Coral forests diversity in the outer shelf of the south Sardinian continental margin

Ecological theory predicts that heterogeneous habitats allow more species to co-exist in a given area, but to date, the knowledge about the relationships between habitat heterogeneity and biodiversity of coral forests in the lower shelf and upper slope along continental margins is rather limited. We investigated biodiversity of coral forests from 8 sites spread over two different geomorphological settings (namely, pinnacles vs. canyons) in the lower shelf along the Sardinian continental margin. Using a combination of multivariate statistical analyses, we show here that differences in the composition of coral assemblages among different geomorphological settings were not statistically significant, whereas significant differences emerged among sites within the same geomorphological setting (i.e. among pinnacles and among canyons). Our results reveal that environmental and bathymetric factors such as sediment coverage, slope of the substrate, terrain ruggedness, bathymetric positioning index and aspect were important drivers of the observed patterns of coral biodiversity in both settings. Spatial variability of coral forests' biodiversity is affected by environmental factors that act at the scale of each geomorphological setting (i.e. within pinnacles and in canyons) rather than by the geomorphological settings themselves (i.e. the widest spatial scale that includes both pinnacles and canyons). This result allows us to suggest that simple categorization of benthic communities according topographically defined habitat is unlikely to be sufficient for addressing conservation purposes.