The aim of the present study was to quantify the effect of formalin-ethanol preservation on the carbon and nitrogen stable isotope values of five deep-sea species (Abra longicallus, Molpadia musculus, Sipunculus norvegicus, Chirimia biceps and Nephthys hystricis). To examine temporal changes in the effects of preservation and to determine if preservation induces predictable shifts in δ13C and δ15N values, analyses were carried out after 1, 6 and 12months of preservation. The data indicated variable effects on carbon and nitrogen isotope values among species after formalin and ethanol preservation. Formalin fixation did not affect δ15N values of any of the five species analysed, while it did affect δ13C values, with a depletion trend observed in all of the species. In general ethanol preservation did not affect nitrogen values for up to 6months of preservation, and only the δ15N values of S. norvegicus became depleted after 12months. Ethanol fixation only affected the carbon isotopic composition of M. musculus, with a progressive depletion from 1 to 12months after preservation. Due to the different effects of preservation on stable isotope values, the use of a general and systematic correction factor was not possible. Since no effect on δ15N values of either formalin or ethanol fixation is evident after 6months, we recommend that these methods be used for short-term (<6months) conservation and only if studies are focused on the identification of trophic levels. If changes in carbon and nitrogen isotopic values from long-preserved samples are to be used for reconstructing a food web, it is necessary to establish the effects of preservation in the whole spectrum of species evaluated. © 2010 Elsevier B.V.

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