周防灘におけるＣｈａｔｔｏｎｅｌｌａ耐久細胞の分布と夏季の赤潮

Abstract

It seems that the dormant cells of Chattonella (Raphidophyceae) play an important role in initiating red tide in the summer through their capability of overwintering in bottom sediments. From this point of view, we investigated the distributions of dormant cells in spring and of vegeta-tive cells in summer in Suo-Nada, western Seto Inland Sea, in 1984. Densities of dormant cells enumerated by the extinction dilution method ranged from 3 to 158 cells/cm3 wet sediment, with an average of 63. Dormant cells were fairly abundant in the central area. While, they were scarce in the western coastal part, where high concentrations of vegetative cells were observed during the period from July 12 to 14. Bottom water temperature, which affects the germination of dormant cells, was optimum for germination in the western coastal area but lower at central deep water area during the period from July 12 to 14. Surface water temperature was optimum for the growth of vegetative cells in the whole area during July. The density of Chattonella in western coastal area was relatively higher than that in the offshore water and developed into the red tide in late July. The winds blowing to western coastal area con-stantly prevailed during July, which presumably accumulated Chattonella there. A scheme of Chattonella red tide outbreak was discussed based on the germination of dormant cells, growth of vegetative cells, accumulation, and organic and inorganic nitrogen supply.