Biological characterization of a whale-fall near Vancouver Island,British Columbia,Canada

Video analysis of a whale-fall discovered in the northeast Pacific Ocean, off Vancouver Island at a depth of 1288 m during ROV diving operations has identified 26 taxa of deep-sea benthic organisms inhabiting the seafloor immediately surrounding remnants of the whale skeleton. A photo-mosaic derived from high-definition video provides a quantitative visual record of the present condition of the site, the species richness, and substrate preference. Only the skull and caudal vertebrae remains of this large whale skeleton are estimated to have been approximately 16.5 m in length. Most organisms identified near the whale-fall are common benthic deep-sea fauna, typical of this water depth and seafloor composition. Much of this species richness comes from sessile suspension feeding cnidarians attached to the numerous glacial dropstones found throughout the area rather than the presence of the whale skeleton. Seep and bone specialists are rare (4 taxa) and may be, in part, a remnant population from a sulphophilic stage of whale-fall decomposition. Evidence of past colonization by Osedax sp. is visible on the remaining bones and we conclude that rapid degradation of the missing bones has occurred at this site as has been observed at whale-falls off central California in Monterey Canyon.     

Three-year investigations into sperm whale-fall ecosystems in Japan

We report the first study of sperm whale‐fall ecosystems, based on mass sinking of whale carcasses at shelf depths in the northwest Pacific. We conducted three observations over a 2‐year period on replicate sperm‐whale carcasses implanted at depths of 219–254 m off the southern part of Japan from July 2003 to August 2005. The study was made possible by a mass stranding of sperm whales in January 2002, and the subsequent sinking of 12 carcasses in the waters off Cape Nomamisaki. Dense aggregations of unique chemosynthesis‐based fauna had formed around the whale carcasses after 18 months (July 2003). The mytilid mussel Adipicola pacifica was the most abundant macrofaunal species and covered most of the exposed bone surfaces. The general composition of the fauna was similar to that of deep‐water reducing habitats, but none of the species appearing in this study has been found at hydrothermal vents, cold seeps or deep‐water whale falls. A new species of lancelet, which was the first record of the subphylum Cephalochordata from reducing environments, a new species of Osedax; a rarely encountered benthic ctenophore, and a rare gastropod species were discovered at this sperm whale‐fall site. Benthic communities were similar across all the carcasses studied, although the body sizes of the whales were very different. The succession of epifaunal communities was relatively rapid and the sulphophilic stage was considerably shorter than that of other known whale falls.     

Experimental evidence of habitat provision by aggregations of Riftia pachyptila at hydrothermal vents on the East Pacific Rise

Habitat created or modified by the physical architecture of large or spatially dominant species plays an important role in structuring communities in a variety of terrestrial, aquatic, and marine habitats. At hydrothermal vents, the giant tubeworm Riftia pachyptila forms large and dense aggregations in a spatially and temporally variable environment. The density and diversity of smaller invertebrates is higher in association with aggregations of R. pachyptila than on the surrounding basalt rock seafloor. Artificial substrata designed to mimic R. pachyptila aggregations were deployed along a gradient of productivity to test the hypothesis that high local species diversity is maintained by the provision of complex physical structure in areas of diffuse hydrothermal flow. After 1 year, species assemblages were compared among artificial aggregations in low‐, intermediate‐, and high‐productivity zones and compared to natural aggregations of R. pachyptila from the same site. Hydrothermal vent fauna colonized every artificial aggregation, and both epifaunal density and species richness were highest in areas of high chemosynthetic primary production. The species richness was also similar between natural aggregations of R. pachyptila and artificial aggregations in intermediate‐ and high‐productivity zones, suggesting that complex physical structure alone can support local species diversity in areas of chemosynthetic primary production. Differences in the community composition between natural and artificial aggregations reflect the variability in microhabitat conditions and biological interactions associated with hydrothermal fluid flux at low‐temperature hydrothermal vents. Moreover, these local ecological factors may further contribute to the maintenance of regional species diversity in hydrothermal vent communities on the East Pacific Rise.     

Life after death: shallow‐water Mediterranean invertebrate communities associated with mammal bones

Invertebrate and microbial marine communities associated with mammal bones are interesting and poorly understood habitats, mainly known from studies on deep‐water whale remains. In order to characterize these communities in the shallow‐water Mediterranean, we present here the results of a pioneering experiment using mammal bones. Minke whale, pig and cow bones were experimentally deployed on three different background communities: rocky substrate, soft‐bottom and a Posidonia oceanica meadow. Bones were deployed for a year at about 20 m depth and collected every 3 months, and the invertebrate fauna colonizing the bones was identified to the lowest possible taxonomic level. As expected, mammal bones showed remarkable differences when compared with background communities. Within bones, four different clusters could be identified, primarily on the basis of the polychaete fauna, the most abundant and diverse group in the survey. Clusters A1–A3 corresponded to high to moderately altered successional stages composed by a fauna closer to that of anthropogenically enriched shallow‐water environments. These clusters were characterized by the occurrence of the opportunist polychaetes Ophryotrocha puerilis, Neanthes caudata (Cluster A1), Protodorvillea kefersteini (Cluster A2) and Ophryotrocha alborana (Cluster A3). Cluster B was characterized by the presence of the polychaete Oxydromus pallidus together with typical invertebrate background fauna, which suggests that this community, after a year of deployment, was closer to that found in natural conditions. As opposed to similar shallow‐water studies in other geographic areas, no occurrence of the polychaete Osedax (commonly known as bone‐eating worms) was reported from our experiments. Apart from the study on the invertebrate communities, insights about the population dynamics of three of the most abundant species (O. puerilis, O. alborana, N. caudata) are given as well as remarks on a hypothetical trophic network based on fecal pellet analysis.     

Consideration of the oasis analogy for chemosynthetic communities at Gulf of Mexico hydrocarbon vents

The analogy between desert oasis and deep-sea chemosynthetic community arose from the biomass contrast between vents and the relatively depauperate background benthic fauna. Fully developed, the analogy helps pose questions about interactions with the background fauna with respect to resources, colonization, and persistence. The chemosynthetic sites of the Gulf of Mexico provide an opportunity to consider possible interactions between vent and nonvent fauna over a 3000-m depth range. It is postulated that deep chemosynthetic communities require the operation of geochemical transporting and concentrating processes to overcome low levels of in situ methane and sulfide production. Clathrate reservoirs may serve these functions. A few chemosynthetic species at the Gulf of Mexico upper slope sites are related to shallow-water sulfide species, but it can be speculated that the dominant chemosynthetic fauna may have originated in a wide spread deep sulfide biome of the Cretaceous. Generic endemism of consumers is low in Gulf of Mexico sites, suggesting a high level of colonization from the surrounding benthos. Chemosynthetic communities may avoid excessive colonization by predators in spite of the apparent food limitation of the surrounding benthos due to toxicity or an evolutionary mechanism selecting against specialized predators. The abundance of large predators is related to the composition of the surrounding benthos and is high at the Gulf of Mexico upper slope sites. Exclusion of chemosyntheic communities from shallower depths may be due to excessive predation by generalists.     

Fauna of whale falls: systematics and ecology of a new polychaete (Annelida: Chrysopetalidae) from the deep Pacific Ocean

Vigtorniella flokati, a new species of polychaete worm associated with decaying whale remains, is described. Three separate V. flokati populations were sampled using submersibles: two associated with implanted gray whale carcasses in the San Diego Trough (1240 m depth) and the Santa Cruz Basin (1670 m) off California, and one from sperm whale and balaeanopterid bones implanted on the slope of Oahu, Hawaii at 1000 m. Extraordinarily large numbers of live specimens were observed and videotaped in situ using submersibles in the San Diego Trough and the Santa Cruz Basin. The populations on the carcass implanted for 4 months in San Diego Trough, and on the bones implanted for 2 years off Oahu, were composed only of small sized individuals (including juveniles). V. flokati most closely resembles the poorly known V. zaikai Kiseleva, 1992, described from the Black Sea. Forty-six morphological characters were used in a phylogenetic analysis of selected nereidiform polychaetes. The resulting most-parsimonious trees indicate sister taxon status between V. flokati and V. zaikai, and that this clade is sister to the putatively ancient polychaete clade Chrysopetalidae. Whale falls, which are intense point sources of organic enrichment at the deep-sea floor, pass through three successional stages. V. flokati appears to colonize the middle, “enrichment opportunist” stage, inhabiting organic-rich bones and sediments 4–24 months after carcass arrival. V. flokati exhibits remarkable behavior, clinging posteriorly to whale bones or nearby sediments to form a writhing carpet at densities exceeding 8000 m⁻². Its extraordinary abundance on whale falls, and apparent absence from other habitats, suggests it to be a whale-fall specialist. The precise feeding mechanism of the worm remains unknown, but we hypothesize that it may utilize dissolved organic carbon derived from the organic-rich setting of whale falls. The widespread occurrence of V. flokati on ephemeral, food-rich habitat islands in the Pacific suggests life-history strategies analogous to those for hydrothermal-vent and cold-seep species.     

New gastropods from deep-sea hydrocarbon seeps off West Africa

Thirteen new species of gastropods are described from the Zairov 1-2 and Biozaire 1-3 cruises to the methane seeps off the Congo River: Patellogastropoda: Paralepetopsis sasakii sp. nov. (Neolepetopsidae); Cocculiniformia: Pyropelta oluae sp. nov. and P. sibuetae sp. nov. (Pyropeltidae); Tentaoculus granulatus sp. nov. (Pseudococculinidae); Neomphalina: Leptogyra costellata sp. nov. (Family uncertain); Vetigastropoda: Puncturella similis sp. nov. (Fissurellidae); Lepetodrilus shannonae sp. nov. (Lepetodrilidae); Caenogastropoda: Provanna reticulata sp. nov. and P. chevalieri sp. nov., Cordesia provannoides gen. et sp. nov. (Provannidae); Phymorhynchus coseli sp. nov. and P. cingulata sp. nov. (Conidae); Heterobranchia: Hyalogyrina rissoella sp. nov. (Hyalogyrinidae). All species except T. granulatus (from a settlement trap) belong to groups known from cold seeps and the entire seep fauna here is new to science. Biogeographical affinity of this gastropod fauna is to the West Atlantic seeps, not to the Mediterranean seeps or Mid-Atlantic vents. Fragments of the autecology of the species are presented. The evolution of the seep gastropod fauna is briefly discussed and a continuous immigration of taxa is supported. The oldest verified occurrences of modern taxa in the seeps date back to Cenomanian (Cretaceous) time, while some taxa seem not to appear until very late Tertiary.     

Hydrothermal vent meiobenthos associated with mytilid mussel aggregations from the Mid-Atlantic Ridge and the East Pacific Rise

Deep-sea hydrothermal vents occur along the mid-ocean ridges and back-arc basins around the globe. There are very few community analyses of vent meiobenthos. The central objectives of this study were to identify and quantify for the first time the entire metazoan meiobenthic community associated with mussel aggregations of Bathymodiolus thermophilus Kenk and Wilson, 1985 from the EPR, 11°N and of Bathymodiolus puteoserpentis Cosel et al., 1994 from the Mid-Atlantic Ridge (MAR), 23°N. Using a quantitative sampling method, abundance, biomass, sex ratio, species richness, diversity, evenness, and trophic structure were studied based on three samples from each site. Meiobenthic abundance in each sample was unexpectedly low, but similar between sites. The community was composed of nematodes, copepods, ostracods, and mites, with a total of 24 species at EPR vents, and 15 species at MAR vents. While most copepod species were vent endemics within the family Dirivultidae, nematodes and harpacticoid copepods belonged to generalist genera, which occur at a variety of habitats and are not restricted to hydrothermal vents or the deep sea. The meiobenthos of hydrothermal-vent mussel beds constitutes a unique community unlike those of other sulfidic habitats, including the thiobios of shallow-water sediments and the meiobenthos of deep-sea, cold-seep sediments. The trophic structure was dominated by primary consumers, mainly deposit feeders, followed by parasites. Predatory meiofaunal species were absent.     

Biological community and sediment fatty acids associated with the deep-sea whale skeleton at the Torishima Seamount

A whale skeleton was discovered on the flat-topped summit of the Torishima Seamount, 4037 m deep, northwest Pacific Ocean, during a dive by the submersibleShinkai 6500 in 1992. The skeleton was encrusted with mytilid mussels and harbored benthic animals such as galatheid crabs, echinoderms, sea anemones, and unidentifiable tube worms. The whale skeleton was revisited in 1993. Sediment samples were collected to outline the chemical-microbial distribution in the sediment associated with the skeleton. In the sediment, there was a gradient of sulfide concentration with the peak of 20 n moles per gram sediment just beneath a bone. Corresponding gradients were observed in thiosulfate-oxidizing enzyme activity, bacterial colony counts and fatty acid amounts. Direct analysis of the sediment fatty acid composition suggested the occurrence of methane-oxidizing bacteria and sulfur-reducing bacteria in close association with the whale skeleton. These observations imply that the methane and sulfides were formed during the saprogenic process and utilized for the chemosynthetic bacterial production to feed the whale skeleton-animal community.     

Discovery of a recent,natural whale fall on the continental slope off Anvers Island,western Antarctic Peninsula

Whale falls provide a substantial, nutrient-rich resource for species in areas of the ocean that may otherwise be largely devoid of food. We report the discovery of a natural whale fall at 1430 m depth in the cold waters of the continental slope off the western Antarctic Peninsula. This is the highest-latitude whale fall reported to date. The section of the carcass we observed—the tail fluke—was more complete than any previously reported natural whale fall from the deep sea and in the early stages of decomposition. We estimate the entire cetacean to measure 5–8 m in length. The flesh remained almost intact on the carcass but the skin was missing from the entire section except for the end of the fluke, clearly exposing blubber and soft tissue. The absence of skin indicates rapid and Homogeneous loss. The dominant macrofauna present were crustaceans, including most prominently the lithodid crab Paralomis birsteini, and zoarcid fish typical of the ‘mobile-scavenger’ successional stage. The density of mobile macrofauna was greatest on the carcass and declined to background levels within 100 m, indicating that they were attracted to the whale fall. This whale fall offers an important opportunity to examine the decomposition of a carcass under deep-sea conditions at polar latitudes.     

Bottom fauna associated with mussel beds and alvinellid communities in the hydrothermal field at 9° N of the East Pacific Rise

Samples from mytilid mollusk and alvinellid polychaet communities and associated fauna were collected during cruise 49 of R/V Akademik Mstislav Keldysh at 9° N of the East Pacific Rise. The mytilids Bathymodiolus thermophylus occupied zones of diffuse releases of hydrothermal solutions with temperature anomalies a few degrees in amplitude. The alvinellid assemblages were located in the hottest parts of hydrothermal vents (～ 40°C) over sulfide mounds. The taxonomic compositions of these kinds of assemblages are different. The taxonomic richness of mytilid communities is almost twice higher. A comparison of the samples using Jaccard’s index showed a greater similarity among the alvinellid samples than that between the mytilid ones. With respect to the species number, polychaets formed the most diverse group, while gastropods were the second most diverse. The dominant species had greater proportions in alvinellid communities than in mytilid ones. This study showed great differences between the mytilid and alvinellid associations in their species composition and community structure.     

Depth-related structure and ecological significance of cold-seep communities—a case study from the Sea of Okhotsk

We discovered and investigated several cold-seep sites in four depth zones of the Sea of Okhotsk off Northeast Sakhalin: outer shelf (160–250 m), upper slope (250–450 m), intermediate slope (450–800 m), and Derugin Basin (1450–1600 m). Active seepage of free methane or methane-rich fluids was detected in each zone. However, seabed photography and sampling revealed that the number of chemoautotrophic species decreases dramatically with decreasing water depth. At greatest depths in the Derugin Basin, the seeps were inhabited by bacterial mats and bivalves of the families Vesicomyidae (Calyptogena aff. pacifica, C. rectimargo, Archivesica sp.), Solemyidae (Acharax sp.) and Thyasiridae (Conchocele bisecta). In addition, pogonophoran tubeworms of the family Sclerolinidae were found in barite edifices. At the shallowest sites, on the shelf at 160 m, the seeps lack chemoautotrophic macrofauna; their locations were indicated only by the patchy occurrence of bacterial mats.Typical seep-endemic metazoans with chemosynthetic symbionts were confined to seep sites at depths below 370 m. A comparative analysis of the structure of seep and background communities suggests that differences in predation pressure may be an important determinant of this pattern. The abundance of predators such as carnivorous brachyurans and asteroids, which can invade seeps from adjacent habitats and efficiently prey on sessile seep bivalves, decreased very pronouncedly with depth. We conclude from the obvious correlation with the conspicuous pattern in the distribution of seep assemblages that, on the shelf and at the upper slope, predator pressure may be high enough to effectively impede any successful settlement of viable populations of seep-endemic metazoans. However, there was also evidence that other depth-related factors, such as bottom-water current, sedimentary regimes, oxygen concentrations and the supply of suitable settling substrates, may additionally regulate the distribution of seep fauna in the area.As a consequence of the pronounced pattern in the distribution of seep communities, their ecological significance as food sources of surrounding background fauna increased with water depth. Isotopic analyses suggest that in the Derugin Basin seep colonists feed on chemoautotrophic seep organisms, either directly or by preying on metazoans with chemosynthetic symbionts. In contrast, seep organisms apparently do not contribute to the nutrition of the adjacent background fauna on the shelf and at the slope. In this area, elevated epifaunal abundances at seep sites were caused primarily by the availability of suitable settling substrates rather than by an enrichment of food supply.     

Spatial organization of food webs along habitat gradients at deep-sea hydrothermal vents on Axial Volcano,Northeast Pacific

Deep-sea hydrothermal vents are characterized by steep spatial gradients and high temporal variability in habitat conditions. This leads to the organization of species distribution along spatial habitat gradients, which may constrain food resource utilization and food web structure. We conducted a stable-isotope-based study to test the hypothesis that food resource utilization is constrained by spatial habitat variability at diffuse hydrothermal vents on Axial Volcano, Northeast Pacific. Our study included the ten most biomass-prominent species and considered the temporal change in food web structure at recently created vent sites during three consecutive years. We related species average stable isotopic composition to their position between the center and the periphery of vent sites, using previously published data. Species spread widely along the δ¹³C axis, and showed a small variability in δ¹⁵N. This indicates that most species partition food resources between isotopically different carbon sources, and that they are not organized along predator–prey trophic chains. Particulate organic matter (POM) stable isotopic composition from a concomitant study corresponds to the signature of the expected diet for most organisms. Species average δ¹³C was significantly correlated to their relative position between the center and the periphery of vent sites. We relate this spatial variability in species isotopic composition to variability in the isotopic signature of both dissolved inorganic carbon (DIC) and POM. This spatial isotopic signal of consumers reveals the spatial structuring of food (POM) production and its consumption by the fauna. Accrual of species during the development of diffuse sites increased the inter-specific spread in δ¹³C, but did not increase the range in δ¹⁵N. Our results show that the spatial organization of species distribution results in a fragmented food web where species partition POM food resources according to their position in space. Shaping of species distribution by habitat gradients therefore constrains food web structure and the occurrence of predator–prey and competitive interactions.     

Importance of seep primary production to Lophelia pertusa and associated fauna in the Gulf of Mexico

To investigate the importance of seep primary production to the nutrition of Lophelia pertusa and associated communities and examine local trophic interactions, we analyzed stable carbon, nitrogen, and sulfur compositions in seven quantitative L. pertusa community collections. A significant seep signature was only detected in one of the 35 species tested (Provanna sculpta, a common seep gastropod) despite the presence of seep fauna at the three sample sites. A potential predator of L. pertusa was identified (Coralliophila sp.), and a variety of other trophic interactions among the fauna occupying the coral framework were suggested by the data, including the galatheid crab Munidopsis sp. 2 feeding upon hydroids and the polychaete Eunice sp. feeding upon the sabellid polychaete Euratella sp. Stable carbon abundances were also determined for different sections of L. pertusa skeleton representing different stages in the growth and life of the aggregation. There was no temporal trend detected in the skeleton isotope values, suggesting that L. pertusa settles in these areas only after seepage has largely subsided. Isotope values of individual taxa that were collected from both L. pertusa and vestimentiferan habitats showed decreasing reliance upon seep primary production with average age of the vestimentiferan aggregation, and finally, no seep signature was detected in the coral collections. Together our data suggest that it is the presence of authigenic carbonate substrata, a product of past seep microbial activity, as well as hydrodynamic processes that drive L. pertusa occurrence at seep sites in the Gulf of Mexico, not nutritional dependence upon primary production by seep microbes.     

Spatial structures of hydrothermal vents and vent-associated megafauna in the back-arc basin system of the Okinawa Trough,western Pacific

Spatial patterns and morphology of hydrothermal vents and the occurrence of vent-associated megafauna were investigated in the back-arc basin system of the Okinawa Trough, western Pacific. Amongst hydrothermal vent fields located on the rising slopes to the NE and S of the basin, the Iheya North area has been subjected to a series of intensive diving surveys. Hydrothermal vents demonstrated concentrated patterns of distribution on different spatial scales. In Iheya North, the majority of vents occurred in lines parallel to the NE to W/SW alignment of the spreading axis, within a radius of ca. 200 m around the most active sulphide structure with the highest recorded fluid temperature of over 300°C. The morphology of hydrothermal vents varied greatly from an incipient flat rock with crevices to a 20- to 30-m-tall, multi-flanged structure with concomitant variation in the distribution and abundance of vent-associated megafauna, particularly a galatheid Shinkaia crosnieri and Bathymodiolus mussels. Comparison of active and inactive vents revealed that the spatial extent of Shinkaia ‘aggregation’ (a group of individuals with short nearest-neighbour distances) effectively defined a habitat unit of this species, and active hydrothermal chimneys contained more of these units, leading to greater spatial occupancy by Shinkaia. Given the temporally unstable nature of vent structures as recognised by repeated surveys, vent assemblages are thought to be closely dictated by the spatio-temporal dynamics of vents in the Okinawa Trough back-arc system.     

Cold-seep assemblages on a giant pockmark off West Africa: spatial patterns and environmental control

A giant pockmark colonised by dense cold‐seep assemblages near 3160 m depth along the Congo‐Angola margin has been surveyed by the ROV Victor 6000. The quantitative distribution of chemosynthetic communities was mapped along the dive tracks from a video study using GIS and image mosaicking. Several types of faunal assemblages, either dominated by bivalves of the families Mytilidae (Bathymodiolus sp.) or Vesicomyidae (Calyptogena sp., ‘Vesicomya’ aff. chuni), or by Siboglinidae polychaetes (Escarpia southwardae) were mapped over the 800‐m diameter pockmark area and sampled for fauna, water and sediment. The isotopic analyses (δ¹³C) of tissues from symbiont‐bearing species were within the range typical of nutrition via symbiosis using methane for mussels and sulphide for vesicomyids and siboglinids. The living chemosynthetic communities were distributed on a SW‐NE axis, corresponding to the expression at the sediment surface of a main buried channel providing fluids to the pockmark. The site was characterised by a more active central part in a depression with abundant carbonate concretions where high‐density clusters of siboglinids and mytilids dominate. Large fields of dead and live vesicomyids with a lower mean density were observed in the external areas. The mean coverage of each of the three symbiotic taxa in these two contrasted areas was estimated from mosaic analysis and was up to 30% in the central area dominated by E. southwardae bushes (23%). Symbiont‐bearing species distribution was consistent with methane concentrations in seawater that were generally higher in mytilid beds than in the vicinity of siboglinids and vesicomyids. A Principal Component Analysis performed on environmental factors at the ten sampling sites revealed that 37% of the observed variance in the distribution of symbiont‐bearing species may be explained by variation in both methane and oxygen concentrations, while a Canonical Redundancy Analysis selected methane concentration as the only variable which explains symbiont‐bearing species densities. This spatial distribution of chemosynthetic species at the pockmark scale may reflect temporal patterns of succession of both substrate and fauna, and may be related to different individual pockmarks visible on the microbathymetry mapped using ROV data.     

Ecological aspects of hydrothermal vent animals in captivity at atmospheric pressure

Hydrothermal vent animals were kept and displayed at atmospheric pressure with an artificial hydrothermal vent system in Enoshima Aquarium, Fujisawa, Kanagawa, Japan. The artificial hydrothermal vent system was composed of a main rearing tank, a heating tank, a hot water outlet with added Na₂S as the source of H₂S, and added CO₂ for chemosynthetic bacteria and pH regulation. When the need arises, a dissolved oxygen control unit and submersible heaters can be attached. We are now rearing hydrothermal vent crabs (Austinograea yunohana), hydrothermal vent galatheid crabs (Shinkaia crosnieri), vestimentiferan tubeworms (Lamellibrachia satsuma), hydrothermal vent shrimp (Opaepele spp.), hydrothermal vent barnacles (Ashinkailepas seepiophilia and Neoverruca sp.), and tonguefish (Symphurus sp.). In the artificial hydrothermal vent tank, shrimp and crabs have been observed to cluster close to the artificial hydrothermal vent. In particular, large (adult) crabs needed a heat source to live in the aquarium over a long term. Additionally, some species (A. yunohana, S. crosnieri, Opaepele sp. and Symphurus sp.) have spawned and hatched in captivity. It is likely higher water temperatures are needed for egg and larval development compared with temperatures for adult requirements.     

Colonization of Sulfurovum sp. on the gill surfaces of Alvinocaris longirostris, a deep-sea hydrothermal vent shrimp

Deep‐sea hydrothermal vents are unique light‐independent ecosystems that are sustained by chemosynthetic bacteria. For many of the invertebrates inhabiting in such environments, bacteria play essential roles in both energy acquisition and detoxification of potentially toxic gases such as H₂S. In this study, the bacterial flora present on the gills of Alvinocaris longirostris (Bresiliidae: Caridea), a shrimp inhabiting hydrothermal vents (1532 m depth) at the Hatoma Knoll of the Okinawa Trough, was investigated. Bacterial 16S rDNA fragments were successfully amplified from the gills and 70% of these fragments showed an identical pattern in the restriction fragment length polymorphism analysis. These fragments were assigned to the ribotype AL‐1. Phylogenetic analyses suggest that AL‐1 forms a monophyletic clade with Sulfurovum spp. (ε‐Proteobacteria). Fluorescence in situ hybridization for AL‐1 and electron microscopy showed the presence of short‐rod bacteria lining up on the cuticular layer of the surface of the gill filaments. These results suggest that bacterial association with gills also occurs in bresiliid shrimps.     

Cold seep communities in the deep eastern Mediterranean Sea: composition, symbiosis and spatial distribution on mud volcanoes

Two mud volcano fields were explored during the French–Dutch MEDINAUT cruise (1998) with the submersible NAUTILE, one south of Crete along the Mediteranean Ridge at about 2000 m depth (Olimpi mud field) and the other south of Turkey between 1700 and 2000 m depth (Anaximander mud field) where high methane concentrations were measured. Chemosynthetic communities were observed and sampled on six mud volcanoes and along a fault scarp. The communities were dominated by bivalves of particularly small size, belonging to families commonly found at seeps (Mytilidae, Vesicomyidae, Thyasiridae) and to Lucinidae mostly encountered in littoral sulfide-rich sediments and at the shallowest seeps. Siboglinid polychaetes including a large vestimentiferan Lamellibrachia sp. were also associated. At least four bivalve species and one siboglinid are associated with symbiotic chemoautotrophic bacteria, as evidenced by Transmission Electronic Microscopy and isotopic ratio measurements. Among the bivalves, a mytilid harbors both methanotrophic and sulfide-oxidizing bacteria. Video spatial analysis of the community distribution on three volcanoes shows that dense bivalve shell accumulations (mainly lucinids) spread over large areas, from 10% to 38% of the explored areas (2500–15000 m²) on the different volcanoes. Lamellibrachia sp. had different spatial distribution and variable density in the two mud volcano fields, apparently related with higher methane fluxes in the Anaximander volcanoes and maybe with the instability due to brines in the Olimpi area. The abundance and richness of the observed chemosynthetic fauna and the size of some of the species contrast with the poverty of the deep eastern Mediterranean. The presence of a specialized fauna, with some mollusk genera and species shared with other reduced environments of the Mediterranean, but not dominated by the large bivalves usually found at seeps, is discussed.