Feeding activity of mussels Mytilus edulis related to near-bed currents and phytoplankton biomass

The feeding activity of blue mussels Mytilus edulis was investigated in the field and related to near-bottom current velocities and the phytoplankton biomass in the near-bottom water layers for four days. The body content of Chl-a in mussels and their shell gap size were used as indices of filtratio n activity. During days 1 and 2 the near-bed current velocities were low (1 .2-2.1 cm s(-1)), and the near-bed phytoplankton biomass was at the same ti me lower than near the water surface. Between 44 and 69% of the mussels had closed shells and accumulated only small amounts of Chl-a in the body. Dur ing day 3 and day 4 the near-bed current velocities increased to 6.5 and 3. 9 cm s(-1). respectively, and the Chl-a was homogeneously distributed in th e water column. Now only 17 and 25% of the mussels had closed valves and th ey accumulated a larger amount of Chl-a. The actual population filtration r ates were estimated from the density of active mussels times the estimated filtration rates (based on the gap size of the mussels and literature value s for corresponding filtration rates). Actual population filtration rates r anged from 6.4 to 22.8 m(3) m(-2) d(-1) on days 1 and 3, respectively, corr esponding to 27 and 98% of the estimated population filtration capacity. (C ) 2000 Elsevier Science B.V. All rights reserved.