Effects of preservation methodology on stable isotope compositions of sea stars

Abstract

Rationale:Stable isotope analysis is used to investigate the trophic ecology of organisms and, in order to use samples from archived collections, it is important to know whether preservation methods alter the results. This study investigates the long-term effects of four preservation methods on isotopic compositions and isotopic niche parameters of sea stars. Methods:We assessed the effects of preservation method (freezing, drying, formaldehyde, ethanol) and duration (0, 1, 3, 6, 9, 12, 24 months) on the stable isotope ratios of carbon, nitrogen and sulfur of sea star tissues. Isotopic ratios were measured using continuous-flow elemental analysis and isotope ratio mass spectrometry. We also monitored the evolution of commonly used ecological metrics (isotopic niche parameters) throughout the experiment. Results: Clear changes in δ 13 C values were observed for samples stored in formaldehyde and ethanol. None of the preservation methods had significant or consistent effects on δ 15 N values. Formaldehyde preservation induced a decrease in δ 34 S values. All these changes could be mitigated using correction factors. Isotopic niche parameters slightly changed over time when computed with δ 13 C and δ 15 N values, but inconsistent variations occurred when computed with δ 13 C and δ 34 S values.Conclusions: Overall, these results show that preservation may affect the stable isotope ratios of sea stars. Correction factors can be used to mitigate the effects of the preservation method on stable isotope ratios. Isotopic niche parameters are overall unchanged. Consequently, in most cases, museum samples are suitable for calculation of isotopic niche parameters.

Toward a reliable assessment of potential ecological impacts of deep‐sea polymetallic nodule mining on abyssal infauna

“…For stable isotope analysis, samples should be stored frozen (−20°C or lower), oven‐dried, or freeze‐dried. In both cases, chemical preservatives (formalin, ethanol) should be avoided as they can may alter samples and influence measurements (Bosley and Wainright 1999; Carabel et al 2009; Couturier et al 2020; Le Bourg et al 2020).…”

Quantitative Food Webs Indicate Modest Increases in the Transfer of Allochthonous and Autochthonous C to Macroinvertebrates Following a Large Wood Addition to a Temperate Headwater Stream

“…was 36.94 ± 0.2 (upper confidence interval = 1 and lower confidence interval = 0.97) across our sample period, indicating separation of the two C sources. δ 13 C signatures were not corrected for C fractionation rates as they are likely low and unpredictable (McCutchan et al, 2003).…”

Intra-Body Variations of Stable Isotope Ratios (δ13C, δ15N) and Influence of Storage Methods in Aquatic and Post-Aquatic Stages of the Common Toad, Bufo bufo

“…Another important question relates to the methods of material preservation prior to isotopic analysis. Freeze drying and subsequent dry storage is considered the most convenient conservation method [33], which does not affect the isotopic composition of the material [34][35][36]. However, the use of a freeze-dryer for the preservation of samples during field studies is very difficult, since this is a piece of stationary laboratory equipment that is difficult to transport to the field.…”

“…Under these conditions, samples can be frozen in the freezer of a household or mobile refrigerator (usually at −18 • C) or fixed with preservative liquids, among which ethanol is most frequently used [37]. However, ethanol is known to alter stable isotope ratios in samples [27,36,38]. Furthermore, the impacts of storage methods are taxon-specific, age-specific (see e.g., [33,39,40]) and can even be tissue-specific.…”