Studies on characteristics of occurrence the chain-forming toxic dinoflagellate Gymnodinium catenatum in Inokushi Bay [Japan] and mechanism of accumulation of paralytic shellfish toxin in the culture scallop Chlamys nobilis

The chain-forming toxic dinoflagellate Gymnodinium catenatum Graham is one of the causative species responsible for paralytic shellfish poisoning (PSP). This species was first reported in the Gulf of California by Graham in 1943. An apparent increase of PSP outbreaks due to G. catenatum blooms has occurred worldwide. In Japan this organism was first reported in Hiroshima Bay in 1967 and first outbreaks of shellfish toxicity occurred in Senzaki Bay in 1985. Since 1996 G. catenatum blooms and associated PSP contamination in shellfish have been reported in Inokushi and Ogamae Bay in Oita Prefecture. Since then, G. catenatum blooms have frequently been observed around Kyushu Island; Suo-Nada, Karatsu Bay in Saga Prefecture, Furue Bay in Hirado Island Nagasaki Prefecture and the southern region of Mie Prefecture. Incidents of PSP contamination due to G. catenatum have increased and it is a concern for the shellfish aquaculture and public health. Therefore prediction of G. catenatum blooms and prevention of PSP-contamination in shellfish are desired by the fishery industry as well as for public health. However measures to enable a plan to prevent G. catenatum blooms from occurring in Inokushi and Ogamae Bay have not been identified because PSP contamination is thought to occur at very low cell densities and show a low seasonal pattern of outbreak. To elucidate the biological background underlying the mechanism of G. catenatum blooms and associated PSP outbreak in the scallop Chlamys nobilis, the present study carried out an intensive field investigation in Inokushi and Ogamae Bay. The winter weather of Inokushi and Ogamae Bay (Saiki City, Kamae area) is a typical Pacific climate type that is mild, with low precipitation and a high amount of sunlight throughout the year. In Inokushi Bay, water temperature and salinity in the water column ranged from 14.5 to 29.9 deg C and from 21.33 to 34.75 PSU, respectively. Especially in due to lower run off of the fresh water from rivers. Seasonal changes of inorganic nutrient concentrations are low. Characteristics of water movement during winter in which G. catenatum blooming season was an inverse estuarine circulations driven by the cooling the sea surface and inflow of warm the Kuroshio Current into surface of this Bay.