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 the 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 second in which density was increased by adding 'dummy' (non-living) scallops. The dummies occupied space but did not compete for food resources. For the first series, increasing the density from 25 to 250 ind. net-1 caused a marked decrease in growth. In contrast, no significant decrease occurred in the series in which density was increased by adding dummies. This demonstrated that food depletion is the major factor causing decreased growth at high densities. The only evidence suggesting an effect of space was a decrease in the mass of the muscle and other soft tissues with increasing density in the series with dummies; however, this decrease was not significant. Density did not affect rates of mortality, either in the absence or presence of dummy scallops.