LIFE-CYCLE STRATEGIES OF THE RED TIDE CAUSING FLAGELLATES CHATTONELLA (RAPHIDOPHYCEAE) IN THE SETO INLAND SEA

Chattonella antiqua (Hada) Ono and Chattonella marina (Subrahmanyan) Hara et Chihara are the most noxious red tide flagellates which cause serious damage to fish farming, especially to yellowtail culture, in Japanese coastal waters such as the Seto Inland Sea during summer. Cysts of Chattonella were identified from sediments of the Seto Inland Sea. These cysts overwinter in sea bottom and play an important role in initiating the summer red tides. Most of the cysts adhere to solid surfaces such as diatom frustules and sand grains, which may aid in keeping the cyst populations within seed beds for the red tides. Temperature is a principal factor affecting the physiology of cysts of Chattonella. No cysts germinate at 10-degrees-C. Optimum temperature range is between 20-degrees and 25-degrees-C for germination. For maturation (acquisition of germinability) of the cysts, low storage temperature of 11-degrees-C or below for more than four months is essential, whereas no significant maturation is observed at 20-degrees-C or more. In freshly collected sediments, marked seasonality of germinability was confirmed in Suo-Nada. The cysts have germinability between spring and early summer. The cysts spend a period of spontaneous dormancy between autumn and the next spring, and they mature during the winter season. The life cycle of Chattonella is therefore well adpted to the seasonal temperature fluctuation in the Seto Inland Sea. And further, alternation between benthic and planktonic stage is presumably unconstrained by virtue of shallowness of the Seto Inland Sea. The life cycle of Chattonella can be regarded as superior strategies in conclusion for the occurrences of the red tides in temperate waters such as the Seto Inland Sea.