Filter-feeding in the Freshwater Prosobranch Snail Bithynia tentaculata: Bioenergetic Partitioning of Ingested Carbon and Nitrogen

Filter-feeding has been studied in specimens of Bithynia tentaculata from a population in Oneida Lake, New York. Chlorella vulgaris cultures provided filterable material for studies of feeding and assimilation in this freshwater prosobranch snail. Concomitant analyses of assimilation, respiration and excretion allowed assessment of bioenergetic partitioning. Weight-specific hourly rates for ingestion, egestion, respiration and nitrogen excretion were measured. These parameters provided data for calculation of assimilation and nonrespired assimilation rates. Such weight-specific rates were used to construct bioenergetic profiles for carbon and nitrogen allocation in postbreeding snails. Filtering rates were also measured at three different concentrations of filterable material. Results from filtering rate experiments show that individuals of Bithynia can increase weight-specific clearance rates as concentration of filterable material is decreased. The present study provides data which complement studies of grazing in specimens of Bithynia tentaculata. Relative to grazing, filter-feeding allows individuals of this species to accrue a higher net gain of nitrogen (protein) and carbon per respired costs. The data suggest an explanation for interpopulation differences in feeding modes. Further, substantive data have been gathered which may help explain the displacement of pleurocerids by Bithynia in some upstate New York habitats.