Benthic foraminiferal assemblages in Osaka Bay, southwestern Japan : faunal changes over the last 50 years

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概要

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• Live benthic foraminiferal assemblages from surface sediment in Osaka Bay collected in 1999 were analyzed to characterize the distribution of the modern foraminiferal assemblages. Foraminiferal assemblages were compared with those of previous studies to document environmental changes in Osaka Bay over the past 50 years. Sixty-one species of foraminifera belonging to 37 genera were recognized from the 1999 surface sediment samples. An agglutinated assemblage containing Trochammina hadai and Eggerella advena is dominant in the inner part of the bay and is related to eutrophication. The foraminiferal assemblage in areas deeper than about 20m is composed of Eggerella advena, Ammonia beccarii forma A, and Pseudorotalia gaimardii. This assemblage may be influenced by the large clockwise Okinose Circulation Current which extends throughout the western bay. Foraminiferal assemblages in Osaka Bay have changed dramatically during the last 50 years. The Trochammina hadai-Eggerella advena assemblage became established in the inner part of the bay, reflecting eutrophication that progressed from the 1960s through the 1970s. This assemblage became dominant in 1983, and typically dominated the inner part of the bay. From 1983 to 1999, however, the abundance of taxa belonging to this assemblage decreased greatly following implementation of 1973 Osaka City bylaws that restricted wastewater discharge. Changes in benthic assemblages such as the decrease of Ammonia beccarii forma A and increase of Eggerella advena have occurred in response to decreased incidence of red tides, and floral change in the species that cause these tides. The results of this study demonstrate that the abundance and distribution of benthic foraminifers in Osaka Bay are intimately related to environmental changes related to the urbanization of coastal areas.

• 日本古生物学会の論文
• 2006-06-30

著者

• Nomura Ritsuo

  Foraminiferal Laboratory Faculty Of Education Shimane University

• Tsujimoto Akira

  Division Of Biology And Geosciences Graduate School Of Science Osaka City University

• Yoshikawa Shusaku

  Division Of Biology And Geosciences Graduate School Of Science Osaka City University

• Yasuhara Moriaki

  926a U.s. Geological Survey

• Nomura Ritsuo

  Shimane Univ. Matsue Jpn

関連論文

• Bio- and Chronostratigraphy of Cenozoic Sequences on the Pacific Coast of South America : A Contribution to Studies on Pacific Neogene Events in Japan and South America
• Trans-Pacific Correlation of Neogene Geologic Events
• Benthic foraminiferal assemblages in Osaka Bay, southwestern Japan : faunal changes over the last 50 years
• Foraminal structures of some Japanese species of the genera Ammonia and Pararotalia, family Rotaliidae (Foraminifera)
• The suprageneric classification of the foraminiferal genus Murrayinella and a new species from Japan
• Quantification of optically granular texture of benthic foraminiferal walls

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