composition of cladoceran communities among the different water body types. Average local and total diversity tended to be highest for lakes and lowest for streams. Despite the relatively high number of species supported by lakes, small water bodies seem to contribute considerably more to the total cladoceran richness of an average landscape in Flanders than lakes, because of their high abundance. With respect to biodiversity conservation at the landscape scale, our results point to the importance of maintaining a diversity of water body types of different size, permanence and flow regimes.
  • Hydrobiologia

    The ecology of European ponds: defining the characteristics of a neglected freshwater habitat

    R. Cereghino, J. Biggs, B. Oertli, Steven A.J. Declerck
    There is growing awareness in Europe of the importance of ponds, and increasing understanding of the contribution they make to aquatic biodiversity and catchment functions. Collectively, they support considerably more species, and specifically more scarce species, than other freshwater waterbody types. Ponds create links (or stepping stones) between existing aquatic habitats, but also provide ecosystem services such as nutrient interception, hydrological regulation, etc. In addition, ponds are powerful model systems for studies in ecology, evolutionary biology and conservation biology, and can be used as sentinel systems in the monitoring of global change. Ponds have begun to receive greater protection, particularly in the Mediterranean regions of Europe, as a result of the identification of Mediterranean temporary ponds as a priority in the EU Habitats Directive. Despite this, they remain excluded from the provisions of the Water Framework Directive, even though this is intended to ensure the good status of all waters. There is now a need to strengthen, develop and coordinate existing initiatives, and to build a common framework in order to establish a sound scientific and practical basis for pond conservation in Europe. The articles presented in this issue are intended to explore scientific problems to be solved in order to increase the understanding and the protection of ponds, to highlight those aspects of pond ecology that are relevant to freshwater science, and to bring out research areas which are likely to prove fruitful for further investigation.
  • Hydrobiologia

    Limnological and ecological characteristics of tropical highland reservoirs in Tigray, Northern Ethiopia

    T. Dejenie, T. Asmelash, Luc De Meester, A. Mulugeta, A. Gebrekidan, S. Risch, A. Pals, K. van der Gucht, W. Vyverman, J. Nyssen, J. Deckers, Steven A.J. Declerck
    The semi-arid highlands of Northern Ethiopia (Tigray) have numerous small reservoirs that have been created by microdams in an attempt to provide water supply for irrigation and livestock drinking. Although the reservoirs have substantial added value to residents, their use as water resource is jeopardized by eutrophication and a high occurrence of blooms of toxic cyanobacteria. So far, there is no systematic information available on the limnological and aquatic ecological characteristics of these dams. We carried out a standardized survey of 32 reservoirs and assessed a wide set of morphometric, abiotic and biotic variables. The sampling was performed during two seasons, September-October 2004 (end of the wet season/start of the dry season) and April-May 2005 (towards the end of the dry season). Using multivariate analysis, we revealed dominating patterns of variable associations and compared the variability in these patterns among seasons. According to standardized PCA and RDA analyses, the most important axis of variation was mainly represented by a gradient in nutrients and altitude that was also positively associated with phytoplankton biomass, suspended matter and oxygen concentration, and negatively with water transparency. For most variables, correlations between the wet and dry season were weak, which suggests that individual reservoirs behaved rather differently in their response to seasonal changes. Nevertheless, a Mantel correlation (r = 0.32; P = 0.035) showed a weak but significant overall concordance in the variable association patterns among seasons. A number of reservoirs became very shallow or fell dry in the dry season, a process that was associated with an increase in suspended matter and conductivity and a decrease in transparency. These reservoirs contained lower amounts of fish and tended to be less eutrophic than the deeper, permanent systems, as they had lower levels of phosphorus and chlorophyll-a. With multiple regression analysis, we constructed most parsimonious models in an attempt to explain the variation in key biotic variables: phytoplankton and cyanobacteria biomass, cladoceran biomass, fish biomass and the abundance of submerged vegetation. Phytoplankton and fish biomass tended to be positively related with the concentration of total phosphorus, whereas cladoceran biomass was not associated with nutrient concentrations. The positive association of fish and phytoplankton with nutrient concentrations suggests a bottom-up control, whereas the absence of an association between zooplankton and nutrient concentrations may be indicative for top-down control. The biomass of cyanobacteria was negatively related to the biomass of cladocerans (Daphnia), which likely reflects a top-down effect. Most reservoirs were turbid. The occurrence and abundance of macrophytes tended to be positively related to water transparency and was negatively associated to TP and the amount of livestock frequenting the reservoirs. However, macrophytes were not limited to clear-water reservoirs.
  • Limnology and Oceanography

    Asexuality and polyploidy in Daphnia from the tropical Andes

    X. Aguilera, J. Mergeay, A. Wollebrants, Steven A.J. Declerck, Luc De Meester
    We assessed genetic variation at microsatellite loci within and among populations of the planktonic crustacean Daphnia pulex in 12 Bolivian Andean lakes, located above 4,000 m above sea level. Genetic analyses show that all populations consisted of obligately asexual lineages, a fact that was confirmed by observations from laboratory cultures. Moreover, microsatellite phenotypes indicate that these tropical lineages are polyploid. Levels of genetic diversity were comparable to those found in polyploid Daphnia from arctic regions, indicating a local origin rather than an accidental colonization from arctic regions. This is the first record of polyploid cladocerans in a tropical region. We suggest that their origination and abundance have probably been facilitated by the extreme environmental conditions in Andean lakes. Our analysis of multilocus genotype frequencies in relation to variation in environmental conditions indicates lineage sorting along a food availability and fish predation gradient.
  • Hydrobiologia

    The importance of drawdown and sediment removal for the restoration of the eutrophied shallow Lake Kraenepoel (Belgium)

    J. Van Wichelen, Steven A.J. Declerck, K. Muylaert, I. Hoste, V. Geenens, J. Vandekerkhove, E. Michels, N. De Pauw, Michael B Hoffmann, Luc De Meester, W. Vyverman
    Lake Kraenepoel (Belgium) is a shallow lake (22 ha), divided in two basins since 1957 by a shallow dike. The lake was used for fish farming until World War II and was drawn down about every 5 years to harvest fish. Despite its dense historical carp population, it had clear water and a rich Littorelletea vegetation. During the course of the 20th century, the lake became eutrophic and the Littorelletea vegetation degraded. The northern basin, which was still drawn down about every decade after 1957, retained its clear water and had a dense submerged macrophyte vegetation. The southern basin, which was never drawn down after 1957 and which received direct surface water inputs, had become a turbid shallow lake with phytoplankton blooms in summer. In 2000, efforts were taken to restore the lake: the entire lake was drawn down, the fish community was biomanipulated, nutrient-rich surface water inputs were diverted from the southern basin and sediments were removed (only in the northern basin). Fish biomanipulation and sediment removal were successful in the northern basin, as nutrient levels declined and the Littorelletea vegetation recovered. In the southern basin, sediment analyses indicated that drawdown resulted in sediments with a lower water and organic matter content and water column turbidity decreased after the drawdown. But pH in the southern basin declined to <4, probably because sulphides in the sediment were oxidized during drawdown and sediment desiccation. In contrast, desiccated sediments were removed from the northern basin and pH did not decline below 6 after restoration. In spite of the still high dissolved nutrient concentrations, phytoplankton biomass declined significantly in the southern basin, probably due to acidification. However, no Littorelletea species colonised the lake bottom in the southern basin. Thus, lake drawdown may be a useful management technique to promote clear water conditions in shallow lakes. However, acidification due to sulphide oxidation may be an undesirable outcome and should be considered in drawdown and sediment desiccation manipulations.
  • Proceedings of the National Academy of Sciences of the United States of America

    The power of species sorting: Local factors drive bacterial community composition over a wide range of spatial scales

    K. van der Gucht, K. Cottenie, K. Muylaert, N. Vloemans, S. Cousin, Steven A.J. Declerck, Erik Jeppesen, J-M. Conde-Porcuna, K. Schwenk, G. Zwart, H. Degans, W. Vyverman, Luc De Meester
    There is a vivid debate on the relative importance of local and regional factors in shaping microbial communities, and on whether microbial organisms show a biogeographic signature in their distribution. Taking a metacommunity approach, spatial factors can become important either through dispersal limitation (compare large spatial scales) or mass effects (in case of strongly connected systems). We here analyze two datasets on bacterial communities [characterized by community fingerprinting through denaturing gradient gel electrophoresis (DGGE)] in meso- to eutrophic shallow lakes to investigate the importance of spatial factors at three contrasting scales. Variation partitioning on datasets of both the bacterial communities of 11 shallow lakes that are part of a strongly interconnected and densely packed pond system 2,500 km) shows a strong impact of local environmental factors on bacterial community composition, with a marginal impact of spatial distance. Our results indicate that dispersal is not strongly limiting even at large spatial scales, and that mass effects do not have a strong impact on bacterial communities even in physically connected systems. We suggest that the fast population growth rates of bacteria facilitate efficient species sorting along environmental gradients in bacterial communities over a very broad range of dispersal rates.
  • Wetlands

    High-altitude peatland temporary pools in Bolivia house a high cladoceran diversity

    J. S. Coronell, Steven A.J. Declerck, L. Brendonck
    We studied richness and composition of the cladoceran species in 61 temporary peat-pools (pools within high-altitude peatland mires) in the Cordillera del Tunari in Cochabamba (Bolivia) during one wet season. Of the 21 species collected, two were new to science and five were new records to Bolivia. Across all 61 pools, species richness per pool varied from 3-16 (mean = 8.3 + 2.8 SD). Rarefaction analysis revealed that more than 80% of all collected species was represented by a subsample of 25 pools. This is the first study to comprehensively present the cladoceran fauna of temporary peat-pools in the high Andes. The cladoceran diversity is comparable with many permanent systems in the region and other temporary pool systems around the world, and underlines the conservation value of these peatland systems (bofedales) for the aquatic biodiversity of South America.[1166:Hptpib]2.0.Co;2
  • Ecology

    Plankton biodiversity along a gradient of productivity and its mediation by macrophytes

    Steven A.J. Declerck, M. Vanderstukken, A. Pals, K. Muylaert, Luc De Meester
    We studied the effect of aquatic vegetation on the process of species sorting and community assembly of three functional groups of plankton organisms (phytoplankton, seston-feeding zooplankton, and substrate-dwelling zooplankton) along a primary productivity gradient. We performed an outdoor cattle tank experiment (n = 60) making an orthogonal combination of a primary productivity gradient (four nutrient addition levels: 0, 10, 100, and 1000 mu g P/L; N/P ratio: 16) with a vegetation gradient (no macrophytes, artificial macrophytes, and real Elodea nuttallii). We used artificial plants to evaluate the mere effects of plant physical structure independently from other plant effects, such as competition for nutrients or allelopathy. The tanks were inoculated with species-rich mixtures of phytoplankton and zooplankton. Both productivity and macrophytes affected community structure and diversity of the three functional groups. Taxon richness declined with increasing plankton productivity in each functional group according to a nested subset pattern. We found no evidence for unimodal diversity-productivity relationships. The proportional abundance of Daphnia and of colonial Scenedesmus increased strongly with productivity. GLM analyses suggest that the decline in richness of seston feeders was due to competitive exclusion by Daphnia at high productivity. The decline in richness of phytoplankton was probably caused by high Daphnia grazing. However, partial analyses indicate that these explanations do not entirely explain the patterns. Possibly, environmental deterioration associated with high productivity (e.g., high pH) was also responsible for the observed richness decline. Macrophytes had positive effects on the taxon richness of all three functional plankton groups and interacted with the initial productivity gradient in determining their communities. Macrophytes affected the composition and diversity of the three functional groups both by their physical structure and through other mechanisms. Part of the macrophyte effect may be indirect via a reduction of phytoplankton production. Our results also indirectly suggest that the often reported unimodal relationship between primary productivity and diversity in nature may be partially mediated by the tendency of submerged macrophytes to be most abundant at intermediate productivity levels.
  • Belgian Journal of Zoology

    Analysis of the inland cladocerans of Flanders (Belgium) - Inferring changes over the past 70 years

    G. Louette, T. De Bie, J. Vandekerkhove, Steven A.J. Declerck, Luc De Meester
  • Journal of Fish Biology

    Assessment and control of non-indigenous brown bullhead Ameiurus nebulosus populations using fyke nets in shallow ponds

    G. Louette, Steven A.J. Declerck
    In order to evaluate fyke nets as a tool for population assessment and mass removal of brown bullhead Ameiurus nebulosus populations, small, shallow ponds were sampled during late summer in 1999 and 2000. Catch efficiency, species and size selectivity of fyke nets were investigated with the mark-recapture method. Two different strategies were applied: (1) on six occasions, the mark-recapture method was applied to entire populations, and (2) in six other cases, sampling was done in two replicated enclosed areas (625 m(2)). When applied to entire populations, fyke nets were found to be size selective, and capture efficiency significantly increased with standard length. Conversely, no size selectivity of fyke nets was found in enclosed areas. Sampling in replicated enclosures yielded reproducible estimates of population density and biomass. The results suggest that double fyke nets, when combined with the mark-recapture technique, are a very useful tool for the efficient and reliable assessment of brown bullhead populations. The results of the study also suggest that double fyke nets may potentially be a cost-effective tool for the mass removal of non-indigenous brown bullhead populations.
  • 2006

    Biodiversity in European shallow lakes: a multilevel-multifactorial field study

    Luc De Meester, Steven A.J. Declerck, Jan H. Janse, J. J. Dagevos, R. Portielje, E.H.R.R. Lammens, Erik Jeppesen, T. Lauridsen, K. Schwenk, K. Muylaert, K. van der Gucht, W. Vyverman, G. Zwart, E.J. Van Hannen, Pjtm van Puijenbroek, J-M. Conde-Porcuna, P. Sánchez-Castillo, J. Vandekerkhove, L. Brendonck
  • Limnologica

    An evaluation of the role of daphnids in controlling phytoplankton biomass in clear water versus turbid shallow lakes

    K. Muylaert, Steven A.J. Declerck, J. Van Wichelen, Luc De Meester, W. Vyverman
    Phytoplankton and zooplankton were monitored during 2 years in four eutrophic shallow lakes (two turbid and two clear water) from two wetland reserves in Belgium. In each wetland, phytoplankton biomass was significantly higher in the turbid lake than in the clear water lake. Although total macrozooplankton biomass and the contribution of daphnids to total zooplankton biomass was comparable in the clear water and the turbid lakes, the grazing pressure of macrozooplankton on phytoplankton as estimated from zooplankton to phytoplankton biomass ratios was higher in the clear water lakes. Estimated grazing by daphnids in the clear water lakes was always high in spring. In summer, however, daphnid biomass was low or daphnids were even absent during prolonged periods. During those periods phytoplankton was probably controlled by smaller macrozooplankton or by submerged macrophytes through nutrient competition, allelopathic effects or increased sedimentation rates in the macrophyte vegetation. (c) 2006 Elsevier GmbH. All rights reserved.
  • Biological Conservation

    Ecological characteristic's of small farmland ponds: Associations with land use practices at multiple spatial scales

    Steven A.J. Declerck, T. De Bie, D. Ercken, H. Hampel, S. Schrijvers, J. Van Wichelen, V. Gillard, R. Mandiki, B. Losson, D. Bauwens, S. Keijers, W. Vyverman, B. Goddeeris, Luc De Meester, L. Brendonck, K. Martens
    Despite their restricted surface area, small farmland ponds often have a high conservation value because they contribute significantly to regional biodiversity and contain rare or unique species. For this reason, the creation of new ponds has become a widely applied practice in many countries. information on the effects of land use on farmland ponds is very scarce. Farmland ponds differ from larger ponds, lakes and livers in many aspects and can therefore be expected to be affected by land use via other mechanisms operating at different spatial scales. We here present a study on 126 ponds distributed over the entire territory of Belgium (surface area: 30.500 km(2)). We assessed variables related to turbidity state and vegetation complexity and related them to land use variables assessed at several spatial scales ranging from the pond edge up to 32 km(2) circular areas. According to redundancy analysis, trampling by cattle and percentage cover of nearby crop land were positively associated with turbid state related variables. Conversely, ponds with high coverage by forest in the immediate neighbourhood tended to be more associated with the clear water state. Multiple regression analysis demonstrated a negative effect of trampling and coverage by crop land on vegetation complexity. Effects of crop lands and forest were strongest at the local scale (<200 m radius) which indicates that adverse external influences can most efficiently be mitigated at a small scale. Based on these results we suggest several recommendations for pond construction and conservation. (c) 2006 Elsevier Ltd. All rights reserved.
  • Archiv für Hydrobiologie

    Trophic coupling in the microbial food web of a eutrophic shallow lake (Lake Visvijver, Belgium)

    K. Muylaert, Liang Zhao, K. van der Gucht, S. Cousin, Steven A.J. Declerck, W. Vyverman
    Two fractionation experiments were carried out to study trophic interactions in the microbial food web in the shallow eutrophic lake Visvijver. Despite an order of magnitude difference in biomass of bacteria, heterotrophic nanoflagellates (HNF) and ciliates between the two experiments, the trophic interactions observed were similar. Bacteria were consumed by HNF and oligotrich ciliates, oligotrich ciliates fed on HNF as well as bacteria and cyclopoid copepod nauplii preyed on the oligotrich ciliates. While cyclopoid copepods had no effect on any component of the microbial food web, Daphnia fed on bacteria and HNF. No or a weak and slow trophic cascade occurred from oligotrich ciliates to HNF and bacteria. The lack of a pronounced trophic cascade was ascribed to the importance of the omnivorous oligotrich ciliates in the microbial food web. In both experiments, removal of trophic levels by size fractionation resulted in changes in the identity of the dominant bacterivores, but this had little effect on total bacterial grazing losses. Bacterial community composition (monitored in the second experiment using DGGE analysis), on the contrary, was more strongly influenced by changes in the identity of the dominant bacterivores, suggesting the presence of a 'cryptic trophic cascade'.
  • Freshwater Biology

    Daphnia community analysis in shallow Kenyan lakes and ponds using dormant eggs in surface sediments

    J. Mergeay, Steven A.J. Declerck, D. Verschuren, Luc De Meester
    1. Water fleas of the genus Daphnia are considered rare in tropical regions, and information on species distribution and community ecology is scarce and anecdotal. This study presents the results of a survey of Daphnia species distribution and community composition in 40 standing waterbodies in southern Kenya. The study sites cover a wide range of tropical standing aquatic habitats, from small ephemeral pools to large permanent lakes between approximately 700 and 2800 m a.s.l. Our analysis combines data on Daphnia distribution and abundance from zooplankton samples and dormant eggs in surface sediments. 2. Nearly 70% (27 of 40) of the sampled waterbodies were inhabited by Daphnia. Although their abundance in the active community was often very low, this high incidence shows that Daphnia can be equally widespread in tropical regions as in temperate regions. 3. Analysis of local species assemblages from dormant eggs in surface sediments was more productive than snapshot sampling of zooplankton communities. Surface-sediment samples yielded eight Daphnia species in total, and allowed the detection of Daphnia in 25 waterbodies; zooplankton samples revealed the presence of only four Daphnia species in 16 waterbodies. 4. Daphnia barbata, D. laevis, and D. pulex were the most frequently recorded and most abundant Daphnia species. Canonical correspondence analysis of species-environment relationships indicates that variation in the Daphnia community composition of Kenyan waters was best explained by fish presence, temperature, macrophyte cover and altitude. Daphnia barbata and D. pulex tended to co-occur with each other and with fish. Both species tended to occur in relatively large (> 10 ha) and deeper (> 2 m) alkaline waters (pH 8.5). Daphnia laevis mainly occurred in cool and clear, macrophyte-dominated lakes at high altitudes.
  • Limnologica

    Tropical high Andes lakes: A limnological survey and an assessment of exotic rainbow trout (Oncorhynchus mykiss)

    X. Aguilera, Steven A.J. Declerck, Luc De Meester, Inés Maldonado-Lasunción, F. Ollevier
    Tropical high Andes lakes are aquatic ecosystems with peculiar limnological characteristics that are related to their geographical location and high altitude, yet they remained understudied. We present the results of a standardized survey of morphometric, physico-chemical and biotic variables in 32 high altitude lakes of the Cordillera del Tunari (Eastern Andes of Bolivia). Based on the variables measured, we identified three lake types. One group of lakes differed from the other lakes by a relatively high pH and biological productivity (as evidenced from higher densities of phytoplankton, zooplankton, and fish). A second group of lakes consisted of relatively large and deep water bodies with neutral to slightly acid pH and with a relatively high occurrence of the large cladoceran Daphnia pulex. The third group contained relatively small, shallow, and acid lakes with no Daphnia. Rainbow trout occurred in more than half of the lakes and catch yields were very variable. Overall, the abundances of different organism groups tended to be positively associated (e.g. phytoplankton, copepods, rotifers, fish) indicating the existence of a major productivity gradient. We found no negative associations between trout catches and densities of any of the major zooplankton groups, suggesting moderate to low top-down effects of trout on the zooplankton communities. (c) 2006 Elsevier GmbH. All rights reserved.
  • Oikos

    Small habitat size and isolation can promote species richness: second-order effects on biodiversity in shallow lakes and ponds

    M. Scheffer, G.J. Van Geest, K. Zimmer, Erik Jeppesen, M. Søndergaard, M.G. Butler, M.A. Hanson, Steven A.J. Declerck, Luc De Meester
    Contemporary ecological landscape planning is often based on the assumption that small isolated habitat patches sustain relatively few species. Here, we suggest that for shallow lakes and ponds, the opposite can be true for some groups of organisms. Fish communities tend to be poor or even absent in small isolated lakes. However, submerged vegetation is often more abundant in such waterbodies. As a consequence of low fish biomass and high vegetation abundance, the richness of aquatic birds, plants, amphibians and invertebrates is often relatively high in small, shallow, isolated lakes. Although the rarity of fish is in line with expectations from the ruling paradigms about effects of habitat fragmentation in landscape ecology, the relative richness of various other groups of organisms in small ponds is opposite to these expectations. The case of shallow lakes illustrates that incorporating ecological interactions is essential to understanding the potential effects of habitat fragmentation. Single-species meta-population approaches may be misleading if ecological interactions are strong. A meta-community approach that explicitly incorporates biotic interactions, also those involving different trophic levels, is needed. Our diagnosis suggests that connection of isolated habitat fragments may in some cases reduce, rather than enhance, landscape-level biodiversity, and implies that biodiversity at the regional level will be maximized if the local habitat patches vary widely in size and degree of connectivity.
  • Polish Journal of Ecology

    Diel Vertical Migration of zooplankton in tropical, high mountain lakes (Andes, Bolivia)

    X. Aguilera, G. Crespo, Steven A.J. Declerck, Luc De Meester
    Diel Vertical Migration (DVM) is a widespread behavior in zooplankton. Although considered to be a predator avoidance behavior in most cases, DVM is also influenced by the distribution of food, competitive interactions and UV (Ultraviolet) radiation. In this paper we report the day and nighttime vertical distribution of the common zooplankton species in nine high altitude tropical Andean lakes to obtain an idea of the range in vertical distribution patterns in Andean lakes. The lakes are situated between 4000 and 4545 m a.s.l. The maximum depth of the lakes varied from 5 to 24 m, and the area varied between 0.6 and 20.75 ha. Daphnia pulex (Leydig 1860) showed tendencies for a normal vertical migration behavior in all lakes sampled h.-respective of whether the lakes contained fish. The population resided deeper in the water column during the daytime than during the night, although migration amplitude differed strongly among lakes. In many lakes, there was an important daytime "deficit" in the number of individuals caught, suggesting that the animals stay close to the bottom of the lake during the day. It suggests that UV radiation is the more likely factor influencing the DVM of Daphnia. Copepods and rotifers showed reverse DVM in some lakes. Our data suggest that the DVM behavior of copepods and rotifers in the studied lakes may in part be determined by the avoidance of competition from Daphnia pulex.
  • Oecologia

    Ecological implications of parasites in natural Daphnia populations

    Ellen Decaestecker, Steven A.J. Declerck, Luc De Meester, Dieter Ebert
    In natural host populations, parasitism is considered to be omnipresent and to play an important role in shaping host life history and population dynamics. Here, we study parasitism in natural populations of the zooplankton host Daphnia magna investigating their individual and population level effects during a 2-year field study. Our results revealed a rich and highly prevalent community of parasites, with eight endoparasite species (four microsporidia, one amoeba, two bacteria and one nematode) and six epibionts (belonging to five different taxa: Chlorophyta, Bacillariophyceae, Ciliata, Fungi and Rotifera). Several of the endoparasites were associated with a severe overall fecundity reduction of the hosts, while such effects were not seen for epibionts. In particular, infections by Pasteuria ramosa, White Fat Cell Disease and Flabelliforma magnivora were strongly associated with a reduction in overall D. magna fecundity. Across the sampling period, average population fecundity of D. magna was negatively associated with overall infection intensity and total endoparasite richness. Population density of D. magna was negatively correlated to overall endoparasite prevalence and positively correlated with epibiont richness. Finally, the reduction in host fecundity caused by different parasite species was negatively correlated to both parasite prevalence and the length of the time period during which the parasite persisted in the host population. Consistent with epidemiological models, these results indicate that parasite mediated host damages influence the population dynamics of both hosts and parasites.
  • Aquatic Conservation: Marine and Freshwater Ecosystems

    Ponds and pools as model systems in conservation biology, ecology and evolutionary biology

    Luc De Meester, Steven A.J. Declerck, R. Stoks, G. Louette, F. Van de Meutter, T. De Bie, E. Michels, L. Brendonck
    1. Ponds and pools, broadly defined in this paper to include all small and shallow standing waters that permanently or temporarily contain water, are numerous, diverse and important from a conservation point of view. We here argue that ponds and pools offer powerful potential for studies in ecology, evolutionary biology and conservation biology. 2. An outline is given of the characteristics of pools and ponds that make them good model systems for large-scale surveys and hypothesis testing through experimental manipulation. Such Studies will not only increase understanding Of Community and genetic structure, as well as of patterns of biodiversity, in small aquatic habitats themselves, but may also contribute significantly to testing general theory. 3. These merits are illustrated by the recent progress on the understanding of the relative importance of local versus regional factors in structuring populations and communities, as well as of the impact of hydroperiod on community and ecosystem functioning. Copyright (c) 2005 John Wiley & Sons, Ltd.
  • Ecology

    Multi-group biodiversity in shallow lakes along gradients of phosphorus and water plant cover

    Steven A.J. Declerck, J. Vandekerkhove, L. Johansson, K. Muylaert, J-M. Conde-Porcuna, K. van der Gucht, C. Pérez-Martínez, T. Lauridsen, K. Schwenk, G. Zwart, W. Rommens, J. López-Ramos, Erik Jeppesen, W. Vyverman, L. Brendonck, Luc De Meester
    This study aimed at unraveling the structure underlying the taxon-richness matrix of shallow lakes. We assessed taxon richness of a large variety of food-web components at different trophic levels (bacteria, ciliates, phytoplankton, zooplankton, fish, macro-invertebrates, and water plants) in 98 shallow lakes from three European geographic regions: Denmark (DK), Belgium/The Netherlands (BNL), and southern Spain (SP). Lakes were selected along four mutually independent gradients of total phosphorus (TP), vegetation cover (SUBMCOV), lake area (AREA), and connectedness (CONN). Principal-components analysis (PCA) indicated that taxon diversity at the ecosystem level is a multidimensional phenomenon. Different PCA axes showed associations with richness in different subsets of organism groups, and differences between eigenvalues were low. Redundancy analysis showed a unique significant contribution to total richness variation of SUBMCOV in all three regions, of TP in DK and SP, and of AREA in DK and BNL. In DK, several organism groups tended to show curvilinear responses to TP, but only one was significantly hump shaped. We postulate that the unimodal richness responses to TP that are frequently reported in the literature for many organism groups may be partly mediated by the unimodal response of macrophyte vegetation to lake productivity. [KEYWORDS: biodiversity ; conservation management for species richness ; phosphorus ; productivity ; richness ; richness–productivity relationships ; shallow lake ; shallow-lake species richness structure ; water plants]
  • Limnol. Oceanogr. Meth.

    Uncovering hidden species: hatching diapausing eggs for the analysis of cladoceran species richness

    J. Vandekerkhove, Steven A.J. Declerck, L. Brendonck, J-M. Conde-Porcuna, Erik Jeppesen, Liselotte S. Johansson, Luc De Meester
    Effective methods for the detection of species are highly needed in biodiversity research. The assessment of richness is especially difficult for short-lived aquatic organisms, like plankton. Because of the high degree of spatial and temporal variation in plankton community composition, the compilation of complete plankton species lists requires intensive sampling programs. Many large-scale studies on planktonic organisms are based on single occasion samplings and inevitably fail to detect a substantial fraction of the species. In the present study, we assessed species richness of Cladocera (Branchiopoda, Crustacea) in 88 European lakes by repeated sampling of the active communities and by an alternative method based on the hatching of diapausing eggs from the lake sediments. Identification of hatchlings obtained from egg bank samples enabled the detection of about twice as many cladoceran species than identification of an equal number of individuals retrieved from active community samples. Loglinear analyses revealed a strong species by method interaction, suggesting that both methods are highly complementary and should preferably be applied in combination. Some species were underrepresented in the active community samples, probably because of the lack of spatial and temporal integration in these samples. Other species were underrepresented in the hatching assemblages as a result of species-specific propensities to produce diapausing eggs or hatch from such eggs.
  • Freshwater Biology

    Plankton dynamics in a tropical floodplain lake: fish, nutrients, and the relative importance of bottom-up and top-down control

    Danny Rejas, Steven A.J. Declerck, J. Auwerkerken, P.P. Tak, Luc De Meester
    1. Two enclosure experiments were carried out in Laguna Bufeos, a neotropical varzea lake located in the floodplain of River Ichilo (Bolivia). The experiments aimed (i) to assess the relative importance of bottom-up and top-down control on the plankton community, (ii) to assess the relative impact of direct and indirect effects of planktivorous fish on the zooplankton, and (iii) to attempt to identify the mechanisms responsible for these effects. 2. During the first experiment, bottom-up control seemed to dominate the planktonic food web. Compared with fishless enclosures, oxygen concentrations, chlorophyll a levels and the population densities of all cladoceran zooplankton taxa increased in enclosures with fish. Birth rates of Moina minuta, the dominant taxon, were substantially higher in the presence than in the absence of fish, whereas death rates did not differ between treatments. These results are the first to suggest that the positive effects of fish on crustacean zooplankton via effects on nutrient cycling and the enhancement of primary production can compensate for losses because of fish-related mortality. 3. During the second experiment, the direction of control appeared to vary between trophic levels: the phytoplankton appeared to be bottom-up controlled whereas the zooplankton was mainly top-down controlled. Chlorophyll a concentrations were enhanced by both fish and nutrient additions. The majority of the zooplankton taxa were reduced by the presence of fish. Birth rates of most cladoceran taxa did not differ between treatments, whereas death rates were higher in the enclosures with fish than in the fishless enclosures. Bosminopsis deitersi reached higher densities in the presence of fish, probably because of a release from predation by Chaoborus. 4. We convincingly showed strong deviations from trophic cascade-based expectations, supporting the idea that trophic cascades may be weak in tropical lakes.
  • FEMS Microbiology Ecology

    Characterization of bacterial communities in four freshwater lakes differing in nutrient load and food web structure

    K. van der Gucht, T. Vandekerckhove, N. Vloemans, S. Cousin, K. Muylaert, K. Sabbe, M. Gillis, Steven A.J. Declerck, Luc De Meester, W. Vyverman
    The phylogenetic composition of bacterioplankton communities in the water column of four shallow eutrophic lakes was analyzed by partially sequencing cloned 16S rRNA genes and by PCR-DGGE analysis. The four lakes differed in nutrient load and food web structure: two were in a clearwater state and had dense stands of submerged macrophytes, while two others were in a turbid state characterized by the occurrence of phytoplankton blooms. One turbid and one clearwater lake had very high nutrient levels (total phosphorus > 100 mu g/l), while the other lakes were less nutrient rich (total phosphorus <100 mu g/l). Cluster analysis, multidimensional scaling and ANOSIM (analysis of similarity) were used to investigate differences among the bacterial community composition in the four lakes. Our results show that each lake has its own distinct bacterio plankton community. The samples of lake Blankaart differed substantially from those of the other lakes; this pattern was consistent throughout the year of study. The bacterioplankton community composition in lake Blankaart seems to be less diverse and less stable than in the other three lakes. Clone library results reveal that Actinobacteria strongly dominated the bacterial community in lake Blankaart. The relative abundance of Betaproteobacteria was low, whereas this group was dominant in the other three lakes. Turbid lakes had a higher representation of Cyanobacteria, while clearwater lakes were characterized by more representatives of the Bacteroidetes. Correlating our DGGE data with environmental parameters, using the BIOENV procedure, suggests that differences are partly related to the equilibrium state of the lake. (c) 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.
  • Freshwater Biology

    Hatching of cladoceran resting eggs: temperature and photoperiod

    J. Vandekerkhove, Steven A.J. Declerck, L. Brendonck, J-M. Conde-Porcuna, Erik Jeppesen, Luc De Meester
    1. We identified temperature and photoperiod conditions under which the hatching of 45 cladoceran species could be elicited. Identification of appropriate hatching cues is of primary importance for the exploration of the ties between active and diapausing stages. 2. Incubation temperature affected the hatching success of resting eggs isolated from Danish, Belgian/Dutch and Spanish sediments. In general, most hatchlings and species were retrieved at 15 degreesC. Danish and Belgian/Dutch resting eggs hatched more successfully under a long day photoperiod than in continuous illumination. 3. Most species could be retrieved after incubation of resting eggs isolated from a limited amount of sediment (0.4 kg) under a single, well chosen combination of temperature and photoperiod. Processing additional sediment samples under seven more incubation regimes only allowed detection of 21% (Spain) to 34% (Denmark) more species. 4. The incubation period for resting eggs to hatch was strongly influenced by incubation temperature. Our results show that hatching experiments aimed at assessing cladoceran species richness and conducted at 15 degreesC should be continued for a period of at least 2 weeks, after which a random subset of hatchlings (e.g. n = 100) can be selected from the total hatchling assemblage.
  • Oecologia

    Dormant propagule banks integrate spatio-temporal heterogeneity in cladoceran communities

    J. Vandekerkhove, Steven A.J. Declerck, Erik Jeppesen, J-M. Conde-Porcuna, L. Brendonck, Luc De Meester
    The dynamics of populations of short-lived organisms are very patchy, both in space and time. The production of dormant propagules, however, results in an effective increase in generation time. We hypothesize that prolonged dormancy, together with variable regeneration niches, result in integration of temporal variability in community structure. In addition, in aquatic habitats, mechanisms such as sediment focussing can contribute to the integration of spatial variability. We tested the hypothesis that dormant propagule banks integrate spatial and temporal variation in active zooplankton communities. This was done by comparing cladoceran species richness and the community structure of hatchling assemblages retrieved from propagule bank samples collected on a single occasion with assemblages encountered in active community samples covering spatial variation ( littoral and pelagic zone), diel ( day and night), intra-year ( May October) and inter-year variation ( 1996 - 2000). The egg bank community structure differed significantly from the active community structure, but the dissimilarity decreased as spatial and temporal variation was better covered by the active community samples. Furthermore, the identification of all fully grown hatchlings (n = 214) yielded an equally high number of species (n = 22) to that occurring in all active community samples together ( a total of 1,730 individuals were analysed). We conclude that the analysis of dormant propagules may form a cost-efficient alternative tool to the analysis of active community samples for an integrated assessment of cladoceran communities.
  • Arch. Sci.

    Temporary shallow pools in high-Andes 'bofedal' peatlands: a limnological characterization at different spatial scales

    J.S. Coronel, Steven A.J. Declerck, Inés Maldonado-Lasunción, F. Ollevier, L. Brendonck
    This study is the first to characterize the limnological features of high-altitude peatland pools in the Andes cordillera (>4000 m). Data were collected at two different spatial scales: the scale of individual patches of peatland (bofedales; areas ranging between 0.0 1 and 10 ha) and the scale of 'localities' (areas of approximately 7 km(2)). Patterns of variable associations were similar at the different spatial scales. The major gradient of variation appeared to represent a productivity gradient. Water plant cover and richness were associated with alkalinity.
  • Hydrobiologia

    Hatching rate and hatching success with and without isolation of zooplankton resting stages

    J. Vandekerkhove, B. Niessen, Steven A.J. Declerck, Erik Jeppesen, J-M. Conde-Porcuna, L. Brendonck, Luc De Meester
    Zooplankton resting egg banks accumulate resting stages of various zooplankton species that are active in different habitats and different periods of the year. As such, hatching of resting eggs from lake sediments may potentially be very useful in zooplankton diversity studies. In this study, we tested whether the efficiency of the cost-effective technique is increased by isolating the resting eggs from the sediment prior to incubation. Isolation of the eggs was advantageous for the overall hatching success (+26% after 36 days of incubation compared to incubation of sediment). Furthermore, isolation of resting eggs makes egg bank diversity analyses less time consuming in two ways. ( 1) It reduced the time needed for the eggs to hatch with on average 35%. In the isolation treatment all responsive resting eggs hatched within the first 4 weeks of incubation, while in the non-isolation treatment neither the cumulative number of macrozooplankton hatchlings nor the cumulative number of hatched cladoceran species levelled off after 36 days of incubation. ( 2) In contrast to the non-isolation treatment, where large differences occurred between taxa in incubation time, isolation reduced such inter-specific differences, so that even very short incubation periods kept bias within acceptable limits.
  • Hydrobiologia

    Impact of fish predation on coexisting Daphnia taxa: a partial test of the temporal hybrid superiority hypothesis

    Steven A.J. Declerck, Luc De Meester
    Fish predation was tested as a factor mediating the coexistence of Daphnia taxa in the shallow, hypertrophic Lake Blankaart. Naturally co-occurring populations of D. galeata and the hybrid D. galeata x cucullata were subjected to different levels of fish predation in in situ enclosures. In control enclosures without fish, the largest taxon D. galeata rapidly became dominant over the intermediate sized D. galeata x cucullata, mainly as a result of higher birth rates. In enclosures with fish, population densities of D. galeata dropped relative to D. galeata x cucullata, due to higher mortality rates. These results are in concordance with the 'temporal hybrid superiority hypothesis', and can be explained by a higher vulnerability of the large and more conspicuous D. galeata to the size selective predation exerted by visually hunting planktivorous fishes. After approximately one month, however, population growth rates of D. galeata and D. galeata x cucullata in the enclosures with fish converged, due to a relative reduction in the mortality rate of D. galeata. This suggests that, in the presence of fish, D. galeata may co-exist with hybrids due to a decrease in its relative vulnerability to visual predation with time. Indeed, both D. galeata and the hybrid showed strong reductions in adult body size in the enclosures with fish, but this size reduction tended to be stronger in D. galeata than in D. galeata x cucullata. In addition, turbidity increased in the enclosures with fish and may additionally have reduced the relative advantage of D. galeata x cucullata with regard to mortality caused by visual predation.
  • Aquatic Ecology

    Zooplankton, phytoplankton and the microbial food web in two turbid and two clearwater shallow lakes in Belgium

    K. Muylaert, Steven A.J. Declerck, V. Geenens, J. Van Wichelen, H. Degans, J. Vandekerkhove, K. van der Gucht, N. Vloemans, W. Rommens, Danny Rejas, R. Urrutia, K. Sabbe, M. Gillis, Kris Decleer, Luc De Meester, W. Vyverman
    Components of the pelagic food web in four eutrophic shallow lakes in two wetland reserves in Belgium ('Blankaart' and 'De Maten') were monitored during the course of 1998-1999. In each wetland reserve, a clearwater and a turbid lake were sampled. The two lakes in each wetland reserve had similar nutrient loadings and occurred in close proximity of each other. In accordance with the alternative stable states theory, food web structure differed strongly between the clearwater and turbid lakes. Phytoplankton biomass was higher in the turbid than the clearwater lakes. Whereas chlorophytes dominated the phytoplankton in the turbid lakes, cryptophytes were the most important phytoplankton group in the clearwater lakes. The biomass of microheterotrophs (bacteria, heterotrophic nanoflagellates and ciliates) was higher in the turbid than the clearwater lakes. Biomass and community composition of micro- and macrozooplankton was not clearly related to water clarity. The ratio of macrozooplankton to phytoplankton biomass - an indicator of zooplankton grazing pressure on phytoplankton was higher in the clearwater when compared to the turbid lakes. The factors potentially regulating water clarity, phytoplankton, microheterotrophs and macrozooplankton are discussed. Implications for the management of these lakes are discussed.
  • Canadian Journal of Fisheries and Aquatic Sciences

    Intraspecific density dependence in the dynamics of zooplankton under hypertrophic conditions

    Steven A.J. Declerck, V. Geenens, N. Podoor, J-M. Conde-Porcuna, Luc De Meester
    Intraspecific interactions may limit population growth of small cladoceran taxa under food-rich, hypertrophic conditions. Multiple-regression models significantly explained a large proportion of the variation in the body size adjusted fecundity and population growth rate of crustacean zooplankton taxa in a shallow, hypertrophic lake. The results of partial correlation analyses suggested exploitative competition to have only limited significance in determining the zooplankton dynamics. The analyses also revealed strong negative relationships between biomass and both body size adjusted fecundity and population growth rate within most taxa. Most of these relationships cannot be explained by food shortage or predation and suggest alternative mechanisms such as chemically mediated, intraspecific interference competition or life history shifts.
  • Journal of Plankton Research

    Genetic differentiation in life history between Daphnia galeata population: an adaptation to local predations regimes?

    Steven A.J. Declerck, Anke Weber
    Species of the water flea Daphnia exhibit constitutive as well as phenotypically inducible anti-predator defence strategies, involving life history, morphological and behavioural traits. We explored the hypothesis of genetic differentiation in anti-predator defence strategies using Daphnia clones originating from two different water bodies: Tjeukemeer (the Netherlands) and Fish Pond (Belgium). Both water bodies are inhabited by zooplanktivorous fish. In contrast to Tjeukemeer, Fish Pond is also inhabited by larvae of the phantom midge Chaoborus. The life history responses of the two sets of clones to kairomones from fish (Perca), to kairomones from Chaoborus, and to a mixture of both were compared. Clones from Tjeukemeer and Fish Pond showed strong responses to the presence of fish kairomone, with reductions in adult and neonate body length, in age at first reproduction and in the total number of neonates produced during the first three adult instars. Responses to Chaoborus kairomone were much less pronounced, although there was a tendency towards an increase in the number of neonates in the first brood. Significant inter-population genetic differences were found for all the investigated traits. However, there was no indication for genetic adaptation of the Fish Pond clones to negative size-selective predation by Chaoborus. Compared to Tjeukemeer clones, Fish Pond clones had a lower size at first reproduction, produced smaller neonates and produced a higher number of neonates in their first brood. This suggests adaptation to positive rather than to negative size selective predation. Genetic differences between populations were observed mainly for constitutive life history traits, rather than for phenotypic shifts in response to the presence of predator kairomones.
  • Applied and Environmental Microbiology

    Rapid screening for freshwater bacterial groups by using reverse line blot hybridization

    G. Zwart, E.J. Van Hannen, M.P. Kamst-van Agterveld, K. van der Gucht, E.S. Lindström, J. Van Wichelen, T. Lauridsen, B.C. Crump, S.K. Han, Steven A.J. Declerck
    The identification of phylogenetic clusters of bacteria that are common in freshwater has provided a basis for probe design to target important freshwater groups. We present a set of 16S ribosomal RNA gene-based oligonucleotide probes specific for 15 of these freshwater clusters. The probes were applied in reverse line blot hybridization, a simple method that enables the rapid screening of PCR products from many samples against an array of probes. The optimized assay was made stringent to discriminate at approximately the single-mismatch level. This made 10 of the probes highly specific, with at least two mismatches to the closest noncluster member in the global database. Screening of PCR products from bacterioplankton of 81 diverse lakes from Belgium, The Netherlands, Denmark, Sweden, and Norway showed that the respective probes were reactive against 5 to 100% of the lake samples. Positive reactivity of six highly specific probes showed that bacteria from actinobacterial clusters ACK-M1 and Sta2-30 and from verrucomicrobial cluster CLO-14 occurred in at least 90% of the investigated lakes. Furthermore, bacteria from alpha-proteobacterial cluster LD12 (closely related to the marine SAR11 cluster), beta-proteobacterial cluster LD28 and cyanobacterial cluster Synechococcus 6b occurred in more than 70% of the lakes. Reverse line blot hybridization is a new tool in microbial ecology that will facilitate research on distribution and habitat specificity of target species at relatively low costs
  • Journal of Fish Biology

    Patterns of diet overlap between populations of non-indigenous and native fishes in shallow ponds

    Steven A.J. Declerck, G. Louette, T. De Bie, Luc De Meester
    No significant differences in the diet composition were detected for any of the populations of four non-indigenous fish species (brown bullhead Ameiurus nebulosus, pumpkinseed Lepomis gibbosus, topmouth gudgeon Pseudorasbora parva and eastern mudminnow Umbra pygmaea) and two native fish species (gudgeon Gobio gobio and roach Rutilus rutilus), between two small shallow ponds and between habitats within the ponds, during late summer. Based on diet composition, groups of size classes within species (' functional groups ') were distinguished. For most functional group combinations of exotic fishes, diet overlap values were low. Although chironomid larvae formed the most important food source, differential consumption of chironomid size classes allowed an important degree of niche differentiation between non-indigenous fishes. In contrast, high diet overlap was found between the functional groups of indigenous gudgeon and of several non-indigenous fishes, indicating a high potential for interspecific exploitative competition. The diet of roach consisted almost entirely of non-animal remains (detritus and plant material). The high proportion of such low-energy food in the diet of this species may be indicative for a competition induced niche shift to suboptimal food sources. (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.
  • Freshwater Biology

    Evidence for local adaptation in neighbouring Daphnia populations: a laboratory transplant experiment

    Steven A.J. Declerck, C. Cousyn, Luc De Meester
    1. We tested whether two neighbouring Daphnia galeata populations (from Lake Blankaart and Fish Pond), separated only by 5 m of land and with the occasional exchange of water were genetically differentiated in allozyme markers and life history traits. Allozyme electrophoresis revealed that the populations differed in allelic as well as in genotypic composition. 2. In a laboratory transplant experiment, in which animals of four clones of each of the populations were raised in the water of both ponds, survival in Blankaart water was high for both the Blankaart and Fish Pond clones, whereas survival in Fish Pond water was high for the Fish Pond clones, but low for the Blankaart clones. 3. Fish Pond clones produced fewer neonates than Blankaart clones when cultured in Blankaart water. High egg mortality was observed for animals that were raised in Blankaart water, and this egg mortality was higher for Fish Pond clones than for Blankaart clones. 4. Our results provide evidence for genetic differentiation between Daphnia populations inhabiting neighbouring water bodies and suggest local adaptation to environmental conditions other than direct predation.
  • 2000

    Clear water and charophytes in a hypertrophic pond

    Steven A.J. Declerck, Luc De Meester, P. De Smedt, W. Rommens, W. Vyverman, V. Geenens, J. Van Wichelen, H. Degans, Kris Decleer
  • Journal of Plankton Research

    Regulation of rotifer species by invertebrate predators in a hypertrophic lake: Selective predation on egg-bearing females and induction of morphological defences

    J-M. Conde-Porcuna, Steven A.J. Declerck
    Temporal changes in the biomass of rotifer plankton were examined in a shallow hypertrophic lake during 1 month (April/May), when the predatory rotifer Asplanchna brightwelli develops. The abundance of herbivorous rotifers was regulated by predation from A.brightwelli and from the copepod Acanthocyclops robustus. The densities and fecundity rates of Keratella cochlearis and Keratella quadrata were negatively related with the biomass of predators. Stomach analyses showed that Asplanchna fed selectively on reproductive females of K. cochlearis, reducing the fecundity of this species. Predators induced longer caudal spines in K. quadrata, which were negatively related to the fecundity of this rotifer, suggesting a reproductive cost associated with spine production. In contrast, spine length of K. cochlearis was not related to predators, but to temperature. These results showed that predators can reduce rotifer densities through increasing mortality and through decreasing rotifer fecundity rates regardless of phytoplankton biomass. We also show that morphological defences of K. cochlearis and K. quadrata are induced in different ways.
  • Hydrobiologia

    Phenotypic plasticity of Daphnia life history traits in response to predator kairomones: genetic variability and evolutionary potential

    Anke Weber, Steven A.J. Declerck
    Cladoceran populations can respond to changing predation regimes by a phenotypical response as well as by shifts in genotype frequencies. In this study, we investigated the phenotypic plasticity exhibited by life history traits of D. galeata in response to the presence of predator kairomones, as well as the extent to which natural selection may act on these traits and their phenotypic plasticity. In a life-table experiment, seven clones of a natural D. galeata population were subjected to kairomones from fish (Perca), from an invertebrate predator (Chaoborus) or a mixture of both. Life history traits were affected by the kairomones of both predators, but effects of Chaoborus were neutralised by Perca in the kairomone mix. No apparent trade-off was found between growth-and reproduction related traits: although daphnids from the Chaoborus treatment grew faster than daphnids from the other treatments, no reduction in the reproductive output was observed. Broad-sense heritabilities were found to be relatively high for some life history traits (size at maturity, neonate size, number of neonates) as well as for the phenotypic plasticity response of these traits. This reflects the evolutionary potential of life history traits and their phenotypic response to predator kairomones in the D. galeata population. [KEYWORDS: broad-sense heritability; Chaoborus; Perca; kairomone mixture Invertebrate predators; zooplankton community; chaoborus; pulex; size; behavior; hyalina; shifts; magna; fish]
  • Hydrobiologia

    The relevance of size efficiency to biomanipulation theory: a field test under hypertrophic conditions

    Steven A.J. Declerck, Luc De Meester, N. Podoor, J-M. Conde-Porcuna
    The superiority of large zooplankton in suppressing phytoplankton growth has often been inferred from the Size Efficiency Hypothesis (S.E.H.). The S.E.H. has originally been formulated to account for the competitive superiority of large to small zooplankton under food limiting conditions. Extrapolation of its predictions to the suppression of phytoplankton by zooplankton under high food availability, should be done with care. In an attempt to assess the relevance of the S.E.H. to biomanipulation theory in hypertrophic systems, a fish exclosure experiment was carried out in which the efficiency of two differently structured zooplankton communities in reducing phytoplankton biomass was examined. By inoculating part of the enclosures with laboratory grown Daphnia magna, a community dominated by this large cladoceran species could be compared with a community mainly consisting of Bosmina and smaller Daphnia species. After the exclusion of fish, there was an exponential increase of total. zooplankton biomass. Phytoplankton growth was efficiently suppressed to equal levels in both treatments, though there was a difference in timing: chlorophyll-a levels in the enclosures inoculated with D. magna dropped one week earlier than in non-inoculated enclosures. The time-lag was even more pronounced when large phytoplankton was considered. In accordance with the S.E.H., the time lags could be explained by differences in population growth potential as well as by differences in zooplankton grazing rates (indirectly measured as the minimal zooplankton biomass needed to suppress phytoplankton growth) and food particle size range.

Projects & collaborations


  • Construction of a barcode reference library of Dutch freshwater zooplankton

    Project 2022
    Water fleas (Cladocera) form a species rich group that play an important ecological role in freshwater ecosystems, such as ponds, lakes, ditches, canals and pools. Biodiversity research on this group is hampered because of the highly specialized taxonomic expertise and large time investments required for the analysis of samples. However, the rapid development of next generation sequencing (NGS) techniques creates the prospect of automatizing the identification of species in community samples through bulk DNA sequence analysis (metabarcoding). To be reliable and successful, such approach requires an extensive and curated library of regionally acquired barcodes. Unfortunately, West-European populations of cladoceran species are not or only very poorly represented in publicly available databases (e.g. Boldv4, NCBI). The aim of this project therefore is to establish a high-quality, curated reference library for the marker gene COI (cytochrome c oxidase I) of all cladoceran species in The Netherlands. For this, a large variety of freshwater habitats are being sampled across The Netherlands. Cladocerans retrieved from these samples are identified individually by Martin Soesbergen (Rijkswaterstaat), an expert in Cladoceran taxonomy, after which their COI gene is sequenced at NIOO-KNAW. The resulting reference library will strongly facilitate end users to identify unknown specimens and contribute to the detection of cryptic diversity. Together with a bioinformatics pipeline, also assembled at NIOO-KNAW, this library will strongly enhance our ability to monitor and survey zooplankton communities in The Netherlands.
    Martin Soesbergen (Rijkswaterstaat), our partner in crime
  • Cryptic diversity in the monogonont rotifer Brachionus calyciflorus

    Project 2022–Present
    In the latest decade, the application of DNA sequencing technology has resulted in the discovery of many species new to science. Most of these species have long remained undetected because they were difficult to distinguish morphologically from described species. In this project, we have applied reverse taxonomy with the aim to detect and describe formerly unrecognized ‘cryptic’ species in the species complex Brachionus calyciflorus, a very commonly studied and cosmopolitan freshwater rotifer. The combination of a molecular and morphological analysis resulted in the discovery and (re)description of four species, i.e. B. calyciflorus s.s., B. elevatus, B. fernandoi and B. dorcas (Papakostas et al., 2016; Michaloudi et al., 2018). While some evidence accumulates that the species differ ecologically (Papakostas et al., 2016; Zhang et al. 2020), we have also demonstrated that reproductive barriers between the two most closely related sibling species, B. calyciflorus s.s. and B. elevatus are strong but not impenetrable (Zhang & Declerck 2021, 2022). The observation of hybridization leads to the question how species maintain their integrity in the face of genetic exchange. Currently, we perform a phylogeographic analysis with the aim to study the geographic structure of molecular divergence within the species complex and the degree to which this bears the signature of hybridization. Future studies will also focus on ecological divergence and its implications for the long-term fate and coexistence of these sibling species.
    Brachionus calyciflorus
  • Securing biodiversity, functional integrity and ecosystem services in DRYing rivER networks (Dryver)

    Project 2020
    Securing biodiversity, functional integrity and ecosystem services in DRYing rivER networks (Dryver)
    Stakeholders at the Genal River, Spain
  • Rapid evolutionary adaptation to multiple stressors: cross-tolerance or cross-inhibition?

    Project 2019–Present
    Due to anthropogenic activities, the global environment is changing rapidly, and is expected to continue doing so over the coming decades. Many of these changes lead to increased levels of stress to living organisms with negative impacts on their natural populations. Rapid evolutionary adaptation is increasingly recognized as an important mechanism that increases the coping ability of multicellular organisms to deal with increased stress levels. Applying an experimental evolution approach with freshwater zooplankton, we aim at testing specific hypotheses related to the causes and consequences of rapid adaptation to increased stress levels (e.g. poor food quality, salinization, warming and copper contamination). Our recent research focuses strongly on a multiple stressor context and addresses questions such as whether adaptation to one stressor impedes or enhances abilities to cope with other stressors and how past selection regimes determine the evolutionary potential of populations to adapt to new stressors.
    Second stage set-up
  • Ecological stoichiometry of freshwater zooplankton

    Project 2014–Present
    In many ecosystems, human impacts have strongly altered the quantities and relative ratios of elements such as carbon, phosphorus, nitrogen. This may have important consequences, not only for the plants, but also for the animals that use these plants as food source. Animals need specific ratios of elements for their optimal growth, survival and reproduction. Deviations from these ratios (‘stochiometric mismatch’) may lead to substantial performance reductions with important ecological and microevolutionary consequences. In this project, we investigate how populations of zooplankton herbivores respond to and cope with both shortage and excess of critical elements in their diet, both from ecological and microevolutionary perspectives.
  • The zooplankton-microbiome (MicroZoo): beyond microbe-host associations

    Project 2016–Present
    Zooplankton is a crucial component of aquatic food webs
    Collection of approaches taken in MicroZoo