Deep coral communities along Sardinian submarine canyons

Submarine canyons deeply incise the Mediterranean continental margins, becoming authentic conduits between the continental shelves and deep-sea basins. Enhanced habitat heterogeneity and organic inputs allow a noticeable benthic biodiversity development, creating authentic “hotspots” of biodiversity. However, if knowledge on distribution and composition of benthic assemblages dwelling in different canyon systems across the Mediterranean basin is considerably increasing; on the other hand, factors driving their distribution and biodiversity at multiple spatial scales are still difficult to discern and thus far to being well understood. Among these benthic communities, suspension feeders take considerable advantages from environmental features of canyons; because of this, they are often dominant showing dense patches of large Anthozoan. These organisms, along with other components of the benthos such as sponges, ascidians and bryozoans, enhance the three-dimensional development of the habitat, constituting the so called ‘animal forests’ which play a key ecological role in the benthic-pelagic coupling processes. Moreover, due to their slow growth rates, longevity and tridimensional structure, these species are particularly vulnerable towards mechanical injuries inflicted by fishing gears. In this regard, supporting knowledge on their distribution patterns and ecology are needed in order to develop sound conservation measures. Therefore, through a non-invasive protocol based on ROV footage coupled with multi-beam dataset, this thesis aims to document Sardinian deepwater coral forests communities dwelling along different canyons and other geological features of the Sardinian continental margin. The present work compares local, and regional biodiversity of coral communities inhabiting contrasting and similar geological features of the continental margin, considering different spatial scales and also exploring the role of a subset of environmental descriptors, obtained through the image analysis, in determining the observed patterns. Overall, multi-variate analyses emphasized a higher variability in the composition of coral communities at the smallest spatial scale investigated that overcomes the variability at regional/geographical scale. In particular, in the first study, patterns of observed diversity were significant different within the same geological feature rather than among contrasting geological setting, and the tested environmental variables explained the patterns of observed diversity. In the second study, results suggested that coral community composition differed across canyons within the same area, but not among the three geographical areas, and that variations patterns appeared to be mainly constrained by differences in the hydrodynamic conditions operating on local scales. The last part of the thesis aimed to describe the distribution and demographic features of scleractinian habitat-forming cold water coral Madrepora oculata encountered in the north eastern and southern western canyons of the island of Sardinia. These species are documented for the first time in the northeast Sardinian continental margin, extending the geographical framework of the recently discovered “Sardinian cold water coral province”. Results revealed that, as for all the best developed CWC situations present in the Mediterranean Sea, the new Sardinian province is clearly dominated by patches of M. oculata occurring with small/medium size colonies in two different type of substrate (rocky wall and inclined silted bottom). Results from the present thesis increase knowledge on deep coral assemblages inhabiting Sardinian submarines canyons, providing new insights on the scale-dependent structure and dynamics of deep dwelling coral assemblages. These results will likely have considerable implications for the spatial development of forthcoming conservation strategies to preserve such biodiversity hotspots.