Annual life cycle of Chattonella spp., causative flagellates of noxious red tides in the Inland Sea of Japan

Effects of storage temperature on the dormancy and maturation of dormant cells of Chattonella spp. were investigated by the extinction dilution method using sediment samples collected in 1984 after the blooming in Harima-Nada. Seasonality of germinability in fresh sediments was also studied in 1985. A storage period of more than 4 months with a low temperature (11°C) was essential for the maturation to induce the germination capacity of dormant cells. The optimal temperature for germination (22°C) had no effects on the maturation. Using fresh Suo-Nada sediments, a marked seasonality of germinability was confirmed. It was weak from autumn to early winter, then strengthened gradually up to a high level, which was maintained between spring and early summer, and again decreased rapidly during summer. The annual life cycle of Chattonella spp., including vetetative and dormant phases, was summarized as follows: (1) vegetative cells in early summer originate from germination of dormant cells in sediments; (2) they form overwintering dormant cells during the summer season; (3) dormant cells spend a period of spontaneous dormancy until next spring; (4) the duration of post dormancy, an enforced one due to low temperatures, follows until early summer. The life cycle of Chattonella spp. is therefore well adapted to the temperature regime in temperate seas such as the Seto Inland Sea of Japan.