Mechanism and Causes of Large-Scale Red Tides in the Inner Part of Ariake Bay

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  • 有明海奥部における大規模な赤潮の発生とその発生メカニズムと原因
  • アリアケカイ オウブ ニ オケル ダイキボ ナ アカシオ ノ ハッセイ ト ソノ ハッセイ メカニズム ト ゲンイン

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Abstract

In Ariake Bay, red tides have occurred more frequently since the late １９９０s, and the scale of these red tides has enlarged markedly in the inner part of the bay since１９９８. Frequent occurrence and enlargement of the scale of red tides tends to increase the amount of organic discharge to the sea floor, and this is one of the main causes of hypoxic water. In this paper, I review the recent environmental studies of Ariake Bay, including analyses of water quality, tidal current, and bottom environment. In Ariake Bay, the occurrence of red tide did not follow the progress of eutrophication of the water, which is caused by an increase of nutrient discharge from the coastal areas. It occurred at the surface layer with low salinity and extremely high nutrient concentration, when the water was stratified. Therefore, the frequent occurrence and enlargement of the red tide seem to depend on how often the water was stratified, and／or how long the water was stratified. It is difficult to attribute the main cause of the development of stratified water ; however, it may be related to a decrease of vertical mixing of the water column by a decrease of tidal amplitude. The stratification of the water might develop due to changes in the tidal current itself.

Journal

  • Bulletin on Coastal Oceanography

    Bulletin on Coastal Oceanography 49 (2), 165-174, 2012

    Coastal Oceanography Research Committee, the Oceanographic Society of Japan

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