日本プランクトン学会報
Online ISSN : 2434-0839
Print ISSN : 0387-8961
63 巻, 1 号
選択された号の論文の16件中1~16を表示しています
原著論文
  • 山田 智, 柳橋 茂昭, 武田 和也, 広海 十朗, 鈴木 輝明
    2016 年 63 巻 1 号 p. 1-7
    発行日: 2016/02/25
    公開日: 2019/03/13
    ジャーナル フリー

    The biomass (wet weight) of the mesozooplankton in Mikawa Bay, a eutrophic bay of central Japan, was investigated monthly at four stations in the bay from 1981 to 2010, using 0.33-mm mesh plankton nets. The copepod communities and their abundance in these samples were also examined at the four stations during 1981–1987 and at a single station during 2000–2006. The annual mesozooplankton biomass was significantly greater in the 2000s than it was in the 1980s–1990s. Temora, which was the dominant copepod, increased markedly from the 1980s to the 2000s.

    The annual means of mesozooplankton biomass and copepod abundance, and the means calculated during the summer months (July–September) when the hypoxic area generally developed, were not significantly correlated with the surface water temperature or levels of chlorophyll a. However, the means of the mesozooplankton biomass and copepod abundance calculated during the summer months were significantly negatively correlated with the hypoxic area of the bay. In June and July 1984, when the hypoxic area was well developed, the combined production rates of the three dominant copepod families—Acartiidae, Paracalanidae, and Corycaeidae—which composed more than 95% of the copepod community, were estimated to be 5.33 (June) and 0.95 (July) mg C m-3 day-1, respectively. The rates corresponded to only 20.9% and 5.5%, respectively, of the daily feeding rates of Japanese sardines in these months. This indicated that copepods were not adequate prey for the pelagic fish. The present results provide evidence that the development of the hypoxic area in Mikawa Bay results in a reduction in zooplankton biomass and causes shortage of food for zooplanktivorous pelagic fish.

総説
  • 帰山 秀樹
    2016 年 63 巻 1 号 p. 8-15
    発行日: 2016/02/25
    公開日: 2019/03/13
    ジャーナル フリー

    Anthropogenic radionuclides have been deposited into the ocean since the era of atmospheric nuclear weapon tests in the 1950s. In 2011, the Fukushima Dai-ichi nuclear power plant accident resulted in additional release of anthropogenic radionuclides into marine ecosystems. This review summarizes field studies concerning anthropogenic radionuclides in zooplankton before and after the Fukushima accident. Before the Fukushima accident, the concentrations of cesium-137 (137Cs) in zooplankton around Japan were 10-2 Bq/kg-wet, and the concentration ratios of them were in the order of 101. The concentration ratios of 137Cs for zooplankton reported around Japan were comparable to those values reported from European areas, such as the Mediterranean Sea. These results suggest that dynamic equilibrium had been reached between zooplankton and surrounding seawater before the Fukushima accident. The Fukushima accident resulted in elevation of concentrations of 137Cs in coastal seawater by three to four orders of magnitude off Fukushima prefecture soon after the accident, and decreased rapidly. The concentration of 137Cs in zooplankton was also elevated, and their temporal change (decrease with time) seemed to be correlated with that of seawater. The scatter plots between concentrations of 137Cs in seawater and apparent concentration ratio of 137Cs for zooplankton could be good indicators of the changes in 137Cs contamination in zooplankton from the beginning of the Fukushima accident to the restoration phase.

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