Grazing on a natural assemblage of ciliate and dinoflagellate cysts by the eastern oyster Crassostrea virginica

Abstract

A natural dinoflagellate- and ciliate-cyst community from anoxic sediment collected from New Haven, Long Island Sound, was concentrated with a particle sorter and fed to oysters Cras- sostrea virginica. The total number of cysts and the species composition of cysts in beakers contain- ing live oysters were measured before and after feeding by the oysters. The oysters significantly reduced the numbers of both dinoflagellate and ciliate cysts. Both empty cyst walls and filled (live) cysts were consumed. The oysters decreased the number of total cysts to less than half compared to control beakers containing empty oyster shells. Results from the experiment show that natural assem- blages of cysts in sediment are degraded by the feeding activities of oysters. If toxic cysts were pre- sent in natural sediments resuspended from the bottom, digestion of resting cysts could lead to toxin accumulation in oysters. There was no major shift in species composition of cysts; cysts known as fossilizable were destroyed, as well as cysts not known to be very resistant or preservable.