ANATOMICAL DISTRIBUTION AND SPATIOTEMPORAL VARIATION IN PARALYTIC SHELLFISH TOXIN COMPOSITION IN 2 BIVALVE SPECIES FROM THE GULF OF MAINE

Marine bivalve molluscs accumulate paralytic shellfish poisoning (PSP) toxins through filter-feeding on blooms of toxic dinoflagellates, spe cifically, Alexandrium spp. on the Atlantic coast of North America. To determine the seasonal variation in PSP toxin composition in various anatomical compartments, inshore and offshore populations of the sea s callop Placopecten magellanicus and the surfclam Spisula solidissima, two bivalve species noted for prolonged toxin retention, were sampled periodically over two consecutive years in the Gulf of Maine. Individu als were dissected into tissue fractions for the determination of toxi n composition (molar% and nmol g-1) by high-performance liquid chromat ography with fluorescence detection (HPLC-FD). The individual tissues included digestive gland, adductor muscle, gill and mantle, plus sipho n and foot for clams and gonads for scallops. The calculated toxicity (mugSTXeq 100 g-1 shellfish tissue) confirmed the distributional trend of parallel mouse bioassays performed upon the tissues, but did not m atch quantitatively the bioassay results over a seasonal time scale. P artitioning of PSP toxin components among various organs was markedly different for the two bivalve species. For both sea scallops and surfc lams, substantial differences in the relative amounts of PSP toxins am ong tissue compartments and seasonal variation were more evident than were differences between geographical populations of the same species. Analysis of PSP toxin profiles from a representative isolate of Alexa ndrium tamarense from the Gulf of Maine supported previous findings th at the toxin composition in bivalves may differ considerably from that of toxigenic dinoflagellates. A pronounced seasonal toxin shift from the less potent N-sulfocarbamoyl toxins (C1/C2), which dominate in the dinoflagellate, to higher toxicity carbamate derivatives (e.g., GTXs, NEO, and STX) was found in both bivalve species. Relative to sea scal lops, surfclams have a much higher capacity for in vivo PSP toxin conv ersion to decarbamoyl analogues. Metabolic and physico-chemical mechan isms which may be involved in PSP toxin transformation are compared am ong bivalve species.