HUMAN PREDATION ALONG APULIAN ROCKY COASTS (SE ITALY) - DESERTIFICATION CAUSED BY LITHOPHAGA-LITHOPHAGA (MOLLUSCA) FISHERIES

The date mussel Lithophaga lithophaga is a Mediterranean boring mollus c living in calcareous rocks. Its populations are intensely exploited by SCUBA divers, especially in southern Italy. Collection is carried o ut by demolition of the rocky substratum, so that human predation on d ate mussels causes the disappearance of the whole benthic community. T he impact of this activity along the Apulian coast was evaluated by 2 surveys carried out by SCUBA diving inspection of the Salento peninsul a. The Ionian coast of Apulia, from Taranto to Torre dell'Orso (Otrant o), was surveyed in 1990 and in 1992 by 2 series of transects (from 0 to 10 m depth, 2 km from each other), covering 210 km. Observations we re transformed into an index of damage, ranging from 0 (no damage) to 1 (complete desertification). 159 km of the inspected coast are rocky. The first survey (1990) allowed us to estimate that a total of 44 km was heavily affected by this human activity (the index of damage rangi ng between 0.5 and 1), whereas the second survey showed heavy damage a long a total of 59 km. This increase in length was accompanied by a hi gh increase in the index of damage along parts of coast that were less intensely exploited in 1990 than in 1992. The second survey (1992) wa s extended to 90 km of the Adriatic coast of Apulia (from Otranto to T orre S. Sabina, Brindisi), with 47 km of rocky coast and a total of 10 km heavily affected by date mussel fishery. Date mussel collection is one of the most destructive human activities along the Apulian coast and it has long-term effects because sea urchin grazing probably preve nts recolonization of barren areas. Rarefaction of the resource due to overexploitation and habitat destruction caused rapid 'evolution' of the techniques of predation, with an increase in searching efficiency achieved by the use of underwater vehicles. Similar impacts of date mu ssel collection have been recorded in other parts of the Italian coast , especially Campania and Sardinia, and it is possible that such situa tions are common, but still undetected, in other areas of the Mediterr anean.