Measuring Stable Carbon and Nitrogen Isotopes in Mytilus galloprovincialis to Elucidate the Sources of Organic Matter in Three Different Nearshore Marine Environments

Stable carbon and nitrogen isotopes (delta C-13 and delta N-15) in mussels (Mytilus galloprovincialis) were used to elucidate the sources of sedimentary organic matter in nearshore marine environments at three different locations: (1) Naples harbour, (2) Formia harbour, and (3) Gulf of Gaeta (Tyrrhenian Sea). The sites showed different environmental characteristics, with the latter one considered as the control site, because it hosts "mussel farms'' cultivated for human food. Significant differences in both delta C-13 and delta N-15 were found at Naples harbour compared to the other two sites. In particular, the lowest delta N-15 (> 4%) and the highest delta C-13 (>= 1.6%) values were found in mussels collected in Naples harbour, while similar delta C-13 and delta N-15 values were detected in Formia harbour and in the Gulf of Gaeta. As shown by a Stable Isotope Analysis in R (SIAR)-mixing model, N-15-depleted and C-13-enriched mussels highlight the influence of anthropogenic inputs on this area, particularly of organic fertilizers.