Analysis of stable carbon and nitrogen isotopes as a tool for assessing the environmental impact of aquaculture: a case study from the western Mediterranean

Stable carbon and nitrogen isotope ratios (13C/12C and 15N/14N) of in situdominant primary producers and consumers were investigated to assess the impact on anatural ecosystem of a land-based fish farm along the south-western coast of Sicily(Italy). The putatively impacted area close to the farm along outfall was compared withother locations at increasing distances from the outfall. Carbon and mainly nitrogenstable isotopes revealed evidence of widespread aquaculture waste in the study site:benthic organisms collected in the impacted area showed more enriched d15N signaturesthan those at greater distances from the outfall, suggesting a large contribution ofaquaculture waste to the food web. By contrast, both nekton-benthic and pelagicorganisms seemed to be less influenced by discharge, probably due to their mobile habit.