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 photoacclimation of phytoplankton assemblages. The sampling stations encompassed the inner and outer shelf of the southern East China Sea. Field 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 water could be ascribed to high turbidity and low nutrient availability, respectively. The highest P-max(B) observed in the upwelling plume station probably could be ascribed to both copious nutrient supply by upwelling processes and higher light availability. Light-manipulation experiments showed that in the well-mixed coastal water, the light response curves for samples taken from different depths of the euphotic zone were very similar. In both the upwelling region and the Kuroshio water, phytoplankton assemblages living below the mixed-layer depth were shade-acclimated while those living above that depth were light-acclimated. Overall, our results indicate that photosynthetic available radiance, light history and nutrient availability are crucial in controlling the spatial variation of algal photosynthetic performance in the study area.