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A Mediterranean \"roche du large\" ecosystem, represented by four rocky shoals, located a few miles apart on a muddy bottom at 70-130 m depth in the gulf of St. Eufemia (Calabria, South Tyrrhenian Sea), was studied by means of Remotely Operated Vehicle (ROV) photo imaging. The shoals host highly diversified coral communities, mainly composed of arborescent colonies of gorgonians (Callogorgia verticillata, Paramuricea clavata, Paramuricea macrospina, Bebryce mollis, Villogorgia bebrycoides, Corallium rubrum, and Leptogorgia sarmentosa), and antipatharians (Antipathella subpinnata, Antipathes dichotoma and Parantipathes larix). The coral colonies reach high densities (up to ca. 17 colonies m(-2)) and large sizes, such as the over 1.5 m wide antipatharian colonies. We hypothesized that the abundance and composition of the coral assemblages differed significantly among the rocky shoals and with respect to the surrounding soft bottoms. Various environmental variables were tested as possible explanatory factors of the observed differences. Moreover, due to their off-coast localization, we report here that these unique ecosystems are potentially subjected to a strong pressure from the local fishing activities, which were tentatively characterized. The recorded coral β-diversity among the shoals supports the hypothesis that these habitats behave like small oases of hard substrata interspersed in a muddy bottom. Because of their intrinsic beauty and rarity and their biological and ecological value, we stress the need of specific actions aimed at the urgent protection of these oases of biodiversity.

Rocky pinnacles arising from soft bottoms of the circa-littoral zone may host oases of deepwater coral biodiversity: Engineer species that enhance ecosystem’s three-dimensional complexity often acting as shelter for associated fauna that can comprise commercially relevant species. Although variations in beta diversity of these coral oases were recently documented at different spatial scales, information on the role of geomorphogical features of rocky outcrops can be considered mostly an unaddressed issue. To comply with this task, five rocky pinnacles showing different geomorphological features (average slope, ruggedness, sediment accumulation), dwelling between 120 and 170 m depth along south Sardinia continental margin, were investigated by means of ROV imaging. We tested the null hypothesis that coral abundance and diversity [estimated using four black corals (Antipatharia) and seven gorgonians (Alcyonacea) as target species] did not differ among investigated sites. Overall, total coral abundance varied from 1.35 to 7.23 col m²; Callogorgia verticillata, followed by Eunicella cavolinii and Corallium rubrum were the most abundant gorgonians, while Antipathella subpinnata and Parantipathes larix were the most abundant black corals. Through uni- and multivariate analyses, significant differences in corals biodiversity were identified, allowing us to reject the null hypothesis, emphasizing a remarkable variability in beta diversity, apparently following variations in geomorphological features of investigated pinnacles. Moreover, a visual census of anthropogenic debris revealed that lost fishing gears represented the most frequently observed debris, stressing the need to identify further and more focused strategies of conservation to protect these oases of coral biodiversity.