EFFECT OF KAOLINITE CLAY ON THE FEEDING-ACTIVITY OF THE EASTERN OYSTER CRASSOSTREA-VIRGINICA (GMELIN)

Estuarine bivalve molluscs live and grow in the presence of substantial concentrations of suspended inorganic material. These organisms have adapted to tolerate and even benefit from their turbid environment. We carried out several experiments to determine if suspended kaolinite clay particles affect the amount of food cleared, rejected in pseudofeces, and/or ingested by a common estuarine bivalve, the eastern oyster Crassostrea virginica (Gmelin). Juvenile oysters were fed a diet consisting of C-14-labelled algae (Isochrysis galbana Parke) and H-3-labelled rice starch, with or without kaolinite. Starch was selectively rejected in oyster pseudofeces, compared with algae. Oysters were able to sort algal cells from starch particles more efficiently with no kaolinite in the water than when kaolinite was added to the chambers. This disruption of selection by kaolinite caused oysters to ingest more starch under certain conditions. Kaolinite did not significantly affect the amount of algae cleared or rejected. Kaolinite particles adsorbed a small but statistically significant amount of dissolved organic material from the food.