Lipid extraction has little effect on the δ15N of aquatic consumers

Travis Ingram, Blake Matthews, Chris Harrod, Tom Stephens, Jonathan Grey, Russell Markel, Asit Mazumder

Limnol. Oceanogr. Methods 5:338-342 (2007) | DOI: 10.4319/lom.2007.5.338

ABSTRACT: Proper application of stable isotopes (e.g. δ15N and δ13C) to food web analysis requires an understanding of all non-dietary factors that contribute to isotopic variability. Lipid extraction is often used during stable isotope analysis (SIA), because synthesized lipids have a low δ13C and can mask the δ13C of a consumer's diet. Recent studies indicate that lipid extraction intended to adjust δ13C may also cause shifts in δ15N, but the magnitude of and reasons for the shift are highly uncertain. We examined a large data set (n = 854) for effects of lipid extraction (using Bligh & Dyer's (1959) chloroform-methanol solvent mixtures) on the δ15N of aquatic consumers. We found no effect of chemically extracting lipids on the δ15N of whole zooplankton, unionid mussels and fish liver samples, and found a small increase in fish muscle δ15N of ~0.4‰. We also detected a negative relationship between the shift in δ15N following extraction and the C:N ratio in muscle tissue, suggesting that effects of extraction were greater for tissue with lower lipid content. As long as appropriate techniques such as Bligh & Dyer (1959) are used, effects of lipid extraction on δ15N of aquatic consumers need not be a major consideration in the SIA of food webs.