大阪湾の人工護岸における高密度に生息するウニ類の摂食による海藻群落の生産量の増大  [in Japanese] Increase of production rate of seaweed community with grazing of sea urchins on a seawall in Osaka Bay  [in Japanese]

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Abstract

大阪湾の人工護岸上の高密度にウニ類が生息している藻場において,3 年間にわたりウニ類の密度を人為的に調節した実験区で海藻群落の年間生産量を推定した。ウニ類の現存量が大きくなるほど海藻の全生産量も大きくなり,現在のウニ生息量の約 2 倍(2000 g 湿重/m<sup>2</sup>,60 個体/m<sup>2</sup>)でも海藻群落は維持された。このことから,大阪湾の人工護岸上の藻場では,ウニ類の摂食圧が増大すると海藻の生産量も同時に増大し,磯焼けとはならずに,海藻群落を維持しながらウニ類が高密度で共存できることが明らかとなった。<br>

  Seaweed production rates were estimated at an intact and two manipulated urchin-dominated seawall communities in Osaka Bay for three years from 2002 to 2005. Three experimental sections were made at a depth of 2 m, in which the densities of sea urchins were kept at three levels: ‘removal’ (1.3-4.8 ind./m<sup>2</sup>), ‘control (intact)’ (11.7-22.3 ind./m<sup>2</sup>), and ’double density’ (30.0-59.6 ind./m<sup>2</sup>). Monthly feeding rates of sea urchins were estimated to be 5 to 20 g-dry weight/m<sup>2</sup>/month at ‘removal’, 40 to 80 g-dry weight/m<sup>2</sup>/month at ‘control’, 100 to 250 g-dry weight/m<sup>2</sup>/month at ‘double density’.<br>    On the other hand, the biomass of seaweed community was maintained at a stable level within the range of 300 to 800 g-dry weight/m<sup>2</sup> regardless of density of sea urchins. The amount of seaweeds grazed by sea urchins could be regenerated by the remaining thalli immediately, because the growth rates of seaweeds were much higher. Thus, seaweed production rates were larger where there was a higher density of sea urchins, resulting in the maintenance of seaweed community even at 2000 g-wet weight /m<sup>2</sup> (60 ind./m<sup>2</sup>). The major reason for the coexistence of high density of sea urchins and seaweed community is supposed to be the eutrophicated nature of the area.<br>

Journal

  • NIPPON SUISAN GAKKAISHI

    NIPPON SUISAN GAKKAISHI 74(1), 45-54, 2008-01-15

    The Japanese Society of Fisheries Science

References:  27

Codes

  • NII Article ID (NAID)
    110006595207
  • NII NACSIS-CAT ID (NCID)
    AN00193422
  • Text Lang
    JPN
  • Article Type
    ART
  • ISSN
    00215392
  • NDL Article ID
    9349687
  • NDL Source Classification
    ZR26(科学技術--農林水産--水産)
  • NDL Call No.
    Z18-345
  • Data Source
    CJP  NDL  NII-ELS  IR  J-STAGE 
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