SEPARATING EFFECTS OF LIMITED FOOD AND SPACE ON GROWTH OF THE GIANT SCALLOP PLACOPECTEN-MAGELLANICUS IN SUSPENDED CULTURE

Effects of limitations in space and food resources on the growth of th e giant scallop Placopecten magellanicus (Gmelin, 1791) were examined by growing juveniles in pearl nets at different densities in 2 series, one in which density was increased by adding living scallops and d se cond in which density was increased by adding 'dummy' (non-living) sca llops. The dummies occupied space but did not compete for food resourc es. For the first series, increasing the density from 25 to 250 ind. n et-1 caused a marked decrease in growth. In contrast, no significant d ecrease occurred in the series in which density was increased by addin g dummies. This demonstrated that food depletion is the major factor c ausing decreased growth at high densities. The only evidence suggestin g an effect of space was a decrease in the mass of the muscle and othe r soft tissues with increasing density in the series with dummies; how ever, this decrease was not significant. Density did not affect rates of mortality, either in the absence or presence of dummy scallops.