THE SEASONAL DISTRIBUTION OF THE STANDING STOCK OF PHYTOPLANKTON IN THE SOURCE AREA OF THE KUROSHIO AND ADJACENT AREAS

The size-fractionated chlorophyll a concentration was observed in the source area of the Kuroshio and the adjacent area during the winter of 2001,the spring and autumn of 2002,which is to the east of the Ryukyu Islands,Taiwan Island and Luzon Island.The results showed that the surface average chlorophyll a concentration in the winter is higher than that in the spring and autumn.The surface average chlorophyyll a concentration is higher in the north surveyed area(east of the Island China) than that in the southern surveyed area.The vertical distribution of chlorophyll a concentration is rather uniform;the average chlorophyll a concentration in the surface layer is lower than that in the deep sampling layers;and it increased with depth in the euphotic layer;but it decreased with depth under the euphotic layer to depth 200m.The size-fractionated chlorophyy a concentration in spring and autumn showed that picoplankton predominated(86%),the contributions of nanoplankton are 9% and 11% respectively,and those of netplankton are only 5% and 3% respectively.In autumn,the cell abundance of phytoplankton in the surface layer is 1.3×10~3~13.5×10~3 cell/dm~3,and small cell-sized diatoms are predominant,which implies the importance of picoplankton in the observation sea area.