FILTRATION AND ABSORPTION OF PHAEOCYSTIS CF GLOBOSA BY THE MUSSEL MYTILUS-EDULIS L

Mussels, Mytilus edulis L., were exposed to natural seawater, suppleme nted with variable amounts of Phaeocystis cf. globosa solitary cells a nd colonies and to a reference diet consisting of natural seawater, su pplemented with Phaeodactylum tricornutum. Clearance rate showed a lin ear decrease with the amount of colonies present, expressed as total ' circular equivalent surface area'. Extension of the exposure period fo r 28 h resulted in a further decreased clearance rate. Recovery of the clearance rate began immediately after exposure to untreated natural seawater. In the absence of colonies, there was a moderate clearance r ate reduction. Filtration at reduced clearance rates was not compensat ed by increased particle concentrations and no adaptative response to the diet was observed. In an earlier experiment, we observed that the absorption efficiency of ingested Phaeocystis diet was not significant ly different from the reference diet. It is concluded that the adverse effects of Phaeocystis blooms are mainly determined by the total colo ny surface area. There is no adaptation over time to diets with coloni es. Once ingested, Phaeocystis is absorbed normally and has significan ce as food. Copyright (C) 1997 Elsevier Science B.V.