Analysis of the efficacy of artificial reefs located in five different areas of the Adriatic Sea

Five artificial reefs of identical design, but of different size, were constructed along the Italian Adriatic coast between 1987 and 1988, at depths ranging from 10 to 14 m. Four reefs were deployed on sandy-muddy bottom far from natural reefs, while the fifth was placed in a bay surrounded by rocky shores. The reefs were formed of cubic concrete blocks (2 X 2 X 2 m) arranged in pyramids. Concrete cages (4 X 6 X 5 m) for shellfish culture were placed among the pyramids. Underwater observations and sampling showed rapid colonization of the concrete block reefs at all locations. The sessile community was dominated by filterfeeders, mainly represented by mussels (Mytilus galloprovincialis) and oysters (Ostrea edulis and Cras.wstrea gigas). At all sites, fishing surveys conducted with a standard trammel net were started I year before reef deployment and have been continued. The aim was to compare the effectiveness of the reefs in the different areas in terms of fishing yield and their impact on the fish assemblage of the original habitat. The effects of the artificial reefs were particularly evident at sites far from natural hard substrates. Catches at these sites after reef deployment showed a gradual increase in fish abundance, in species richness (both mean and total) and diversity. Evidence for this was the appearance and/or the increase in catches of some hard-substrate species of fish (e.g., Sciaena umbra, Umbrina cirrosa and Scorpaena porcus) and molluscs (Eledone moschata and Rapana venosa) which were rare or completely absent in the original sand-plain habitat. The increase of these species seemed to be directly correlated to the reef dimensions in terms of volume of immersed materials and of area covered. Different results were obtained at the site near natural hard substrates, where many reef-dwelling species were also caught before the reef construction, and total richness was already very high (49 species caught) in comparison to the other four sites (22-31 species).