福井県浦底湾におけるミズクラゲの生態-VI. : 成体型クラゲの垂直分布の季節変化

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概要

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• Although the jelly-fish, Aurelia aurita (LINNE), is one of the commonest large Scyphomedusa found along the coastal waters of Japan, there is very little informations on its biology in the natural condition. The present report deals with the seasonal change in the vertical distribution of the medusa in the sea. For one year beginning from April 1969,sampling was carried out every month by means of vertical hauls with a closing plankton-net (100 cm in mouth aperture, 2 mm in mesh size and 230 cm in length). Usually, the sampling was made at every two or three meters depth from the bottom to the surface at the outer-western part of Urazoko Bay, a small inlet on the southern coast of Wakasa Bay facing the Japan Sea, where a dense distribution of medusae often appeared. Simultaneously, hydrographic and meteorological observations were made. The results obtained are : 1) The medusae were distributed throughout the whole layers and their conditions of vertical distribution showed divergent or irregular patterns during spring and early summer, forming a dense accumulation in the bottom layer below 15 m in mid summer. They were commonly found in the upper 5 m from autumn to winter. This tendency was especially noticeable throughout the autumn season. 2) Underwater illumination appeared to exert a far greater influence on the vertical distribution of the medusae than any other environmental factors such as surface wind wave, water temperature and chlorinity. The medusae were observed to distribute in the upper layer when the illumination was less than 10^4 lux, while they were restricted to the layer deeper than 15 m when the surface-layer illumination was above 10^4 to 10^5 lux. Underwater illumination seemed to give different influence on the beating of the umbrella and the vertical distribution of the medusae according to the season when the illuminstion became gradually stronger day by day (spring to early summer) and to the season when it became progressively weaker (late summer to winter).

• 1971-09-30

著者

• 安田 徹

  福井県水産試験場

関連論文

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