A case of consistent spatial differences in content of diarrhetic shellfish toxins (DST) among three bivalve species: Mytilus edulis, Ostrea edulis and Cerastoderma edule

Content of diarrhetic .shellfi.sh toxins (DST) was compared among mussels (Mytilus edulis), oysters (Ostrea edulis). and cockles (Cercuioderma edule) at two spatial scales: regions (100 km apart) and locations within regions (5 km apart). Samples were analysed for DST using protein phosphatase inhibiton assay in individual digestive glands. Concentrations of DST in all oysters and cockles were below the detection limit in the assay, whereas mussels from both regions and all locations contained mean levels of DST above the regulation limit for harvest and marketing. Thus interspecific differences in content of DST were found along the Swedish west coast. Some behavioral and physiological phenomena are proposed to explain the differences among species. These include differential uptake and processing of toxic algae, biotransformation of toxins, and reduced filtration at low temperatures. These findings may have some implications for harvest and cultivation of bivalves and suggest a possibility that cockles and oysters could be marketed for human consumption during periods of elevated levels of DST in mussels.