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 delta C-13 and delta N-15 is complicated by the influence of multiple factors such as the tissuespecific lipid content. The aim of this work was to evaluate the effects of lipid extraction on delta C-13 and delta N-15 compositions in muscle, hepatopancreas and gonads of a marine decapod crustacean, the spider crab Maja brachydacryla. Samples were analyzed for stable isotopes before and after lipid removal, using a derived Soxhlet extraction method. Differences in delta C-13 and delta N-15 were measured among tissues before and after treatment. Lipid extraction of muscle did not have a significant effect on either delta C-13 or delta N-15. By contrast, ecologically significant shifts forbothearbon and nitrogen stable isotopes ratios (+2.9 +/- 0.8 parts per thousand for delta C-13, and +1.2 +/- 0.7 parts per thousand for delta N-15) were noticed in the hepatopancreas. In regard to gonads, lipid extraction led to a shift only on delta C-13 (+1.3 +/- 0.3 parts per thousand). Finally, the derived Soxhlet extraction method removed the lipid influence for delta C-13, and had an effect on delta N-15 composition for lipid-rich samples. We recommend this treatment for carbon stable isotope studies on decapod crustacean lipid-rich tissues