CHEMORECEPTION IN THE SEA SCALLOP PLACOPECTEN-MAGELLANICUS (GMELIN) .1. STIMULATORY EFFECTS OF PHYTOPLANKTON METABOLITES ON CLEARANCE AND INGESTION RATES

Suspension-feeding in bivalves is a dynamic process that is influenced by various physical, chemical, and biological factors in the natural environment. Many previous workers have shown that changes in temperature, salinity, pH, and particle concentration can affect pumping, clearance, and ingestion rates. Few workers, however, have considered chemical signals as important factors in mediating bivalve feeding, even though chemically mediated feeding behavior in another class of molluscs, the Gastropoda, has been shown to be very important. In this study, we demonstrate that the sea scallop Plaeopecten magellanicus (Gmelin) increases its clearance and ingestion rates in response to metabolites from the diatom Chaetoceros muelleri Lemmermann. Dose-response data indicate that the stimulation saturates at a low concentration of diatom extract (equivalent to 5 cells.mul-1). To our knowledge, this is the first time that such a response has been demonstrated in a marine bivalve, and we suggest that chemical cues from phytoplankton are important factors that allow scallops to adjust feeding rates in Nature.