LIGHT EFFECTS ON PHYTOPLANKTON PHOTOSYNTHETIC PERFORMANCE IN THE SOUTHERN EAST-CHINA-SEA NORTH OF TAIWAN

Phytoplankton primary production was measured in different regions in the southern East China Sea north of Taiwan in the fall of 1994. Light -manipulation experiments were also performed on-board to study the ph otoacclimation of phytoplankton assemblages. The sampling stations enc ompassed the inner and outer shelf of the southern East China Sea. Fie ld observation showed that the in situ maximal chlorophyll-normalized photosynthetic rates (P-max(B)) varied 3-fold among stations, ranging from 4.0 to 12.0 mgC mgChl(-1) h(-1). The low P-max(B) values recorded in the nutrient-laden coastal water and the oligotrophic Kuroshio wat er could be ascribed to high turbidity and low nutrient availability, respectively. The highest P-max(B) observed in the upwelling plume sta tion probably could be ascribed to both copious nutrient supply by upw elling processes and higher light availability. Light-manipulation exp eriments showed that in the well-mixed coastal water, the light respon se curves for samples taken from different depths of the euphotic zone were very similar. In both the upwelling region and the Kuroshio wate r, phytoplankton assemblages living below the mixed-layer depth were s hade-acclimated while those living above that depth were light-acclima ted. Overall, our results indicate that photosynthetic available radia nce, light history and nutrient availability are crucial in controllin g the spatial variation of algal photosynthetic performance in the stu dy area.