Research
Current Research Projects:
The relative influence of biodiversity and biotic interactions on the early stages of phytoplankton bloom formation (BLIC).
Funded by German Science Foundation (DFG), Prof. Dr. H. Stibor; Dr. M. Stockenreiter; PhD Student: Sophia Kopp
The global loss of biodiversity is also visible in aquatic ecosystems. How biodiversity affects ecosystem functions is mechanistically only partially understood. Such biodiversity - ecosystem function relationships are already documented at the level of primary producers, in pelagic systems this is phytoplankton. Phytoplankton is involved in about 50% of the global primary production, essentially controls global cycles of important elements and is the basis of important ecosystem services such as fisheries. Phytoplankton is characterized by a special dynamic, the ability to quickly accumulate large amounts of biomass. These so-called phytoplankton blooms can often occur on a regular basis (e.g., in spring, so-called spring blooms) and provide important food for higher trophic levels, or can be triggered by external factors (e.g., external nutrient supply, eutrophication). Phytoplankton blooms are usually supported by one or a few species; in the case of toxic or poorly edible species, blooms can have significant negative effects on the transfer of energy and matter in food webs. A question that has been studied essentially only theoretically is whether the diversity of phytoplankton communities has an impact on the formation of phytoplankton blooms. With increasing diversity, the probability that there is a species in the community that can monopolize resources and form blooms is higher (selection effect). At the same time, as diversity increases, complementarity and efficiency of resource use may increase, and it becomes increasingly difficult to monopolize resources (complementarity effect).
BLIC is investigating this issue using a mechanistic up-scaling approach. In controlled laboratory experiments, increasingly diverse communities are exposed to nutrient pulses and the strength of selection effects and complementarity are quantified. In a next step, diversity-manipulated field communities will be exposed to nutrient pulses and investigated to what extent the change in diversity makes blooms more likely or not. Finally, mesocosm experiments are planned with natural phytoplankton communities along natural diversity gradients. All experiments will take place in the same way with marine and freshwater laboratory and field communities.
Besides experimental approaches, the second pillar of BLIC is the theoretical model analysis of these research questions. So-called "trait" based multi - dimensional mathematical models will analyze in detail the early stages of phytoplankton blooms. The models will receive important parameterizations from the experiments and at the same time have an important influence on the execution of individual experiments, which can then investigate particularly interesting environmental combinations for bloom formation arising from the model in detail.
AQUACOSM-plus: Network of Leading Ecosystem Scale Experimental AQUAtic MesoCOSM Facilities Connecting Rivers, Lakes, Estuaries and Oceans in Europe and beyond
Funded by: European Commission, Directorate-General for Research & Innovation (EU - H2020), Prof. Dr. Herwig Stibor; Dr. Maria Stockenreiter
AQUACOSM-plus advances European mesocosm-based aquatic RI by integrating the leading mesocosm infrastructures into a coherent, interdisciplinary, and interoperable network covering all ecoregions of Europe. AQUACOSM-plus widens the user base by extending TA provision (> 13000 person-days), and strengthening the offered services, with 10 new partners, including an NGO and doubling of SMEs. We initiate actions to increase competence in mesocosm science in new EU member states (Hungary and Romania), and emphasise training of young scientists through summer schools covering various disciplines including effective science communication. AQUACOSM-plus develops near-real-time Open Data flows and improved metadata, thus promoting Open Mesocosm Science in collaboration with leading EU-supported initiatives in the EOSC and fosters wider sharing of information, knowledge, and technologies across fields and between academia, industry, and policy makers/advisers.
AQUACOSM-plus develops new technological capabilities for mesocosm research, to effectively execute scenario-testing for Climate Change -related pressures on aquatic systems from upstream fresh waters to the sea. These developments include mobile large-scale mesocosm approaches, leading-edge imaging technologies, and affordable methods to obtain high- frequency data on community change and greenhouse gas fluxes in mesocosm settings.
AQUACOSM-plus will progress beyond current achievements by actively pursuing RI-RI collaboration with European environmental RIs (LTER, ICOS, DANUBIUS, JERICO) at all project activity levels (NA, JRA, TA). Multidisciplinary joint research, combining observational data and modelling approaches with targeted mesocosm experiments, is a key step towards successfully tackling current and future Grand Challenges. This involves shared capacity building via symposia, expert summits, and open workshops, with the aim of co-designing future aquatic research actions and their RI demands.
Genetic and ecological characterization of the invasive freshwater jellyfish Craspedcausta sowerbii
Prof. Dr. H. Stibor; Dr. S. Gießler; PhD Student: Stefan Dehos
The increasing introduction of non-native species into new ecosystems is a consequence of growing mobility. The freshwater jellyfish Craspedacusta sowerbii is one example of a recently globally distributed species, which originated from China. Since 1905 it is known to be present in German lakes. Although mass occurrences of medusae were recorded and effects on aquatic food web dynamics are expected, the consequences of the jellyfish's introduction to aquatic systems has not been analyzed yet. To figure out the trophic position of medusae, mesocosm experiments will be conducted. In laboratory experiments, competitiveness of medusa and polyp with other organism will be determined. To check for long-time establishment and evolutionary dynamics, genetic and sexual diversity will be quantified using molecular markers. These results will give evidence if multiple introductions are likely and if both sexes and different genotypes are present. Combined analyses of genetic diversity and ecological function of this species, will allow a better understanding of cause and effect relationships within aquatic food webs exposed to invasion.
The importance of prevailing nitrogen to phosphorus ratios in Bavarian lakes for the growth of whitefish (NitroFlex II)
LMU: Prof. Dr. H. Stibor, PostDoc: Dr. G. Spörl; PhD Student: P. Galvan
Large differences in the growth of native whitefish species (Coregonus spec.) can be found among Bavarian lakes. One hypothesis suggests that the concentrations of nutrients are the underlying cause for these variations. During the last decades, anthropogenic activities have influenced the global cycles of nitrogen (N) and phosphorous (P) significantly. Increasing ratios of dissolved N to P are the consequences for freshwater lake ecosystems.
Changes in N:P ratios may have severe impacts on entire lake food webs. Phytoplankton represents the basis of aquatic food webs and its communities in general react rapidly and directly to alterations in the nutrient pools of N and P. Resulting effects can be passed on to zooplankton grazers and reduce zooplankton abundances and diversity . This can lead to a reduction in food quantity for planktivorous whitefish and potentially a reduced growth potential of whitefish stocks in Bavarian lakes.
Previous findings derived from mesocosm experiments strongly support this hypothesis. However, there is a lack of reliable field data which would allow a profound evaluation of growth conditions for whitefish populations in Bavarian lakes.
The purpose of this project is to study the correlations between differing N:P ratios and whitefish growth in selected Bavarian lakes. With the support and in cooperation with
the Bayerischen Staatsministerium für Umwelt und Verbraucherschutz
the Bayerischen Staatsministerium für Ernährung, Landwirtschaft und Forsten
the Landesamt für Umwelt (LfU) (Dr. Schaumburg)
the Bayerischen Landesanstalt für Landwirtschaft, Institut für Fischerei (Dr. Schubert)
the Fachberatung für Fischerei des Bezirks Oberbayern (Dr. Wunner, Dr. Gum)
and the Fischereigenossenschaft Chiemsee
we perform comparative analyses of ecologically relevant parameters among different lakes in Southern Bavaria. Parameters of interest concern water chemistry, nutrients, phytoplankton and zooplankton growth, taxonomical compositions of phytoplankton and zooplankton communities and feeding behavior as well as growth of local whitefish species (Coregonus spec.).
Effects of silicate input on the macrophytes and plankton community in a eutrophic lake (MesoSiP):
Prof. Herwig Stibor; Dr. Maria Stockenreiter; PhD student: Nigar Talibova.
Supported by the municipality of Riedering
Freshwater ecosystems are increasingly threatened by human activities such as the expansion of agricultural landscapes and climate change. As a result, freshwater biodiversity is steadily declining, which can negatively impact ecosystem functioning.
Many attempts are being made to halt this trend.
One approach today is to target specific nutrients. For example, silicate (added as a powder in this context) has recently been introduced into lakes with excessive macrophyte growth to reduce their growth. The main reason for the reduced growth, according to these studies, is increased mineralization of the sediment. In previous studies, also carried out at Seeon Limnological as part of the transnational access AQUACOSMplus, the question of the effect of the addition of silicate powder on the plankton community was investigated experimentally, as this aspect had not or hardly been investigated in other studies. In many lakes and ponds, silicon is often a limiting resource, especially if they are fed only by rainwater. However, for diatoms, silicon is an important resource and can support their growth.
Macrophytes are important competitors of planktonic algae for nutrients. The much larger surface area of macrophytes allows for more efficient uptake; unlike most phytoplankton, they can also store these nutrients. Thus, macrophytes can displace phytoplankton. If macrophyte growth is reduced, phytoplankton can grow again, which can lead to an undesirable bloom of cyanobacteria, especially in eutrophic lakes during the hot summer months. These, in turn, can cause tremendous problems in the food web due to their potential toxicity and poor food quality. However, under ideal conditions, diatoms can be good competitors for cyanobacteria. They are of high food quality and can therefore be beneficial to the food web in a lake. An addition of silicate can therefore promote the growth of diatoms and, in the best case, prevent a cyanobacterial bloom.
Although cyanobacterial blooms have been observed for a long time, they have recently become more common. These blooms have negative impacts on the use of freshwater bodies. Local recreation is severely impacted as swimmers find the blooms unpleasant and they can lead to health problems such as skin irritation. More importantly, these blooms can cause long-lasting changes in the overall food web of the lake. They reduce the food quality of the phytoplankton community for invertebrates and fish. Eutrophication (input of nitrogen (N) and phosphorus (P)) is an important aspect that promotes cyanobacterial growth. However, the response of phytoplankton communities to nutrient inputs in the form of N and P is also determined by the absolute availability of silica. If the water is rich in silica (Si), N and P loading will promote Si-requiring diatoms, and the risk of a cyanobacterial bloom can certainly be limited as long as dissolved silica is available. In systems where Si and P are scarce and N is contributed by intensive agricultural use, the Si:P ratio predicts the potential mass occurrence of cyanobacteria. Thus, a relatively new attempt to reduce the abundance of cyanobacteria is to introduce Si into the affected lakes.
Such an approach is being pursued for one of the lakes near the SLS. This provides an opportunity to conduct an experiment on an entire lake. However, combining this with an experiment in a mesocosm opens up the possibility of understanding mechanistically the effects of the role of Si on cyanobacterial blooms in freshwaters. Therefore, I will participate in a mesocosm experiment at SLS to investigate the effect of dissolved silica addition on the food web of a shallow lake. For this purpose, a series of mesocosms will be installed prior to fertilization of the entire lake. The mesocosms will include the entire water column, including sediment. Treatments will include control mesocosms with no added nutrients and treatments factorially enriched with various Si:P ratios in combination with and without mesozooplankton.
Completed Research Projects:
Flexibility matters: Interplay between trait diversity and ecological dynamics using aquatic communities as model systems (DynaTrait)
Funded by German Science Foundation (DFG), Dr. M. Stockenreiter; Prof. Dr. H. Stibor; PD Dr. P. Fink (University Köln); PhD Student: S. Hammerstein
In this project we focus on the effects of diversity loss and trait dynamics in natural plankton communities (DYNATLOSS). Considering traits as mechanistic links between biodiversity loss and ecosystem services we focus on questions (1) how a loss of traits is affecting phytoplankton production, zooplankton composition and food web transfer efficiency?; (2) and do such trait dynamics result in feedback effects on the phytoplankton community? These questions will be addressed with diversity manipulated natural phytoplankton communities in lab and large scale field experiments.
Impacts and dynamics of nitrogen supply in lake ecosystems (MesoNitro)
Funded by German Science Foundation (DFG), Dr. G. Trommer, PhD Student: M. Poxleitner
Anthropogenically enhanced nitrogen supply in lakes often implies changes in the lakes ecosystems and due to the worlds' increasing food demand and the related nitrogen rich fertilizers, nitrogen supply will further increase in the future. This study investigates the influence of enhanced nitrogen load on plankton communities in lakes in Upper Bavaria (Lakes Brunnsee, Klostersee and Thalersee near the Limnological Research Station in Seeon) and determines changes of the nitrogen load in the past. For the evaluation of the recent nitrogen flux from the atmosphere to lake sediments, nitrogen concentrations are measured in precipitation, lake pelagial and lake sediments. Analyses of total nitrogen content and nitrogen stable isotopes in lake sediment cores allow to detect changes in the nitrogen load of the past ~150 years. In mecocosm-experiments on the lakes, the influence of enhanced nitrogen supply on biomass stoichiometry and biodiversity of natural phytoplankton communities and the interaction with zooplankton will be investigated.
Genetic and ecological characterization of the invasive freshwater jellyfish Craspedcausta sowerbii
Funded by German Science Foundation (DFG), Prof. Dr. H. Stibor; Dr. S. Gießler; PhD Student: K. Schachtl; Yuanyuan Wang
The increasing introduction of non-native species into new ecosystems is a consequence of growing mobility. The freshwater jellyfish Craspedacusta sowerbii is one example of a recently globally distributed species, which originated from China. Since 1905 it is known to be present in German lakes. Although mass occurrences of medusae were recorded and effects on aquatic food web dynamics are expected, the consequences of the jellyfish's introduction to aquatic systems has not been analyzed yet. To figure out the trophic position of medusae, mesocosm experiments will be conducted. In laboratory experiments, competitiveness of medusa and polyp with other organism will be determined. To check for long-time establishment and evolutionary dynamics, genetic and sexual diversity will be quantified using molecular markers. These results will give evidence if multiple introductions are likely and if both sexes and different genotypes are present. Combined analyses of genetic diversity and ecological function of this species, will allow a better understanding of cause and effect relationships within aquatic food webs exposed to invasion.
The importance of prevailing nitrogen to phosphorus ratios in Bavarian lakes for the growth of whitefish (NitroFlex)
LMU: Prof. Dr. H. Stibor, Dr. G. Spörl; PhD Student: P. Lorenz
Large differences in the growth of native whitefish species (Coregonus spec.) can be found among Bavarian lakes. One hypothesis suggests that the concentrations of nutrients are the underlying cause for these variations. During the last decades, anthropogenic activities have influenced the global cycles of nitrogen (N) and phosphorous (P) significantly. Increasing ratios of dissolved N to P are the consequences for freshwater lake ecosystems.
Changes in N:P ratios may have severe impacts on entire lake food webs. Phytoplankton represents the basis of aquatic food webs and its communities in general react rapidly and directly to alterations in the nutrient pools of N and P. Resulting effects can be passed on to zooplankton grazers and reduce zooplankton abundances and diversity . This can lead to a reduction in food quantity for planktivorous whitefish and potentially a reduced growth potential of whitefish stocks in Bavarian lakes.
Previous findings derived from mesocosm experiments strongly support this hypothesis. However, there is a lack of reliable field data which would allow a profound evaluation of growth conditions for whitefish populations in Bavarian lakes.
The purpose of this project is to study the correlations between differing N:P ratios and whitefish growth in selected Bavarian lakes. With the support and in cooperation with
the Bayerischen Staatsministerium für Umwelt und Verbraucherschutz
the Bayerischen Staatsministerium für Ernährung, Landwirtschaft und Forsten
the Landesamt für Umwelt (LfU) (Dr. Schaumburg)
the Bayerischen Landesanstalt für Landwirtschaft, Institut für Fischerei (Dr. Schubert)
the Fachberatung für Fischerei des Bezirks Oberbayern (Dr. Wunner, Dr. Gum)
and the Fischereigenossenschaft Chiemsee
we perform comparative analyses of ecologically relevant parameters among different lakes in Southern Bavaria. Parameters of interest concern water chemistry, nutrients, phytoplankton and zooplankton growth, taxonomical compositions of phytoplankton and zooplankton communities and feeding behavior as well as growth of local whitefish species (Coregonus spec.).
Trait-related feedback dynamics in natural plankton communities
Funded by Deutsche Forschungsgemeinschaft (DFG), Dr. M. Stockenreiter; Prof. Dr. H. Stibor; PD Dr. P. Fink (University of Cologne); PhD student: L. Benitez-Requena
Biodiversity loss is often accompanied by a loss of traits related to resource use and growth, which are important for food web dynamics and trophic transfer efficiencies. In the DYNATLOSS II project, we specially focus on the feedback loop from reduced phytoplankton trait diversity to phytoplankton dynamics via diversity-mediated shifts in zooplankton. We will address this general objective with field experiments with natural plankton communities to estimate the direction and strength of total feedback effects. Additionally, we will analyse the individual components of the complex and multifactorial set of feedback effects (mainly by laboratory experiments).
Our work programme will focus on the following main research question: Can altered grazing, due to shifts in phytoplankton diversity result in multiple (and partially interdependent) feedback effects?
We will address this research question with a chain of testable hypotheses. Field experiments allow analysing total feedback effects under natural conditions. To disentangle individual feedback mechanisms such as linked to grazing dependent size distribution and nutrient availability, additional, highly controlled laboratory experiments will be performed.
These feedback mechanisms may all affect the community of herbivorous zooplankton. This could potentially compensate short-term effects of phytoplankton related shifts in zooplankton composition. In addition to the experimental approaches in laboratory and in the field, we will also model the proposed feedback effect using an extension of established nutrient dynamics models in phytoplankton – zooplankton systems.
Regime shifts in freshwater ecosystems exposed to multiple stressors by increasing temperature, fertilizers and pesticides (CLIMSHIFT)
Funded by German Science Foundation (DFG)
Prof. Dr. H. Stibor; Dr. M. Stockenreiter; PhD Student: Nora Kipferler
In Cooperation with LIEC (Metz, FR), EcoLab (Toulouse, FR), IGB (Berlin, DE) and UFZ (Leipzig, DE)
Shallow freshwater systems provide vital ecosystem functions, but are threatened by multiple stressors. Complex interactions between pelagic and benthic organisms and processes result in two alternative stable states. These are characterized by either phytoplankton or macrophyte dominance. Disturbances can push a macrophyte dominant system into phytoplankton dominance, which is associated with a loss in important ecosystem functions. Examples for such disturbances are rising temperatures through climate change or fertilizers and toxins originating from agriculture. The aim of the cooperation CLIMSHIFT is an examination of the ecological consequences and gaining an understanding of stressor interaction in shallow aquatic systems. Computer model supported micro- and mesocosm experiments will show whether rising temperatures, nutrient concentrations and toxins act additively, synergistically or antagonistically. The experimental systems will be composed of different pelagic and benthic primary producers and herbivores.