Urea and lipid extraction treatment effects on delta N-15 and delta C-13 values in pelagic sharks

作者：Li, Yunkai; Zhang, Yuying; Hussey, Nigel E.; Dai, Xiaojie^*

来源：Rapid Communications in Mass Spectrometry, 2016, 30(1): 1-8.

DOI：10.1002/rcm.7396

• STABLE-ISOTOPE RATIOS
• FISH-TISSUES
• ELASMOBRANCH FISHES
• TROPHIC STRUCTURE
• FOOD-WEB
• CARBON
• ECOLOGY
• FRACTIONATION
• CONSEQUENCES
• ECOSYSTEM

RationaleStable isotope analysis (SIA) provides a powerful tool to investigate diverse ecological questions for marine species, but standardized values are required for comparative assessments. For elasmobranchs, their unique osmoregulatory strategy involves retention of delta N-15-depleted urea in body tissues and this may bias delta N-15 values. This may be a particular problem for large predatory species, where delta N-15 discrimination between predator and consumed prey can be small.
MethodsWe evaluated three treatments (deionized water rinsing [DW], chloroform/methanol [LE] and combined chloroform/methanol and deionized water rinsing [LE+DW]) applied to white muscle tissue of 125 individuals from seven pelagic shark species to (i) assess urea and lipid effects on stable isotope values determined by IRMS and (ii) investigate mathematical normalization of these values.
ResultsFor all species examined, the delta N-15 values and C:N ratios increased significantly following all three treatments, identifying that urea removal is required prior to SIA of pelagic sharks. The more marked change in delta N-15 values following DW (1.3 0.4 parts per thousand) and LE+DW (1.2 +/- 0.6 parts per thousand) than following LE alone (0.7 +/- 0.4 parts per thousand) indicated that water rinsing was more effective at removing urea. The DW and LE+DW treatments lowered the %N values, resulting in an increase in C:N ratios from the unexpected low values of <2.6 in bulk samples to similar to 3.1 +/- 0.1, the expected value of protein. The delta C-13 values of all species also increased significantly following LE and LE+DW treatments.
ConclusionsGiven the mean change in delta N-15 (1.2 +/- 0.6 parts per thousand) and delta C-13 values (0.7 +/- 0.4 parts per thousand) across pelagic shark species, it is recommended that muscle tissue samples be treated with LE+DW to efficiently extract both urea and lipids to standardize isotopic values. Mathematical normalization of urea and lipid-extracted delta N-15(LE+DW) and delta C-13(LE+DW) values using the lipid-extracted delta N-15(LE) and delta C-13(LE) data were established for all pelagic shark species.

• 出版日期2016-1-15
• 单位上海海洋大学