Fatty acid biomarkers to verify cyanobacteria feeding abilities of herbivorous consumers

To search useful fatty acid biomarkers for cyanobacteria feeding abilities of control organisms, we compared fatty acid composition of six cultured algal species in four taxonomic groups (Cryptophyceae, Bacillariophyceae, Chlorophyceae, and Cyanophyceae) and evaluated several fatty acid biomarkers using data from three lakes that varied in trophic status. In addition, a laboratory feeding experiment was conducted to verify fatty acid markers for cyanobacteria using Selenastrum capricornutum (Chlorophyceae) and Microcystis aeruginosa (Cyanophyceae). Two strains of M. aeruginosa had the highest content of 18:36 while Anabaena sp. had a relatively high content of 18:17 among the six species. Both 18:17 and 18:36 (-linolenic acid, GLA) concentrations showed significant linear relationships with cyanobacteria biomass in natural systems. In the laboratory feeding experiment, a principal component analysis score plot indicate that fatty acid composition of Branchinella kugenumaensis fed with M. aeruginosa became similar to that of the cyanobacterial population. In S-plot of partial least square discriminant analysis, 18:36 and 18:17 were selected for fairy shrimps feeding on M. aeruginosa, whereas 18:33 (ALA, -linolenic acid) and 18:19 were selected for those feeding on S. capricornutum. 18:36 content of B. kugenumaensis fed with M. aeruginosa significantly increased after the third day and 18:17 content was significantly different from the other feeding group after six days. In particular, 18:36 appeared to be a useful fatty acid biomarker for M. aeruginosa in tracing trophic relations of herbivorous organisms in freshwater ecosystems.