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Journal of Micropalaeontology An open-access journal of The Micropalaeontological Society
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Volume 24, issue 2
J. Micropalaeontol., 24, 159–167, 2005
https://doi.org/10.1144/jm.24.2.159
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 4.0 License.
J. Micropalaeontol., 24, 159–167, 2005
https://doi.org/10.1144/jm.24.2.159
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 4.0 License.

  01 Oct 2005

01 Oct 2005

Correlation of Virgulinella fragilis Grindell & Collen (benthic foraminiferid) with near-anoxia in Aso-kai Lagoon, central Japan

Hiroyuki Takata1, Koji Seto1, Saburo Sakai2, Satoshi Tanaka3, and Katsumi Takayasu1 Hiroyuki Takata et al.
  • 1Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan (e-mail: )
  • 2Institute for Frontier Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2–15 Natsushimacho, Yokosuka 237-0061, Japan
  • 3Kyoto University of Education, 1 Fujinomori, Fukakusa, Kyoto 612-8522, Japan

Keywords: Virgulinella fragilis, Aso-kai Lagoon, hydrography, near-anoxia, oxygen deficiency

Abstract. The distribution of Virgulinella fragilis and the hydro-environment of Aso-kai Lagoon, central Japan, were studied to clarify the foraminifer’s adaptation to low-oxygen conditions. The hypolimnion of the lagoon is oxygen-poor during much of the year. Two faunas (A and B) are recognized, based on cluster analysis. Cluster A fauna consists of species common in brackish lagoons, such as the genera Trochammina and Ammonia, and occurs in seasonally oxygenated waters. Virgulinella fragilis, the predominant species of Cluster B fauna, dominates the central part of the lagoon. This species can tolerate more severe oxygen deficiencies than the typical brackish foraminifers (e.g. Trochammina spp.) and can adapt to long periods of oxygen-poor conditions in coastal lagoon environments, as well as in pelagic to hemi-pelagic settings. In order to survive in the near-anoxia of Aso-kai Lagoon, V. fragilis may have adapted to environments in which little reactive iron is available in the sediment, leaving pore-water and bottom-water sulphide available for symbionts, or may utilize sulphur denitrification processes.

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