Trait-related feedback dynamics in natural plankton communities

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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.