A bacterium (Strain CA2) that enhances survival and growth of larvae o
f the oyster Crassostrea gigas (Thunberg) was used in a series of expe
riments 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 digest
ive systems. Ingestion of C-14-labelled bacteria occurred at all bacte
rial concentrations tested from 1 x 10(5) to 1 x 10(7) cells ml-1. Ret
ention of carbon by axenic oyster larvae, fed either C-14-labelled liv
e or heat-killed bacteria in 'pulse-chase' feeding experiments, demons
trates the endogenous ability of larvae to digest and assimilate bacte
rial carbon.