Effect of velocity on the filter feeding of dreissenid mussels (Dreissena polymorpha and Dreissena bugensis):: implications for trophic dynamics

Fluid dynamic forces were found to significantly affect the ability of freshwater dreissenid mussels (Dreissena polymorpha and Dreissena bugensis) to clear plankton. Tests conducted in a flow chamber at <1 cm s(-1) were consistent with published clearance rates from standard tests involving unstirred containers (i.e., 60-70 mt mussel(-1).h(-1) for 11-mm-long mussels). Increasing ambient velocity up to similar to 10 cm.s(-1) led to clearance rates at least twice those of standard testing methods. Higher velocities (similar to 20 cm.s(-1)) were inhibitory and resulted in reduced clearance rates. There were no detectable differences in the clearance rates of D. polymorpha and D. bugensis of equal size tested at similar to 10 cm.s(-1), but large mussels had greater clearance rates than small ones. These results were found to be consistent with observations from marine bivalves and indicate that fluid dynamic issues are of importance in freshwater ecosystems, especially those that are shallow and (or) flowing. The trophic dynamics of these ecosystems will be better understood when the effects of fluid dynamics on the organism's ability to filter feed and the local delivery of seston through turbulent mixing are considered.