Yessotoxins in Norwegian blue mussels (Mytilus edulis): uptake from Protoceratium reticulatum, metabolism and depuration

The Protoceratium reticulatum cell density at Flødevigen reached a maximum of 2200 cells/L on 16 May 2001. The levels of yessotoxins (YTXs) in blue mussels (Mytilus edulis) at the same site increased sharply by 14 May and peaked on 28 May, after which they steadily declined. No other algal species present showed a similar pattern of correspondence. Together with the recent finding that Norwegian strains of P. reticulatum produce YTXs, these results indicate that P. reticulatum causes yessotoxin (YTX) contamination of shellfish in Norway, and that only relatively low cell densities are necessary for this to occur. The mussels from Flødevigen were analyzed by LC-MS for YTX, 45-hydroxyYTX, carboxyYTX, and a new yessotoxin believed to be 45-hydroxycarboxyYTX, and by ELISA for YTXs. The seasonal variations in toxin content versus time measured by the two methods were qualitatively very similar, although the response in the ELISA was 3-9 times higher due to the antibodies detecting other YTXs that were not detected by the LC-MS method. Changes in the LC-MS profile for YTXs, and in the ratio of YTXs by LC-MS to YTXs by ELISA with time, were consistent with extensive metabolism of YTX in the mussels. Kinetic analysis of the LC-MS data showed an initial half-life of 20 days for YTX, and for YTX+45-hydroxyYTX, in the mussels. Similar analysis of the ELISA data gave a half-life of 24 days for YTXs. The depuration rate remained consistent over a 3-month period during which the temperature remained at 13-16 °C.