Permalink : http://hdl.handle.net/2115/57519

JaLCDOI : 10.14943/bull.fish.64.3.89

KEYWORDS : Red tide;Heterosigma akashiwo;Cyst, Ariake Sea;Yatsushiro Sea;Kagoshima Bay;Bottom sediment;MPN method

The fish-killing flagellate Heterosigma akashiwo (Raphidophyceae) has a cyst stage in the life cycle. The cysts play an important role functioning as resistant cells to survive adverse environments. They also play a key role in initiating red tides in early summer in temperate coastal waters. Abundance and distribution of viable H. akashiwo cysts possessing germination ability in bottom sediments were investigated in Ariake Sea, Yatsushiro Sea, and Kagoshima Bay, west and south coast of Kyushu, Japan. Viable cysts showing germination ability were enumerated with the extinction dilution method (most probable number method) using surface sediment samples (top 3-cm depth) collected in June 2003. In Ariake Sea, H. akashiwo cyst density ranged from 244 to 11,613 (mean, 2,240) MPN cm-3 (wet sediment), and from 242 to 10744 (mean, 1,719) MPN cm-3 (wet sediment) in Yatsushiro Sea, and from 238 to 2,244 (mean 782) MPN cm-3 (wet sediment) in Kagoshima Bay, respectively. Abundant points were detected in the areas of H. akashiwo red tide occurrences. Cyst densities have no significant relationships with mud contents (%) in Ariake Sea and Yatsushiro Sea, but cysts tended to be abundant at the points with high mud contents in Kagoshima Bay. The information of cyst densities should be effectively utilized together with the results of monitoring of vegetative cells and bottom water temperature affecting the germination of cysts in red-tide occurring areas.