1Iwate Fisheries Technology Center, Kamaishi, Iwate 026-0001, 2Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Tsukide, Kumamoto 862-8502, 3School of Fisheries Sciences, Kitasato University, Ofunato, Iwate 022-0101, Japan
The occurrence of Alexandrium spp. and their toxin production were investigated along the coast of Iwate Prefecture, Japan. Eight species of Alexandrium were found to occur, among which the appearance of five species (A. insuetum, A. ostenfeldii, A. pseudogonyaulax, A. tamutum and A. minutum) was newly confirmed in this area. Toxin analysis using the cultured cells of these species revealed that all the strains of A. tamarense and A. catenella were toxic, as having been reported previously. In addition to them, one strain of A. ostenfeldii was confirmed to produce toxins dominated by GTX4. Toxin productivity of this strain was estimated to be 7.5 fmole/cell. However, it is suggested that this species is not a cause of significant contamination of bivalves, since its density and frequency in appearance are very low at the present time. On the other hand, the results imply the possibility that the cell density of the toxic Alexandrium species could be overestimated when morphologically similar nontoxic species co-occur in the same water mass. Based on the results obtained in this study, it is necessary to improve the method having been applied to predict contamination of bivalves in the area.