Is Bythotrephes not invasive at home due to prey adaption?

CONTENT OF RESEARCH PROJECT Bythotrephes longimanus is a large predatory water flea home to European clear water lakes. After invading North American lakes several decades ago, Bythotrephes caused substantial changes in food webs of the invaded lakes. In comparison to the intense research carried out in North America, little is known about the importance of Bythotrephes in its native area, which includes lakes in and around the Alps. Supposedly lower impacts of Bythotrephes on its prey in the native range than in the invaded regions has been credited to long time co-evolution, but this assumption has never been tested. Instead, we suggest that Bythotrephes may have a more significant role than previously considered also in the native lakes. We propose to investigate the performance of Bythotrephes and its impacts on zooplankton populations in Austrian montane lakes, with focus on mechanisms of prey defense adaptations in lakes where the predator is present. HYPOTHESES Does Bythotrephes alter the zooplankton prey community in Austrian montane lakes? Are there so many Bythotrephes in montane lakes that they can have strong impacts on its prey similar as what has been shown in North America? Does long time coexistence of Bythotrephes and zooplankton in native range lead to development of prey features to avoid or reduce predation? METHODS We will use a mix of several field and laboratory approaches, both standard and novel. Lake sampling will combine classical zooplankton net-sampling with new high frequency sonar/ADCP and IR-video profiles for overall abundances and vertical migration behavior. We will employ cutting-edge methods based on molecular gut analysis for prey preference and diet composition. The field studies will be accompanied with laboratory experiments on prey adaptations to Bythotrephes presence. WHAT IS NEW AND/OR SPECIAL ABOUT THE PROJECT We have to date a very limited knowledge about the impact of Bythotrephes on the pelagic food web in highly sensitive ecosystems of montane lakes of its native region. We argue that role of Bythotrephes might have been underestimated and that it might increase in time in connection with global climate change.

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