Biodiversity associated with a coralligenous build-up off Sicily (Ionian Sea)

Coralligenous is one of the most important habitats of the Mediterranean Sea hosting a very high biodiversity that, however, has not been fully investigated yet. The paper addressed the study of the biodiversity of a coralligenous bioconstruction collected at a depth of 36.7 m off Marzamemi (SE Sicily, Ionian Sea). The species diversity, composition and structure of the main associated taxonomic groups were investigated in order to identify possible differences between the communities of the hard framework (mainly built by calcified corallinales) and the canopy cover. The examined build-up showed significant species diversity for almost all groups. Bryozoans were the most diversified group and, together with foraminifers, also the most abundant both on the canopy and the frame. Further groups showed high species diversity (except for serpulids) and total abundance (except for molluscs) on the canopy rather than on the frame. Due to their different nature and microenvironmental parameters, the canopy and the frame hosted different communities. Besides juvenile specimens, the canopy mostly hosted unmineralized and weakly mineralized, small-sized, short-lived species well adapted to living on ephemeral and flexible substrates. On the contrary, the rigid and persistent frame mostly hosted highly mineralized, large, long-lived species, which usually contributed to the building and strengthening of the bioconstruction. Unlike mapping and monitoring, a thorough description of coralligenous biodiversity requires accurate naked eye and microscopical analysis assisted by SEM investigation due to the small size and cryptic behaviour of several species.