Artificial reefs do increase secondary biomass production: mechanisms evidenced by stable isotopes

Abstract

A large complex of artificial reefs was deployed in the Bay of Marseilles, North-Western Mediterranean, forthe enhancement of commercial fisheries stocks. Carbon and nitrogen stable isotope and stomach contentanalyses were performed on 23 fish species collected on the artificial reefs to assess their trophic position andfeeding behaviour. Results indicated that fish diets were not modified on the artificial reefs compared to naturalenvironments, nor was the structure of their trophic network. Artificial reefs, with their complex design, providediverse and abundant food sources for fishes. Ranges of δ13C and δ15N of artificial reef fishes were comparable tothose recorded in natural Mediterranean environments, with a similar trophic organization. However, somediscrepancies appeared when comparing fish trophic level based on isotopic or diet results, which calls for acareful interpretation of stable isotope values as direct indicators of trophic level.