Stress antropico e condizioni ecologiche delle praterie diPosidonia oceanica(L.) Delile nel Parco Nazionale di La Maddalena (NE Sardegna) = Stress of anthropic effects and ecological conditions of thePosidonia oceanicafields in the Maddalena National Park (NE Sardinia)

Three years of summer sampling, from 1999 to 2001, have permitted the verification of a close relationship between the depletion ofPosidonia oceanicabed in Maddalena National Park (NE Sardinia) and several factors of anthropogenic origin. Among them, the increase in water turbidity and the effects of boats anchoring on the sea floor are the principal causes for the reduction ofthe density, leaf length and coverage of the phanerogam. 78 circular areas 40 meters in diameter has been monitored by SCUBA diving, glass floored inflatable dinghy and a high definition (600 kHz) side scan sonar with a coverage of approximately 300 hectares, allowing the identification of the most affected areas and the quantification of the effects. The consequences of these effects onP. oceanicabeds are evident by comparison with the values measured in non affected areas.