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Ecological dynamics of the bivalve-killing dinoflagellate Heterocapsa circularisquama and its infectious viruses in different locations of western Japan

Authors

  • Yuji Tomaru,

    1. National Research Institute of Fisheries and Environment of Inland Sea, 2-17-5 Maruishi, Hatsukaichi, Hiroshima 739-0452, Japan.
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  • Naotsugu Hata,

    1. Mie Prefectural Science and Technology Promotion Center, 3564-3 Hamajima, Hamajima, Shima, Mie 517-0404, Japan.
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  • Takeshi Masuda,

    1. Mie Prefectural Science and Technology Promotion Center, 3564-3 Hamajima, Hamajima, Shima, Mie 517-0404, Japan.
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    • Present addresses: Mie Prefectural Science and Technology Promotion Center, 3098-9 Ugata, Ago, Shima, Mie 517-0404, Japan;

  • Masaharu Tsuji,

    1. Mie Prefectural Science and Technology Promotion Center, 3564-3 Hamajima, Hamajima, Shima, Mie 517-0404, Japan.
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    • Mie Prefectural Science and Technology Promotion Center, 215-2 Furusato, Tenmaura, Owase, Mie 519-3602, Japan;

  • Kuniyoshi Igata,

    1. Saga Prefectural Genkai Fisheries Research and Development Center, 6-4948-9 Toubou, Karatsu, Saga 847-0122, Japan.
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    • §

      Saga Prefectural Advanced Fisheries Training School, 6-4948-23 Toubou, Karatsu, Saga 847-0122, Japan.

  • Yuji Masuda,

    1. Saga Prefectural Genkai Fisheries Research and Development Center, 6-4948-9 Toubou, Karatsu, Saga 847-0122, Japan.
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  • Toshifumi Yamatogi,

    1. Nagasaki Prefectural Institute of Fisheries, 1551-4 Taira, Nagasaki, Nagasaki 851-2213, Japan.
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  • Masao Sakaguchi,

    1. Nagasaki Prefectural Institute of Fisheries, 1551-4 Taira, Nagasaki, Nagasaki 851-2213, Japan.
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  • Keizo Nagasaki

    Corresponding author
    1. National Research Institute of Fisheries and Environment of Inland Sea, 2-17-5 Maruishi, Hatsukaichi, Hiroshima 739-0452, Japan.
      *E-mail nagasaki@affrc.go.jp; Tel. (+81) 829 55 3529; Fax (+81) 829 54 1216.
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*E-mail nagasaki@affrc.go.jp; Tel. (+81) 829 55 3529; Fax (+81) 829 54 1216.

Summary

We studied the ecological relationships between the bloom-forming dinoflagellate Heterocapsa circularisquama and its infectious viruses in field surveys conducted in western Japan. The occurrence of H. circularisquama blooms in Imari Bay during 2002 and in Ago Bay during 2002 and 2004 was accompanied by specific increase in abundance of viruses lytic to H. circularisquama. Using northern dot-blot analysis, ∼96% of the clonal virus isolates collected in the field surveys positively reacted with a molecular probe specific for HcRNAV (H. circularisquama RNA virus); hence, viral impacts on H. circularisquama population observed in these field surveys are considered largely due to HcRNAV and/or its closely related viruses. The dynamics of type UA viruses and type CY viruses having complementary host ranges to H. circularisquama clones were different in each survey and considered to reflect fluctuations in abundance of their suitable host cells in situ. The dynamics of H. circularisquama and its viruses in Ago Bay from 2002 to 2004 suggests the concentration of HcRNAV in the sediment prior to the host's blooming season is a significant factor in determining the size and length of the H. circularisquama blooms. These results support the hypothesis that HcRNAV infection is one of the significant factors affecting the population dynamics of H. circularisquama in both quantity (biomass) and quality (clonal composition).

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