IN-SITU FEEDING AND ABSORPTION RESPONSES OF SEA SCALLOPS PLACOPECTEN-MAGELLANICUS (GMELIN) TO STORM-INDUCED CHANGES IN THE QUANTITY AND COMPOSITION OF THE SESTON

Time-series of hourly clearance, ingestion and absorption rates and ab sorption efficiency were measured over 48 h for adult sea scallops (Pl acopecten magellanicus) held in situ in a coastal embayment in Nova Sc otia, Canada, during a wind-induced resuspension event. Temporal varia tions in oceanographic variables, and seston quantity and composition (organic matter, organic carbon, nitrogen, chlorophyll a, and inorgani c particle size spectra) were monitored during the study with moored i nstruments and hourly water sampling. Resuspension of bottom materials during the storm resulted in large changes in the amount (1 to 30 mg l(-1) total particulate matter) and nutritional quality (25 to 50% org anic content) of seston. High sedimentation rates after the storm were accelerated by flocculation, resulting in the rapid settling of resus pended particles and an increase in seston quality. Observed short-ter m (hourly) fluctuations in clearance rate were not related to storm-or tide-induced changes in seston characteristics but were directly rela ted to flow velocity. Significantly lower clearance rates were observe d at relatively low (<4 cm s(-1)) and high (> 9 cm s(-1)) flow speeds. The overall reduction in ingestion rates after the storm resulted fro m decreased food availability. Hourly absorption efficiency (AE) measu rements were closely related to seston quality (total organic, organic C and N content) and AE declined exponentially with decreasing seston quality. Reductions in AE during the resuspension event were offset b y the increased ingestion rate, resulting in no significant changes in absorption rates for organic matter, C, or N over the sampling period . As the low food quality of the resuspended matter was balanced by in creased availability, any physiological regulation of food acquisition (i.e. clearance rate regulation) would have been irrelevant to mainta ining food intake constant. (C) 1998 Elsevier Science B.V.