Fatty acid and elemental composition of the marine diatom Chaetoceros gracilis Schütt. Effects of silicate deprivation, temperature and light intensity

Fatty acid composition and content of C, N and P were measured in cultures of the marine diatom Chaetoceros gracilis Schutt at different degrees of silicate limitation in continuous and batch cultures, and in batch cultures with different temperatures and light intensities. Temperature optimum for growth was between 30 and 32 °C. Levels of total (n−3) and long-chained (C ⩾ 20) highly unsaturated (number of double bonds ⩾ 4) (n−3) fatty acids decreased with decreasing silicate availability. Silicate limitation did not affect C: N: P ratios. C: Si ratios increased with increasing degree of limitation. C: N ratios were higher in batch cultures than in continuous cultures, and N: P ratios were similar in batch and continuous cultures. Levels of (n−3) fatty acids which increased with increasing light intensity had no effect on elemental composition of cells in the range from 83 to 1428 μE · s−1 · m−2. Temperature clearly influenced fatty acid composition. Levels of unsaturated fatty acids and ratios of (n−3)(n−6) fatty acids were highest at the lowest temperatures. Levels of C and N per biovolume unit followed a pattern of temperature dependence similar to growth rate.