九州西方海域における現生浮遊性有孔虫群集の季節変化

概要

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Seasonal variation in standing stock and assemblage of living planktic foraminifera were investigated using plankton-net samples from the northeastern part of the East China Sea (ECS), in 1995 and 1998-1999. As a result, a distinctive alternation of major species among seasons was confirmed. Whereas the summer assemblage was apparently characterized by dominance of Globigerinoides sacculifer and Globigerinoides ruber, those 3 species like Globigerinita glutinata, Globigerina bulloides and Pulleniatina obliquiloculata were abundant in winter. Neogloboquadrina dutertrei and Globigerinella aequilateralis were observed in all samples. Globorotalia inflata was found to dwell shallower in winter, by contrast deeper than 100m in summer in ECS, clearly suggesting its ecology to change the favorable depth in their life cycle. Because vertical distribution of the standing stock of planktic foraminifera and chlorophyll-a concentration during the examined interval was well correlated, one of the principle factors to control absolute abundance of planktic foraminifera is inferred to be food conditions. Further, it is suggested that the potential impact of a flood of the ChangJiang River in summer, 1999 on the hydrographic environment in ECS was rather an eutrophication at the sea surface caused by the river discharge, than an influx of low salinity waters, bringing an increase of standing stock of shells together with no drastic change in assemblage.
2010-03-31