Fatty acid composition in photosynthetic products of natural phytoplankton population in Lake Biwa, Japan

Fatty acid composition of phytoplankton photosynthetic productswas determined by a ¹³C tracer and gas chromatography-mass spectrometry(¹³C-GC-MS) method from August 1985 to June 1986 in Lake Biwa,Japan. The total fatty acid production rate varied from 2.8to 10.9 µg C l^–1 day^–1 at the water surfaceand accounted for 9.1–30% of photosynthetic productionof particulate organic carbon. A high contribution of fattyacid to the particulate organic carbon production rate was noticedduring winter time, and an increase in the fatty acid contributionresulted in an increase in the C/N value in the photosyntheticproducts. The fatty acid composition varied throughout the year,mainly depending on the seasonal change in the dominant phytoplanktonspecies. The contribution of polyunsaturated fatty acids tototal fatty acids was low during the summer period, probablydue to nitrogen limitation of phytoplankton growth.