An arithmetic correction for the effect of lipid on carbon stable isotope ratios in muscle and digestive glands of the American lobster (Homarus americanus)

Fischer-Rush, Jonathan; Rochette, Remy; Paton, Emily; Dickey, Alexandra; Hayden, Brian

University of New Brunswick

Lipid correction models, which use elemental carbon:nitrogen ratios to estimate the effect of lipids on δ13C values, provide a fast and inexpensive alternative to chemically removing lipids from animal tissues prior to analysis. However, the performance of these models varies, especially in whole body invertebrate samples.  We generated tissue-specific lipid-correction models to account for the influence of lipid on the δ13C values in muscle and digestive glands of American lobsters, an economically and ecologically important species in Eastern North America. Isotope analysis was conducted to determine δ13C and δ15N values before and after lipid extraction, and four different models were assessed to predict post-extraction δ13C based on the pre-extraction isotope values and the C:N ratios. Accuracy of model predictions was tested using paired t-tests, and the performance of the different models was compared using Akaike information criterion (AIC) score. The accuracy of each model’s assessment of post-lipid extraction δ13C varied between tissues, however, a natural logarithmic model, preformed the best in both tissues and produced estimates of lipid-free δ13C which did not significantly differ from the measured values. Whereas previous work has found that whole-body models poorly estimate lipid bias in invertebrates, we show that non-linear, tissue-specific lipid-correction models can generate accurate estimates of lipid free δ13C values in lobster.