The Use and Interpretation of δ 13 C Values as a Means of Establishing Dietary Composition

Abstract

The use of 613C values as a means of establishing the fractional composition of estuarine invertebrate diets is investigated, with particular reference to the invasive C4 cord-grass, Spartina anglica. Organisms from salt-marsh and mudflats were sampled at two sites, in Essex and Suffolk, and local carbon sources analysed. It is demonstrated that assumptions regarding the availability of potential food sources can result in differing interpretations of results obtained. Interpretation of 613C values is more robust to other assumptions, nonetheless, where dietary habits can shift rapidly, it is unlikely that analysis of 63C values will adequately reflect this. Additionally, analysis of carbon isotope ratios cannot be used to determine trophic levels.