BACTERIVORY IN PACIFIC OYSTER CRASSOSTREA-GIGAS LARVAE

A bacterium (Strain CA2) that enhances survival and growth of larvae of the oyster Crassostrea gigas (Thunberg) was used in a series of experiments to determine the occurrence of bacterivory in straight-hinged bivalve larvae. Size and carbon content of this bacterium was found to be within the range reported for naturally occurring marine bacteria. Unattached, motile, DAPI-stained CA2 cells were readily captured and ingested by oyster larvae and were seen to accumulate in larval digestive systems. Ingestion of C-14-labelled bacteria occurred at all bacterial concentrations tested from 1 x 10(5) to 1 x 10(7) cells ml-1. Retention of carbon by axenic oyster larvae, fed either C-14-labelled live or heat-killed bacteria in 'pulse-chase' feeding experiments, demonstrates the endogenous ability of larvae to digest and assimilate bacterial carbon.