CARBON CONTRIBUTION THROUGH BACTERIVORY IN LARVAE OF THE PACIFIC OYSTER CRASSOSTREA-GIGAS

A bacterium (Strain CA2) that enhanced survival and growth of oyster Crassostrea gigas (Thunberg) larvae was used to determine the potential contribution of bacterial carbon towards the total carbon requirements of bivalve larvae. Experimental methods that reduced label recycling in C-14 feeding trials permitted determination of larval retention efficiencies for bacterial and algal (Isochrysis galbana) carbon when these foods were provided to larvae at equivalent carbon concentrations. Straight-hinged oyster larvae (ca 100 mu m mean shell length) fed CA2 bacteria at 1.5x10(7) cells ml(-1) could meet 147% of their total metabolic carbon requirements with bacterial carbon retained in 'pulse-chase' C-14 feeding experiments. In addition, this bacterial carbon represented 48.5% of the carbon retained by straight-hinged larvae fed on a similar biomass of algal carbon (I. galbana at 54000 cells ml(-1)). The potential contribution of bacterial carbon towards the metabolic carbon requirements of oyster larvae decreased as larvae grew in size. Only 41% of the total metabolic carbon requirements of a 283 mu m larva could be met by the bacterial carbon retained after feeding on CA2 bacteria at 1.5x10(7) cells ml(-1).