Discovering Mediterranean black coral forests: Parantipathes larix (Anthozoa: Hexacorallia) in the Tuscan Archipelago, Italy

Black coral communities in the Mediterranean Sea are now recognized to be far more common than what was expected a few years ago; however, among the species reported for this basin, Parantipathes larix is one of the least well known. This species is characterized by tall, monopodial or sparsely branched colonies showing a distinctive bottle-brush pinnulation pattern and fairly elongated whitish polyps. Rarely reported in the literature, this species, despite frequently occurring as fishing bycatch, has never been observed in dense populations and all available information mainly concerns its morphological features. Two forests of P. larix were discovered during a remotely operated vehicle (ROV) survey conducted in July 2012 on board the R/V Astrea between 100 and 200m on two continental rocky shoals located about 10 miles southeast of the Island of Montecristo (Tuscan Archipelago, Tyrrhenian Sea). Video footage was analyzed using the ROV imaging technique, and the coral communities were described in terms of abundance, size-frequency distribution and associated fauna. P. larix is the dominant component of both coral communities showing a maximal abundance of 4 colonies m(-2). Sixteen different patches of P. larix, each covering an approximate area of 30m(2) and spaced on average 60m apart, were counted on the rocky shoals, representing, with an average height of the colonies of about 1m, the only true three-dimensional habitat of the study areas. The forests of P. larix of Montecristo represent, as far as we know, a unique case for the exceptional abundance of the colonies and their distribution in discrete patches, which is likely a result of the limited dispersal ability of the larvae. Moreover, their occurrence on isolated banks may suggest a preference for topographic structures subjected to local turbulent hydrographic regimes which are known to support filter-feeding communities.