Variation in the response of crustacean zooplankton species richness and composition to the invasive predator Bythotrephes longimanus.

The predacious invertebrate Bythotrephes longimanus has now invaded >90 freshwater lakes in North America.There is some evidence that B. longimanus has a negative effect on summer zooplankton species richness; however,no study has examined the effect of B. longimanus throughout the ice-free season in more than one lake. Wevisited 10 invaded and 4 reference lakes every 2 weeks from May to September, collecting B. longimanus, crustaceanzooplankton, and water chemistry samples. Composite samples were pooled across the study season for each lake.Bythotrephes longimanus significantly reduced cladoceran species richness, diversity, and abundance, and the total zooplanktoncommunity also exhibited decreased richness, diversity, and abundance. Seasonal sampling was better thansynoptic surveys at detecting changes in abundance, but richness estimates were similar. As B. longimanus continues tospread across lake landscapes, we expect it will have profound impacts on local and regional richness and species distributionpatterns.