| Abstract: | Deep-sea ecosystems represent the largest biome of the global biosphere, butknowledge of their biodiversity is still scant. The Mediterranean basin has beenproposed as a hot spot of terrestrial and coastal marine biodiversity but hasbeen supposed to be impoverished of deep-sea species richness. We summarized allavailable information on benthic biodiversity (Prokaryotes, Foraminifera,Meiofauna, Macrofauna, and Megafauna) in different deep-sea ecosystems of theMediterranean Sea (200 to more than 4,000 m depth), including open slopes, deepbasins, canyons, cold seeps, seamounts, deep-water corals and deep-hypersalineanoxic basins and analyzed overall longitudinal and bathymetric patterns. Weshow that in contrast to what was expected from the sharp decrease in organiccarbon fluxes and reduced faunal abundance, the deep-sea biodiversity of boththe eastern and the western basins of the Mediterranean Sea is similarly high.All of the biodiversity components, except Bacteria and Archaea, displayed adecreasing pattern with increasing water depth, but to a different extent foreach component. Unlike patterns observed for faunal abundance, highest negativevalues of the slopes of the biodiversity patterns were observed for Meiofauna,followed by Macrofauna and Megafauna. Comparison of the biodiversity associatedwith open slopes, deep basins, canyons, and deep-water corals showed that thedeep basins were the least diverse. Rarefaction curves allowed us to estimatethe expected number of species for each benthic component in differentbathymetric ranges. A large fraction of exclusive species was associated witheach specific habitat or ecosystem. Thus, each deep-sea ecosystem contributessignificantly to overall biodiversity. From theoretical extrapolations weestimate that the overall deep-sea Mediterranean biodiversity (excludingprokaryotes) reaches approximately 2805 species of which about 66% isstill undiscovered. Among the biotic components investigated (Prokaryotesexcluded), most of the unknown species are within the phylum Nematoda, followedby Foraminifera, but an important fraction of macrofaunal and megafaunal speciesalso remains unknown. Data reported here provide new insights into the patternsof biodiversity in the deep-sea Mediterranean and new clues for futureinvestigations aimed at identifying the factors controlling and threateningdeep-sea biodiversity. |
