Effects of storage and preservation on the δ13C and δ15N signatures of selected marine organisms

Abstract

The effects of freezing, oven-drying, and formalin and ethanol preservation on stable isotope signatures of 3 unrelated marine species (fish, octopus and kelp) were studied over a period of 3 mo to investigate temporal changes in δ13C and δ15N. The effects on stable isotope ratios during the short-term confinement of live littorinid snails were also examined. Freezing and oven-drying did not result in a significant change in the initial isotope ratio for both carbon and nitrogen over the period of investigation. Formalin preservation significantly decreased, while ethanol preservation significantly increased δ13C values by ∼0.6 to 1.5% after 1 to 12 wk in both the animals and the kelp. The δ15N signatures tended to increase slightly, but not significantly, during both formalin and ethanol preservation. Data from this and previous studies suggest that preserved samples should not be used for δ13C analysis as the effects of preservatives on carbon isotope signatures vary greatly between species and studies. In contrast, the effect of preservatives on δ15 N signatures was comparatively small, which may facilitate the use of preserved samples in studies of stable nitrogen isotopes. Animal confinement had an almost immediate effect on stable isotope signatures of littorinids. δ13C exhibited a significant increase after 6 h and δ15N became significantly depleted after 12 h of confinement. The results of this study suggest that the methods used for preserving samples for stable isotope analysis should be carefully chosen. Samples intended for isotope analysis should be frozen, freeze-dried or oven-dried, preservatives may be used only for δ15N analysis and organisms should be sacrificed immediately after collection.