Discoloration　of 　Nori（Porphyra）and 　Characteristics　of　Wsater　Quality　in　Eastern Bisan　Seto

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  • 備讃瀬戸東部（香川県沿岸） におけるノリ色落ちと水質環境
  • ビサンセト トウブ カガワケン エンガン ニ オケル ノリ イロオチ ト スイシツ カンキョウ

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Abstract

In fiscal 2002, Nori (Porphyra) production along the Kagawa prefectural coast, Eastern Bisan Seto, greatly decreased to 60% of the normal annual yield. The ocean area where the sub-standard harvest occurred and discoloration of Nori was observed was confined primarily to the northern and southwestern areas of Shodo Island, where the annual yield was about 30% of an average year. Annual Nori yields for the most recent 12 years are positively correlated with rainfall during the Nori harvest season; most likely being a result of nutrient influx from rivers. Hydrographic observations in the harvest area when discoloration of Nori occurred in January 2003 indicated that salinity was higher than 33 (psu), and that these values were higher than that of a normal year. Further, NO_3+NO_2 was lower than 3μM, and these values were lower than that of a normal year. It is suggested that nutrient-laden fresh water did not flow into this area in comparison with a normal year. On the other hand, salinity was lower during the June 2003 rainy season and NO_3+NO_2 was higher. Also, in January 2004, salinity was lower and NO_3+NO_2 was higher compared with those in January 2003. From these results, we believe that the sub-standard Nori harvest during fiscal 2002 was caused by inadequate rainfall in the autumn. It was also suggested that the nutrient supply from the Yoshii River in Okayama Prefecture is an important production factor for the Shodo Island Nori harvest area.

Journal

  • Bulletin on Coastal Oceanography

    Bulletin on Coastal Oceanography 43 (1), 77-84, 2005

    Coastal Oceanography Research Committee, the Oceanographic Society of Japan

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