The effect of ethanol fixation on stable isotope signatures in benthic organisms

Abstract

Stable isotope analyses are often used for the estimation of food web structures based on empirical fractionation (i.e., enrichment of carbon isotope signatures at 0-1‰ with one trophic level, and that of nitrogen at 3-4‰). We examined the effect of 80% ethanol fixation on both carbon and nitrogen stable isotope signatures of six species of macrobenthos samples. The effect of fixation was inconsistent (i.e. both enrichment and depletion occurred). The shift of nitrogen isotope signatures due to fixation ranged from Ϫ0.3 to ϩ0.8‰, and the carbon signatures of fixed samples showed enrichment by Ϫ0.3 to ϩ1.3‰ depending on the species. These changes would clearly affect estimation of trophic levels and energy flow in food webs. Ethanol fixation may not be a smart choice because of the inconsistency of the effect on isotope signatures. However, if the effect was corrected for each species, ethanolfixed samples can be practically useful for food web analyses using stable isotopes.

Reciprocal trophic niche shifts in native and invasive fish: salmonids and galaxiids in Patagonian lakes

“…Fortunately, the bias can be corrected through experiments contrasting an ethanol preservation treatment to a control treatment (Kelly, Dempson & Power, 2006;Barrow Lindy, Bjorndal Karen & Reich Kimberly, 2008;Yoshino et al, 2010). In our study, however, ethanol preservation was necessary because sampling took place in remote areas where no better preservation method was available.…”

“…In our study, however, ethanol preservation was necessary because sampling took place in remote areas where no better preservation method was available. Fortunately, the bias can be corrected through experiments contrasting an ethanol preservation treatment to a control treatment (Kelly, Dempson & Power, 2006;Barrow Lindy, Bjorndal Karen & Reich Kimberly, 2008;Yoshino et al, 2010). Correa (in press) conducted such an experiment by comparing, for a sample of each species, stable isotope measurements from tissue preserved in ethanol (treatment) versus tissue preserved by freezing for <5 day and then drying (control).…”