Response of Plankton Biomass Across Gradients of Fish Density and Lake Trophic State: Experimental Test of the Fish X Lake Trophic State Interaction Hypothesis

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Ecologists have hypothesized that regulation of plankton communities by planktivores varies with lake trophic state, suggesting that an interaction effect exists between fish effects and lake trophic state effects on plankton communities. A fish x lake trophic state interaction effect is one that cannot be predicted by considering fish effects independently of lake trophic state effects. To date, there have been no tests of this fish x lake trophic state interaction hypothesis. In the proposed study, there are two principle parts: (1) a test of the fish x lake trophic state interaction hypothesis using outdoor tank experiments to examine the effects of five different densities of a planktivore, bluegill (Lepomis macrochirus), on the biomass and species composition of picoplankton, nanoplankton, microplankton, mesoplankton, and macroplankton from six lake communities representing the range of trophic states of southwestern reservoirs, and (2) the development of regression models for predicting biomass of picoplankton, nanoplankton, microplankton, mesoplankton, and macroplankton across gradients of fish density and lake trophic state. The study will provide the first view of how the impacts of different densities of fish on plankton biomass change with lake trophic state.