Infection of the giant scallop Placopecten magellanicus from Newfoundland with an endozoic alga

Abstract

Some aspects of the relationship between a unicellular alga and the giant scallop, Placopecten magellanicus, are presented. The relationship is confined to the shallow water populations of the pectinid species (Port au Port Bay, St. Mary's Bay, Bonavista Bay, Newfoundland). Scallops from deeper water, including Georges Bank, are particularly free of the alga. It is believed that the alga's requirements for light prevents its establishment beyond a certain depth. The larger, older scallops, especially those with damaged or deformed shells, are particularly susceptible to the alga. Infections usually involve the peripheral mantle tissue, but may extend into the distal end of the gonad and the bases of the posterior adductor muscle. When present in large numbers, the alga has an adverse effect on its host; however, there is no evidence of parasitic castration.