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洞海湾の河口循環流と赤潮形成(シンポジウム:内湾環境における河口循環流の役割)

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Title: 洞海湾の河口循環流と赤潮形成(シンポジウム:内湾環境における河口循環流の役割)
Other Titles: Estuarine Circulation and Red Tide Outbreaks in the Dokai Bay, Japan(Symposium: Role of estuarine circulation in the coastal marine environment)
Authors: 多田, 邦尚1 Browse this author →KAKEN DB
一見, 和彦2 Browse this author →KAKEN DB
濱田, 建一郎3 Browse this author
上田, 直子4 Browse this author
山田, 真知子5 Browse this author
門谷, 茂6 Browse this author →KAKEN DB
Authors(alt): Tada, Kuninao1
Ichimi, Kazuhiko2
Hamada, Kenichiro3
Ueda, Naoko4
Yamada, Machiko5
Montani, Shigeru6
Keywords: 河口循環流
赤潮
植物プランクトン
洞海湾
Issue Date: 28-Feb-2007
Publisher: 日本海洋学会沿岸海洋研究会
Journal Title: 沿岸海洋研究
Volume: 44
Issue: 2
Start Page: 147
End Page: 155
Abstract: 過度に富栄養化した内湾である北九州市の洞海湾における河口循環流と赤潮形成について,著者らがこれまでの調査・研究から得た知見を総合して考察した.洞海湾においては,年間を通じて栄養塩濃度が極めて高いにもかかわらず,植物プランクトン現存量は珪藻類が優占する夏季に大きく,その他の季節は小さいことが特徴である.即ち,本湾では夏季にのみ珪藻類の赤潮が発生し,鞭毛藻類が卓越しない.洞海湾では河口循環流が周年卓越し,湾奥の表層水は鉛直混合することなく2.0〜2.5日で湾外に流出する.そのため,水温,光環境が好適な夏季にのみ増殖速度の大きい珪藻類が卓越でき,一方,鞭毛藻類は夏季の環境条件下にあっても湾外への流出速度を上回る増殖速度を有しておらず,本湾で大きく増殖することはきわめて困難であることが示唆された.なお,鞭毛藻類は鉛直移動することが知られているが,その鉛直移動速度よりも潮汐残渣流の速度の方がはるかに大きい.また,湾内の海水中で高濃度のNH_4が本湾の優占種のSkeletonemaの増殖を阻害しないのに対し,鞭毛藻類の増殖を阻害することも本湾で鞭毛藻類が卓越しない要因と考えられた.さらに,湾奥の貧酸素環境下において本湾の優占種のSkeletonemaの休眠期細胞の発芽が影響を受けないのに対し,鞭毛藻類のシストの発芽率が低下することも要因として考えられた.
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.
Type: article
URI: http://hdl.handle.net/2115/56489
Appears in Collections:水産科学院・水産科学研究院 (Graduate School of Fisheries Sciences / Faculty of Fisheries Sciences) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 門谷 茂

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