Diversity of Meiofauna from the 9°50′N East Pacific Rise across a Gradient of Hydrothermal Fluid Emissions

Background

We studied the meiofauna community at deep-sea hydrothermal vents along a gradient of vent fluid emissions in the axial summit trought (AST) of the East Pacific Rise 9°50′N region. The gradient ranged from extreme high temperatures, high sulfide concentrations, and low pH at sulfide chimneys to ambient deep-sea water conditions on bare basalt. We explore meiofauna diversity and abundance, and discuss its possible underlying ecological and evolutionary processes.

Methodology/Principal Findings

After sampling in five physico-chemically different habitats, the meiofauna was sorted, counted and classified. Abundances were low at all sites. A total of 52 species were identified at vent habitats. The vent community was dominated by hard substrate generalists that also lived on bare basalt at ambient deep-sea temperature in the axial summit trough (AST generalists). Some vent species were restricted to a specific vent habitat (vent specialists), but others occurred over a wide range of physico-chemical conditions (vent generalists). Additionally, 35 species were only found on cold bare basalt (basalt specialists). At vent sites, species richness and diversity clearly increased with decreasing influence of vent fluid emissions from extreme flow sulfide chimney (no fauna), high flow pompei worm (S: 4–7, H''_loge: 0.11–0.45), vigorous flow tubeworm (S: 8–23; H''_loge: 0.44–2.00) to low flow mussel habitats (S: 28–31; H''_loge: 2.34–2.60).

Conclusions/Significance

Our data suggest that with increasing temperature and toxic hydrogen sulfide concentrations and increasing amplitude of variation of these factors, fewer species are able to cope with these extreme conditions. This results in less diverse communities in more extreme habitats. The finding of many species being present at sites with and without vent fluid emissions points to a non endemic deep-sea hydrothermal vent meiofaunal community. This is in contrast to a mostly endemic macrofauna but similar to what is known for meiofauna from shallow-water vents.     

Detecting the Influence of Initial Pioneers on Succession at Deep-Sea Vents

Deep-sea hydrothermal vents are subject to major disturbances that alter the physical and chemical environment and eradicate the resident faunal communities. Vent fields are isolated by uninhabitable deep seafloor, so recolonization via dispersal of planktonic larvae is critical for persistence of populations. We monitored colonization near 9°50′N on the East Pacific Rise following a catastrophic eruption in order to address questions of the relative contributions of pioneer colonists and environmental change to variation in species composition, and the role of pioneers at the disturbed site in altering community structure elsewhere in the region. Pioneer colonists included two gastropod species: Ctenopelta porifera, which was new to the vent field, and Lepetodrilus tevnianus, which had been rare before the eruption but persisted in high abundance afterward, delaying and possibly out-competing the ubiquitous pre-eruption congener L. elevatus. A decrease in abundance of C. porifera over time, and the arrival of later species, corresponded to a decrease in vent fluid flow and in the sulfide to temperature ratio. For some species these successional changes were likely due to habitat requirements, but other species persisted (L. tevnianus) or arrived (L. elevatus) in patterns unrelated to their habitat preferences. After two years, disturbed communities had started to resemble pre-eruption ones, but were lower in diversity. When compared to a prior (1991) eruption, the succession of foundation species (tubeworms and mussels) appeared to be delayed, even though habitat chemistry became similar to the pre-eruption state more quickly. Surprisingly, a nearby community that had not been disturbed by the eruption was invaded by the pioneers, possibly after they became established in the disturbed vents. These results indicate that the post-eruption arrival of species from remote locales had a strong and persistent effect on communities at both disturbed and undisturbed vents.     

First survey of sessile communities on subtidal rocks in an area with hydrothermal vents: Milos Island,Aegean Sea

The major epibenthic communities on subtidal rocks of Palaeochori Bay and the marine tract on the southern coast of Milos Island (Greece) were described down to 44 m depth. Six sites were investigated by snorkelling and SCUBA diving. Samples, photographs and video images were also taken to integrate information. Three out of the six sites were close to hydrothermal vents, a common feature in the area. In total, nine major epibenthic communities were found, most of which were characterised by a diverse algal growth down to the maximum depth explored. Macrobenthic cover was severely reduced only in the close proximity of vents, a white flocculent bacterial mat covering the rock at the point from which fluid escaped. Large-scale effects of vents on the epibenthic communities were not detected. However, the abundance of species with warm-water affinity was recognisable in both algal and animal dominated communities, which may be related to higher winter temperature in the vent area. Epifaunal communities under overhangs were composed of distinct groups of suspension feeders at vent as compared to non-vent sites: this might indicate differences in trophic conditions. Mounds of the bioconstructional coralline alga Mesophyllum lichenoides were conspicuous only at vent sites, thus suggesting enhanced biodeposition of carbonates due to vent activity.     

Ecology and Biogeography of Free-Living Nematodes Associated with Chemosynthetic Environments in the Deep Sea: A Review

Background

Here, insight is provided into the present knowledge on free-living nematodes associated with chemosynthetic environments in the deep sea. It was investigated if the same trends of high standing stock, low diversity, and the dominance of a specialized fauna, as observed for macro-invertebrates, are also present in the nematodes in both vents and seeps.

Methodology

This review is based on existing literature, in combination with integrated analysis of datasets, obtained through the Census of Marine Life program on Biogeography of Deep-Water Chemosynthetic Ecosystems (ChEss).

Findings

Nematodes are often thriving in the sulphidic sediments of deep cold seeps, with standing stock values ocassionaly exceeding largely the numbers at background sites. Vents seem not characterized by elevated densities. Both chemosynthetic driven ecosystems are showing low nematode diversity, and high dominance of single species. Genera richness seems inversely correlated to vent and seep fluid emissions, associated with distinct habitat types. Deep-sea cold seeps and hydrothermal vents are, however, highly dissimilar in terms of community composition and dominant taxa. There is no unique affinity of particular nematode taxa with seeps or vents.

Conclusions

It seems that shallow water relatives, rather than typical deep-sea taxa, have successfully colonized the reduced sediments of seeps at large water depth. For vents, the taxonomic similarity with adjacent regular sediments is much higher, supporting rather the importance of local adaptation, than that of long distance distribution. Likely the ephemeral nature of vents, its long distance offshore and the absence of pelagic transport mechanisms, have prevented so far the establishment of a successful and typical vent nematode fauna. Some future perspectives in meiofauna research are provided in order to get a more integrated picture of vent and seep biological processes, including all components of the marine ecosystem.     

Transient Changes in Bacterioplankton Communities Induced by the Submarine Volcanic Eruption of El Hierro (Canary Islands)

The submarine volcanic eruption occurring near El Hierro (Canary Islands) in October 2011 provided a unique opportunity to determine the effects of such events on the microbial populations of the surrounding waters. The birth of a new underwater volcano produced a large plume of vent material detectable from space that led to abrupt changes in the physical-chemical properties of the water column. We combined flow cytometry and 454-pyrosequencing of 16S rRNA gene amplicons (V1–V3 regions for Bacteria and V3–V5 for Archaea) to monitor the area around the volcano through the eruptive and post-eruptive phases (November 2011 to April 2012). Flow cytometric analyses revealed higher abundance and relative activity (expressed as a percentage of high-nucleic acid content cells) of heterotrophic prokaryotes during the eruptive process as compared to post-eruptive stages. Changes observed in populations detectable by flow cytometry were more evident at depths closer to the volcano (~70–200 m), coinciding also with oxygen depletion. Alpha-diversity analyses revealed that species richness (Chao1 index) decreased during the eruptive phase; however, no dramatic changes in community composition were observed. The most abundant taxa during the eruptive phase were similar to those in the post-eruptive stages and to those typically prevalent in oceanic bacterioplankton communities (i.e. the alphaproteobacterial SAR11 group, the Flavobacteriia class of the Bacteroidetes and certain groups of Gammaproteobacteria). Yet, although at low abundance, we also detected the presence of taxa not typically found in bacterioplankton communities such as the Epsilonproteobacteria and members of the candidate division ZB3, particularly during the eruptive stage. These groups are often associated with deep-sea hydrothermal vents or sulfur-rich springs. Both cytometric and sequence analyses showed that once the eruption ceased, evidences of the volcano-induced changes were no longer observed.     

Deep-sea hydrothermal vent Epsilonproteobacteria encode a conserved and widespread nitrate reduction pathway (Nap)

Despite the frequent isolation of nitrate-respiring Epsilonproteobacteria from deep-sea hydrothermal vents, the genes coding for the nitrate reduction pathway in these organisms have not been investigated in depth. In this study we have shown that the gene cluster coding for the periplasmic nitrate reductase complex (nap) is highly conserved in chemolithoautotrophic, nitrate-reducing Epsilonproteobacteria from deep-sea hydrothermal vents. Furthermore, we have shown that the napA gene is expressed in pure cultures of vent Epsilonproteobacteria and it is highly conserved in microbial communities collected from deep-sea vents characterized by different temperature and redox regimes. The diversity of nitrate-reducing Epsilonproteobacteria was found to be higher in moderate temperature, diffuse flow vents than in high temperature black smokers or in low temperatures, substrate-associated communities. As NapA has a high affinity for nitrate compared with the membrane-bound enzyme, its occurrence in vent Epsilonproteobacteria may represent an adaptation of these organisms to the low nitrate concentrations typically found in vent fluids. Taken together, our findings indicate that nitrate reduction is widespread in vent Epsilonproteobacteria and provide insight on alternative energy metabolism in vent microorganisms. The occurrence of the nap cluster in vent, commensal and pathogenic Epsilonproteobacteria suggests that the ability of these bacteria to respire nitrate is important in habitats as different as the deep-sea vents and the human body.     

Mineralogy Drives Bacterial Biogeography of Hydrothermally Inactive Seafloor Sulfide Deposits

Mid-ocean ridge hydrothermal venting creates sulfide deposits containing gradients in mineralogy, fluid chemistry, and temperature. Even when hydrothermal circulation ceases, sulfides are known to host microbial communities. The relationship between mineralogy and microbial community composition in low-temperature, rock-hosted systems has not been resolved at any spatial scale, local or global. To examine the hypothesis that geochemistry of seafloor deposits is a dominant parameter driving environmental pressure for bacterial communities at low-temperature, the shared community membership, richness, and structure was measured using 16S rRNA gene sequences. The focus of the study was on hydrothermally inactive seafloor deposits from multiple locations within one deposit (e.g., single extinct chimney), within one vent field (intra-vent field), and among globally distributed vent fields from three ocean basins (inter-vent field). Distinct mineral substrates, such as hydrothermally inactive sulfides versus basalts, host different communities at low temperature in spite of close geographic proximity and contact with the same hydrothermally influenced deep-sea water. Furthermore, bacterial communities inhabiting hydrothermally inactive sulfide deposits from geographically distant locations cluster together in community cladograms to the exclusion of other deep-sea substrates and settings. From this study, we conclude that at low temperature, mineralogy was a more important variable determining microbial community composition than geographic factors. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.     

Long-term Disturbance Effects in the Nematode Communities of South Mississippi Woodlands

The effects of soil disturbance on the nematode community were assessed at 30 sites on the outer coastal plain of Mississippi, representing four ages since soil disturbance plus a control group of six undisturbed sites. Thirty-five taxa were encountered, dominated in abundance and taxonomic richness by plant and bacterial feeders. Nematodes were more abundant and more taxonomically rich in sites with a low slope and deep litter cover, distant from trees. Plant feeders were more numerous at sites with a dense herb cover, suggesting limitation by food availability. When sites were arranged as a chronosequence, herb cover, litter depth, soil organic matter, soil moisture, and tree canopy cover increased through time consistent with succession to forest. The abundance of most trophic groups decreased in the 10 to 20 years following disturbance and increased thereafter, a pattern repeated in taxonomic richness of plant and bacterial feeders. Fifty years after disturbance, nematode abundance had not returned to levels observed in control sites. These results suggest that nematode succession following soil disturbance is a gradual process regulated by establishment of aboveground vegetation. There was no evidence of dispersal limitation or facilitation by colonist nematode species.     

Microbial colonization of metal sulfide minerals at a diffuse‐flow deep‐sea hydrothermal vent at 9°50′N on the East Pacific Rise

Metal sulfide minerals, including mercury sulfides (HgS), are widespread in hydrothermal vent systems where sulfur‐oxidizing microbes are prevalent. Questions remain as to the impact of mineral composition and structure on sulfur‐oxidizing microbial populations at deep‐sea hydrothermal vents, including the possible role of microbial activity in remobilizing elemental Hg from HgS. In the present study, metal sulfides varying in metal composition, structure, and surface area were incubated for 13 days on and near a diffuse‐flow hydrothermal vent at 9°50′N on the East Pacific Rise. Upon retrieval, incubated minerals were examined by scanning electron microscopy with energy‐dispersive X‐ray spectroscopy (SEM‐EDS), X‐ray diffraction (XRD), and epifluorescence microscopy (EFM). DNA was extracted from mineral samples, and the 16S ribosomal RNA gene sequenced to characterize colonizing microbes. Sulfur‐oxidizing genera common to newly exposed surfaces (Sulfurimonas, Sulfurovum, and Arcobacter) were present on all samples. Differences in their relative abundance between and within incubation sites point to constraining effects of the immediate environment and the minerals themselves. Greater variability in colonizing community composition on off‐vent samples suggests that the bioavailability of mineral‐derived sulfide (as influenced by surface area, crystal structure, and reactivity) exerted greater control on microbial colonization in the ambient environment than in the vent environment, where dissolved sulfide is more abundant. The availability of mineral‐derived sulfide as an electron donor may thus be a key control on the activity and proliferation of deep‐sea chemosynthetic communities, and this interpretation supports the potential for microbial dissolution of HgS at hydrothermal vents.     

Imprint of past environmental regimes on structure and succession of a deep-sea hydrothermal vent community

Dramatic perturbations of ecological communities through rapid shifts in environmental regime do not always result in complete mortality of residents. Instead, legacy individuals may remain and influence the succession and composition of subsequent communities. We used a reciprocal transplant experiment to investigate whether a legacy effect is detectable in communities experiencing an abrupt increase or decrease in hydrothermal fluid flux at deep-sea vents. Vent habitats are characterized by strong gradients in productivity and physico-chemical stressors, both of which tend to increase with increasing vent fluid flux. In our experiments, many species survived transplantation from cool (water temperatures <2°C above ambient) to warm (4–30°C above ambient) habitats, resulting in significantly higher species richness on transplanted than remaining experimental substrata. A legacy effect was much less apparent in transplantation from warm to cool habitat, although a few vestimentiferan tubeworms, normally restricted to warm habitat, survived transplantation. The asymmetry in influence of legacy individuals suggests that productivity enhancement may outweigh potential physiological stress in setting limits to distributions of vent invertebrates. This influence of biological processes contrasts with theory developed in the rocky intertidal that predicts the predominance of physical control at the high-stress end of an environmental gradient. Prediction of successional transitions in vents and other habitats experiencing regime shifts in which remnant species may survive must take into account the possible influence of historical effects.     

Experimental ecology at deep-sea hydrothermal vents: a perspective

In situ and laboratory experiments conducted over the past quarter of a century have greatly increased our understanding of the ecology of deep-sea hydrothermal systems. Early experiments suggested that chemosynthetic primary production constituted the principal source of organic matter for biological communities associated with vents, although subsequent studies have revealed many complexities associated with interactions between microbes and higher organisms inhabiting these ecosystems. A diversity of host-microbial symbiont relationships has been identified and experimental studies have revealed the exquisite physiological adaptations within the giant tubeworm, Riftia pachyptila, for the uptake, fixation, and assimilation of carbon. In vitro experiments demonstrated the unusual sulfide binding properties of tubeworm hemoglobin that prevent inhibition of the cytochrome-c oxidase enzyme system during transport of sulfide to symbiont-bearing tissues. Studies of respiration and growth of several species of vent organisms conducted over the past two decades transformed earlier views that low metabolism and slow growth are characteristics of all organisms inhabiting all deep-sea environments. Results of recent experiments suggest that metabolic rates correlate with the degree of mobility of the organisms rather than with any specific attribute of the deep-sea environment itself, and growth rates of certain vent organisms (e.g., R. pachyptila) were found to be among the highest in any marine environments. While extreme thermal tolerance has been suggested as characteristic of certain vent fauna (e.g., alvinellid polychaetes and alvinocarid shrimp), the majority of vent metazoans live at temperatures below 20 °C and additional experiments are necessary to reconcile field experiments documenting thermal tolerance in situ, thermal tolerance in vivo, and thermal sensitivity of biochemical constituents of vent organisms. Transplantation and clearance experiments, as well as in situ characterization of vent fluid chemistry, have greatly increased our understanding of organism–environment interactions. Early analyses of metazoan egg size and larval morphology, coupled with in vivo larval culture experiments, available physical oceanographic data, and genetic studies of gene flow, have contributed greatly to our understanding of mechanisms of dispersal between widely separated vent sites. The documentation of invertebrate colonization and succession of new vents following a volcanic eruption, and a series of manipulative field experiments, provide considerable insights into the relative roles of abiotic conditions and biotic interactions in structuring vent communities. Recent and emerging technological developments, such as in situ chemical analyzers, observatory approaches, and laboratory-based pressure culture systems, should provide invaluable new experimental tools for tackling many remaining questions concerning the ecology of deep-sea hydrothermal systems.     

Characterization of Bacterial Communities in Deep-Sea Hydrothermal Vents from Three Oceanic Regions

Deep-sea hydrothermal vents are considered to be one of the most spectacular ecosystems on Earth. Microorganisms form the basis of the food chain in vents controlling the vent communities. However, the diversity of bacterial communities in deep-sea hydrothermal vents from different oceans remains largely unknown. In this study, the pyrosequencing of 16S rRNA gene was used to characterize the bacterial communities of the venting sulfide, seawater, and tubeworm trophosome from East Pacific Rise, South Atlantic Ridge, and Southwest Indian Ridge, respectively. A total of 23,767 operational taxonomic units (OTUs) were assigned into 42 different phyla. Although Proteobacteria, Actinobacteria, and Bacteroidetes were the predominant phyla in all vents, differences of bacterial diversity were observed among different vents from three oceanic regions. The sulfides of East Pacific Rise possessed the most diverse bacterial communities. The bacterial diversities of venting seawater were much lower than those of vent sulfides. The symbiotic bacteria of tubeworm Ridgeia piscesae were included in the bacterial community of vent sulfides, suggesting their significant ecological functions as the primary producers in the deep-sea hydrothermal vent ecosystems. Therefore, our study presented a comprehensive view of bacterial communities in deep-sea hydrothermal vents from different oceans.     

Prolonged recovery time after eruptive disturbance of a deep-sea hydrothermal vent community

Deep-sea hydrothermal vents are associated with seafloor tectonic and magmatic activity, and the communities living there are subject to disturbance. Eruptions can be frequent and catastrophic, raising questions about how these communities persist and maintain regional biodiversity. Prior studies of frequently disturbed vents have led to suggestions that faunal recovery can occur within 2–4 years. We use an unprecedented long-term (11-year) series of colonization data following a catastrophic 2006 seafloor eruption on the East Pacific Rise to show that faunal successional changes continue beyond a decade following the disturbance. Species composition at nine months post-eruption was conspicuously different than the pre-eruption ‘baseline'' state, which had been characterized in 1998 (85 months after disturbance by the previous 1991 eruption). By 96 months post-eruption, species composition was approaching the pre-eruption state, but continued to change up through to the end of our measurements at 135 months, indicating that the ‘baseline'' state was not a climax community. The strong variation observed in species composition across environmental gradients and successional stages highlights the importance of long-term, distributed sampling in order to understand the consequences of disturbance for maintenance of a diverse regional species pool. This perspective is critical for characterizing the resilience of vent species to both natural disturbance and human impacts such as deep-sea mining.     

Community Structure of Macrobiota and Environmental Parameters in Shallow Water Hydrothermal Vents off Kueishan Island,Taiwan

Hydrothermal vents represent a unique habitat in the marine ecosystem characterized with high water temperature and toxic acidic chemistry. Vents are distributed at depths ranging from a few meters to several thousand meters. The biological communities of shallow-water vents have, however, been insufficiently studied in most biogeographic areas. We attempted to characterize the macrofauna and macroflora community inhabiting the shallow-water vents off Kueishan Island, Taiwan, to identify the main abiotic factors shaping the community structure and the species distribution. We determined that positively buoyant vent fluid exhibits a more pronounced negative impact to species on the surface water than on the bottom layer. Species richness increased with horizontal distance from the vent, and continuing for a distance of 2000 m, indicating that the vent fluid may exert a negative impact over several kilometers. The community structure off Kueishan Island displayed numerous transitions along the horizontal gradient, which were broadly congruent with changes in environmental conditions. Combination of variation in Ca²⁺, Cl^-, temperature, pH and depth were revealed to show the strongest correlation with the change in benthic community structure, suggesting multiple factors of vent fluid were influencing the associated fauna. Only the vent crabs of Kueishan Island may have an obligated relationship with vents and inhabit the vent mouths because other fauna found nearby are opportunistic taxa that are more tolerant to acidic and toxic environments.     

Recovery of zooplankton diversity in a restored Mediterranean temporary marsh in Doñana National Park (SW Spain)

Over 30 years after drainage for agriculture, a 2700 ha temporary marshland was recently restored in Doñana National Park. We describe the recovery of zooplankton communities (copepods, cladocerans and rotifers) in 47 new temporary ponds excavated as part of the restoration project during the first two hydroperiods (April 2006 and 2007), and compare them to those of eight reference sites in the surrounding marshland. Major changes in the species composition and abundance occurred in new ponds between years. While rotifers and cyclopoid copepods dominated in terms of number of individuals in 2006, calanoid copepods and cladocerans were the most abundant groups in 2007. Rotifer species richness was significantly lower in 2007, but there was an increase in Simpson and β-diversity in 2007 owing largely to a dramatic decline in the abundance of Hexarthra cf. fennica (rare in reference sites) from 93% of all rotifer individuals in new ponds in 2006 to only 32% in 2007. In contrast, species richness of copepods and cladocerans was significantly higher in new ponds in 2007, but there were no changes in Simpson diversity. β-Diversity of cladocerans was also significantly higher in 2007. In 2006, the species richness of cladocera and copepods was significantly lower in new ponds than in reference sites, but by 2007 there were no differences in richness or Simpson diversity. Overall, 7 copepod, 13 cladoceran and 26 rotifer taxa were recorded in new ponds, including 80% of taxa recorded in reference sites. These results indicate that zooplankton communities can be rapidly restored in Mediterranean temporary wetlands, at least when large source populations in the surrounding area reduce dispersal limitation. They also illustrate the importance of comparing different metrics of richness and diversity in studies of zooplankton restoration.     

Individual hydrothermal vents at Axial Seamount harbor distinct subseafloor microbial communities

The microbial community structure of five geographically distinct hydrothermal vents located within the Axial Seamount caldera, Juan de Fuca Ridge, was examined over 6 years following the 1998 diking eruptive event. Terminal restriction fragment length polymorphism (TRFLP) and 16S rRNA gene sequence analyses were used to determine the bacterial and archaeal diversity, and the statistical software primer v6 was used to compare vent microbiology, temperature and fluid chemistry. Statistical analysis of vent fluid temperature and composition shows that there are significant differences between vents in any year, but that the fluid composition changes over time such that no vent maintains a chemical composition completely distinct from the others. In contrast, the subseafloor microbial communities associated with individual vents changed from year to year, but each location maintained a distinct community structure (based on TRFLP and 16S rRNA gene sequence analyses) that was significantly different from all other vents included in this study. Epsilonproteobacterial microdiversity is shown to be important in distinguishing vent communities, while archaeal microdiversity is less variable between sites. We propose that persistent venting at diffuse flow vents over time creates the potential to isolate and stabilize diverse microbial community structures between vents.     

Discovery of new hydrothermal activity and chemosynthetic fauna on the Central Indian Ridge at 18°-20° S

Indian Ocean hydrothermal vents are believed to represent a novel biogeographic province, and are host to many novel genera and families of animals, potentially indigenous to Indian Ocean hydrothermal systems. In particular, since its discovery in 2001, much attention has been paid to a so-called 'scaly-foot' gastropod because of its unique iron-sulfide-coated dermal sclerites and the chemosynthetic symbioses in its various tissues. Despite increasing interest in the faunal assemblages at Indian Ocean hydrothermal vents, only two hydrothermal vent fields have been investigated in the Indian Ocean. Here we report two newly discovered hydrothermal vent fields, the Dodo and Solitaire fields, which are located in the Central Indian Ridge (CIR) segments 16 and 15, respectively. Chemosynthetic faunal communities at the Dodo field are emaciated in size and composition. In contrast, at the Solitaire field, we observed faunal communities that potentially contained almost all genera found at CIR hydrothermal environments to date, and even identified previously unreported taxa. Moreover, a new morphotype of 'scaly-foot' gastropod has been found at the Solitaire field. The newly discovered 'scaly-foot' gastropod has similar morphological and anatomical features to the previously reported type that inhabits the Kairei field, and both types of 'scaly-foot' gastropods genetically belong to the same species according to analyses of their COI gene and nuclear SSU rRNA gene sequences. However, the new morphotype completely lacks an iron-sulfide coating on the sclerites, which had been believed to be a novel feature restricted to 'scaly-foot' gastropods. Our new findings at the two newly discovered hydrothermal vent sites provide important insights into the biodiversity and biogeography of vent-endemic ecosystems in the Indian Ocean.     

Microbial diversity of Loki's Castle black smokers at the Arctic Mid‐Ocean Ridge

Hydrothermal vent systems harbor rich microbial communities ranging from aerobic mesophiles to anaerobic hyperthermophiles. Among these, members of the archaeal domain are prevalent in microbial communities in the most extreme environments, partly because of their temperature‐resistant and robust membrane lipids. In this study, we use geochemical and molecular microbiological methods to investigate the microbial diversity in black smoker chimneys from the newly discovered Loki's Castle hydrothermal vent field on the Arctic Mid‐Ocean Ridge (AMOR) with vent fluid temperatures of 310–320 °C and pH of 5.5. Archaeal glycerol dialkyl glycerol tetraether lipids (GDGTs) and H‐shaped GDGTs with 0–4 cyclopentane moieties were dominant in all sulfide samples and are most likely derived from both (hyper)thermophilic Euryarchaeota and Crenarchaeota. Crenarchaeol has been detected in low abundances in samples derived from the chimney exterior indicating the presence of Thaumarchaeota at lower ambient temperatures. Aquificales and members of the Epsilonproteobacteria were the dominant bacterial groups detected. Our observations based on the analysis of 16S rRNA genes and biomarker lipid analysis provide insight into microbial communities thriving within the porous sulfide structures of active and inactive deep‐sea hydrothermal vents. Microbial cycling of sulfur, hydrogen, and methane by archaea in the chimney interior and bacteria in the chimney exterior may be the prevailing biogeochemical processes in this system.     

The discovery of new deep-sea hydrothermal vent communities in the southern ocean and implications for biogeography

Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than previously recognised.     

Plant succession in areas of scorched and blown-down forest after the 1980 eruption of Mount St. Helens,Washington

Abstract. Patterns of plant succession were studied in areas of scorched and blown-down forest resulting from the 1980 eruption of Mount St. Helens, Washington. Changes in species abundance were observed for 7 years in permanent sample plots representing four post-disturbance habitats, or site types. Total plant cover and species richness increased with time on all site types. In blown-down forests supporting snowpack at the time of eruption, understory recovery was dominated by the vegetative regeneration of species persisting through disturbance. In forests without snowpacks, plant survival was poorer. Increases in cover and diversity were dominated first by introduced grasses, then by colonizing forbs characteristic of early successional sites. Epilo-bium angustifolium and Anaphalis margaritacea showed widespread recruitment and clonal expansion throughout the devastated area. As a result, species composition on previously forested sites converged toward that on formerly clearcut sites, where early serai forbs resprouted vigorously from beneath the tephra. Total plant cover and species diversity were poorly correlated with post-disturbance habitat and general site characteristics (e.g. distance from the crater, elevation, slope, and aspect). However, distributions of several life-forms (e.g. low sub-shrubs and tall shrubs) were strongly correlated with depth of burial by tephra and with cover of tree rootwads. Thus, early community recovery may reflect microsite variation or chance survival and recruitment rather than broad-scale gradients in environment or disturbance. Recovery of pre-disturbance composition and structure will undoubtedly be much slower than after other types of catastrophic disturbance. The rate and direction of community recovery will largely depend on the degree to which original understory species survived the eruption.