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Transmission electron micrographs show the branchial epithelium of the ascidian Ciona intestinalis to be composed of three kinds of cells: ciliated, parietal, and "dark." Absorptive processes of phagocytosis appear in ciliated and parietal cells; moreover, apocrine-like secretion is evident exclusively in the parietal cells. Finally, the occurrence of secretory cells in the branchial epithelium suggests a digestive role of the ascidian branchial sac.

Cold seep communities are sustained by massive methane-rich fluid expulsion through mud volcanoes located at about 5000 m in the Barbados Trench. These communities, dependent on chemosynthetic processes, are dominated by a vesicomyid bivalve assumed to be a new species related to the genus Calyptogena, and by large bushes of the sponge Cladorhizidae. Both are associated with symbiotic bacteria and are indicative of methane release in seawater and sulphide production in sediments. Non-symbiotic organisms, such as large fields of filter-feeding polychaetes and high densities of meiofauna are indicative of enhanced biological production in the sediments. The spatial distribution of the bivalve populations was mapped using video observations and a computer method based on a simple calculation of the area covered by a submersible camera. The observation of clam beds of variable densities allows us to define two types of fine-scale fluid expulsion pattern: dense Calyptogena beds (up to 150 ind.m−2) are associated with“vents” with relatively high fluid discharge velocities of about 10 cm s−1 and focused by high permeability conduits, whereas dispersed clams (1–10 ind.m−2) are probably sustained only by slow, diffusive “seepages”. The distribution of the chemosynthetic zones from the centre to the edges of the volcano, highlighting the heterogeneity of the concentric zones from the centre to the edges of the volcano, highlighting the heterogeneity of the fluid expulsion pattern at the scale of the volcano. The spatial distribution of the chemosynthetic communities characterizes the fluid expulsion on several types of volcanoes: two mud volcanoes, identified as diatremes, named Atalante and Cyclope, are flat with a central lake of warm fluid mud that is devoid of life, whereas Calyptogena beds are located in the outer regions. On the two other structures, mounds shaped as cones, all activity is concentrated near the summit and seems to be related to higher flow vents than on diatremes. However, the scarceness of bivalves on the flanks of these volcanoes indicates that low flow seepages are less developed than on diatremes. The high mean clam density and the presence of large Cladorhizidae bushes on the volcano Atalante show that larger quantities of methane are emitted through this structure than on the others, and suggest a more evolved surface, favouring chemosynthetic production, than on the other diatreme, named Cyclope. The level of colonization and the spatial patterns of the chemosynthetic communities, when compared on the different volcanoes, suggest that they are at different stages of activity.

Newly discovered hydrothermal vent communities at Lucky Strike on the Mid-Atlantic Ridge (37°18'N, 32°16'W) are comprised of an invertebrate fauna sufficiently different from known vent faunas of TAG and Snake Pit to consider Lucky Strike part of a new biogeographic province. The dominant component of the fauna is a new species of mussel, and the most unusual feature of the fauna is an echinoid echinoderm, Echinus sp. An abundance of small mussels (< 5 mm) indicates a recent recruitment event at Lucky Strike, and modal analysis of length-freque ncy data indicate a discontinuous recruitment process in space and time. Copyright © 1996 Elsevier Science Ltd

The Barbados trench is characterized by large fields of volcanoes and mounds located over a distance of 30 km above the northern slope of a basement ridge corresponding to an inactive transform fault. Sediments from various locations were collected and analyzed for their lipid contents. Bacterial input to the overall biomass was estimated through the analysis of phospholipid ester-linked fatty acid (PLFA) profiles and glycerol ether lipids. Results indicated a eubacterial biomass estimated to be 109cells (g dry wt)−1. Individual fatty acid profiles revealed the presence of sulfur-oxidizing bacteria common to many deep-sea sites but also a large contribution of type I and type II methanotrophs to the eubacterial biomass. The presence of methanotrophs was further supported by the analysis of specific biomarkers of these microorganisms as well as some unusual trans fatty acid isomers. Anaerobic bacteria and presumbly sulfate reducing bacteria were also present, as well as archaebacteria and primarily methanogens, as indicated by glycerol ether lipid analysis.

Dense bush-l~ke clumps of several hundred ~ n d ~ v l d u a l s of a new specles of Cladorhiza (Demosponglae, Poeciloscler~da) were observed near methane sources in mud volcanoes 4718 to 4943 m dcep In the Barbddos Trench The sponge tissue contalns 2 maln mo~pho log~ca l types of extracellular symbiotic bacteria small rod-shaped cells and larger cocco~d cells with stacked membranes Stdble carbon ~so tope values, the presence of methanol dehydrogenase and ultrastructural observatlons all lndlcate that at least some of the syrnblonts are methdnotrophic Ultrastructural e v ~ d e n c e of ~n l r ace l l~~ la r d ~ g e s t ~ o n of thp s y n ~ b ~ o n t s and the stable C and X values suggest that thc sponge obtalns a slgnlflcdnt portion of its nutr~tlon from the symbionts Ultrdstructure of the sponqe embryo suggests d ~ r e c t ransmission throuqh qc.neratlons In brooded embryos The sponge also ma~ntrilns a carnivorous feed~ng hdblt on tin\ swlmmlng prey, as do other cladorhlzlds K E Y L\/ORDS. Methanotrophy POI-~fera . Deep-sea . Symbiosis . Cold-seep communities

Three sectors of the south Barbados prism between 1000 and 2000 m depth were explored by the French submersible Nautile. Chemosynthesis-based benthic communities were discovered on several structures affected by diapirism, including mud volcanoes, domes and an anticlinal ridge. The communities are associated with the expulsion of methane-rich fluids which is a wide-spread process in the area. These communities are dominated by large bivalves and vestimentiferans which harbour chemoautotrophic symbiotic bacteria. The symbiotic bivalves include two species of Mytilidae and one of Vesicomyidae, with dominance of a methanotrophic mussel. Cartography of the benthic communities, interpretation of thermal measurements and observation of sedimentary patterns have been used to define the life habits of each of the three species of symbiotic bivalves. Each species has a characteristic preference for different conditions of edaphic and fluid flow: the dominant methanotrophic mussel appears to require high velocity vents and hard substratum. The vesicomyids and the other species of mussel are able to take up sulfide from the sediments, and so are associated with low seepages, but also require soft sediment. The three bivalve species are assumed successively to colonize the top of a diapiric ridge, in a succession related to the temporal evolution of fluid flow and sedimentation. The composition of the bivalve assemblages, their densities and biomasses all differ between the several mud volcanoes and domes studied, and these parameters are thought to be related to the spatial and temporal variations of fluid expulsion through the structures, and the lithification processes linked to fluid expulsion. One very active dome is at present colonized by an exceptionally large and dense population of the methanotrophic mussel. In contrast, communities in another area, on the domes and volcanoes that are currently inactive, were colonized by only a few living vesicomyids and mussels, both associated with sulfur-oxydizing bacteria, and there were numerous empty shells. The densities and biomasses of symbiotic bivalves were far greater in the area studied than in a deeper mud volcano field on the same prism that had been studied previously. This is consistent with a report that methane production is greater in the southern region of this accretionary prism than in the northern. Numerous non-symbiotic organisms were observed in and around the areas of the seeps, some are endemic to the seep communities, including some gastropods and shrimps, others are either colonists or vagrants from the surrounding deep-sea floor. Filter feeders were very abundant, and some of these, like the serpulids and large sponges, may also be dependent on the chemosynthetic production. Faunistic composition of both symbiotic and non-symbiotic taxa, of the assemblages around these cold seeps, is closely related to that reported for communities living on hydrocarbon seeps in the Gulf of Mexico.

Fiala-Medioni, A. ... et. al.-- 18 pages, 12 figures, 2 tables, 52 years after the first explorations in the Lacaze-Duthiers Canyon and the observation of living populations of cold-water corals, recent video surveys using deployments of the ROV "Super-Achille" and the submersible "REMORA" (COMEX), have allowed the discovery of new sites colonized by cold-water coral populations (Lophelia pertusa, Madrepora oculata, Dendrophyllia cornígera and Desmophyllum dianthus). Dense populations were observed, from 250 to 535 m, either on blocks or cliffs. The coral community consisted of a rich fauna of invertebrates including numerous sponges, brachiopods, echinoderms, oysters, ascidians and bryozoans as well as vagile cephalopods and fishes. Among the 51 identified species, 4 species are protected by the French regulation (corals), 13 species are cited in European directives 79/109/EEC (Art 4) and 92/43/EEC (Annex 2), 2 species are cited in the OSPAR convention and 15 are of commercial interest. Direct observations allowed also establishing an increase of anthropogenic wastes mainly related to fishing

Four mud volcanoes of several kilometres diameter named Amon, Osiris, Isis, and North Alex and located above gas chimneys on the Central Nile Deep Sea Fan, were investigated for the first time with the submersible Nautile. One of the objectives was to characterize the seafloor morphology and the seepage activity across the mud volcanoes. The seepage activity was dominated by emissions of methane and heavier hydrocarbons associated with a major thermal contribution. The most active parts of the mud volcanoes were highly gas-saturated (methane concentrations in the water and in the sediments, respectively, of several hundreds of nmol/L and several mmol/L of wet sediment) and associated with significantly high thermal gradients (at 10 m below the seafloor, the recorded temperatures reached more than 40 °C). Patches of highly reduced blackish sediments, mats of sulphide-oxidizing bacteria, and precipitates of authigenic carbonate were detected, indicative of anaerobic methane consumption. The chemosynthetic fauna was, however, not very abundant, inhibited most likely by the high and vigorous fluxes, and was associated mainly with carbonate-crust-covered seafloor encountered on the southwestern flank of Amon. Mud expulsions are not very common at present and were found limited to the most active emission centres of two mud volcanoes, where slow extrusion of mud occurs. Each of the mud volcanoes is fed principally by a main narrow channel located below the most elevated areas, most commonly in the centres of the structures. The distribution, shape, and seafloor morphology of the mud volcanoes and associated seeps over the Central Nile Deep Sea Fan are clearly tectonically controlled. © 2007 Elsevier Ltd. All rights reserved.

cited By 52; International audience; Specimens of shrimp (Rimicaris exoculata) and mussel (Bathymodiolus puteoserpentis) were collected 3500 m below the ocean surface at the hydrothermal vents of the mid-Atlantic Ridge (TAG and Snake Pit sites, respectively). Arsenic, a potentially toxic element, is among the substances emitted by the hydrothermal vents. The hydrothermal vent shrimp, which are known to be a primary consumer of the primary producing chemolithoautotrophic bacteria, contained arsenic at 13 μg g-1 almost exclusively as arsenobetaine (AsB). Arsenic was present in the soft tissues of the mussel at 40 μg g-1 and the major part of the extractable arsenic species in the adductor muscle/mantle tissues and in the gill were present as dimethylarsinylriboside-derivatives (arsenosugars), while AsB was present at 16 and 3.6%, respectively, in these tissues. In spite of the absence of biosynthetically active algae, the pattern of arsenic species found in the shrimp and mussel species in the deep-sea is similar to that found in their counterparts from the ocean surface. It is concluded that the autotrophic bacteria of the hydrothermal vent ecosystem and the symbiotic bacteria harboured in the mussel species are responsible for the biosynthesis of the organoarsenicals detected in the two hydrothermal vent animal species. It is not known if the formation of the same organoarsenicals in the surface and deep sea ecosystems is primarily a detoxification process of inorganic arsenic, or whether these compounds play a physiological role.

International audience

Since 1987, Japanese and French geologists, geophysicists, and biologists have been studying the North Fiji Basin Ridge within the framework of a joint project named STARMER (Science and Technology Agency of Japan—IFREMER of France). This ridge was first geologically, geophysically, and geochemically surveyed during the 1985 SEAPSO 3 cruise of the R/V Jean Charcot [Auzende et al., 1988]. At that time, water sampling and morphotectonic analysis indicated that the North Fiji Basin Ridge was technically and hydrothermally active. Within the STARMER project, four surface ship cruises have been conducted {Kaiyo 87-88-89 and Yokosuka 90). One significant result of these surveys is the complete mapping of the entire ridge between 14°S and 22°S (Figure 1), an area approximately 900 km long and more than 50 km wide (Sea Beam and Furuno multibeam swath-mapping systems were used). During the Kaiyo 87 cruise, the presence of active hydrothermalism (sulfide deposits, chimneys expelling shimmering water, and associated living animal colonies) was discovered through water sampling and video deep towing.

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