Zooplankton influences on phytoplankton, water clarity, and nutrients in Lake Tahoe

The grazing effects of zooplankton communities are predicted to be strongest in mesotrophic lakes relative to eutrophic and oligotrophic lakes, an idea known as the Mesotrophic Maximum Hypothesis. We tested if the predictions of this hypothesis depend on the community of zooplankton present by evaluating whether the community of zooplankton, in addition to lake trophic state, interact to determine the magnitude of grazing effects. We conducted mesocosm experiments to evaluate the effects of Daphnia spp. , Epischura nevadensis , and juvenile and adult Mysis diluviana on ecosystem function in oligotrophic Lake Tahoe and its more productive embayment, Emerald Bay. In the Lake Tahoe experiment, the Daphnia and the Adult Mysid treatments produced lower dissolved organic carbon concentrations, and the Epischura treatment yielded lower soluble reactive phosphorus concentrations compared to a Control treatment that lacked macrozooplankton. In the Emerald Bay experiment, the Daphnia treatment lowered chlorophyll a concentrations , the Daphnia and Juvenile Mysid treatments reduced small particle (diameter 0.5 –