Effects of ethanol-preservation on stable carbon and nitrogen isotopic signatures in marine predators

抄録

The effect of 70% ethanol preservation (for three days) on bulk stable isotope measurements of carbon and nitrogen in marine predators (squid and fish) were examined. A total of 17 different species collected from a wide range of latitudes (15°S–65°N) in the Pacific Ocean were used in the analysis. In agreement with previous studies, ethanol preservation significantly increased δ¹⁵N by 0.8–1.7‰ relative to frozen control samples, regardless of species. Ethanol enriched δ¹³C of squid mantle tissue as well, but showed variable alterations in fish muscle compared with the control (lipids extracted by chloroform and methanol). An additional extraction treatment with 99.5% ethanol increased δ¹³C by 1.3–2.0‰ for squid, and by 0.3–1.3‰ for fish relative to the control, without a further shift of δ¹⁵N, and reduced the variability of δ¹³C alterations of fish muscle. After this treatment, both δ¹⁵N and δ¹³C of the controls could be estimated from the samples preserved in ethanol by fitting to regression lines with high correlation coefficients (r²>0.90). These results suggest that, with additional treatment, marine predator samples preserved in 70% ethanol are able to be used for stable isotopic analysis.