Year-to-year Changes in the Rocky-shore Malacofauna of Bansho Cape, Central Japan: Rising Temperature and Increasing Abundance of Southern Species

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Abstract: Year-to-year changes in the distribution of rocky intertidal molluscs were monitored at Bansho Cape on the southern Pacific coast of mainland Japan from 1985 to 1994. All the molluscan species except opisthobranchs were recorded from each of 69 quadrats(8x8m)in April or May each year. Over the ten years, 183 species of molluscs were recorded, of which the Gastropoda made up 74%, Bivalvia 20%, and Polyplacophora 6%. Species with a southern geographic range (northern limit35°c N) constituted the remainder. Species distribution patterns in relation to height on the shore and wave exposure were consistent throughout the ten years, and the non-southern species always exceeded the southern species in terms of mean number of quadrats in which they occurred. On the other hand, the southern species increased significantly over the ten years in terms of both number of species and cumulative number of quadrats occupied. Air and water temperatures increased significantly in winter near the study site, and the distance from the shore to the warm Kuroshio Current decreased significantly during the period from 1980 to 1994. The increase in near-shore water temperature in winter was 1.7-1.9° from the early 1980s to the early 1990s. The present and previous results suggest that temperature and/or the Kuroshio affected the structure of the molluscan assemblage in the study area by controlling the abundance of southern species. Low mortality in winter due to the temperature rises, and an enhanced supply of larvae from the Kuroshio, are proposed as mechanisms for the recent increase in prevalence of southern species.

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  • BENTHOS RESEARCH

    BENTHOS RESEARCH 54 (2), 47-58, 1999

    日本ベントス学会

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