Cold-seep benthic communities in the Japan subduction zones: Geological control of community development

A large number of Calyptogena-dominated benthic communities, apparently chemosynthetically-based, were discovered at methane-rich pore-water seeps in the Japan subduction zones (3850–6000 m depth). Photographic and video surveys from four submersible dives were analyzed to study the influence of faulting, topography and substratum on exploitation of cold seeps by megafauna. Pore-water seepage occurred in a variety of geological settings, including subduction-erosion and accretionary prism formation, always in association with major faults which likely facilitated upward migration of fluids from a deep high-pressure zone. Sediment cover and manganese crusts on the seafloor appeared to block pore-water discharge, except where interrupted by erosion, slumping or outcropping. Sediment or mudstone substrata may increase lateral diffusion of rising fluids, permitting more extensive biological exploitation than where fluids discharge directly from exposed rock. Cold seeps are ephemeral. Large long-lived “fields” of cold seeps may be important in the maintenance of regional populations of seep organisms and the transfer of cold-seep productivity to the surrounding deep-sea ecosystem

Deep-sea habitat heterogeneity influence on meiofaunal communities in the Gulf of Guinea

To estimate the degree of spatial heterogeneity of benthic deep-sea communities, we carried out a multiple-scale (from m's to 200km) investigation in the Congo-Angola margins (Equatorial West African margin, 3150-4800 m) in which we examined the metazoan meiofauna at a variety of habitats along the Congo Channel system and in the associated cold seep. We investigate the structure, density, vertical distribution patterns in the sediment and biomass of meiofaunal communities in the Gulf of Guinea and how they are controlled by hydrologic and biogeochemical processes The meiofaunal. communities in the Gulf of Guinea were shaped by heterogeneous conditions on the margin, and reflect the multiple-scale spatial variability that corresponds with the different identified habitats. The two control sites, located at > 100 krn away from the canyon, were inhabited by very dense and the most diverse meiobenthic communities. Similar meiobenthic communities inhabited the transition zone between the canyon and the cold seep. Sites located along the Congo Channel were obviously affected by the local high-velocity bottom currents and unstable sedimentary conditions in this active submarine system. Extremely low meiobenthic densities and very low proportions in the most surficial sediment layers provided evidence for recently highly disturbed sediments at these sites. The remote operated vehicle (ROV) Victor 6000 provided images of the cold seep, showing a patchy distribution of several types of patchy distributed megafaunal communities dominated by three key symbiotic taxa (Mytilidae, Vesicomyidae and Siboglinidae). These cold seep sediments were colonised by a unique meiobenthic community, characterised by a high small-scale (m's) patchiness, low species richness and the prominent dominance of two large-sized nematode species: Sabatieria mortenseni, which is a cosmopolitan nematode known from littoral habitats, and an undescribed Desmodora species. The high individual body weight of S. mortenseni and its dominance at the cold seep site resulted in a significantly higher nematode biomass at the seep compared to the surrounding sites. In addition, the vertical nematode profiles, with maximum proportions in subsurficial layers, points to a chemosynthesis-based meiobenthic community in this cold seep, in contrast to the phytodetritus-based communities at the control sites and at the transition zone

Deep-Sea Biodiversity in the Mediterranean Sea: The Known, the Unknown, and the Unknowable

Deep-sea ecosystems represent the largest biome of the global biosphere, but knowledge of their biodiversity is still scant. The Mediterranean basin has been proposed as a hot spot of terrestrial and coastal marine biodiversity but has been supposed to be impoverished of deep-sea species richness. We summarized all available information on benthic biodiversity (Prokaryotes, Foraminifera, Meiofauna, Macrofauna, and Megafauna) in different deep-sea ecosystems of the Mediterranean Sea (200 to more than 4,000 m depth), including open slopes, deep basins, canyons, cold seeps, seamounts, deep-water corals and deep-hypersaline anoxic basins and analyzed overall longitudinal and bathymetric patterns. We show that in contrast to what was expected from the sharp decrease in organic carbon fluxes and reduced faunal abundance, the deep-sea biodiversity of both the eastern and the western basins of the Mediterranean Sea is similarly high. All of the biodiversity components, except Bacteria and Archaea, displayed a decreasing pattern with increasing water depth, but to a different extent for each component. Unlike patterns observed for faunal abundance, highest negative values of the slopes of the biodiversity patterns were observed for Meiofauna, followed by Macrofauna and Megafauna. Comparison of the biodiversity associated with open slopes, deep basins, canyons, and deep-water corals showed that the deep basins were the least diverse. Rarefaction curves allowed us to estimate the expected number of species for each benthic component in different bathymetric ranges. A large fraction of exclusive species was associated with each specific habitat or ecosystem. Thus, each deep-sea ecosystem contributes significantly to overall biodiversity. From theoretical extrapolations we estimate that the overall deep-sea Mediterranean biodiversity (excluding prokaryotes) reaches approximately 2805 species of which about 66% is still undiscovered. Among the biotic components investigated (Prokaryotes excluded), most of the unknown species are within the phylum Nematoda, followed by Foraminifera, but an important fraction of macrofaunal and megafaunal species also remains unknown. Data reported here provide new insights into the patterns of biodiversity in the deep-sea Mediterranean and new clues for future investigations aimed at identifying the factors controlling and threatening deep-sea biodiversity

Ast\ue9rides abyssales de l\u27Atlantique sud. (R\ue9sultats de la campange Walda, juin-juillet-ao\ufbt 1971)

Volume: 289Start Page: 281End Page: 29

Ophidiaster reyssi, nouvelle esp\ue8ce d\u27Ast\ue9ride bathyale de l\u27oc\ue9an Atlantique

Volume: 494Start Page: 1085End Page: 109

\uc9chinodermes de la mer d\u27Alboran

Volume: 231Start Page: 789End Page: 80