抄録
The biogeographical distribution of species of the genus Alexandrium, which includes PSP causative species, was studied using preserved plankton samples collected in the western part of the North Pacific. Alexandrium spp. were present in over 90% of the samples and eight described species and several undescribed morphotypes were observed. The distribution pattern of each species was distinctive. Alexandrium leei was recorded only at Kyusyu and Okinawa in the Japanese coast. However, this species was commonly distributed in subtropical open ocean. While the occurrence of A. insuetum was limited to enclosed areas in temperate, this species commonly occurred in tropical open ocean. In contrast, the well-known toxic species A. tamarense and A. catenella were not observed in open ocean but only in temperate coastal waters. Another toxic species A. minutum, which often occurred in Southeast Asian brackish water, had a wide distributiton in the North Pacific area.
