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Lipid Correction for Carbon Stable Isotope Analysis of Deep-sea Fishes
Citation:
HOFFMAN, J. AND T. T. SUTTON. Lipid Correction for Carbon Stable Isotope Analysis of Deep-sea Fishes. Deep Sea Research Part I: Oceanographic Research Papers. Elsevier BV, AMSTERDAM, Netherlands, 57(8):956-964, (2010).
Impact/Purpose:
Our objective was to evaluate an application of a mass balance correction for the effect of lipid content on the d13C of muscle tissue in 30 of 41 examined species of mesopelagic, bathypelagic, and bathydemersal fishes from the North Atlantic.
Description:
Lipid extraction is used prior to stable isotope analysis of fish tissues to remove variability in the carbon stable isotope ratio (d13C) caused by varying lipid content among samples. Our objective was to evaluate an application of a mass balance correction for the effect of lipid content on the d13C of muscle tissue in 30 of 41 examined species of mesopelagic, bathypelagic, and bathydemersal fishes from the North Atlantic. We measured the effect of lipid extraction on the d13C and nitrogen stable isotope ratio (d15N) of muscle tissue. Lipid-extraction significantly enriched tissue d15N (+0.66‰) and d13C (+1.83‰), and decreased the average and variation in C:N. The treatment effect on d15N and C:N did not vary in relation to C:N, a proxy for lipid content, whereas the effect on d13C did. To apply the C:N-based mass balance correction, we estimated two parameters from the data the C:N of lipid-extracted samples (C:Nprotein) and the depletion factor associated with lipid synthesis (Dd13Clipid). The average C:N (± SD) of lipid-extracted samples, C:Nprotein, was 3.76 ±0.07. The average (± SD) lipid depletion factor, Dd13Clipid, was -6.11 ±1.73‰. We then compared the lipid-extracted d13C to the corrected d13C predicted by the mass balance model using values for C:Nprotein and Dd13Clipid estimated from either all individuals (pooled) or species-by-species or using published values (C:Nprotein = 3.7, Dd13Clipid = -7‰). All three approaches produced corrected d13C values that were generally within 0.5‰ of the measured lipid-free d13C and that had a small over-all bias (<0.5‰). We conclude that the mass balance correction model works well for correcting d13C in deep-sea fishes, but recommend caution when applying to fish with low lipid content (C:N<5), owing to high variation in Dd13Clipid estimates, and fish with high lipid content (C:N>8) owing to small sample sizes in this range.