日本近海におけるプランクトン沈澱量の分布-I

Abstract

In the same way as in the survey made in 1954, of which result was already reported by the author as the first paper of the work, net-plankton samples were collected in the neighbouring seas of Japan in 1955 also, and the settling volume was measured. The result is almost similar to that in 1954. In seas east of Japan, generally, the settling volume is larger in the Oyashio region and the mixed-water region north of the Kuroshio main current than in the Kuroshio region. It is remarkably varied seasonaly in the Oyashio. Namely, it increases to about 10 cc. per cubic meter in May-June and decreases to only 0.3-0.5 cc. in February-March, while it is 0.5-1.0 cc. in October-November, almost equal to that of the Kuroshio water. A tendency is found that contacting regions of the Oyashio with the Kuroshio or coastal waters are rich in plankton. The plankton settling volumes of the Kuroshio water do not show any distinct difference between areas east and south of Japan, both being about 0.5-1.0 cc. In areas south of Japan, it increases in the coastal region north of the Kuroshio main current and often in the cold water region around 33°30'N, 137°30'E. In areas east of Japan, warm water masses originated from the Kuroshio water maintain the same volume of plankton as that in the Kuroshio. The seasonal variation is not very obvious, whereas the plankton seems to become abundant to some extent in areas of east Japan in May-June and south in February-March.