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 (mont h) and long-term (3 year) trends in communities settled on hard artifi cial substrata at different depths off Loano (Lat. 44 degrees 07'22'' Long. 8 degrees 16'25''). An artificial reef complex was built in resp onse to protection, mitigation and restoration needs in an area subjec ted to illegal trawling, destruction of seagrass beds and the discharg e of muddy material. The reef complex consisted of large concrete bloc ks (2 X 2 X 2 m) arranged in pyramids and single small concrete blocks (1.2 X 1.2 X 1.2 m). Short-term observations were intended to show se asonal changes in the settlement periods for exploitable resources suc h as oysters (Ostrea edulis). The long-term investigations were intend ed to show the pattern of sessile biota development, climax stages and interaction with fishes. To accomplish these objectives, asbestos pan els (20 X 30 X 0.4 cm) were immersed for 1, 3, 6, 9 and 12 months at f our stations in different depths. Photographic and removal sampling ha ve been used since 1986. Results indicated consistent increases in bio mass, cover and number of sessile species with time of panel immersion . Decreases were observed in relation to depth, particularly from stat ions at -18 m to -30 m. Similar patterns of community development occu rred over all 3 years. After 1 year the community was dominated by enc rusting bryozoans, serpulids, hydroids, barnacles, ascidians, bivalves and algae (also Corallinaceae), although they occurred in different p roportions according to depth. Mussels were never dominant, as has bee n described for other artificial reefs in the Adriatic (Ancona) and Mi ddle Tyrrhenian Sea (Fregene). The activity of the sea-urchins Paracen trotus lividus and Arbacia lixula in cleaning the substrata is describ ed. Five years after the immersion of concrete blocks a climax has not yet been reached. The community is still changing: in particular larg e algae and sponges are increasing.