Influence of sample preparation on estuarine macrofauna stable isotope signatures in the context of contaminant bioaccumulation studies

Abstract

The ratios of stable isotopes of carbon and nitrogen provide important information on food sources of aquatic organisms and trophic structure of aquatic food webs. For many studies, trophic position and food source are linked to bioaccumulation and trophic transfer of contaminants from prey to predators. In these cases, it is useful to use measurements on whole organisms to make direct comparisons of contaminant bioaccumulation and food web attributes. There is a great deal of variation in methods used for stable isotope analysis, particularly in the selection of tissue type and sample preparation prior to stable isotope analysis. While there have been aquatic studies that examined methodological differences, few have focused on estuarine organisms. In this study, the effects of depuration and tissue dissection on the stable isotope enrichment of common estuarine invertebrates and fish were examined. Homogenized tissues of non-depurated whole organisms were compared to dissected muscle tissue or depurated whole organisms. A 24 h depuration did not change the mean δ15N and δ13C values for most species examined. Additionally, as expected, significant differences in carbon and nitrogen signatures were found when muscle tissues were compared to whole organisms. However, differences were small enough that food source as inferred by δ13C or trophic level as inferred from δ15N would not be inaccurately represented (differences of <1.9‰ for δ13C and <1.2‰ for δ15N). The results of this study suggest that for these common estuarine fish and macroinvertebrates, stable isotopes ratios of samples can be analyzed without depuration in the same way as samples for contaminant analysis, but differences in tissue types must be taken into account when combining data from different sources.

Implications of Trophic Variability for Modeling Biomagnification of POPs in Marine Food Webs in the Svalbard Archipelago

“…Variation in biomagnification may be induced by different individual-specific covariates, such as length or lipid content, or methodological differences pertaining to the sampling protocol (i.e., sampling tissue). 25,62,63 Computed median TMFs in this study were slightly lower thanbut within a factor of 2 ofthe corresponding obtained TMFs gathered by Walters et al 41 (see Table S8 in the Supporting Information). While standard errors for TMFs in the study by Walters et al were relatively high, our computed TMFs were not significantly different from these measured TMFs.…”

Abundant Chitinous Structures in Chilostomella (Foraminifera, Rhizaria) and Their Potential Functions

“…We speculate that because the synthetic cost of the chitinous plates is substantial, the balance of C metabolism in C. ovoidea is likely to be different from other foraminiferal species. For instance, 12 C may be preferentially used for chitinous plate synthesis and other organic compounds consequently become enriched in 13 C. Differences in d 13 C values between chitinous exoskeletons and soft tissue have been reported for some crustaceans, including by 1.5& in the green crab Carcinus maenas (Curtis et al 2017), supporting this speculation. However, we cannot evaluate these factors quantitatively because the information on the synthetic pathway of chitin in foraminifera, and its frequency and turnover rates are not available.…”