Fatty acids in profundal benthic invertebrates and their major food resources in Lake Erken, Sweden: seasonal variation and trophic indications

Fatty acid (FA) concentrations and their seasonal variations were quantified for profundal benthic invertebrates, surficial sediment, and sedimenting matter from Lake Erken, Sweden. Food quality for profundal zoobenthos, as indicated by the concentrations of long-chain polyunsaturated FA, omega3 FA, or eicosapentaenoic acid (EPA) in sediment and sedimenting matter, was highest in spring and autumn and markedly lower in summer. Surficial sediment was consistently lower in all FA than was sedimenting matter. Palmitoleic acid (16:1 omega7) was the dominating FA in both sedimenting matter and sediment. In fauna samples, EPA, palmitic acid (16:0), palmitoleic acid, and vaccenic acid (18:1 omega7) were among the dominant FA. Docosahexaenoic acid was found only in the predators Chaoborus and Procladius. Differences between functional feeding guilds were found for the diatom-indicating FA palmitoleic acid and the bacteria-specific FA isoseptadecanoic acid (17:0iso). Furthermore, principal components analysis showed marked differences in FA composition among taxa. These differences reflect the relative contribution of food from autotrophic (phytoplankton production) and heterotrophic sources (detrital food web) in profundal invertebrate taxa.