Patterns of Sessile Macrobenthos Community Development on an Artificial Reef in the Gulf of Genoa (Northwestern Mediterranean)

The aim of this study is to increase our knowledge of short-term (month) and long-term (3 year) trends in communities settled on hard artificial substrata at different depths off Loano (Lat. 44°07′22″ Long. 8°16′25″). An artificial reef complex was built in response to protection, mitigation and restoration needs in an area subjected to illegal trawling, destruction of seagrass beds and the discharge of muddy material. The reef complex consisted of large concrete blocks (2 × 2 × 2 m) arranged in pyramids and single small concrete blocks (1.2 × 1.2 × 1.2 m). Short-term observations were intended to show seasonal changes in the settlement periods for exploitable resources such as oysters (Ostrea edulis). The long-term investigations were intended to show the pattern of sessile biota development, climax stages and interaction with fishes. To accomplish these objectives, asbestos panels (20 × 30 × 0.4 cm) were immersed for 1, 3, 6, 9 and 12 months at four stations in different depths. Photographic and removal sampling have been used since 1986. Results indicated consistent increases in biomass, cover and number of sessile species with time of panel immersion. Decreases were observed in relation to depth, particularly from stations at −18 m to −30 m. Similar patterns of community development occurred over all 3 years. After 1 year the community was dominated by encrusting bryozoans, serpulids, hydroids, barnacles, ascidians, bivalves and algae (also Corallinaceae), although they occurred in different proportions according to depth. Mussels were never dominant, as has been described for other artificial reefs in the Adriatic (Ancona) and Middle Tyrrhenian Sea (Fregene). The activity of the sea-urchins Paracentrotus lividus and Arbacia lixula in cleaning the substrata is described. Five years after the immersion of concrete blocks a climax has not yet been reached. The community is still changing: in particular large algae and sponges are increasing.