Scuba diver behaviour and its effects on the biota of a Mediterranean marine protected area.

The effects of diving activity in different Mediterranean subtidal habitats are scarcely known. This study evaluates diver behaviour (for example time spent in each habitat), use (contacts made with the substrate) and immediate effects of diver contact on benthic species in a marine protected area (MPA) in Sicily. Over a two-year period, intentions of 105 divers were observed within seven subtidal habitats: algae on horizontal substrate, algae on vertical substrate, Posidonia oceanica, encrusted walls, caves, sand and pebbles. Divers selected a habitat in proportion to its availability along the scuba trail. On average, each diver made 2.52 contacts every seven minutes, and no differences were detected among the levels of diver scuba certification. The highest rates of total and unintentional contacts were recorded on caves and encrusted walls, and the slow growing species Eunicella singularis and Astroides calycularis were the most frequently injured by divers. Most of the contacts were concentrated in the first minutes of the dives. The identification of diving effects in different habitats will enable management strategies to specifically control this impact at a habitat scale, for example restricting the start of the dive to low vulnerability habitats would reduce damage to benthic organisms, allowing sustainable use of MPAs.