PARENT SESSION
Contributed Oral Session 108: Aquatic Trophic Systems II
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 524 C, Level 5, Palais des congrès de Montréal
Grazers drive community metabolism in freshwater Closed Ecological Systems.
Taub , Frieda *,1, 1 University of Washington, Seattle, WA, USA
ABSTRACT- Although Daphnia magna were minor contributors to community respiration, their population dynamics controlled algal abundance, and presumably, associated bacteria. There were the usual lags between algal and grazer abundances. Algal abundance (as estimated by in vivo fluorescence and a green-ness index) determined the range of daytime O2 production and nighttime O2 use (respiration). In general, daytime O2 increase and nighttime O2 decrease were tightly linked so that the day (24hr) Net Ecosystem Production (NEP) values were small. For periods when algal abundance was increasing, daytime O2 increase slightly exceeded O2 nighttime decrease; when the algal abundance was decreasing as a result of Daphnia grazing, the daytime O2 production was slightly less than nighttime O2 use. In open systems, oxygen changes are the result of physical processes (e.g., diffusion and convection), and biological processes; small errors of estimation of physical processes can obscure the fine tuning of biological processes. One reason to study Closed Ecological Systems is to minimize the effects of physical processes, so that biological processes can be observed. These 250 ml systems contained 3 species of green algae and Daphnia magna, along with the microbiota associated with the uni-algal and conventional culture of Daphnia. A 12:12 hour L:D cycle was maintained (except during some short manipulations). Oxygen concentration and pH were recorded each 5 minutes. Testing hypotheses in small, simplified, model systems can help sharpen the questions we ask of larger, complex, natural ecosystems.
Key words: Community Metabolism, Phytoplankton, Daphnia, Algae-Grazer Interactions