Abstract
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.
Highlights
Mediterranean Sea biodiversity has been deeply studied over the past centuries; large portions of it, especially in the deep realm, still remain largely unknown [1,2,3,4]
The progressively lower light conditions have a profound influence on the biocoenoses composition mostly because of reduced primary production, but this zone continues to be characterized by high biodiversity and biomass levels, at times comparable to those found in shallow waters [4,7,8]
Ethics Statement The Remotely Operated Vehicle (ROV) surveys and the sampling operations in the study areas of Calabria were conducted with regular permits (Aut. 79 ICRAM, R031250, Giu. 08– GE/DN7005; Aut. 96 ICRAM, R090737, Lug. 08; MARISTAT 2008 P261430Z; Reggio Calabria Port Authority Nu15 2008) released by the Italian Navy Hydrographic Institute and by the Calabria Port Authorities
Summary
Mediterranean Sea biodiversity has been deeply studied over the past centuries; large portions of it, especially in the deep realm, still remain largely unknown [1,2,3,4]. With respect to the traditional bionomic characterization of the Mediterranean Sea [5], only few quantitative data currently exist dealing with the distribution of the megafaunal ‘‘roche du large’’ benthic communities These represent poorly studied biocoenoses of the deep circa-littoral rocky bottoms mainly composed of sponges, anthozoans, bryozoans and brachiopods and generally lacking the macroscopic algal component [5,6]. Found near the border of the continental shelf, these biocoenoses, dwelling to 250 m depth, usually occupy rough bottoms where current and turbidity are reasonably important [5] In these habitats, the progressively lower light conditions have a profound influence on the biocoenoses composition mostly because of reduced primary production, but this zone continues to be characterized by high biodiversity and biomass levels, at times comparable to those found in shallow waters [4,7,8]. Such biological and ecological richness is influenced by several constraining factors, related to environmental and biological cues and to human activities, since most of these habitats are a potential fishing ground [4,8]
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