Is acidification of common estuarine macroinvertebrates in stable isotope approaches necessary to analyze aquatic food webs?

Abstract We evaluated the effect of in situ acidification of common estuarine macroinvertebrates from the Elbe estuary on stable isotope ratios, as the non‐removal of non‐dietary carbon can significantly influence aquatic food web analyses. A 10% HCl solution was used to remove inorganic carbon from crustaceans, which potentially biases the true ratio of assimilated dietary carbon. We detected significant differences in the δ 13 C values of all investigated crustaceans except for the mysid shrimp Mesopodopsis slabberi after acid treatment. On the contrary, acidification impacts on δ 15 N were only observed in Gammarus spp. samples. A carbonate proxy was additionally computed to evaluate the necessity of acidification because high values indicate high inorganic carbon in the tissue that may alter true δ 13 C values. Our results indicate that the necessity of acid treatment of common estuarine macroinvertebrates before stable isotope analysis depends on the species‐specific carbonate content. Acid treatment is therefore not required for all species when analyzing aquatic food webs.