Planktology
Research topics and current projects in the Plankton Ecology Group
Key area 1: ECOLOGICAL STOICHIOMETRY OF FOOD WEBS
In the last decades, the biogeochemistry of major mineral nutrients has changed dramatically on global and regional spatial scales. Marine coastal ecosystems are strongly affected by these changes, which essentially create a new abiotic environment for primary production and trophic transfer. Recent biogeochemical changes of the North Sea include a strong increase in the available N:P ratio, shifting the ecosystem towards P-limitation. Shifts in the identity of primarily limiting nutrients alter the chemical food quality of primary producers and the regeneration of nutrients by consumers and the microbial food web. Ecological stoichiometry (ES) has proven to be a suitable framework to predict consequences of changed nutrient availability and ratios for trophic interactions. These consequences of altered biogeochemistry will on top be strongly affected by global change induced altered temperature and atmospheric CO2 concentrations. Higher temperatures will increase respiration, but will affect photosynthesis only under light saturation; thereby global warming will increase the heterotroph:autotroph ratio in pelagic food webs. Elevated CO2 concentrations will lead to higher C-at lower P-availability, which will increase phytoplankton C:P and thus decrease its nutritional value for primary consumers. Such synergistic effects have hardly ever been investigated together so far and not at all in a realistic experimental framework.
Current projects
Experimental appraoch to analyse zooplankton-phytoplankton interactions in relation to resource availability
“ELSER” EcoLogical Stoichiometry in aquatic food webs (2009-2012)
funded by: DFG Hi 848/7-1 (in Cooperation with AWI/BAH, DFG Ma4501/1-1)
The ecological stoichiometry theory has been successful in enhancing our understanding of trophic interactions between consumer and prey species. Consumer and prey dynamics depend on the nutrient composition of the prey relative to the nutrient demand of the consumer. However, most experiments on this topic used a single consumer species and very simple prey communities. Therefore, little is known about the validity of stoichiometric constraints on trophic interactions in more natural food webs. This project seeks to enhance our understanding of nutritional constraints in marine pelagic food webs by testing the consumer’s ability to select high quality food, by addressing the importance of food quality in multispecies zooplankton-phytoplankton interactions and by investigating the propagation of different phytoplankton quality via herbivores to predatory zooplankton and fish larvae. These aspects will be experimentally analysed in microcosms and mesocosms and fundamentally enhance our ability to predict the consequences of anthropogenically altered biogeochemistry in coastal waters on trophic transfer in ecosystems.
Involved scientists: Helmut Hillebrand, N.N.
Collaborators:Arne Malzahn, Maarten Boersma, Cedric Meunier (Alfred Wegener Institut, Helgoland)
The Jena-experiment
Effects of plant diversity on the ecological stoichiometry of ecosystem functioning (2010-2013)
funded by DFG Hi848/11-1 within the research group Jena Experiment
This subproject of the Jena Research group will analyze the relationship between plant diversity and the ecological stoichiometry of multiple ecosystem processes and trophic interactions. Ecological stoichiometry is a theoretical framework allowing the prediction of competitive and trophic interactions based on the balance between resource supply and resource needs of interacting species. The balance of multiple elements (C, N, P, and K) in the soil, plants and their consumers will be investigated across the gradient of plant diversity and species composition in the JenaExperiment. In the main experiment, we will track the stoichiometry of plant and insect chemical composition along the experimental gradients of species richness and functional diversity. We will test (i) whether plant diversity enhances the uptake and thus content of multiple elements on the community level, and (ii) whether differential stoichiometry will change consumption patterns by insect herbivores. In the trait-based experiment, we will address stoichiometry of elements on a species-specific basis, asking whether plant diversity alters the resource content and ratios of plant species depending on their traits and the traits of their co-occurring species. We will test whether (iii) higher coverage of the resource use traits increases resource use efficiency for multiple elements, and (iv) whether plant stoichiometry responds plastically to the competitive environment. Thereby we will address the question how species diversity affects ecosystem multifunctionality, i.e., whether more species are required to maintain the processing of different elements. Moreover, we will analyze whether functional turnover occurs, i.e., whether different species carry function in resource use efficiency and trophic transfer across time.
Involved: Helmut Hillebrand, Robet Ptacnik
Collaboration: Prof. Dr. M. Kleyer (Univ. Oldenbrug), Prof. Elizabeth T. Borer (University of Minnesota) und Prof. Stan Harpole (Iowa State University)
Link to the research group homepage
Nutritional bioindicators and ecological stoichiometry
funded by: Alexander von Humboldt-Stiftung (3.1-KAN/1139289 STP)
Involved: Paul C. Frost, Helmut Hillebrand
Former projects
2005-2008 The role of the microbial loop in benthic communities – combining food web theory and ecological stoichiometry” (DFG: Hi 848 4-1; 4-2)
2001-2002 Structure and stoichiometry of microbenthic communities Marie Curie Individual Fellowship (MCFI-CT-2000-00912)
1999-2001 Simultaneous effects of top-down and bottom-up regulating forces on periphyton (DAAD and Erken Fellowship)
Key area 2. Regulation of biodiversity and consequences of biodiversity loss
Concerning the mechanisms regulating diversity in local assemblages, a variety of factors increasing, decreasing and maintaining diversity have been identified. These mechanisms operate on different scales, from short-term ecological interactions to regional factors such as history of climate, evolution and migration. Conceptually, the assembly of a local community can be visualised as species passing through a series of filters. These represent historical (e.g. dispersal, speciation) and ecological (e.g. competition, predation, disturbance, abiotic environmental factors) constraints on the arrival and survival of organisms at a certain locality. Several contributions tried to disentangle the importance of regional and local constraints on local species richness. Generally, these studies agree on an important influence of both, regional and local factors, but the relative importance of these factors is still uncertain since they act on different temporal and spatial scales. We will use experimental and analytical tools to address local and regional cosntraints of species coexistence.
The impact of diversity on ecosystem processes (productivity) and properties (stability) is one of the most debated questions in ecology right now. Experimental tests of this impact are mainly confined to terrestrial environments. Special characteristics of aquatic ecosystems such as fairly open propagule and material exchange, steeper physical and chemical gradients, often more rapid biological processes (such as short generation times of primary producers), and higher phylogenetic diversity (especially in marine systems) limit the ability to transfer these conclusions. In turn, however, these characteristics provide excellent opportunities for hypothesis testing through experimental manipulations.
Rockpools are excellent systems for biodiversity - function experiments (Fotos: Monika Feiling).
Current projects
Relevance of functional diversity in microbial food webs: effects of grazer diversity on prey diversity and composition (2008-2011)
Funded by: DFG Mo 1931/1-1
Involviert: Stefanie Moorthi, Joanna Filip, Helmut Hillebrand
Kooperation mit: Ulrike.-G. Berninger und Steve Wickham, Universität Salzburg (A), David A. Caron, University of Southern California, USA
Effects of plant diversity on the ecological stoichiometry of ecosystem functioning (2010-2013)
funded by DFG Hi848/11-1 within the research group Jena Experiment
See description of project in key area 1.
Scientific basis of monitoring of the German Bight; subproject: case study biodiversity
funded by: Niedersächsisches Ministerium für Wissenschaft und Kultur (MWK) und Niedersächsisches Ministerium für Umwelt und Klimaschutz (MU)
Involved: Dorothe Hodapp, Helmut Hillebrand
Coordinator: Dietmar Kraft
ComSat: Biodiversity, community saturation and ecosystem function in lakes
funded by: Norwegian Research Council NFR
Involved: Robert Ptacnik, Helmut Hillebrand
Coordinator: Tom Andersen, Univ. Oslo (N)
TheNutrient Network
funded by: National Science Foundation (USA)
Involved: Helmut Hillebrand
Coordinator: Elizabeth Borer and Eric Seabloom, Univ. of Minnesota (USA)The relation between biodiversity and resilience in source-sink meta-communities
funded by: Dutch Science Council NWO
Involved: Helmut Hillebrand
Coordinator: Klemens Eriksson, Univ. Groningen (NL)
Resilience and diversity in aquatic metacommunities: Effects of dispersal and the spatial scale of disturbance (2009-2012)
funded by: DFG Hi 848/8-1
See description of project in key area 4.
Former projects
2009 Functional consequences of aquatic biodiversity for ecosystem biogeochemistry and element cycling (DFG round table discussion, DFG Hi848 10-1)
2004-2005 Diversity of marine invertebrates enhances the functioning of the ecosystem” Deutscher Akademischer Austauschdienst (DAAD: D04/04378)
2003-2006 Experimental test of biodiversity effects on ecosystem functioning in marine environments (DFG: Hi 848 1-1/-2)
2002-2003 Quantification of global patterns of biodiversity Vetenskapsrådet (VR: 621-2002-215)
Ecologists in their natural habitat: Dan Gruner (Univ. Maryland), Elisabeth Borer (Univ. Minnesota) and Helmut Hillebrand at the German NutNet site in Papenburg (Foto: Monika Feiling).
Key area 3: COASTAL ECOSYSTEMS AND CLIMATE CHANGE
Observed changes in global climate will have dramatic consequences for coastal ecosystems. These include direct effects of increased temperature and CO2 concentrations on, e.g., seasonality, trohic mismatch as well as indirect effects mediated by changed currents or resuspension. These indirect and direct effects will change biotic communties. The potential consequences of global warming on the biota in terrestrial and aquatic ecosystems represent one of the predominant questions of recent ecological research.
The response of species composition and biological diversity to warming warrants special attention for two major reasons. On one hand, global warming is expected to become a major driver of future species extinctions and diversity loss (Millenium Ecosystem Assessment). On the other hand, diversity itself is supposed to work as an insurance against changing conditions, i.e., more diverse communities are supposed to show faster recovery due to higher response diversity. Thus, the link between global change and biodiversity is important from two perspectives: how does global change drive diversity and how does diversity affect ecosystem responses to global change.
Current projects
Recurrent Extreme Events in Spatially Extended Excitable Systems: Mechan-isms of their Generation and Termination
funded by: VolkswagenStiftung
Although extreme events (ExEvs) occur in a wide variety of contexts, there is no common definition of an ExEv, though everybody has a certain understanding of such phenomena de-pending on the specific context. In general, ExEvs are considered to be rare events characte-rized by a large impact on a particular system which is measured in terms of very different quantities. In this proposed project we will study phenomena in excitable systems which ap-pear recurrently in rather large, irregularly spaced time intervals. Particularly we will focus on two such ExEvs, namely the recurrent occurrence of harmful algal blooms (HAB) in the ocean and the recurrent emergence of epileptic seizures (ES) in the human brain. Our part project will conduct time-sieres and experimental work on HAB, which appear when a toxic species (e.g. dinoflagellates or cyanobacteria) becomes extremely abundant and domi-nant in a plankton community. The emergence of such blooms can not only be dangerous for direct competitors or consumers of the toxic algae, but also for higher organisms such as shellfish, fish, birds, and mammals as well as for human beings, either by direct toxin effects or indirectly by propa¬gating effects up the food web (e.g., algal toxins accumulate in fish or shellfish that are consumed). Therefore, these blooms can have dramatic effects on human health and industry, affecting for in-stance coastal fish- and shellfish farms as well as tourism by prohibiting swimming in endangered areas. At first glance, both phenomena appear to have nothing in common. However, both HAB and ES occur in spatially extended systems where the dynam-ics in a localized region of the ocean or in the brain can be modeled as an excitable system.
For the plankton blooms this offers the opportunity to study the emergence or termination of a HAB by an extreme weather situation. Since different noises can be realized in plankton expe-riments, our hypotheses about possible triggers of ExEvs can be directly tested. We will ma-nipulate factors proposed to trigger HAB. The concise treatments will depend on the output of the modeling and the time series analysis. However, the chemostat system allows a flexible array of manipulating the mean and temporal variance of abiotic (e.g., temperature and nu-trient supply) and biotic conditions (competitor and grazer concentrations). The temporal va-riance can comprise different colors of noise as well as anomalously large fluctuations. Such fluctuations have been shown to influence population dynamics, a.o. in plankton , and rep-esent the conceptual basis of altered bloom dynamics through climatic variability. We will also manipulate the absolute magnitude and temporal fluctuation of resource supply. Grazing and the supply of resources are often considered as major triggers of harmful algal blooms.
Involviert: Michaela Busch, Stefanie Moorthi, Helmut Hillebrand
Koordination des Gesamprojektes: Ulrike Feudel (Theoretical Physics/Complex Systems, Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg)
Kooperation: Holger Kantz (Max-Planck-Institute for Physics of Complex Systems, Dresden), Jürgen Kurths (Potsdam-Institute for Climate Impact Research, Potsdam), Klaus Lehnertz (Department of Epileptology and Interdisciplinary Center for Complex Systems, University of Bonn), Dr. D. Caron and Dr. A. Schnetzer, University of Southern California (USC), Los Angeles.
Former projects
2009 Effect of global change on carbon sequestration and food web structure across ecosystems (DFG, Hi 848/9-1)
2005-2009 Long- and short-term effects of climate variability and physical forcing on the diversity of aquatic organisms (DFG Hi 848/3-1; 3-2 im Schwerpunktprogramm Aquashift)
2005-2008 Comparing trophic structure across ecosystems, National Center of Environmental Analysis & Synthesis, NCEAS, Santa Barbara, Ca, USA, together with Jonathan B. Shurin and Daniel Gruner
NCEAS Workgroup TropComp
Key area 4: Spatial and temporal dynamics in plankton
A common feature of diversity studies is that most of them deal with the local number of species (or another diversity measure), i.e. the standing alpha diversity at a certain time. However, this focus may actually miss more important aspects of anthropogenic changes in diversity. There is reason to hypothesize that before the local number of species is affected by a gradual change in, e.g., temperature, we might see shifts in local species dominance and temporal turnover. Especially the temporal sequence of species occurrence (i.e. beta-diversity over time) is prone to be accelerated by increasing temperature, which might go unnoticed as the observed diversity at any point in time will not change significantly. Species-time relationships (STR) have been introduced as one analytical tool to describe the increase of species richness over cumulative sampling time. The slope of the STR, which is an indicator of temporal turnover, has been shown to depend on the spatial scale of sampling, the organism group and ecosystem, as well as the sample and cumulative diversity.
Current projects
Resilience and diversity in aquatic metacommunities: Effects of dispersal and the spatial scale of disturbance (2009-2012)
funded by: DFG Hi 848/8-1
Recent years have seen stringent advances in the analysis of spatial ecological dynamics embedded in the concept of metacommunities, in which species coexistence is mediated by local interactions and regional dispersal. However, we lack information on how metacommunity dynamics alter responses of diversity and resilience to disturbance and environmental fluctuations, especially if these disturbances differ in their spatial extent. To test this idea, we will establish experimental metacommunities consisting of connected microcosms inhabited by phytoplankton (and their consumers). The metacommunities differ in their dispersal rates (which affect regional and local diversity) and their coexistence mechanism (patch dynamics versus source-sink dynamics). In these communities, we will alter mortality by removing biomass in local or regional extent and measure the recovery of community composition and important ecosystem functions (primary production, nutrient retention) after this disturbance. We except resilience to be a function of dispersal rate, local richness and regional richness, but we expect different relative importance of these factors at different spatial scales of mortality. In a second set of experiments, we will address the importance of spatial coexistence for the stability of ecosystem processes over time under undisturbed but fluctuating environmental conditions. The results from this project will allow addressing the importance of spatial insurance mechanisms in fragmented landscapes in cases of habitat destruction, which are considered to be major causes of biodiversity loss in future environments.
Involviert: Helmut Hillebrand, Nils Gülzow
Kooperation mit: Birte Matthiessen, IfM-GEOMAR Kiel; Bradley J. Cardinale, Univ. Michigan (USA)
funded by start-up money
This projects combines observational and experimetnal approaches to test the factors regulating spatial and temporal turnover of plankton spcies composition. We will use a field survey and experimental metacommunities to address changes in species composition across spatial, temporal and environmental gradients.
Involved: Helmut Hillebrand, Sandra Meier
Collaboration: Dr. Janne Soininen, University of Helsinki (FI)
Key area 5: Mixotrophy in marine ecosystems
Current projects
Role of light for consumer-dynamics and nutrient turnover in microbial food webs of the marine pelagial (2010-2013)
funded by: DFG Pt 5/ 3-1
The bulk of marine bacterial and primary production is consumed by unicellular grazers (‘protists’). Recent research revealed that pigmented grazers (‘mixotrophs’) represent an important consumer group of bacteria and phytoplankton. Especially in oligotrophic waters, mixotrophs play a pivotal role as consumers of the pico-plankton. These mixotrophs combine autotroph photosynthesis with ingestion of particulate food items. This dual mode of nutrition provides clear advantages under limitation of either energy or essential nutrients. However, the combination of multiple strategies exerts additional costs for building dual cell machineries compared to specialized competitors. Given the tremendous importance of mixotrophs for marine ecosystems, it is mandatory to develop a mechanistic model predicting the relative importance of mixotrophs in the environment, as well as their implications for food webs. Based on preliminary results and existing data, it is postulated that light intensity and grazing pressure represent major factors controlling the relative importance of mixotrophy in microbial food webs. We will study the competition between mixotrophic and heterotrophic grazers systematically in artificial food webs, applying gradients of light and loss rate. The collected data will eventually be the basis for a stoichiometric model of the microbial food web, taking the specific role of mixotrophy into account.
Involved: Robert Ptacnik, N.N.
Collaboration: Prof. Tom Andersen, Univ. of Oslo, Norway, and Prof. Herwig Stibor, IUEM, Technopôle Brest-Iroise, France
funded by: EU Mesoaqua
LightDynaMix - Dynamics of microbial food webs and mixotrophy in a light gradient (2010)
Pigmented grazers (‘mixotrophs’) contribute significantly to microbial grazing, especially in oligotrophic lakes and oceans. Recent studies show that the bulk of bacterivory in the ‘blue ocean’ can in fact be attributed to pigmented grazers. The type of grazing (mixotrophy vs. heterotrophy) is expected to have major implications on the resulting remineralisation rates of nutrients in the microbial food web. Heterotrophic protists are limited by the amount of energy in their prey, and function as net-remineralizers in the food web (Azam et al. 1983). Conversely, mixotrophs may cover their energy demand by light and utilize all nutrients ingested with their prey for synthesis of new biomass. However, the competitive edge of mixotrophs over their heterotrophic competitors is bound to the availability of light. We thus hypothesize that light is a major agent in determining the relative importance of mixotrophic vs. heterotrophic grazing, and hence the relative nutrient regeneration rates within microbial food webs. We will test this hypothesis in a mesocosm experiment at the HCMR facility, where the natural plankton community will be exposed to a light gradient. The experimental design includes tracer studies for measurement of nutrient regeneration rates, molecular probes for the identification of the picoplankton and estimation of grazing rates, and specific measurement of photosynthetic yield. Finally, by relating zooplankton growth to seston stoichiometry, we also aim at testing the L:N hypothesis in this ultra-oligotrophic environment.
Involved: Robert Ptacnik, Stefanie Moorthi, Radka Ptacnikova
Collaboration: Paraskevi Pitta at Hellenic Centre for Marine Research (HCMR), Maren Striebel (WasserCluster Lunz, A)
Texts: Anja Fitter and Helmut Hillebrand