Effects of storage and preservation on the delta C-13 and delta N-15 signatures of selected marine organisms

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 VC and WIN, 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 delta C-13 values by similar to0.6 to 1.5 % after 1 to 12 wk in both the animals and the kelp. The delta N-15 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 VC analysis as the effects of preservatives on carbon isotope signatures vary greatly between species and studies. In contrast, the effect of preservatives on delta N-15 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. delta C-13 exhibited a significant increase after 6 h and delta N-15 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 delta N-15 analysis and organisms should be sacrificed immediately after collection.