The inter-relationships between the fish assemblage of experimental artificial reefs (ARs), four 1.2m sided concrete cubes, and those of the surrounding natural habitats were investigated. ARs were deployed in 20m of water on a flat, rocky substrate offshore Haifa. Variables investigated were: recruitment and colonization rates, enrichment or depletion of the surrounding seabed, radius of influence, affinity of commercial fish and the proportion of Lessepsian migrants in the assemblages. Data collected by SCUBA over 12 months, included fish species and number, relative size and spatial location in relation to the AR units. Censuses were performed in pre-deployed 5X5m quadrates marked with lines around each unit and at set distances from the unit on the surrounding seabed as well as in complex and flat natural rocky control areas. Stills and video photography supplied complementary information. AR units were found to contain a mean of 85.7 individuals and 7.6 species per quadrate and contribute 237g/m2/yr of biomass. These numbers are 2 and 5 times the density, 1.15 and 2.22 times the richness and 5 and 20 times the biomass of complex and flat control quadrate values. ARs also encouraged recruitment of Lessepsian migrants: they contribute 65.3% of the commercially valuable fish biomass and 25.2% of the individuals in the ARs. This compare to 30% and 40.1% of the biomass and 11.9% and 2.1% of the abundance in complex and plain control quadrates respectively. The AR was found to enrich the surrounding habitat in a radius of ~20m. Yet, an inner halo of relative depletion was created around the units in a 3-10m radius. This halo is apparent in density, biomass and species richness and diversity. It is postulated that when fish get within sensory distance from the AR they prefer to get closer within a radius of 3m from it.
