Effect of lipid removal on carbon and nitrogen stable isotope ratios in crustacean tissues

The analysis of tissue's naturally occurring stable carbon and nitrogen isotope ratios is a useful tool to delineate trophic relationships. However, the interpretation of δ13C and δ15N is complicated by the influence of multiple factors such as the tissue-specific lipid content. The aim of this work was to evaluate the effects of lipid extraction on δ13C and δ15N compositions in muscle, hepatopancreas and gonads of a marine decapod crustacean, the spider crab Maja brachydactyla. Samples were analyzed for stable isotopes before and after lipid removal, using a derived Soxhlet extraction method. Differences in δ13C and δ15N were measured among tissues before and after treatment. Lipid extraction of muscle did not have a significant effect on either δ13C or δ15N. By contrast, ecologically significant shifts for both carbon and nitrogen stable isotopes ratios (+ 2.9 ± 0.8‰ for δ13C, and + 1.2 ± 0.7‰ for δ15N) were noticed in the hepatopancreas. In regard to gonads, lipid extraction led to a shift only on δ13C (+ 1.3 ± 0.3‰). Finally, the derived Soxhlet extraction method removed the lipid influence for δ13C, and had an effect on δ15N composition for lipid-rich samples. We recommend this treatment for carbon stable isotope studies on decapod crustacean lipid-rich tissues.