open access

https://hdl.handle.net/2115/56489

Estuarine Circulation and Red Tide Outbreaks in the Dokai Bay, Japan(Symposium: Role of estuarine circulation in the coastal marine environment)

日本語

洞海湾

2007-02-28

日本海洋学会沿岸海洋研究会

沿岸海洋研究

44(2)

147-155

Dokai Bay, Kitakyusyu City, is the most heavily eutrophic embayment in Japan. Estuarine circulation and red tide outbreak in the bay are discussed based on the knowledge and information obtained from our previous study. Despite sufficient nutrient concentration for phytoplankton growth during the entire year, Dokai Bay is characterized by high phytoplankton biomass dominated by diatoms during summer and low biomass during other seasons. Diatomaceous red tide occurred only in the summer season and flagellate blooms were lacking in this bay. Throughout the year, the surface water mass at the head of the bay was advected out within 2.0 to 2.5 days by a strong estuarine circulation without mixing vertically. Therefore, diatom blooms could form only in summer under high temperature and sufficient irradiance. However, even in summer, the flagellate growth rates were low compared to the flash-out speed of the surface water mass, and therefore they did not form a bloom in this bay. Although it is well known that flagellates can move vertically in the water column, the residual current speed was markedly faster than the daily vertical movement of the flagellates. Moreover, the high concentration of NH_4 in surface waters reduced growth for some phytoplankton species, although the growth of Skeletonema, the dominant species in this bay, was not reduced. The germination number of cysts for some flagellates was also reduced under the low oxygen environment in the interior part of the bay. However, germination of the dominant diatom species, Skeletonema was not influenced. They were also thought to be the reason why flagellates do not form a seasonal bloom.

学術雑誌論文

Version of Record

1342-2758

AN10492259