Shellfish poisoning and the ocurrence of potentially toxic dinoflagellates in Norwegian waters

Phytoplankton observations in Oslofjorden during the last years indicate that the potentially toxic dinoflagellates Gonyaulax excavata, Procentrum minimum, Gyrodinium aureolum and Dinophysis acuminata are regular members of the plankton in spring, summer and autumn. With the exception of D. acuminata these species have formed massive blooms in the fjord after 1978. Also in Sognefjorden, the largest fjord system in Norway, several toxic in dinoflagellates were a regular component of the plankton in 1981–1982,and in the first measurements of paralytic shellfish toxin (PSP) in the area in May and June 1982, relatively high PSP titres were detected in the inner fjord. An epidemic case of illness in the autumn 1979 affecting 41 of 70 persons, which may have been caused by mussels contaminated by toxins from P. minimum (venerupin poisoning), is reported. Based on these observations it is recommended that monitoring of shellfish poisons in Norway includes control of noxious algae in addition to measurements of toxin content in shellfish products, in order to minimize the danger of shellfish poisoning.