VARIATION IN FOOD QUALITY AND PARTICLE SELECTIVITY IN THE SEA SCALLOP PLACOPECTEN-MAGELLANICUS (MOLLUSCA, BIVALVIA)

The sea scallop Placopecten magellanicus (Gmelin) is a suspension-feeding bivalve, common in subtidal regions in the northwest Atlantic. In this study, we examined the feeding responses of scallops to changes in the quantity and quality of natural seston under field and laboratory conditions. Concentrations of natural suspended particles at our study site were < 5 mg l-1, and chlorophyll a concentrations were < 1.4 mug mg-1. Under these seston quantities and qualities, clearance rates were positively correlated with the total amount of chlorophyll-containing particles in the water (mug l-1), while ingestion rates increased with increasing concentration of total suspended particulate matter (mg l-1). Scallops were able to select high-quality chlorophyll-a-containing particles and significantly improve the quality of material ingested. Pseudofaeces production increased slightly with increasing particle concentration, and selection was not based on the size of particles. We suggest that during conditions when the ingestive capacity of scallops is not exceeded, qualitative factors of the seston are more important than quantitative ones in mediating feeding processes.