SEASONAL-VARIATION OF FISH ASSEMBLAGES IN THE LOANO ARTIFICIAL REEF (LIGURIAN SEA NORTHWESTERN MEDITERRANEAN)

Thirty months after the construction of the Loano artificial reef a st udy of fish abundance was started. The method used both direct censuse s at monthly intervals and limited fishing activity with lon,alines an d trammels. The monthly census was carried out by two divers in the ce ntral part of the artificial reef made up of pyramids, each consisting of five concrete cubic blocks with 2-m sides. The census was carried out in two main phases: first the observer counted the fish moving aro und him for 15 min and then he explored the holes and the internal cor ridors. The second phase consisted of a 25-m crosswise movement betwee n two pyramids. Observations were carried out over a period of 2 years , from February 1989 to February 1991, and 66 species of fish and inve rtebrates of fishing importance were caught and/or observed in the Loa no artificial reef; 41 species (of which three were Crustaceans and tw o Cephalopods) were censused during the above-mentioned dives. The mos t numerous families were Sparidae and Labridae, followed by Serranidae . The predominance of the first two families seems to be one of the ge neral characteristics of rocky sea-bed fish communities in the northwe st Mediterranean. Seasonal changes in the qualitative and quantitative assemblages of fish are described. An important contribution to these changes was the appearance of juveniles, mainly in the latter half of the summer and in the autumn. It was in this period that the maximum fish density occurred, while the minimum was registered in June. The n umber of fishes increased with the age of the artificial reef and the evolution of macrobenthos settlement. Tn particular the development of algae improved the reef's attractiveness to the Labridae species.