A FIRST INSIGHT INTO THE CORALLIGENOUS ASSEMBLAGES OF THE WESTERN SARDINIA SHELF (ITALY)

In the context of Marine Strategy Framework Directive (MSFD, 2008/56/EC), coralligenous assemblages are considered as "special habitat type". The knowledge of their distribution and the assessment of their status can contribute to the definition of the environmental status of Mediterranean regions. Seafloor mapping was implemented through multibeam echosounder surveys and video transects in areas not formerly explored within the continental shelf along the north-western coast of Sardinia (Western Mediterranean). A high resolution digital model of the seabed (DTM) was obtained from multibeam data; the DTM was processed by using the tools of the terrain analysis to extract a number of derived variables of the seabed. Furthermore the analysis of the acoustic backscatter associated to multibeam data was used to evaluate the acoustic response of the seabed associated to different habitat types. The combination of those variables, allowed the development of maps of coralligenous distribution. The presence of coralligenous was validated in two sampling areas from 60 to 140 m depth. For each area, three random transects (about 150m length for each transect) were carried out by means of Remote Operating Vehicle (ROV) with high resolution camera. Video images were processed in order to describe the biotic component of dominant populations. The combined analysis of sonograms and video images provided information on the relevant aspects of the investigated seabeds, distinguishing between mineral and biogenic formations, highlighting their distribution, extent and conditions in terms of presence of typical species and communities. This paper reports the preliminary data of the whole study and contributes to the knowledge of deep coralligenous systems of western Sardinian coasts.