Utility of Fatty Acid Signature Analysis in Large Freshwater Food Webs

Non-indigenous species may alter trophic pathways resulting in deleterious impacts to native fish communities. To better understand the trophic structure in aquatic systems, lipid content and fatty acid signatures (FAS) of common species/taxa groups throughout the Lake Michigan food web were determined. Multivariate approaches were taken to assess the degree of similarity in FAS among various components of Lake Michigan biota. Our analyses revealed clear separation among taxa with high overall classification success in spite of within species variation. Sizable annual and seasonal variation in FAS was also noted allowing for within species discrimination based on years and seasons with high classification success. Body size and sampling location had significant effects on fatty acid composition, which likely related to known ontogenetic diet shifts as well as spatial variation in prey assemblage and zooplankton/invertebrate composition throughout Lake Michigan. Despite various sources of variation, within-species variability was relatively small compared to among-species variability in fatty acid profiles. Thus, fatty acid signatures can be used in freshwater systems to study food web interactions and delineate spatiotemporal changes in food web structure.