Freezing and chemical preservatives alter the stable isotope values of carbon and nitrogen of the Asiatic clam (Corbicula fluminea)

Abstract

International audienceWe tested the impacts of most common sample preservation methods used for aquatic sample materials on the stable isotope ratios of carbon and nitrogen in clams, a typical baseline indicator organism for many aquatic food web studies utilising stable isotope analysis (SIA). In addition to common chemical preservatives ethanol and formalin, we also assessed the potential impacts of freezing on δ¹³C and δ¹⁵N values and compared the preserved samples against freshly dried and analysed samples. All preservation methods, including freezing, had significant impacts on δ¹³C and δ¹⁵N values and the effects in general were greater on the carbon isotope values (1.3-2.2% difference) than on the nitrogen isotope values (0.9-1.0% difference). However, the impacts produced by the preservation were rather consistent within each method during the whole 1 year experiment allowing these to be accounted for, if clams are intended for use in retrospective stable isotope studies

Preservation effects on stable isotope ratios and consequences for the reconstruction of energetic pathways

“…The reported isotopic shift is typically small (within 2%) and comparable with the isotopic shifts observed in ecosystem reconstruction using the isotopic signatures of archived sample material (Pruell et al 2003;Solomon et al 2008;Wainright et al 1993). Previous studies have shown that the effects of preservation on stable isotopes depend on organisms and preservatives and are often inconsistent and variable (Barrow et al 2008;Kelly et al 2006;Schmidt et al 2009;Syvaranta et al 2008Syvaranta et al , 2010. These methodological inconsistencies inhibit our ability to appropriately pool data across studies and may adversely affect data interpretation within studies.…”

“…(e.g., Arrington and Winemiller 2002;Barrow et al 2008;Syvaranta et al 2008Syvaranta et al , 2010Ventura and Jeppesen 2009). Our results show that the d 13 C values of every fish species preserved in formalin were depleted with an average about -1% relative to their controls.…”

“…This is comparable with the freezing and freeze-drying methods. For instance, some studies that evaluated the effects of freezing found non-significant shifts in isotope values (Gloutney and Hobson 1998;Kaehler and Pakhomov 2001;Sweeting et al 2004), while other studies found that both d 13 C and d 15 N were significantly altered from the control (Barrow et al 2008;Dannheim et al 2007;Feuchtmayr and Grey 2003;Syvaranta et al 2010). Based on these results, drying seems to be the most suitable preservation method over extended periods, compared with the significant bias caused by chemical preservatives, such as salt, formalin, and ethanol preservation, and even freezing methods (Barrow et al 2008;Kaehler and Pakhomov 2001;Syvaranta et al 2010).…”

Preservation methods alter stable isotope values in gelatinous zooplankton: implications for interpreting trophic ecology

“…Feuchtmayr and Grey 2003;Carabel et al 2009;Syväranta et al 2011). Although these shifts appear less pronounced than they are for 13 C (Bosley and Wainwright 1999;Kaehler and Pakhomov 2001), they are important to consider as 15 N can elucidate the trophic relationships or identify the ecological niche occupied by an organism (consumer) within a food web Epstein 1978, 1981;Post 2002;Wallace et al 2009).…”

“…Lovelock 1957;Jiang et al 1987;Wroblowski et al 1996). This idea is supported by evidence of protein denaturation in a range of Wsh (Mackie 1993;Paredi et al 2010), cephalopod (Paredi et al 2006;Reyes et al 2009) and bivalve species (Makri 2010;Syväranta et al 2011). What is clear, however, is that although freezing is often considered the preferred method of sample preservation for isotope studies, it is not a panacea and the assumptions of no preservation eVect of freezing should not be taken for granted.…”