UTILIZATION OF PHAEOCYSTIS-GLOBOSA COLONIES BY YOUNG MYTILUS-EDULIS

The nutritional value of the bloom-forming alga, Phaeocystis globosa ( Prymnesiophyceae) for the mussel Mytilus edulis was evaluated in labor atory experiments. Young mussels (20mm shell length) were fed P. globo sa single cells and colonies, Phaeodactylum tricornutum, Dunaliella sa lina and P. tricornutum with cell-free medium of dense P. globosa colo ny cultures. After 40 days the mussels showed significant higher meat weight when fed with P. globosa colonies and D. salina in comparison t o the other feeding conditions. When percentage weight increase is cor related with the amount of algal carbon available per mussel, P. trico rnutum becomes the most efficient food. P. globosa colonies were utili zed more effectively than P. globosa single cells. The effective utili zation of P. globosa colonies contradicts the hypothesis of negative e ffects of dense P. globosa blooms on the growth of Mytilus in the Wadd en Sea.