MEPS 219:299-304 (2001)  -  doi:10.3354/meps219299

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 δ¹⁵N 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.

KEY WORDS: Stable isotopes · Preservation · Storage · Fish · Octopus · Kelp · Littorinid