RELATIONSHIPS BETWEEN MULTIBEAM BACKSCATTER, SEDIMENT GRAIN SIZE AND SEAGRASS DISTRIBUTION FROM THE WESTERN SARDINIA INNER SHELF (MEDITERRANEAN SEA).

Multibeam acoustic data were acquired from the inner shelf of central western Sardinia (western Mediterranean sea) in order to evaluate the relationship between acoustic data (backscatter intensity and angular response) and seabed typologies. The study site is characterized by a complex seabed including sandy and gravelly sediments, Posidonia oceanica seagrass beds growing on sedimentary and hard (i.e. calcareous bio-constructions) substrates. A multibeam survey was carried out in order to collect bathymetric and backscatter data by using a RESON 8111 equipment. The bathymetric range of the acquisition sector was 15-55 m. Ground truth data were collected from 57 stations, by grab sampling and direct inspection by divers. 41 ground truth stations were characterized by sedimentary substrate without benthic vegetation, the remaining by Posidonia oceanica beds. Sediment samples were analyzed for grain size. Sediments were mainly sandy-gravelly. Silt+Clay content did not exceed 20%, while 10 samples showed a gravel content >50%.