In situ feeding and absorption responses of sea scallops Placopecten magellanicus (Gmelin) to storm-induced changes in the quantity and composition of the seston

Abstract

Time-series of hourly clearance, ingestion and absorption rates and absorption efficiency were measured over 48 h for adult sea scallops ( Placopecten magellanicus) held in situ in a coastal embayment in Nova Scotia, Canada, during a wind-induced resuspension event. Temporal variations in oceanographic variables, and seston quantity and composition (organic matter, organic carbon, nitrogen, chlorophyll a, and inorganic particle size spectra) were monitored during the study with moored instruments 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% organic content) of seston. High sedimentation rates after the storm were accelerated by flocculation, resulting in the rapid settling of resuspended particles and an increase in seston quality. Observed short-term (hourly) fluctuations in clearance rate were not related to storm- or tide-induced changes in seston characteristics but were directly related to flow velocity. Significantly lower clearance rates were observed 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 from decreased food availability. Hourly absorption efficiency (AE) measurements 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 by 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 increased availability, any physiological regulation of food acquisition (i.e. clearance rate regulation) would have been irrelevant to maintaining food intake constant.