Seasonal change in chlorophyll maximum layer in enclosed coastal sea (Kumihama Bay, Kyoto): The relationship with hypoxic water mass and precipitation

  • Funakoshi Yuki
    Fisheries Technology Department; Kyoto Prefectural Agriculture, Forestry and Fisheries Technology Center Division of Applied Bioscience, Graduate School of Agriculture, Kyoto University
  • Kobayashi Shiho
    Field Science Education and Research Center, Kyoto University
  • Fujiwara Tateki
    Emeritus Professor of Kyoto University Osaka Branch Office, IDEA Consultants, Inc.

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  • 閉鎖性海域(久美浜湾)におけるクロロフィル極大層の季節変化―貧酸素水塊および降水との関係性―
  • ヘイサセイ カイイキ(クミハマワン)ニ オケル クロロフィル キョクダイソウ ノ キセツ ヘンカ : ヒンサンソスイカイ オヨビ コウスイ ト ノ カンケイセイ

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<p>In Kumihama Bay (Kyoto Prefecture), an enclosed sea area, monthly longitudinal and vertical observations and automatic vertical observations at fixed points were carried out to investigate the cause of the recent poor growth of cultured bivalves. The spatial and temporal distribution of chlorophyll, a food indicator, was investigated. The results showed that chlorophyll was distributed in layers regardless of season, and the depth of the maximum layer changed with the season. The chlorophyll maximum layer was the deepest at 6–10 m in April and shallowest at less than 5 m in November and December. When hypoxic water masses developed in the lower layer from June to August, a chlorophyll maximum layer was formed in the middle layer directly above it. At that time, nutrients were depleted and the chlorophyll concentration was generally below 5 μg·L-1 in the upper layer, corresponding to the layer where shellfish are cultivated. Throughout the year, the chlorophyll distribution in the bay strongly depended on the seasonal dynamics of hypoxic water masses. Because the high primary productivity in the bay is concentrated in specific layers, it is plausibly not being fully utilized for bivalve aquaculture.</p>

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