Influence of artificial reefs on coastal nekton assemblages of the Gulf of Castellammare (northwest Sicily)

An artificial reef, of 32 pyramids of concrete block, was built in the coastal waters of the Gulf of Castellammare (NW Sicily) during 1986-1989. Our research objective was to compare the catches and nekton assemblage structure of this reef with those of surrounding natural habitats. Surveys were carried out in 1990-1991 at three different sites: the artificial reef area (ARA), a natural rocky area (NRA) and a control area on a sandy bottom (CA). A trammel net was used to obtain samples at each site, and a qualitative visual assessment of the fish assemblage of ARA was also carried out. Quantitative analysis showed that ARA had significantly more species and a greater number of specimens than CA but no significant difference in catches was recorded, while a general similarity in the nekton assemblage was found comparing ARA and NRA. Overall, ARA displays features intermediate between the two natural sites tested, and the variability of its assemblage could be attributed to the availability of shelter and to the benthic settlement on the concrete boulders. This study is an attempt to understand the role played by artificial reefs in influencing the composition of nekton assemblages in oligotrophic waters, such as those in the southern Tyrrhenian Sea.