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 fres hwater dreissenid mussels (Dreissena polymorpha and Dreissena bugensis) to clear plankton. Tests conducted in a flow chamber at <1 cm s(-1) were consi stent with published clearance rates from standard tests involving unstirre d containers (i.e., 60-70 mt mussel(-1).h(-1) for 11-mm-long mussels). Incr easing ambient velocity up to similar to 10 cm.s(-1) led to clearance rates at least twice those of standard testing methods. Higher velocities (simil ar to 20 cm.s(-1)) were inhibitory and resulted in reduced clearance rates. There were no detectable differences in the clearance rates of D. polymorp ha and D. bugensis of equal size tested at similar to 10 cm.s(-1), but larg e mussels had greater clearance rates than small ones. These results were f ound to be consistent with observations from marine bivalves and indicate t hat fluid dynamic issues are of importance in freshwater ecosystems, especi ally 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 thr ough turbulent mixing are considered.