Fatty acids as specific algal markers in a natural lacustrian phytoplankton

The fatty acid (FA) composition of planktonic particulate matter (size class 1–160 μm) was established during a seasonal study carried out on an oligotrophic lake, Lac Pavin (France). The succession of phytoplanktonic populations with a monospecific trend permits the large differences in FA composition according to phytoplanktonic classes, or even according to genera for dominant algae to be pointed out. Thus, we have established that Chlorophyceae had a high content of 18:3(n-3), 20:4(n-3) and 16:3(n-3) FA, whereas Dinophyceae could be identified by higher 16:0, 18:4(n-3), 20:5(n-3) and 22:6(n-3) FA levels, and lower 18:3(n-3) and C16 polyunsaturated FA levels. Diatoms could be charac terized by high values of the FA ratio [14:0 + 16:1(n-7) + 16:2(n-4) + 16:3(n-4) + 16:4(n-1)/16:0]. In addition, a close relationship was noted, on one hand, between Aulacoseira italica biomass and a high 16:2(n-4), 163(n-4) and 16:4(n-1) FA level and, on the other hand, between Asterionella formosa biomass and high 14:0 and 16:1(n-7) levels. So, the main phytoplanktonic classes or genera were characterized by some FA or ratios of FA, which could be used as specific natural biomarkers for study ing the transfer of organic matter through the aquatic food web.