Effects of preservatives on stable isotope analyses of four marine species

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“…Storage in ethanol after 14-d formalin fixation might have led to the dissociation of formaldehyde-protein bonds previously formed within the samples. Carabel et al (2009) also showed that d 13 C signals of marine invertebrates were mostly indistinct between frozen samples and those preserved in formalinethanol after 6-24 months. Our results for fishes contradict with Arrington and Winemiller (2002) who found that formalin-ethanol preserved fish samples were 13 C-depleted (-1.12 ± 0.07‰) relative to frozen conspecifics; however, the preservation period extended for only 6 weeks compared to almost 1 y in the present study, and the Hong Kong fishes also showed 13 C-depletion (-0.49‰ to -2.00‰, -1.40‰ on average) at Days 30 and 60 (Table 3).…”

“…For instance, effects of formalin and ethanol preservation on d 15 N signatures have been Preservation effects on C/N ratios and stable isotope signatures of freshwater fishes and benthic macroinvertebrates reported to vary within major taxa such as fish (mean range = -0.13‰ to 1.41‰) and insects (-1.24‰ to 0.27‰) (Sarakinos et al 2002;Vander Zanden et al 2003;Syväranta et al 2008), suggesting that preservation effects should not be overgeneralized within or among taxa (Carabel et al 2009). Vander Zanden et al (2003 suggested formalin preservation results in an overall 13 C-depletion of 1.77 ± 0.52‰ in freshwater invertebrates, but more recent studies involving a greater variety of aquatic invertebrate taxa indicate that formalin did not cause significant shifts in d 13 C (Syväranta et al 2008;Carabel et al 2009). Formalin-preserved fishes became 13 C-depleted, but the magnitudes varied among species (-0.03‰ to -2.17‰); in contrast, ethanolpreserved fishes underwent slight 13 C-enrichment (0.7‰ to 0.…”

“…Inconsistencies in the type or concentration of preservatives, and variations in preservation duration, also reduce the robustness of isotope-based trophic comparisons among stored samples, and these effects may be taxon-specific (e.g., Vander Zanden et al 2003, and references therein; Syväranta et al 2008;Carabel et al 2009). For instance, effects of formalin and ethanol preservation on d 15 N signatures have been Preservation effects on C/N ratios and stable isotope signatures of freshwater fishes and benthic macroinvertebrates reported to vary within major taxa such as fish (mean range = -0.13‰ to 1.41‰) and insects (-1.24‰ to 0.27‰) (Sarakinos et al 2002;Vander Zanden et al 2003;Syväranta et al 2008), suggesting that preservation effects should not be overgeneralized within or among taxa (Carabel et al 2009). Vander Zanden et al (2003 suggested formalin preservation results in an overall 13 C-depletion of 1.77 ± 0.52‰ in freshwater invertebrates, but more recent studies involving a greater variety of aquatic invertebrate taxa indicate that formalin did not cause significant shifts in d 13 C (Syväranta et al 2008;Carabel et al 2009).…”

“…Despite this, some isotope-based trophic studies have used preserved samples without correction for any preservation effects, particularly in instances when concurrent gut-content analyses mandated some form of sample preservation (e.g., Hall et al 2001;Mantel et al 2004). Inconsistencies in the type or concentration of preservatives, and variations in preservation duration, also reduce the robustness of isotope-based trophic comparisons among stored samples, and these effects may be taxon-specific (e.g., Vander Zanden et al 2003, and references therein; Syväranta et al 2008;Carabel et al 2009). For instance, effects of formalin and ethanol preservation on d 15 N signatures have been Preservation effects on C/N ratios and stable isotope signatures of freshwater fishes and benthic macroinvertebrates reported to vary within major taxa such as fish (mean range = -0.13‰ to 1.41‰) and insects (-1.24‰ to 0.27‰) (Sarakinos et al 2002;Vander Zanden et al 2003;Syväranta et al 2008), suggesting that preservation effects should not be overgeneralized within or among taxa (Carabel et al 2009).…”

“…Syväranta et al (2008) likewise noted variable 13 C-enrichment over time among three zooplankton taxa preserved in ethanol for 12 months, but there was no overall difference between preserved and frozen samples because of high between-sample variability. Formalin-ethanol preservation caused consistent 15 N-enrichments of two marine molluscs relative to frozen conspecifics over a 24-month period, but effects on other taxa were variable over time (Carabel et al 2009). …”