A large complex of artificial reefs was deployed in the Bay of Marseilles, North-Western
Mediterranean, for the enhancement of commercial fisheries stocks. Carbon and nitrogen stable
isotope and stomach content analyses were performed on 23 fish species collected on the artificial
reefs to assess their trophic position and feeding behaviour. Results indicated that fish diets were not
modified on the artificial reefs compared to natural environments, nor was the structure of their trophic
network. Artificial reefs, with their complex design, provide diverse and abundant food sources for
fishes. Ranges of δ
13C and δ
15N of artificial reef fishes were comparable to those recorded in natural
Mediterranean environments, with a similar trophic organization. However, some discrepancies
appeared when comparing fish trophic level based on isotopic or diet results, which calls for a careful
interpretation of stable isotope values as direct indicators of trophic level.