Sediment resuspension rates, organic matter quality and food utilization by sea scallops (<I>Placopecten magellanicus</I>) on Georges Bank

Abstract

Benthic detritus, bacteria, and settled phytoplankton are transported into the water column by resuspension, potentially providing a high quality food source to suspension feeders. Two aspects of resuspension must be considered in relation to food supplies for suspension feeders: the flux of particles from the sediments to the water column and its food value. Sediment resuspension rates on Georges Bank and the role of resuspended sediment in the diet of sea scallops (Placopecten magellanicus) were determined in laboratory flume experiments and shipboard feeding experiments, respectively. Resuspended carbon flux was estimated from flume bedload transport rates and the mass of organic carbon associated with the silt-clay fraction eroded from Georges Bank sediment during transport. A comparison of sand erosion thresholds with the frequency distribution of shear velocity estimated from field current meters indicated that tidal sediment resuspension will occur 62% of the time. Resuspended material had a carbon content of 4-8% and a C:N of 5-8. Rates of resuspension (33-229 mg C m -2 h -1 ) and settling rates indicate that resuspended sediment in a size range available to scallops (>5 pm) remains in suspension for periods of hours to days. Clearance rates of resuspended sediment by scallops were similar to those for water column particles, and filtration rates increased with increasing concentrations of resuspended material. Feeding experiments demonstrated that scallops absorbed organic matter from resuspended sediments with an efficiency of up to 40%. Therefore, in terms of particle retention, ingestion, and digestion, sea scallops are able to exploit resuspended organic matter from a continental shelf habitat. Furthermore, resuspension occurs with sufficient frequency, and resuspended sediment has long enough residence time in the water column to provide a consistent nutritional benefit to scallops.