冬季,猪串湾と小蒲江湾に出現する Gymnodinium catenatumの個体群形成に影響する海況条件

抄録

The drastic growth of the toxic dinoflagellate Gymnodinium catenatum (a causative organism of paralytic shellfish poisoning) was observed in Inokushi and Ogamae Bays in winter. To elucidate the characteristics of the growth and effects of hydrographical conditions on the growth, we carried out the field observations of monitoring of G. catenatum cells, water temperature, salinity and current velocity in Inokushi and Ogamae Bays from 26 January to 20 April in 2004. The cell density of G. catenatum increased gradually from late in January and reached the maximum (8,858 cell L^-1) late in March in the inmost part of Inokushi Bay. After late in March, the cell density decreased rapidly. The growth phases of G. catenatum were divided into four phases; early phase, stationary phase, exponential phase, senescent phase. The hydrographic condition was changed late in March in Inokushi Bay. From January to late in March, the inverse estuarine circulation occurred and warm water masses intruded into the upper layer of Inokushi Bay. After late in March, the estuarine circulation was induced by precipitation and basin water masses flowed out through the surface layer. The growth of G. catenatum was effected by the hydrographic conditions. The cell density increased when the inverse estuarine circulation was occurred and increased remarkably when the water temperature increased. However, the cell density decreased rapidly when the estuarine circulation occurred and allowed cells to flow out of the bay.