Abstract
Leiopathes glaberrima is a tall arborescent black coral species structuring important facies of the deep-sea rocky bottoms of the Mediterranean Sea that are severely stifled by fishing activities. At present, however, no morphological in vivo description, ecological characterization, age dating and evaluation of the possible conservation actions have ever been made for any population of this species in the basin. A dense coral population was reported during two Remotely Operated Vehicle (ROV) surveys conducted on a rocky bank off the SW coasts of Sardinia (Western Mediterranean Sea). L. glaberrima forms up to 2 m-tall colonies with a maximal observed basal diameter of nearly 7 cm. The radiocarbon dating carried out on a colony from this site with a 4 cm basal diameter revealed an approximately age of 2000 years. Considering the size-frequency distribution of the colonies in the area it is possible to hypothesize the existence of other millennial specimens occupying a supposedly very stable ecosystem. The persistence of this ecosystem is likely guaranteed by the heterogeneous rocky substrate hosting the black coral population that represents a physical barrier against the mechanical impacts acted on the surrounding muddy areas, heavily exploited as trawling fishing grounds. This favorable condition, together with the existence of a nursery area for catsharks within the coral ramifications and the occurrence of a meadow of the now rare soft bottom alcyonacean Isidella elongata in small surviving muddy enclaves, indicates that this ecosystem have to be considered a pristine Mediterranean deep-sea coral sanctuary that would deserve special protection.
Highlights
In the terrestrial environment, trees form complex ecosystems, the forests, which represent important three-dimensional habitats supporting high levels of biodiversity both within their area and in their neighborhoods [1]
The flexible organic skeletons of some alcyonaceans and black corals offer a weaker resistance to the current, allowing them to live in areas with a higher hydrodynamism [9, 10, 11, 12], and, at the same time, may potentially create local turbulence conditions among the ramifications favoring the persistence of food in suspension [13, 14, 3]
The bottom of the Carloforte Shoal hosted a plurispecific megabenthic assemblage with almost 1670 specimens of 8 target coral species counted in the examined frames (Fig. 4): the alcyonaceans Callogorgia verticillata (Pallas, 1766), Acanthogorgia hirsuta Gray, 1857, Bebryce mollis Philippi, 1842, Eunicella cavolinii (Koch, 1887), Isidella elongata (Esper, 1788), the antipatharians L. glaberrima, P. larix, and Antipathes dichotoma Pallas, 1766
Summary
Trees form complex ecosystems, the forests, which represent important three-dimensional habitats supporting high levels of biodiversity both within their area and in their neighborhoods [1]. The existence of Mediterranean deep-sea black coral gardens is well known due to the fact that these species are common in the fishing bycatch [15, 16] and some of them have been sporadically subjected in the past to collection for the jewellery trade [17, 18]. It does not yet exist a comprehensive mapping of the populations of these species, which have always been reported, due to their deep bathymetric distribution, as rare [19]. Mixed populations of black corals and other habitat-forming anthozoans have been observed both along the continental platform [20, 8] and among the bathyal white corals communities up to 500 m depth [21, 22], while only sparse colonies have been recently reported in bathyal habitat along French canyons [23]
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