Rapid Increase in Heterotrophic Dinoflagellate Gyrodinium dominans and Decrease in Heterosigma akashiwo in Hiroshima Bay

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  • 広島湾北西部大野瀬戸における従属栄養性渦鞭毛虫Gyrodinium dominans の急激な増加とHeterosigma akashiwo の衰退
  • ヒロシマワン ホクセイブ オオノ セト ニ オケル ジュウゾク エイヨウセイウズ ベン ケムシ Gyrodinium dominans ノ キュウゲキ ナ ゾウカ ト Heterosigma akashiwo ノ スイタイ

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Description

We conducted weekly field observations at a fixed point in northwest Hiroshima Bay, the Seto Inland Sea, Japan, between 27 April and 26 June 2017 to evaluate the role of heterotrophic dinoflagellate Gyrodinium dominans during a Heterosigma akashiwo bloom. We observed the collapse of the H. akashiwo bloom and rapid increase in G. dominans during the same period. G. dominans had food vacuoles that contained H. akashiwo-like particles. We evaluated the impact of G. dominans on the H. akashiwo population by estimating the apparent gross growth efficiency（GGE）and grazing amount of G. dominans. The GGE estimated from the ratio of the increase in the standing stock of G. dominans to the decrease in that of H. akashiwo was 10．4％ when the decrease in H. akashiwo was due to G. dominans. The apparent GGE（10．4％）was in the range of that in previous laboratory studies. The removal of H. akashiwo by G. dominans estimated by grazing rates and food requirements in the previous laboratory studies accounted for28％ and 32％ of the loss of H. akashiwo in the field. Thus, we concluded that the grazing of G. dominans led to the decrease in H. akashiwo in Hiroshima Bay.

Journal

  • Bulletin on Coastal Oceanography

    Bulletin on Coastal Oceanography 58 (1), 1-10, 2020

    Coastal Oceanography Research Committee, the Oceanographic Society of Japan

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