EFFECTS OF 2 BLOOM-FORMING DINOFLAGELLATES, PROROCENTRUM-MINIMUM AND GYRODINIUM-UNCATENUM, ON THE GROWTH AND SURVIVAL OF THE EASTERN OYSTER, CRASSOSTREA-VIRGINICA (GMELIN 1791)

Laboratory experiments were conducted to investigate the effects of th e dinoflagellates Prorocentrum minimum and Gyrodinium uncatenum on the growth and survival of juvenile eastern oysters, Crassostrea virginic a. In separate experiments lasting 30 d and 18 d for P. minimum and G. uncatenum, respectively, the dinoflagellates were offered to the oyst ers in both unialgal and mixed diets (with the diatom Thalassiosira we isflogii). Eight diets were used in each experiment: (i) the dinoflage llate at bloom density, (ii) the dinoflagellate at 33% bloom density, (iii) the dinoflagellate at 5% bloom density, (iv-vi) the diatom at th e above densities, (vii) 50% dinoflagellate bloom density + 50% diatom bloom density, and (viii) 5% dinoflagellate bloom density + 95% diato m bloom density. P. minimum at bloom density resulted in 100% mortalit y of juvenile oysters within 14 d and at 33% bloom density it resulted in 43% mortality within 22 d. Diets containing 5% P. minimum density did not cause mortality and supported good shell growth. No mortality was observed among oysters fed G. uncatenum and diets which included t his dinoflagellate resulted in significantly greater growth than diets of the diatom T. weisflogii.