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

Abstract

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%0 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%0 for squid, and by 0.3–1.3%0 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.