Effect of lipid extraction on the interpretation of fish community trophic relationships determined by stable carbon and nitrogen isotopes

Stable isotopes of carbon (C) and nitrogen (N) are commonly used to evaluate trophic relationships and food web structure; however, the decision to extract lipids or not may influence the interpretation of results. Lipid extraction is not a universal practice, thus pooling or comparing results across studies may not always be appropriate. Additionally, common lipid extraction techniques remove not only lipids, but also N-containing compounds that may alter the δ 15 N value of a sample. We examined differences in the interpretation of fish community trophic structure derived from δ 13 C and δ 15 N stable isotope data based on lipid-extracted and nonextracted samples from nine freshwater fish species. Lipid extraction significantly increased δ 13 C and δ 15 N, causing a positive shift in overall food web placement. The magnitude of isotopic change did not, however, differ among species, such that the overall interpretation of the fish community structure was not altered. The consistent increase in both C and N isotopes did, however, significantly alter the placement of the food web in coordinate space relative to nonextracted webs. Cross-study comparisons need to consider these procedural inconsistencies when drawing conclusions from multiple studies.