CLEARANCE AND INGESTION RATES OF ISOCHRYSIS-GALBANA BY LARVAL AND JUVENILE BAY SCALLOPS, ARGOPECTEN IRRADIANS CONCENTRICUS (SAY)

The clearance and ingestion rates of larval and juvenile bay scallops Argopecten irradians concentricus were investigated using algal suspen sions of Isochrysis galbana. An inverse relationship existed between c learance rate and algal cell concentration. Mean clearance rate ranged from 0.0034 to 0.0385 mL h(-1) for larvae and 0.14 to 0.41 mL h(-1) f or juveniles of 0.5 mm shell height and increased to 248-420 mL h(-1) for juveniles of 10 mm shell height. Clearance rate increased with she ll size allometrically, with a mean exponent of 2.460 +/- 0.087. Weigh t-specific clearance rate was independent of shell size at >20 cells m u L-1, but slightly decreased with increasing shell size at lower cell concentrations. Larvae and juveniles showed higher ingestion rates at higher algal concentrations, and the hyperbolic relationship was desc ribed using an enzymatic kinetic equation. Maximum ingestion rate occu rred at approximately 20 cells mu L-1 in larvae and at >20 cells mu L- 1 in juveniles. As temperature increased from 10 to 30 degrees C, larv ae and juveniles became more active in feeding. Relative rates of clea rance and ingestion at 10, 15, 20, and 25 degrees C were 8.4, 22.0, 52 .8, and 88.2%, respectively, of the mean rate at 30 degrees C.