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 quantifie d for profundal benthic invertebrates, surficial sediment, and sedimenting matter from Lake Erken, Sweden. Food quality for profundal zoobenthos, as i ndicated by the concentrations of long-chain polyunsaturated FA, omega3 FA, or eicosapentaenoic acid (EPA) in sediment and sedimenting matter, was hig hest in spring and autumn and markedly lower in summer. Surficial sediment was consistently lower in all FA than was sedimenting matter. Palmitoleic a cid (16:1 omega7) was the dominating FA in both sedimenting matter and sedi ment. In fauna samples, EPA, palmitic acid (16:0), palmitoleic acid, and va ccenic acid (18:1 omega7) were among the dominant FA. Docosahexaenoic acid was found only in the predators Chaoborus and Procladius. Differences betwe en functional feeding guilds were found for the diatom-indicating FA palmit oleic acid and the bacteria-specific FA isoseptadecanoic acid (17:0iso). Fu rthermore, principal components analysis showed marked differences in FA co mposition among taxa. These differences reflect the relative contribution o f food from autotrophic (phytoplankton production) and heterotrophic source s (detrital food web) in profundal invertebrate taxa.