Hydrothermal vent fields and chemosynthetic biota on the world's deepest seafloor spreading centre

DNA Polymerization in Icy Moon Abyssal Pressure Conditions

Evidence of stable liquid water oceans beneath the ice crust of moons within the Solar System is of great interest for astrobiology. In particular, subglacial oceans may present hydrothermal processes in their abysses, similarly to terrestrial hydrothermal vents. Therefore, terrestrial extremophilic deep life can be considered a model for putative icy moon extraterrestrial life. However, the comparison between putative extraterrestrial abysses and their terrestrial counterparts suffers from a potentially determinant difference. Indeed, some icy moons oceans may be so deep that the hydrostatic pressure would exceed the maximal pressure at which hydrothermal vent organisms have been isolated. While terrestrial microorganisms that are able to survive in such conditions are known, the effect of high pressure on fundamental biochemical processes is still unclear. In this study, the effects of high hydrostatic pressure on DNA synthesis catalyzed by DNA polymerases are investigated for the first time. The effect on both strand displacement and primer extension activities is measured, and pressure tolerance is compared between enzymes of various thermophilic organisms isolated at different depths.

Microbial eukaryotic predation pressure and biomass at deep-sea hydrothermal vents

Deep-sea hydrothermal vent geochemistry shapes the foundation of the microbial food web by fueling chemolithoautotrophic microbial activity. Microbial eukaryotes (or protists) play a critical role in hydrothermal vent food webs as consumers and hosts of symbiotic bacteria, and as a nutritional source to higher trophic levels. We measured microbial eukaryotic cell abundance and predation pressure in low-temperature diffuse hydrothermal fluids at the Von Damm and Piccard vent fields along the Mid-Cayman Rise in the Western Caribbean Sea. We present findings from experiments performed under in situ pressure that show cell abundances and grazing rates higher than those done at 1 atmosphere (shipboard ambient pressure); this trend was attributed to the impact of depressurization on cell integrity. A relationship between the protistan grazing rate, prey cell abundance, and temperature of end-member hydrothermal vent fluid was observed at both vent fields, regardless of experimental approach. Our results show substantial protistan biomass at hydrothermally fueled microbial food webs, and when coupled with improved grazing estimates, suggest an important contribution of grazers to the local carbon export and supply of nutrient resources to the deep ocean.

A tale of two tubeworms: taxonomy of vestimentiferans (Annelida: Siboglinidae) from the Mid-Cayman Spreading Centre

The vestimentiferan tubeworm genera Lamellibrachia and Escarpia inhabit deep-sea chemosynthesis-based ecosystems, such as seeps, hydrothermal vents and organic falls, and have wide distributions across the Pacific, Atlantic and Indian Oceans. In 2010–2012 during initial explorations of hydrothermal vents of the Mid-Cayman Spreading Centre (MCSC), both genera were found to co-occur at the Von Damm Vent Field (VDVF), a site characterised by diffuse flow, therefore resembling a ‘hydrothermal seep’. Here, we erect two new vestimentiferan tubeworm species from the VDVF, Lamellibrachia judigobini sp. nov. and Escarpia tritentaculata sp. nov. Lamellibrachia judigobini sp. nov. differs genetically and morphologically from other Lamellibrachia species, and has a range that extends across the Gulf of Mexico, MCSC, off Trinidad and Tobago, and Barbados, and also across both vents and seeps and 964–3304-m water depth. Escarpia tritentaculata sp. nov. is distinguished from other Escarpia species primarily based on morphology and is known only from vents of the MCSC at 2300-m depth. This study highlights the incredible habitat flexibility of a single Lamellibrachia species and the genus Escarpia, and historic biogeographic connections to the eastern Pacific for L. judigobini sp. nov. and the eastern Atlantic for E. tritentaculata sp. nov. ZooBank: urn:lsid:zoobank.org:pub:D9F72BD4-FDE1-4C0A-B84B-A08D06F2A981

Metagenomics Reveals Dominant Unusual Sulfur Oxidizers Inhabiting Active Hydrothermal Chimneys From the Southwest Indian Ridge

The deep-sea hydrothermal vents (DSHVs) in the Southwest Indian Ridge (SWIR) are formed by specific geological settings. However, the community structure and ecological function of the microbial inhabitants on the sulfide chimneys of active hydrothermal vents remain largely unknown. In this study, our analyses of 16S rRNA gene amplicons and 16S rRNA metagenomic reads showed the dominance of sulfur-oxidizing Ectothiorhodospiraceae, Thiomicrorhabdus, Sulfurimonas, and Sulfurovum on the wall of two active hydrothermal chimneys. Compared with the inactive hydrothermal sediments of SWIR, the active hydrothermal chimneys lacked sulfur-reducing bacteria. The metabolic potentials of the retrieved 82 metagenome-assembled genomes (MAGs) suggest that sulfur oxidation might be conducted by Thiohalomonadales (classified as Ectothiorhodospiraceae based on 16S rRNA gene amplicons), Sulfurovaceae, Hyphomicrobiaceae, Thiotrichaceae, Thiomicrospiraceae, and Rhodobacteraceae. For CO2 fixation, the Calvin-Benson-Bassham and reductive TCA pathways were employed by these bacteria. In Thiohalomonadales MAGs, we revealed putative phytochrome, carotenoid precursor, and squalene synthesis pathways, indicating a possible capacity of Thiohalomonadales in adaptation to dynamics redox conditions and the utilization of red light from the hot hydrothermal chimneys for photolithotrophic growth. This study, therefore, reveals unique microbiomes and their genomic features in the active hydrothermal chimneys of SWIR, which casts light on ecosystem establishment and development in hydrothermal fields and the deep biosphere.

Recent Developments of Exploration and Detection of Shallow-Water Hydrothermal Systems

A hydrothermal vent system is one of the most unique marine environments on Earth. The cycling hydrothermal fluid hosts favorable conditions for unique life forms and novel mineralization mechanisms, which have attracted the interests of researchers in fields of biological, chemical and geological studies. Shallow-water hydrothermal vents located in coastal areas are suitable for hydrothermal studies due to their close relationship with human activities. This paper presents a summary of the developments in exploration and detection methods for shallow-water hydrothermal systems. Mapping and measuring approaches of vents, together with newly developed equipment, including sensors, measuring systems and water samplers, are included. These techniques provide scientists with improved accuracy, efficiency or even extended data types while studying shallow-water hydrothermal systems. Further development of these techniques may provide new potential for hydrothermal studies and relevant studies in fields of geology, origins of life and astrobiology.

Chemical and isotopic analyses of hydrocarbon-bearing fluid inclusions in olivine-rich rocks

We examined the mineralogical, chemical and isotopic compositions of secondary fluid inclusions in olivine-rich rocks from two active serpentinization systems: the Von Damm hydrothermal field (Mid-Cayman Rise) and the Zambales ophiolite (Philippines). Peridotite, troctolite and gabbroic rocks in these systems contain abundant CH4-rich secondary inclusions in olivine, with less abundant inclusions in plagioclase and clinopyroxene. Olivine-hosted secondary inclusions are chiefly composed of CH4 and minor H2, in addition to secondary minerals including serpentine, brucite, magnetite and carbonates. Secondary inclusions in plagioclase are dominated by CH4 with variable amounts of H2 and H2O, while those in clinopyroxene contain only CH4. We determined hydrocarbon abundances and stable carbon isotope compositions by crushing whole rocks and analysing the released volatiles using isotope ratio monitoring-gas chromatography mass spectrometry. Bulk rock gas analyses yielded appreciable quantities of CH4 and C2H6 in samples from Cayman (4-313 nmol g-1 CH4 and 0.02-0.99 nmol g-1 C2H6), with lesser amounts in samples from Zambales (2-37 nmol g-1 CH4 and 0.004-0.082 nmol g-1 C2H6). Mafic and ultramafic rocks at Cayman exhibit δ13CCH4 values of -16.7‰ to -4.4‰ and δ13CC2H6 values of -20.3‰ to +0.7‰. Ultramafic rocks from Zambales exhibit δ13CCH4 values of -12.4‰ to -2.8‰ and δ13CC2H6 values of -1.2‰ to -0.9‰. Similarities in the carbon isotopic compositions of CH4 and C2H6 in plutonic rocks, Von Damm hydrothermal fluids, and Zambales gas seeps suggest that leaching of fluid inclusions may provide a significant contribution of abiotic hydrocarbons to deep-sea vent fluids and ophiolite-hosted gas seeps. Isotopic compositions of CH4 and C2H6 from a variety of hydrothermal fields hosted in olivine-rich rocks that are similar to those in Von Damm vent fluids further support the idea that a significant portion of abiotic hydrocarbons in ultramafic-influenced vent fluids is derived from fluid inclusions. This article is part of a discussion meeting issue 'Serpentinite in the Earth system'.

Plume Tracing via Model-Free Reinforcement Learning Method

This paper studies the plume-tracing strategy for an autonomous underwater vehicle (AUV) in the deep-sea turbulent environment. The tracing problem is modeled as a partially observable Markov decision process with continuous state space and action space due to the spatio-temporal changes of environment. An long short-term memory-based reinforcement learning framework with full use of history information is proposed to generate a smooth strategy while the AUV interacting with the environment. Continuous temporal difference and deterministic policy gradient methods are employed to improve the strategy. To promote the performance of the algorithm, a supervised strategy generated by dynamic programming methods is utilized as transcendental knowledge of the agent. Historical searching trajectory's form and the exploration technology are specially designed to fit the algorithm. Simulation environments are established based on Reynolds-averaged Navier-Stokes equations and the effectiveness of the learned plume-tracing strategy is validated with simulation experiments.

Autonomous marine environmental monitoring: Application in decommissioned oil fields

Hundreds of Oil & Gas Industry structures in the marine environment are approaching decommissioning. In most areas decommissioning operations will need to be supported by environmental assessment and monitoring, potentially over the life of any structures left in place. This requirement will have a considerable cost for industry and the public. Here we review approaches for the assessment of the primary operating environments associated with decommissioning - namely structures, pipelines, cuttings piles, the general seabed environment and the water column - and show that already available marine autonomous systems (MAS) offer a wide range of solutions for this major monitoring challenge. Data of direct relevance to decommissioning can be collected using acoustic, visual, and oceanographic sensors deployed on MAS. We suggest that there is considerable potential for both cost savings and a substantial improvement in the temporal and spatial resolution of environmental monitoring. We summarise the trade-offs between MAS and current conventional approaches to marine environmental monitoring. MAS have the potential to successfully carry out much of the monitoring associated with decommissioning and to offer viable alternatives where a direct match for the conventional approach is not possible.

Methanofervidicoccus abyssi gen. nov., sp. nov., a hydrogenotrophic methanogen, isolated from a hydrothermal vent chimney in the Mid-Cayman Spreading Center, the Caribbean Sea

A novel hydrogenotrophic methanogen, strain HHB^T, was isolated from a deep-sea hydrothermal vent chimney sample collected from Beebe Vent Field at the Mid-Cayman Spreading Center, Caribbean Sea. The cells were non-motile regular to irregular cocci possessing several flagella. The novel isolate grew at 60-80 °C, pH 5.0-7.4 and with 1-4 % of NaCl (w/v). The isolate utilized H2/CO2 as the only substrates for growth and methane production. The results of phylogenetic analyses of both 16S rRNA and mcrA gene sequences and comparative genome analysis indicated that HHB^T represented a member of the order Methanococcales, and was closely related to the members of the genera Methanothermococcus and Methanotorris. The most closely related species were Methanothermococcus okinawensis IH1^T and Methanotorris igneus Kol 5^T in comparison of 16S rRNA gene sequences (each with 93 % identity), and Methanotorris formicicus Mc-S-70^T in the case of deduced amino acid sequence similarity of mcrA genes (92 % similarity). The ANI and AAI values between HHB^T and the members of the genera Methanothermococcus and Methanotorris were 69-72 % and 66-70 %, respectively. Although many of the morphological and physiological characteristics were quite similar between HHB^T and the species of the genera Methanothermococcus and Methanotorris, they were distinguishable by the differences in susceptibility to antibiotics, formate utilization, growth temperature and NaCl ranges. On the basis of these phenotypic, phylogenetic and genomic properties, we propose that strain HHB^T represents a novel species, of a novel genus, Methanofervidicoccus abyssi gen. nov., sp. nov. The type strain is HHB^T (=JCM 32161^T=DSM 105918^T).

Volcanic-Tectonic Structure of the Mount Dent Oceanic Core Complex in the Ultraslow Mid-Cayman Spreading Center Determined From Detailed Seafloor Investigation

The flanks of the ultraslow-spreading Mid-Cayman Spreading Center (MCSC) are characterized by domal massifs or oceanic core complexes (OCCs). The most prominent of these, Mount Dent, comprises lower-crustal and upper-mantle lithologies and hosts the Von Damm vent field ~12 km west of the axial deep. Here, presented autonomous underwater vehicle-derived swath sonar (multibeam) mapping and deep-towed side-scan sonar imagery lead to our interpretation that: (i) slip along the OCC-bounding detachment fault is ceasing, (ii) the termination zone, where detachment fault meets the hanging wall, is disintegrating, (iii) the domed surface of the OCC is cut by steep north-south extensional faulting, and (iv) the breakaway zone is cut by outward facing faults. The Von Damm vent field and dispersed pockmarks on the OCC's south flank further suggest that hydrothermal fluid flow is pervasive within the faulted OCC. On the axial floor of the MCSC, bright acoustic backscatter and multibeam bathymetry reveal: (v) a volcanic detachment hanging wall, (vi) a major fault rifting the southern flank of Mount Dent, and (vii) a young axial volcanic ridge intersecting its northern flank. These observations are described by a conceptual model wherein detachment faulting and OCC exhumation are ceasing during an increase in magmatic intrusion, brittle deformation, and hydrothermal circulation within the OCC. Together, this high-resolution view of the MCSC provides an instructive example of how OCCs, formed within an overall melt-starved ultraslow spreading center, can undergo magmatism, hydrothermal activity, and faulting in much the same way as expected in magmatically more robust slow-spreading centers elsewhere.

Periodic and Spatial Spreading of Alkanes and Alcanivorax Bacteria in Deep Waters of the Mariana Trench

In subduction zones, serpentinization and biological processes may release alkanes to the deep waters, which would probably result in the rapid spread of Alcanivorax However, the timing and area of the alkane distribution and associated enrichment of alkane-degrading microbes in the dark world of the deep ocean have not been explored. In this study, we report the richness (up to 17.8%) of alkane-degrading bacteria, represented by Alcanivorax jadensis, in deep water samples obtained at 3,000 to 6,000 m in the Mariana Trench in two cruises. The relative abundance of A. jadensis correlated with copy numbers of functional almA and alkB genes, which are involved in alkane degradation. In these water samples, we detected a high flux of alkanes, which probably resulted in the prevalence of A. jadensis in the deep waters. Contigs of A. jadensis were binned from the metagenomes for examination of alkane degradation pathways and deep sea-specific pathways, which revealed a lack of nitrate and nitrite dissimilatory reduction in our A. jadensis strains. Comparing the results for the two cruises conducted close to each other, we suggest periodic release of alkanes that may spread widely but periodically in the trench. Distribution of alkane-degrading bacteria in the world's oceans suggests the periodic and remarkable contributions of Alcanivorax to the deep sea organic carbon and nitrogen sources.IMPORTANCE In the oligotrophic environment of the Mariana Trench, alkanes as carbohydrates are important for the ecosystem, but their spatial and periodic spreading in deep waters has never been reported. Alkane-degrading bacteria such as Alcanivorax spp. are biological signals of the alkane distribution. In the present study, Alcanivorax was abundant in some waters, at depths of up to 6,000 m, in the Mariana Trench. Genomic, transcriptomic, and chemical analyses provide evidence for the presence and activities of Alcanivorax jadensis in deep sea zones. The periodic spreading of alkanes, probably from the subductive plates, might have fundamentally modified the local microbial communities, as well as perhaps the deep sea microenvironment.

Geomorphological evidence of large vertebrates interacting with the seafloor at abyssal depths in a region designated for deep-sea mining

Exploration licences for seafloor mineral deposits have been granted across large areas of the world's oceans, with the abyssal Pacific Ocean being the primary target for polymetallic nodules-a potentially valuable source of minerals. These nodule-bearing areas support a large diversity of deep-sea life and although studies have begun to characterize the benthic fauna within the region, the ecological interactions between large bathypelagic vertebrates of the open ocean and the abyssal seafloor remain largely unknown. Here we report seafloor geomorphological alterations observed by an autonomous underwater vehicle that suggest large vertebrates could have interacted with the seafloor to a maximum depth of 4258 m in the recent geological past. Patterns of disturbance on the seafloor are broadly comparable to those recorded in other regions of the world's oceans attributed to beaked whales. These observations have important implications for baseline ecological assessments and the environmental management of potential future mining activities within this region of the Pacific.

Variation in species diversity of deep-water megafauna assemblages in the Caribbean across depth and ecoregions

Diversity patterns of the deep-sea megafauna in the Caribbean Basin and the Guiana ecoregion were analyzed in order to test the hypothesis of species richness variation as a function of depth and the hypothesis of non-differences between ecoregions by analyzing spatial patterns of five taxa and a merged assemblage. Collections of five taxa (corals, sea stars, sea urchins, sea lilies and gastropods) were obtained from seven oceanographic expeditions aboard the R/V Pillsbury at 310 stations between 60 and 7500 m depth. Data were sorted according to depth zones and ecoregions and were analyzed in order to estimate species richness, changes in species composition and distinction of β-diversity by species turnover or by nestedness. The observed patterns of diversity were consistent between taxa and their assemblage: Species richness increased from the continental shelf (60-200 m deep) to the slope (200-2000 m deep), followed by a decrease at the continental rise-abyssal zone. We detected marked changes in species composition according to depth ranges. Changes in species composition in relation to ecoregions were also detected. In general, the Caribbean Basin lacks important physical barriers, causing high deep-sea ecosystem connectivity; however, variation in composition could be related to changes in environmental conditions associated with productivity and/or continental influences.

Metagenomic investigation of vestimentiferan tubeworm endosymbionts from Mid-Cayman Rise reveals new insights into metabolism and diversity

BACKGROUND

The microbial endosymbionts of two species of vestimentiferan tubeworms (Escarpia sp. and Lamellibrachia sp.2) collected from an area of low-temperature hydrothermal diffuse vent flow at the Mid-Cayman Rise (MCR) in the Caribbean Sea were characterized using microscopy, phylogenetic analyses, and a metagenomic approach.

RESULTS

Bacteria, with a typical Gram negative cell envelope contained within membrane-bound vacuoles, were observed within the trophosome of both tubeworm species. Phylogenetic analysis of the 16S rRNA gene and ITS region suggested MCR individuals harbored highly similar endosymbionts that were > 98% identical, with the exception of two symbionts that showed a 60 bp insertion within the ITS region. All sequences from MCR endosymbionts formed a separate well-supported clade that diverged from those of symbionts of seep and vent vestimentiferans from the Pacific, Gulf of Mexico, and Mediterranean Sea. The metagenomes of the symbionts of two specimens of each tubeworm species were sequenced, and two distinct Gammaproteobacteria metagenome-assembled genomes (MAGs) of more than 4 Mbp assembled. An Average Nucleotide Identity (ANI) of 86.5% between these MAGs, together with distinct 16S rRNA gene and ITS sequences, indicate the presence of multiple endosymbiont phylotypes at the MCR, with one MAG shared between one Escarpia and two Lamellibrachia individuals, indicating these endosymbionts are not specific to either host species. Genes for sulfur and hydrogen oxidation, nitrate reduction (assimilatory and dissimilatory), glycolysis and the Krebs cycle, peptide, sugar, and lipid transporters, and both rTCA and CBB carbon fixation cycles were detected in the MAGs, highlighting key and shared functions with symbiont metagenomes of the vestimentiferans Riftia, Tevnia, and Ridgeia from the Pacific. The potential for a second hydrogen oxidation pathway (via a bidirectional hydrogenase), formate dehydrogenase, a catalase, and several additional peptide transporters were found exclusively in the MCR endosymbiont MAGs.

CONCLUSIONS

The present study adds new evidence that tubeworm endosymbionts can potentially switch from autotrophic to heterotrophic metabolism, or may be mixotrophic, presumably while free-living, and also suggests their versatile metabolic potential may enable both the host and symbionts to exploit a wide range of environmental conditions. Together, the marked gene content and sequence dissimilarity at the rRNA operon and whole genome level between vent and seep symbionts suggest these newly described endosymbionts from the MCR belong to a novel tubeworm endosymbiont genera, introduced as Candidatus Vondammii.

Iron Biogeochemistry in the High Latitude North Atlantic Ocean

Iron (Fe) is an essential micronutrient for marine microbial organisms, and low supply controls productivity in large parts of the world’s ocean. The high latitude North Atlantic is seasonally Fe limited, but Fe distributions and source strengths are poorly constrained. Surface ocean dissolved Fe (DFe) concentrations were low in the study region (<0.1 nM) in summer 2010, with significant perturbations during spring 2010 in the Iceland Basin as a result of an eruption of the Eyjafjallajökull volcano (up to 2.5 nM DFe near Iceland) with biogeochemical consequences. Deep water concentrations in the vicinity of the Reykjanes Ridge system were influenced by pronounced sediment resuspension, with indications for additional inputs by hydrothermal vents, with subsequent lateral transport of Fe and manganese plumes of up to 250–300 km. Particulate Fe formed the dominant pool, as evidenced by 4–17 fold higher total dissolvable Fe compared with DFe concentrations, and a dynamic exchange between the fractions appeared to buffer deep water DFe. Here we show that Fe supply associated with deep winter mixing (up to 103 nmol m⁻² d⁻¹) was at least ca. 4–10 times higher than atmospheric deposition, diffusive fluxes at the base of the summer mixed layer, and horizontal surface ocean fluxes.

Genomic variation in microbial populations inhabiting the marine subseafloor at deep-sea hydrothermal vents

Little is known about evolutionary drivers of microbial populations in the warm subseafloor of deep-sea hydrothermal vents. Here we reconstruct 73 metagenome-assembled genomes (MAGs) from two geochemically distinct vent fields in the Mid-Cayman Rise to investigate patterns of genomic variation within subseafloor populations. Low-abundance populations with high intra-population diversity coexist alongside high-abundance populations with low genomic diversity, with taxonomic differences in patterns of genomic variation between the mafic Piccard and ultramafic Von Damm vent fields. Populations from Piccard are significantly enriched in nonsynonymous mutations, suggesting stronger purifying selection in Von Damm relative to Piccard. Comparison of nine Sulfurovum MAGs reveals two high-coverage, low-diversity MAGs from Piccard enriched in unique genes related to the cellular membrane, suggesting these populations were subject to distinct evolutionary pressures that may correlate with genes related to nutrient uptake, biofilm formation, or viral invasion. These results are consistent with distinct evolutionary histories between geochemically different vent fields, with implications for understanding evolutionary processes in subseafloor microbial populations.

Hydrothermal activity, functional diversity and chemoautotrophy are major drivers of seafloor carbon cycling

Hydrothermal vents are highly dynamic ecosystems and are unusually energy rich in the deep-sea. In situ hydrothermal-based productivity combined with sinking photosynthetic organic matter in a soft-sediment setting creates geochemically diverse environments, which remain poorly studied. Here, we use comprehensive set of new and existing field observations to develop a quantitative ecosystem model of a deep-sea chemosynthetic ecosystem from the most southerly hydrothermal vent system known. We find evidence of chemosynthetic production supplementing the metazoan food web both at vent sites and elsewhere in the Bransfield Strait. Endosymbiont-bearing fauna were very important in supporting the transfer of chemosynthetic carbon into the food web, particularly to higher trophic levels. Chemosynthetic production occurred at all sites to varying degrees but was generally only a small component of the total organic matter inputs to the food web, even in the most hydrothermally active areas, owing in part to a low and patchy density of vent-endemic fauna. Differences between relative abundance of faunal functional groups, resulting from environmental variability, were clear drivers of differences in biogeochemical cycling and resulted in substantially different carbon processing patterns between habitats.

Cutting through the smoke: the diversity of microorganisms in deep-sea hydrothermal plumes

There are still notable gaps regarding the detailed distribution of microorganisms between and within insular habitats such as deep-sea hydrothermal vents. This study investigates the community composition of black smoker vent microorganisms in the Southern Hemisphere, and changes thereof along a spatial and chemical gradient ranging from the vent plume to surrounding waters. We sampled two hydrothermal vent fields, one at the South West Indian Ridge (SWIR), the other at the East Scotia Ridge (ESR). Samples were collected across vent fields at varying vertical distances from the origin of the plumes. The microbial data were sequenced on an Illumina MiSeq platform for the 16SrRNA gene. A substantial amount of vent-specific putative chemosynthetic microorganisms were found, particularly in samples from focused hydrothermal venting. Common vent-specific organisms from both vent fields were the genera Arcobacter, Caminibacter and Sulfurimonas from the Epsilonproteobacteria and the SUP05 group from the Gammaproteobacteria. There were no major differences in microbial composition between SWIR and ESR for focused plume samples. However, within the ESR the diffuse flow and focused samples differed significantly in microbial community composition and relative abundance. For Epsilonproteobacteria, we found evidence of niche-specificity to hydrothermal vent environments. This taxon decreased in abundance by three orders of magnitude from the vent orifice to background water. Epsilonproteobacteria distribution followed a distance-decay relationship as vent-effluents mixed with the surrounding seawater. This study demonstrates strong habitat affinity of vent microorganisms on a metre scale with distinct environmental selection.

Ecology and biogeography of megafauna and macrofauna at the first known deep-sea hydrothermal vents on the ultraslow-spreading Southwest Indian Ridge

The Southwest Indian Ridge is the longest section of very slow to ultraslow-spreading seafloor in the global mid-ocean ridge system, but the biogeography and ecology of its hydrothermal vent fauna are previously unknown. We collected 21 macro- and megafaunal taxa during the first Remotely Operated Vehicle dives to the Longqi vent field at 37° 47′S 49° 39′E, depth 2800 m. Six species are not yet known from other vents, while six other species are known from the Central Indian Ridge, and morphological and molecular analyses show that two further polychaete species are shared with vents beyond the Indian Ocean. Multivariate analysis of vent fauna across three oceans places Longqi in an Indian Ocean province of vent biogeography. Faunal zonation with increasing distance from vents is dominated by the gastropods Chrysomallon squamiferum and Gigantopelta aegis, mussel Bathymodiolus marisindicus, and Neolepas sp. stalked barnacle. Other taxa occur at lower abundance, in some cases contrasting with abundances at other vent fields, and δ¹³C and δ¹⁵N isotope values of species analysed from Longqi are similar to those of shared or related species elsewhere. This study provides baseline ecological observations prior to mineral exploration activities licensed at Longqi by the United Nations.

Subseafloor microbial communities in hydrogen-rich vent fluids from hydrothermal systems along the Mid-Cayman Rise

Warm fluids emanating from hydrothermal vents can be used as windows into the rocky subseafloor habitat and its resident microbial community. Two new vent systems on the Mid‐Cayman Rise each exhibits novel geologic settings and distinctively hydrogen‐rich vent fluid compositions. We have determined and compared the chemistry, potential energy yielding reactions, abundance, community composition, diversity, and function of microbes in venting fluids from both sites: Piccard, the world's deepest vent site, hosted in mafic rocks; and Von Damm, an adjacent, ultramafic‐influenced system. Von Damm hosted a wider diversity of lineages and metabolisms in comparison to Piccard, consistent with thermodynamic models that predict more numerous energy sources at ultramafic systems. There was little overlap in the phylotypes found at each site, although similar and dominant hydrogen‐utilizing genera were present at both. Despite the differences in community structure, depth, geology, and fluid chemistry, energetic modelling and metagenomic analysis indicate near functional equivalence between Von Damm and Piccard, likely driven by the high hydrogen concentrations and elevated temperatures at both sites. Results are compared with hydrothermal sites worldwide to provide a global perspective on the distinctiveness of these newly discovered sites and the interplay among rocks, fluid composition and life in the subseafloor.

Talc-dominated seafloor deposits reveal a new class of hydrothermal system

The Von Damm Vent Field (VDVF) is located on the flanks of the Mid-Cayman Spreading Centre, 13 km west of the axial rift, within a gabbro and peridotite basement. Unlike any other active vent field, hydrothermal precipitates at the VDVF comprise 85-90% by volume of the magnesium silicate mineral, talc. Hydrothermal fluids vent from a 3-m high, 1-m diameter chimney and other orifices at up to 215 °C with low metal concentrations, intermediate pH (5.8) and high concentrations (667 mmol kg(-1)) of chloride relative to seawater. Here we show that the VDVF vent fluid is generated by interaction of seawater with a mafic and ultramafic basement which precipitates talc on mixing with seawater. The heat flux at the VDVF is measured at 487±101 MW, comparable to the most powerful magma-driven hydrothermal systems known, and may represent a significant mode of off-axis oceanic crustal cooling not previously recognized or accounted for in global models.

Pathways for abiotic organic synthesis at submarine hydrothermal fields

Arguments for an abiotic origin of low-molecular weight organic compounds in deep-sea hot springs are compelling owing to implications for the sustenance of deep biosphere microbial communities and their potential role in the origin of life. Theory predicts that warm H2-rich fluids, like those emanating from serpentinizing hydrothermal systems, create a favorable thermodynamic drive for the abiotic generation of organic compounds from inorganic precursors. Here, we constrain two distinct reaction pathways for abiotic organic synthesis in the natural environment at the Von Damm hydrothermal field and delineate spatially where inorganic carbon is converted into bioavailable reduced carbon. We reveal that carbon transformation reactions in a single system can progress over hours, days, and up to thousands of years. Previous studies have suggested that CH4 and higher hydrocarbons in ultramafic hydrothermal systems were dependent on H2 generation during active serpentinization. Rather, our results indicate that CH4 found in vent fluids is formed in H2-rich fluid inclusions, and higher n-alkanes may likely be derived from the same source. This finding implies that, in contrast with current paradigms, these compounds may form independently of actively circulating serpentinizing fluids in ultramafic-influenced systems. Conversely, widespread production of formate by ΣCO2 reduction at Von Damm occurs rapidly during shallow subsurface mixing of the same fluids, which may support anaerobic methanogenesis. Our finding of abiogenic formate in deep-sea hot springs has significant implications for microbial life strategies in the present-day deep biosphere as well as early life on Earth and beyond.

An investigation into mechanical strength of exoskeleton of hydrothermal vent shrimp (Rimicaris exoculata) and shallow water shrimp (Pandalus platyceros) at elevated temperatures

This investigation reports a comparison of the exoskeleton mechanical strength of deep sea shrimp species Rimicaris exoculata and shallow water shrimp species Pandalus platyceros at temperatures ranging from 25°C to 80°C using nanoindentation experiments. Scanning Electron Microscopy (SEM) observations suggest that both shrimp exoskeletons have the Bouligand structure. Differences in the structural arrangement and chemical composition of both shrimps are highlighted by SEM and EDX (Energy Dispersive X-ray) analyses. The variation in the elastic moduli with temperature is found to be correlated with the measured compositional differences. The reduced modulus of R. exoculata is 8.26±0.89GPa at 25°C that reduces to 7.61±0.65GPa at 80°C. The corresponding decrease in the reduced modulus of P. platyceros is from 27.38±2.3GPa at 25°C to 24.58±1.71GPa at 80°C. The decrease in reduced moduli as a function of temperature is found to be dependent on the extent of calcium based minerals in exoskeleton of both types of shrimp exoskeletons.

The origin of methanethiol in midocean ridge hydrothermal fluids

Simple alkyl thiols such as methanethiol (CH3SH) are widely speculated to form in seafloor hot spring fluids. Putative CH3SH synthesis by abiotic (nonbiological) reduction of inorganic carbon (CO2 or CO) has been invoked as an initiation reaction for the emergence of protometabolism and microbial life in primordial hydrothermal settings. Thiols are also presumptive ligands for hydrothermal trace metals and potential fuels for associated microbial communities. In an effort to constrain sources and sinks of CH3SH in seafloor hydrothermal systems, we determined for the first time its abundance in diverse hydrothermal fluids emanating from ultramafic, mafic, and sediment-covered midocean ridge settings. Our data demonstrate that the distribution of CH3SH is inconsistent with metastable equilibrium with inorganic carbon, indicating that production by abiotic carbon reduction is more limited than previously proposed. CH3SH concentrations are uniformly low (∼10(-8) M) in high-temperature fluids (>200 °C) from all unsedimented systems and, in many cases, suggestive of metastable equilibrium with CH4 instead. Associated low-temperature fluids (<200 °C) formed by admixing of seawater, however, are invariably enriched in CH3SH (up to ∼10(-6) M) along with NH4(+) and low-molecular-weight hydrocarbons relative to high-temperature source fluids, resembling our observations from a sediment-hosted system. This strongly implicates thermogenic interactions between upwelling fluids and microbial biomass or associated dissolved organic matter during subsurface mixing in crustal aquifers. Widespread thermal degradation of subsurface organic matter may be an important source of organic production in unsedimented hydrothermal systems and may influence microbial metabolic strategies in cooler near-seafloor and plume habitats.

Patterns of deep-water coral diversity in the Caribbean Basin and adjacent southern waters: an approach based on records from the R/V Pillsbury expeditions

The diversity of deep-water corals in the Caribbean Sea was studied using records from oceanographic expeditions performed by the R/V Pillsbury. Sampled stations were sorted according to broad depth ranges and ecoregions and were analyzed in terms of species accumulation curves, variance in the species composition and contributions to alpha, beta and gamma diversity. According to the analysis of species accumulation curves using the Chao2 estimator, more diversity occurs on the continental slope (200–2000 m depth) than on the upper continental shelf (60–200 m depth). In addition to the effect of depth sampling, differences in species composition related to depth ranges were detected. However, the differences between ecoregions are dependent on depth ranges, there were fewer differences among ecoregions on the continental slope than on the upper continental shelf. Indicator species for distinctness of ecoregions were, in general, Alcyonaria and Antipatharia for the upper continental shelf, but also the scleractinians Madracis myriabilis and Cladocora debilis. In the continental slope, the alcyonarian Placogorgia and the scleractinians Stephanocyathus and Fungiacyathus were important for the distinction of ecoregions. Beta diversity was the most important component of gamma diversity in the Caribbean Basin. The contribution of ecoregions to alpha, beta and gamma diversity differed with depth range. On the upper continental shelf, the Southern Caribbean ecoregion contributed substantially to all components of diversity. In contrast, the northern ecoregions contributed substantially to the diversity of the Continental Slope. Strategies for the conservation of deep-water coral diversity in the Caribbean Basin must consider the variation between ecoregions and depth ranges.

Cryptic species of Archinome (Annelida: Amphinomida) from vents and seeps

Since its description from the Galapagos Rift in the mid-1980s, Archinome rosacea has been recorded at hydrothermal vents in the Pacific, Atlantic and Indian Oceans. Only recently was a second species described from the Pacific Antarctic Ridge. We inferred the identities and evolutionary relationships of Archinome representatives sampled from across the hydrothermal vent range of the genus, which is now extended to cold methane seeps. Species delimitation using mitochondrial cytochrome c oxidase subunit I (COI) recovered up to six lineages, whereas concatenated datasets (COI, 16S, 28S and ITS1) supported only four or five of these as clades. Morphological approaches alone were inconclusive to verify the identities of species owing to the lack of discrete diagnostic characters. We recognize five Archinome species, with three that are new to science. The new species, designated based on molecular evidence alone, include: Archinome levinae n. sp., which occurs at both vents and seeps in the east Pacific, Archinome tethyana n. sp., which inhabits Atlantic vents and Archinome jasoni n. sp., also present in the Atlantic, and whose distribution extends to the Indian and southwest Pacific Oceans. Biogeographic connections between vents and seeps are highlighted, as are potential evolutionary links among populations from vent fields located in the east Pacific and Atlantic Oceans, and Atlantic and Indian Oceans; the latter presented for the first time.

Hyperbaric biofilms on engineering surfaces formed in the deep sea

Biofouling is a major problem for long-term deployment of sensors in the marine environment. This study showed that significant biofilm formation occurred on a variety of artificial materials (glass, copper, Delrin(™) and poly-methyl methacrylate [PMMA]) deployed for 10 days at a depth of 4700 m in the Cayman Trough. Biofilm surface coverage was used as an indicator of biomass. The lowest biofilm coverage was on copper and PMMA. Molecular analyses indicated that bacteria dominated the biofilms found on copper, Delrin(™) and PMMA with 75, 55 and 73% coverage, respectively. Archea (66%) were dominant on the glass surface simulating interior sensor conditions, whereas Eukarya comprised the highest percentage of microflora (75%) on the glass simulating the exterior of sensors. Analysis of Denaturing Gradient Gel Electrophoresis profiles indicated that copper and Delrin(™) shared the same community diversity, which was not the case for glass and PMMA, or between PMMA and copper/Delrin(™). Sequence alignment matches belonged exclusively to uncultivable microorganisms, most of which were not further classified. One extracted sequence found on glass was associated with Cowellia sp., while another extracted from the PMMA surface was associated with a bacterium in the Alterominidaceae, both γ-proteobacteria. The results demonstrate the necessity of understanding biofilm formation in the deep sea and the potential need for mitigation strategies for any kind of long-term deployment of remote sensors in the marine environment.

Reactivity landscape of pyruvate under simulated hydrothermal vent conditions

Pyruvate is an important "hub" metabolite that is a precursor for amino acids, sugars, cofactors, and lipids in extant metabolic networks. Pyruvate has been produced under simulated hydrothermal vent conditions from alkyl thiols and carbon monoxide in the presence of transition metal sulfides at 250 °C [Cody GD et al. (2000) Science 289(5483):1337-1340], so it is plausible that pyruvate was formed in hydrothermal systems on the early earth. We report here that pyruvate reacts readily in the presence of transition metal sulfide minerals under simulated hydrothermal vent fluids at more moderate temperatures (25-110 °C) that are more conducive to survival of biogenic molecules. We found that pyruvate partitions among five reaction pathways at rates that depend upon the nature of the mineral present; the concentrations of H2S, H2, and NH4Cl; and the temperature. In most cases, high yields of one or two primary products are found due to preferential acceleration of certain pathways. Reactions observed include reduction of ketones to alcohols and aldol condensation, both reactions that are common in extant metabolic networks. We also observed reductive amination to form alanine and reduction to form propionic acid. Amino acids and fatty acids formed by analogous processes may have been important components of a protometabolic network that allowed the emergence of life.

Spatial variation in the population structure and reproductive biology of Rimicaris hybisae (Caridea: Alvinocarididae) at hydrothermal vents on the Mid-Cayman Spreading Centre

The dynamics and microdistribution of faunal assemblages at hydrothermal vents often reflect the fine-scale spatial and temporal heterogeneity of the vent environment. This study examined the reproductive development and population structure of the caridean shrimp Rimicaris hybisae at the Beebe and Von Damm Vent Fields (Mid-Cayman Spreading Centre, Caribbean) using spatially discrete samples collected in January 2012. Rimicaris hybisae is gonochoric and exhibits iteroparous reproduction. Oocyte size-frequency distributions (21-823 µm feret diameters) varied significantly among samples. Embryo development was asynchronous among females, which may result in asynchronous larval release for the populations. Specimens of R. hybisae from the Von Damm Vent Field (2294 m) were significantly larger than specimens from the Beebe Vent Field. Brooding females at Von Damm exhibited greater size-specific fecundity, possibly as a consequence of a non-linear relationship between fecundity and body size that was consistent across both vent fields. Samples collected from several locations at the Beebe Vent Field (4944–4972 m) revealed spatial variability in the sex ratios, population structure, size, and development of oocytes and embryos of this mobile species. Samples from the Von Damm Vent Field and sample J2-613-24 from Beebe Woods exhibited the highest frequencies of ovigerous females and significantly female-biased sex ratios. Environmental variables within shrimp aggregations may influence the distribution of ovigerous females, resulting in a spatially heterogeneous pattern of reproductive development in R. hybisae, as found in other vent taxa.

Geochemical and visual indicators of hydrothermal fluid flow through a sediment-hosted volcanic ridge in the Central Bransfield Basin (Antarctica)

In the austral summer of 2011 we undertook an investigation of three volcanic highs in the Central Bransfield Basin, Antarctica, in search of hydrothermal activity and associated fauna to assess changes since previous surveys and to evaluate the extent of hydrothermalism in this basin. At Hook Ridge, a submarine volcanic edifice at the eastern end of the basin, anomalies in water column redox potential (E_h) were detected close to the seafloor, unaccompanied by temperature or turbidity anomalies, indicating low-temperature hydrothermal discharge. Seepage was manifested as shimmering water emanating from the sediment and from mineralised structures on the seafloor; recognisable vent endemic fauna were not observed. Pore fluids extracted from Hook Ridge sediment were depleted in chloride, sulfate and magnesium by up to 8% relative to seawater, enriched in lithium, boron and calcium, and had a distinct strontium isotope composition (⁸⁷Sr/⁸⁶Sr  = 0.708776 at core base) compared with modern seawater (⁸⁷Sr/⁸⁶Sr ≈0.70918), indicating advection of hydrothermal fluid through sediment at this site. Biogeochemical zonation of redox active species implies significant moderation of the hydrothermal fluid with in situ diagenetic processes. At Middle Sister, the central ridge of the Three Sisters complex located about 100 km southwest of Hook Ridge, small water column E_h anomalies were detected but visual observations of the seafloor and pore fluid profiles provided no evidence of active hydrothermal circulation. At The Axe, located about 50 km southwest of Three Sisters, no water column anomalies in E_h, temperature or turbidity were detected. These observations demonstrate that the temperature anomalies observed in previous surveys are episodic features, and suggest that hydrothermal circulation in the Bransfield Strait is ephemeral in nature and therefore may not support vent biota.

Microdistribution of faunal assemblages at deep-sea hydrothermal vents in the Southern Ocean

Chemosynthetic primary production by microbes supports abundant faunal assemblages at deep-sea hydrothermal vents, with zonation of invertebrate species typically occurring along physico-chemical gradients. Recently discovered vent fields on the East Scotia Ridge (ESR) in the Southern Ocean represent a new province of vent biogeography, but the spatial dynamics of their distinct fauna have yet to be elucidated. This study determines patterns of faunal zonation, species associations, and relationships between faunal microdistribution and hydrothermal activity in a vent field at a depth of 2,400 m on the ESR. Remotely operated vehicle (ROV) dives obtained high-definition imagery of three chimney structures with varying levels of hydrothermal activity, and a mosaic image of >250 m² of seafloor co-registered with temperature measurements. Analysis of faunal microdistribution within the mosaiced seafloor reveals a consistent pattern of faunal zonation with increasing distance from vent sources and peak temperatures. Assemblages closest to vent sources are visibly dominated by a new species of anomuran crab, Kiwa n. sp. (abundance >700 individuals m⁻²), followed by a peltospiroid gastropod (>1,500 individuals m⁻²), eolepadid barnacle (>1,500 individuals m⁻²), and carnivorous actinostolid anemone (>30 individuals m⁻²). Peripheral fauna are not dominated by a single taxon, but include predatory and scavenger taxa such as stichasterid seastars, pycnogonids and octopus. Variation in faunal microdistribution on chimneys with differing levels of activity suggests a possible successional sequence for vent fauna in this new biogeographic province. An increase in δ³⁴S values of primary consumers with distance from vent sources, and variation in their δ¹³C values also indicate possible zonation of nutritional modes of the vent fauna. By using ROV videography to obtain a high-resolution representation of a vent environment over a greater extent than previous studies, these results provide a baseline for determining temporal change and investigations of processes structuring faunal assemblages at Southern Ocean vents.

Deep-water chemosynthetic ecosystem research during the census of marine life decade and beyond: a proposed deep-ocean road map

The ChEss project of the Census of Marine Life (2002-2010) helped foster internationally-coordinated studies worldwide focusing on exploration for, and characterization of new deep-sea chemosynthetic ecosystem sites. This work has advanced our understanding of the nature and factors controlling the biogeography and biodiversity of these ecosystems in four geographic locations: the Atlantic Equatorial Belt (AEB), the New Zealand region, the Arctic and Antarctic and the SE Pacific off Chile. In the AEB, major discoveries include hydrothermal seeps on the Costa Rica margin, deepest vents found on the Mid-Cayman Rise and the hottest vents found on the Southern Mid-Atlantic Ridge. It was also shown that the major fracture zones on the MAR do not create barriers for the dispersal but may act as trans-Atlantic conduits for larvae. In New Zealand, investigations of a newly found large cold-seep area suggest that this region may be a new biogeographic province. In the Arctic, the newly discovered sites on the Mohns Ridge (71 °N) showed extensive mats of sulfur-oxidisng bacteria, but only one gastropod potentially bears chemosynthetic symbionts, while cold seeps on the Haakon Mossby Mud Volcano (72 °N) are dominated by siboglinid worms. In the Antarctic region, the first hydrothermal vents south of the Polar Front were located and biological results indicate that they may represent a new biogeographic province. The recent exploration of the South Pacific region has provided evidence for a sediment hosted hydrothermal source near a methane-rich cold-seep area. Based on our 8 years of investigations of deep-water chemosynthetic ecosystems worldwide, we suggest highest priorities for future research: (i) continued exploration of the deep-ocean ridge-crest; (ii) increased focus on anthropogenic impacts; (iii) concerted effort to coordinate a major investigation of the deep South Pacific Ocean - the largest contiguous habitat for life within Earth's biosphere, but also the world's least investigated deep-ocean basin.