Relationships between the blooms of Alexandrium catenella and water quality or meteorological factors were examined in Tanabe Bay, referring to the Meteorological Agency's data (1983-1992).
The blooms of A. catenellaoccurred remarkably in 1984 and 1987, and rarely occurred after 1988. A. catenellawith high density of cells occurred in the water with low DIN (dissolved inorganic nitrogen), DIP (dissolved inorganic phosphorus), and DIN×DIP, and high DIN：DIP ratio. The bloom of A. catenellaoccurred on mid-May with meteorological conditions of high fluctuation of air temperature, and heavy rain or strong wind on mid-April. These characteristics of water quality and meteorological factors suggest that the bloom initiations of A. catenellawere closely connected with the supply of rich nutrients by heavy rain or strong wind, the sudden increase of diatoms with the intense consumption of nutrients, and the capability of utilization of very low concentration of nutrients of A. catenella.