Fatty acid signatures of Lake Michigan prey fish and invertebrates: among-species differences and spatiotemporal variability

Lipid concentration and fatty acid composition of common prey species or taxonomic groups from four distinct regions of Lake Michigan were quantified (n = 894). We used a combination of parametric and nonparametric statistics to assess the differences in fatty acid signatures (FAS) among species and to evaluate intraspecies variation relative to interspecies variation in FAS. Discriminant function analysis performed on 13 species or taxa groups using the 18 most abundant fatty acids revealed clear separation among taxa, with overall classification success reaching 89%. Species were readily distinguished based on their overall fatty acid profile in spite of intraspecies variation (temporal, regional, and size-related). Among species sampled, pelagic and benthic clusters were formed based on the degree of fatty acid profile similarity. In alewife (Alosa pseudoharengus) and round goby (Neogobius melanostomus), fatty acid compositions differed with fish size, sampling location, and temporal variation; however, the magnitude of these differences was small relative to differences between species. Our results demonstrate the utility of fatty acid signatures in studies of food webs in large freshwater ecosystems. This study is also a necessary first step toward development of mechanistic research that investigates the effects of variation in fatty acids within the prey base on top predators.