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WasserCluster Lunz - Biologische Station GmbH Dr. Carl Kupelwieser Promenade 5 A– 3293 Lunz am See Tel. 07486 20060 Fax 07486 20060 20 [email protected] www.wcl.ac.at Effect of chrysophytes on lake secondary production (ChrysoLake) Summary Global change is expected to have far reaching consequences on hydrological processes at the catchment level. For lakes in the temperate zone, it is expected to enhance the intensity and duration of thermal stratification, as well as the input of allochthonous carbon from the catchment into the lakes (‘brownification’). While changes in the plankton of eutrophic lakes (e.g. a proposed dominance of cyanobacteria) are a widely discussed topic in the current literature, the consequences of global change for oligotrophic lakes receive little attention. Mixotrophic chrysophytes are a prevailing element of phytoplankton in oligo- and mesotrophic lakes. Their contribution is predicted to increase with global change-associated phenomena (brownification and enhanced thermal stratification). There is indication for detrimental effects of chrysophytes on zooplankton growth and reproduction, which implies serious consequences for pelagic trophic efficiency and ecosystem services e.g. fish production. However, our current understanding on the bottom-up effect of chrysophytes on secondary production is fragmentary. I propose to study the effects of chrysophytes on zooplankton secondary production and community composition. Laboratory feeding experiments will be combined with field observations to quantify species-specific responses of relevant zooplankton taxa to chrysophytes. The underlying mechanisms will be explored by biochemical analyses of algae and consumers. The proposed research joins several state-of-the-art methods (biochemical lipid and RNA:DNA ratio analyses, traitbased approach) to get a comprehensive understanding on the role of this key group for the functioning of lake ecosystem. Many nutrient-poor lakes (particularly in alpine and northern regions) have highly valuable fish stocks (salmonids) and they represent important recreational sites. Altering zooplankton composition and productivity may contribute to changes in fish community, with serious imprint on ecosystem services. Besides, crysophyte blooms can cause unpleasant fishy odour. My study will be a first step to specifically address the consequences of mixotrophic algae for secondary production in freshwater. Therefore, the proposed research is at the forefront of contemporary research in the context of global change and lake food webs, and will stimulate followup projects. It will significantly contribute to the understanding of carbon flow and nutrient cycling in alpine lakes under global change.