ࡱ> ;=: % bjbjVV .2<<%"""""6666<r 6 0~~~~~YYY$:."YYYYY""~~111YB"~"~1Y111~En6v1u0 1  1 "1DYY1YYYYYYYY YYYY YYYYYYYYY : Abstract of the communication of Virginie Tilot at the Deep Sea Biology symposium, 6 June 2010, in Reykiavik, Iceland. Discovery of new faunal sites on the EPR (16N): abyssal, bathyal and hydrothermal communities Virginie Tilot*, Pascal Gente* and the PARISUB scientific team *CNRS, Universit de Brest, UMR 6538 Domaines Ocaniques, IUEM, Place Nicolas Copernic, 29280 Plouzan Abstract The PARISUB cruise is a multidisciplinary and international research project with the purpose to explore with a manned submersible the area between 15N -16N and 105E-106E where the EPR interacts with a chain of hotspots (Mathematician hotspots). The objectives are to study the axis instabilities, to sample the basalts across and along the axis and to locate possible hydrothermal vents. In particular the aim is to identify the type and the evolution of volcanism by a very high precision bathymetry and by the analysis of bottom magnetic anomalies. The study of the components of faunal communities in the area would serve as indicators of biodiversity and of specific substrates and environmental characteristics. With the support of Ifremer and Genavir with the R/V Atalante, geological, geophysical (magnetism, bathymetry and gravimetry) and biological surveys have been achieved over 122 km2 from a total of 24 dives (110h) with the manned submersible Nautile and 20 dives (112h) with the prototype Autonomous Underwater Vehicle (AUV) ASTER X. A great amount of samples of lava (about 1 ton), 6 fossil chimneys and fauna (257 samples among which DNA samples) have been collected. A new active hydrothermal area including a variety of faunal communities adapted to specific thermal and geochemical conditions has been discovered among which 2 diffuse flow vents and 2 black and white smokers which have been explored and sampled more throughly. The exploration has been achieved between 4500m and 2300m depth revealing abyssal and bathyal faunal communities on pillow lava more or less sedimented. At deeper depths and off the axis, two substrata, pillow lava with ferro-manganese crusts and sediments would prevail with associated faunal communities. The more distant from the axis, the more encrusted was the basalt on which biological communities were characterized by a higher abundance and biodiversity while sedimented areas were highly populated by meiofauna and macrofauna. On the slopes of the axis composed of pillow lava, faunal communities were often represented by suspension feeders with a mixture of abyssal and bathyal species species (octopods, e.g. Grimpoteuthis sp., holothurians e.g. Enypniastes eximia, Peniagone leander..) and bathyal species (e.g. Echinothurioida urchins, rays..). While on the axis, faunal abundance and taxonomic richness was much lower on the fresh basalt with a dominance of carnivorous feeders (Bythitidae fishes, holothurians Synallactids, shrimps Nematocarcinus sp., cerianthids anemones, carnivorous sponges, e.g. Caulophacus sp..). This would imply a shift of trophic and functional guilds related to the physico-chemical, environmental and trophic conditions on the axis, in particular the lack of what would appear as the biota-attractive manganese crust on the lava. A new active hydrothermalism area was discovered over an area of the axis in confluence with the chain of hotspots, with the display of a mosaic of conspicuous faunal communities adapted to specific environmental, thermal and geochemical conditions of diffuse flow vents and black smokers. There appears to be a linear arrangement parallel to the axis: along the western wall of the narrow axial valley lies the active and fossil smokers, while eastwards run first sulphide deposits then diffuse vents with associated communities and biocenoses in the vicinity. Such an arrangement may be related to a thermal gradient linked to the presence of the Mathematicians hotspot west of the area. Faunal communities appeared quite different from the rest of the fauna on the East Pacific Rise (EPR) and would have at first similar characteristics to the fauna of Lau basin. The area included: (1) diffuse flow vents located on sulphide mounds swarming with small amphipods and polynoids. Faunal communities were dominated by Siblogonids Oasisia sp. and squat lobsters Galathea Munidopsis sp. Some Riftia pachyptila, Zoarcid fish Thermaces cerberus, crabs Bythograeidae, transparent shrimps Alvinocaris sp., gastropods Phenacolepadidae, Lepetodrilidae, bivalves Vesicomyidae coexisted in the thickets of these relatively large Vestimentifera. Further, bivalves Calyptogena magnifica were found along fissures and serpulid worms Laminatubus sp. at some distance from the active sites. Bivalves Pectnids Bathypecten vulcani aggregated elsewhere (2) Inactive sulphid mounds hosted Brisingid asteroids, hydroids, sponges (Caulophacus sp...), annelids, hydrozoa, squat lobsters Munidopsis sp., actinians..Nereididae worms, e.g. Nereis sp. or cirripeds Neolepas sp..were present on fossil chimneys (3) In the vicinity of tall active chimneys coexist Zoarcid fishes Thermarces sp., squat lobsters Galathea Munidopsis sp., crabs Bythograeidae, Vestimentifera Riftia pachyptila, cerianthid anemones, octopus Vulcanoctopus hydrothermalis, polynoides Lepidonotopodium sp., polychaetes Alvinella pompeiana... The processes and localization of the hydrothermal activity clearly controls the composition and spatial and temporal distribution of faunal communities. The study of these can provide good indicators on the thermal ranges of the smokers and diffusers as well as other environmental and geochemical parameters of the constraint heat flux in the underlying crust. Also, the understanding of the processes of faunal colonization on active hydrothermal activity, on its genesis and spreading, could increase the knowledge on lifes colonization on new-formed crust. It is a priority to increase knowledge on these hydrothermal biocenoses, and those associated in the vicinity, in order to draw guidelines for the conservation of particularly fragile marine ecosystems in areas earmarked for future deep-sea mining of seafloor massive sulphid deposits. 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