9318452 Vanni This research seeks to understand how detritivorous fish affect lake phytoplankton communities by acting as "nutrient pumps." By feeding on benthic detritus and excreting nutrients (nitrogen and phosphorus) into the limnetic habitat, these fish effectively pump nutrients from benthic to limnetic habitats, where nutrients can stimulate phytoplankton growth and alter phytoplankton community structure. Animals can affect communities in many ways and it is well known that in northern lakes fish can have strong effects on phytoplankton communities through food chain interactions. It is proposed here that in warm-water lakes and reservoirs, fish affect phytoplankton primarily through the nutrient pump mechanism rather than through conventional food chain interactions. The specific objectives are to quantify the community level effects of detritivorous fish on lake phytoplankton communities. Hypotheses to be tested include: 1) detritivorous fish affect phytoplankton via the nutrient pump mechanism, 2) the effects of the nutrient pump mechanism is dependent on fish population structure, and detrital nutrient content, and 3) detritivorous fish are a major source of nutrients to phytoplankton in small reservoirs during times with stream inflows are low. These hypotheses will be tested using a series of empirical observations, field and laboratory experiments. %%% This research will advance our knowledge of food web regulation, top down versus bottom up controls on communities, and benthic-limnetic coupling. Although this project focuses on community effects, it integrates levels of organization from individual to ecosystem. In addition, because nutrient pumps may have effects on the frequency and intensity of nuisance blooms of blue-green algae, the research has implications for water quality management. ***
