Current Research Projects:
Flexibility matters: Interplay between trait diversity and ecological dynamics using aquatic communities as model systems (DynaTrait)
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)
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
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)
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
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.