Effect of nutrient conditions on the composition of photosynthetic products in the East China Sea and surrounding waters

Production rates of organic compounds such as fatty acids and monosaccharides, constituting lipids and carbohydrates, respectively, were determined by 13C tracers and the gas chromatograph/mass spectrometry (GC/MS) method at five stations from the Kuroshio Current to the East China Sea during the summer of 1994. High phytoplankton biomass and primary productivity were found at the estuary of the Changjiang, and the photosynthetic products showed distinctive differences from those at other stations. A high contribution of 16:1(n-7) fatty acid (one of the marker compounds of diatoms) indicates the occurrence of a diatom bloom during our observation period. The ratio of low molecular weight (LMW) to high molecular weight (HMW) carbohydrates off the Changjiang was distinctly higher (1.3) than at the other four stations (0.007–0.091). This suggests that mono-/oligosaccharides did not polymerize to polysaccharides smoothly. The high contribution of glucose in the photosynthetic products at this station indicates that the phytoplankton population was in a nutrient-limited condition. In contrast, the low ratio of LMW to HMW carbohydrates and the lower contribution of glucose at other stations, including oligotrophic Kuroshio water, suggest that phytoplankton populations were not nutrient-limited.