Application of geophysical technologies and hydrodynamical modelling for benthic habitat mapping and classification in the western Mediterranean Sea

Acoustic methods for seafloor mapping have been widely developed over the last decades. In particular, the development of swath bathymetry has allowed obtaining detailed maps of seabed morphology and the analysis of related acoustic backscatter has made it possible to classify sediment types and habitat typology. Those tech-niques, coupled with ground truth data, provide useful information for the evaluation of environmental quality of coastal areas, they are useful for the evaluation of marine geo-hazards (e.g. landslide) and can provide useful data to evaluate marine biological (fishery) and non-biological resources (sand deposits for beach nourishment). Here, I present such an application from a study conducted in the inner shelf of central western Sardinia (western Mediterranean sea), a site characterized by a complex sea bed including sandy and gravelly sediments, Posidonia oceanica seagrass beds growing on hard grounds (i.e. biogenic carbonates) and sedimentary substrates (De Falco et al., 2010). A map of seabed classification, including sediment types and seagrass distribution, was produced through a combination of information derived from backscatter data and morphological features derived from multibeam bathymetry, which were validated by ground-truth data. Furthermore, an evaluation of the hydrodynamics is fundamental to understand the factors which control the distribution of benthic habitats. In this framework, high resolution hydrodynamic numerical models coupled with numerical tools are pre-sented here as a tool for reproducing the ecosystem dynamics. A three-dimensional hydrodynamic modelling was performed in order to simulate the influence of waves and currents at the seabed level on the sedimentary features in the inner-middle shelf of the strait of Bonifacio (western Mediterranean). In particular, two main carbonate factories were identified: Posidonia oceanica seagrass meadows in the shallower zone (<40 m) and Maërl beds (free living calcareous red algae) in deeper water (40-80 m) (De Falco et al., 2011). These were conditioned by hydrodynamics: (i) the sediment carbonate production associated to Posidonia oceanica meadow was higher in sectors sheltered from waves; (ii) currents at the seabed level, forced by the main winds of the region, limited the extension Maërl beds. The application of geophysical technologies allowed high resolution mapping of ben-thic habitats, whereas the hydrodynamic modelling was instrumental to evaluate the spatial distribution of benthic communities producing carbonate sediments in mod-ern temperate shelves.