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Mussels of the genus Bathymodiolus Kenk & Wilson belong to the foundation fauna at hydrothermal vents in the global deep sea. In the western Pacific and Indian oceans, the three nominal taxa B. septemdierum Hashimoto and Okutani, B. brevior Cosel, Métivier & Okutani and B. marisindicus Hashimoto are currently recognized as separate species despite morphological and genetic evidence for their conspecificity. All three are listed with the International Union for Conservation of Nature Red List based on highly restricted ranges. We compile and supplement existing morphometric and molecular data to revise the Bathymodiolus septemdierum species group. We redescribe B. septemdierum as a single species with B. brevior and B. marisindicus recognized as junior synonyms. Given the exceptionally broad range of B. septemdierum, we propose removal of these three taxa from the IUCN Red List.

The distribution of species among spatially isolated habitat patches supports regional biodiversity and stability, so understanding the underlying processes and structure is a key target of conservation. Although multivariate statistics can infer the connectivity processes driving species distribution, such as dispersal and habitat suitability, they rarely explore the structure. Methods from graph theory, applied to distribution data, give insights into both connectivity pathways and processes by intuitively formatting the data as a network of habitat patches. We apply these methods to empirical data from the hydrothermal vent habitats of the Northwest Pacific. Hydrothermal vents are "oases" of biological productivity and endemicity on the seafloor that are imminently threatened by anthropogenic disturbances with unknown consequences to biodiversity. Here, we describe the structure of species assemblage networks at hydrothermal vents, how local and regional parameters affect their structure, and the implications for conservation. Two complementary networks were formed from an extensive species assemblage dataset: a similarity network of vent site nodes linked by weighted edges based on their pairwise assemblage similarity and a bipartite network of species nodes linked to vent site nodes at which they are present. Using these networks, we assessed the role of individual vent sites in maintaining network connectivity and identified biogeographic sub-regions. The three sub-regions and two outlying sites are separated by their spatial arrangement and local environmental filters. Both networks detected vent sites that play a disproportionately important role in regional pathways, while the bipartite network also identified key vent sites maintaining the distinct species assemblages of their sub-regions. These regional connectivity pathways provide insights into historical colonization routes, while sub-regional connectivity pathways are of value when selecting sites for conservation and/or estimating the multivent impacts from proposed deep-sea mining.

The distribution of species among spatially isolated habitat patches supports regional biodiversity and stability, so understanding the underlying processes and structure is a key target of conservation. Although multivariate statistics can infer the connectivity processes driving species distribution, such as dispersal and habitat suitability, they rarely explore structure. Methods from graph theory, applied to distribution data, give insights into both connectivity pathways and processes by intuitively formatting the data as a network of habitat patches. We apply these methods to empirical data from the hydrothermal vent habitats of the Northwest Pacific. Hydrothermal vents are ‘oases’ of biological productivity and endemicity on the seafloor that are imminently threatened by anthropogenic disturbances with unknown consequences to biodiversity. Here, we describe the structure of hydrothermal vent species assemblage networks, how local and regional parameters affect their structure, and the implications this has for conservation. Two complementary networks were formed from an extensive species assemblage dataset: a bipartite network of species nodes linked to vent site nodes at which they are present, and a similarity network of vent site nodes linked by weighted edges based on their pairwise assemblage similarity. Using these networks, we assessed the role of individual vent sites in linking their network and identified biogeographic sub-regions. The three sub-regions and two outlying sites are separated by their spatial arrangement and local environmental filters. Both networks detected vent sites that play a disproportionately important role in regional pathways, while the bipartite network also identified key vent sites maintaining the distinct species assemblages of their sub-regions. These regional connectivity pathways provide insights into historical colonisation routes, while sub-regional connectivity pathways are of value when selecting sites for conservation and/or estimating the multi-vent impacts from proposed deep-sea mining.

Despite significant advances in our understanding of speciation in the marine environment, the mechanisms underlying evolutionary diversification in deep-sea habitats remain poorly investigated. Here, we used multigene molecular clocks and population genetic inferences to examine processes that led to the emergence of the six extant lineages of Alviniconcha snails, a key taxon inhabiting deep-sea hydrothermal vents in the Indo-Pacific Ocean. We show that both allopatric divergence through historical vicariance and ecological isolation due to niche segregation contributed to speciation in this genus. The split between the two major Alviniconcha clades (separating A. boucheti and A. marisindica from A. kojimai, A. hessleri, and A. strummeri) probably resulted from tectonic processes leading to geographic separation, whereas the splits between co-occurring species might have been influenced by ecological factors, such as the availability of specific chemosynthetic symbionts. Phylogenetic origin of the sixth species, Alviniconcha adamantis, remains uncertain, although its sister position to other extant Alviniconcha lineages indicates a possible ancestral relationship. This study lays a foundation for future genomic studies aimed at deciphering the roles of local adaptation, reproductive biology, and host–symbiont compatibility in speciation of these vent-restricted snails.

Assessment of ecosystem health entails consideration of species interactions within and between size classes to determine their contributions to ecosystem function. Elucidating microbial involvement in these interactions requires tools to distil diverse microbial information down to relevant, manageable elements. We used covariance ratios (proportionality) between pairs of species and patterns of enrichment to identify “core communities” of likely interacting microbial (1 mm) taxa within assemblages hosted by a foundation species, the hydrothermal vent tubeworm Ridgeia piscesae. Compared with samples from co-located hydrothermal fluids, microbial communities within R. piscesae assemblages are hotspots of taxonomic richness and are high in novelty (unclassified OTUs) and in relative abundance of Bacteroidetes. We also observed a robust temperature-driven distinction in assemblage composition above and below ~25 °C that spanned micro to macro size classes. The core high-temperature community included eight macro- and meiofaunal taxa and members of the Bacteroidetes and Epsilonbacteraeota, particularly the genera Carboxylicivirga, Nitratifractor and Arcobacter. The core low-temperature community included more meiofaunal species in addition to Alpha- and Gammaproteobacteria, and Actinobacteria. Inferred associations among high-temperature core community taxa suggest increased reliance on species interactions under more severe hydrothermal conditions. We propose refinement of species diversity to “core communities” as a tool to simplify investigations of relationships between taxonomic and functional diversity across domains and scales by narrowing the taxonomic scope.

Environmental Protection Requires Accurate Application of Scientific Evidence.&nbsp

Deep-sea hydrothermal vent habitats are small, rare and support unique species through chemosynthesis. As this vulnerable ecosystem is increasingly threatened by human activities, management approaches should address biodiversity conservation. Diversity distribution data provide a useful basis for management approaches as patterns of β-diversity (the change in diversity from site to site) can guide conservation decisions. Our question is whether such patterns are similar enough across vent systems to support a conservation strategy that can be deployed regardless of location. We compile macrofaunal species occurrence data for vent systems in three geological settings in the North Pacific: volcanic arc, back-arc and mid-ocean ridge. Recent discoveries in the Mariana region provide the opportunity to characterize diversity at many vent sites. We examine the extent to which diversity distribution patterns differ among the systems by comparing pairwise β-diversity, nestedness and their additive components. A null model approach that tests whether species compositions of each site pair are more or less similar than random provides insight into community assembly processes. We resolve several taxonomic uncertainties and find that the Mariana arc and back-arc share only 8% of species despite their proximity. Species overlap, species replacement and richness differences create different diversity distributions within the three vent systems; the arc system exhibits much greater β-diversity than both the back-arc and mid-ocean ridge systems which, instead, show greater nestedness. The influence of nestedness on β-diversity also increased from the arc to back-arc to ridge. Community assembly processes appear more deterministic in the arc and ridge systems while back-arc site pairs deviate little from the null expectation. These analyses reflect the need for a variety of management strategies that consider the character of diversity distribution to protect hydrothermal vents, especially in the context of mining hydrothermal deposits.

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Current methods for biochemical and biogeochemical analysis of the deep-sea hydrothermal vent ecosystems rely on water sample recovery, or in situ analysis using underwater instruments with limited range of analyte detection and limited sensitivity. Even in cases where large quantities of sample are recovered, labile dissolved organic compounds may not be detected due to time delays between sampling and preservation. Here, we present a novel approach for in situ extraction of organic compounds from hydrothermal vent fluids through a unique solid phase microextraction (SPME) sampler. These samplers were deployed to sample effluent of vents on sulphide chimneys, located on Axial Seamount in the North-East Pacific, in the Urashima field on the southern Mariana back-arc, and at the Hafa Adai site in the central Mariana back-arc. Among the compounds that were extracted, a wide range of unique organic compounds, including labile dissolved organic sulfur compounds, were detected through high-resolution LC-MS/MS, among which were biomarkers of anammox bacteria, fungi, and lower animals. This report is the first to show that SPME can contribute to a broader understanding of deep sea ecology and biogeochemical cycles in hydrothermal vent ecosystems.

Slender sole Lyopsetta exilis is an abundant groundfish on the continental shelf and inner waters of British Columbia, Canada, where it reaches a maximum standard length of 44 cm. Benthic image surveys coupled with oxygen measurements in Saanich Inlet document a dense population in bottom conditions near anoxia (0.03 ml l−1 oxygen) where diel migrating zooplankton intersect the bottom; we confirm this species is a planktivore, which limits its depth range to the base of the migration layer. In a comparison with slender sole from a nearby well‐oxygenated habitat, several probable effects of living in severe hypoxia emerge: both sexes are significantly smaller in Saanich and the sex ratio is male‐skewed. Otoliths from the Saanich fish were difficult to read due to many checks, but both sexes were smaller at age with the largest female (20 cm) from the hypoxia zone registering 17 years. Hypoxia appears to have a direct consequence on growth despite good food supply in this productive basin. Hyperventilation, a low metabolic rate and a very low critical oxygen tension help this fish regulate oxygen uptake in severely hypoxic conditions; it will be particularly resilient as the incidence of hypoxia increases on the continental shelf. Data from small‐mesh bottom‐trawl surveys over four decades reveal an increase in mean annual catch per unit effort in southern regions of the province, including the outer shelf and the Strait of Georgia. The California Cooperative Oceanic Fisheries Investigations (CalCOFI) ichthyoplankton database records a general decline in fish larvae on the Oregon–California shelf since 1990, but slender sole larvae are increasing there, as they are in the Strait of Georgia. We project that the slender sole will gain relative benefits in the future warming, deoxygenated northeast Pacific Ocean.

The International Seabed Authority (ISA) is developing regulations to control the future exploitation of deep-sea mineral resources including sulphide deposits near hydrothermal vents, polymetallic nodules on the abyssal seafloor, and cobalt crusts on seamounts. Under the UN Convention on the Law of the Sea the ISA is required to adopt are taking measures to ensure the effective protection of the marine environment from harmful effects arising from mining-related activities. Contractors are required to generate environmental baselines and assess the potential environmental consequences of deep seafloor mining. Understandably, nearly all environmental research has focused on the seafloor where the most direct mining effects will occur. However, sediment plumes and other impacts (e.g., noise) from seafloor mining are likely to be extensive in the water column. Sediment plumes created on the seafloor will affect the benthic boundary layer which extends 10s to 100s of meters above the seafloor. Separation or dewatering of ore from sediment and seawater aboard ships will require discharge of a dewatering plume at some depth in the water column. It is important to consider the potential impacts of mining on the ocean’s midwaters (depths from ~200 m to the seafloor) because they provide vital ecosystem services and harbor substantial biodiversity. The better known epipelagic or sunlit surface ocean provisions the rest of the water column through primary production and export flux (This was not the focus at this workshop as the subject was considered too large and surface discharges are unlikely). It is also home to a diverse community of organisms including commercially important fishes such as tunas, billfish, and cephalopods that contribute to the economies of many countries. The mesopelagic or twilight zone (200-1000 m) is dimly lit and home to very diverse and abundant communities of organisms. Mesopelagic plankton and small nekton form the forage base for many deep-diving marine mammals and commercially harvested epipelagic species. Furthermore, detritus from the epipelagic zone falls through the mesopelagic where it is either recycled, providing the vital process of nutrient regeneration, or sinks to greater depths sequestering carbon from short-term atmospheric cycles. The waters below the mesopelagic down to the seafloor (both the bathypelagic and abyssopelagic) are very poorly characterized but are likely large reservoirs of novel biodiversity and link the surface and benthic ecosystems. Great strides have been made in understanding the biodiversity and ecosystem function of the ocean’s midwaters, but large regions, including those containing many exploration license areas and the greater depths where mining plumes will occur, remain very poorly studied. It is clear that pelagic communities are distinct from those on the seafloor and in the benthic boundary layer. They are often sampled with different instrumentation. The fauna have relatively large biogeographic ranges and they are more apt to mix freely across stakeholder boundaries, reference areas and other spatial management zones. Pelagic organisms live in a three-dimensional habitat and their food webs and populations are vertically connected by daily or lifetime migrations and the sinking flux of detritus from the epipelagic. The fauna do not normally encounter hard surfaces, making them fragile, and difficult to capture and maintain for sensitivity or toxicity studies. Despite some existing general knowledge, ecological baselines for midwater communities and ecosystems that likely will be impacted by mining have not been documented. There is an urgent need to conduct more research and evaluate the midwater biota (microbes to fishes) in regions where mining is likely to occur. Deep-sea mining activities may affect midwater organisms in a number of ways, but it is still unclear at what scale perturbations may occur. The sediment plumes both from collectors on the seafloor and from midwater discharge will have a host of negative consequences. They may cause respiratory distress from clogged gills or respiratory surfaces. Suspension feeders, such as copepods, polychaetes, salps, and appendicularians, that filter small particles from the water and form an important basal group of the food web, may suffer from dilution of their food by inorganic sediments and/or clogging of their fragile mucous filter nets. Small particles may settle on gelatinous plankton causing buoyancy issues. Metals, including toxic elements that will enter the food web, will be released from pore waters and crushed ore materials. Sediment plumes will also absorb light and change backscatter properties, reducing visual communication and bioluminescent signaling that are very important for prey capture and reproduction in midwater animals. Noise from mining activities may alter the behaviors of marine mammals and other animals. Small particles have high surface area to volume ratios, high pelagic persistence and dispersal and as a result greater potential to result in pelagic impacts. All of these potential effects will result in mortality, migration (both horizontal and vertical), decreased fitness, and shifts in community composition. Depending on the scale and duration of these effects, there could be reduction in provisioning to commercial fish species, delivery of toxic metals to pelagic food webs and hence human seafood supply, and alterations to carbon transport and nutrient regeneration services. After four days of presentations and discussions, the workshop participants came to several conclusions and synthesized recommendations. 1. Assuming no discharge in the epipelagic zone, it is essential to minimize mining effects in the mesopelagic zone because of links to our human seafood supply as well as other ecosystem services provided by the mesopelagic fauna. This minimization could be accomplished by delivering dewatering discharge well below the mesopelagic/bathypelagic transition (below ~1000 m depth). 2. Research should be promoted by the ISA and other bodies to study the bathypelagic and abyssopelagic zones (from ~1000 m depths to just above the seafloor). It is likely that both collector plumes and dewatering plumes will be created in the bathypelagic, yet this zone is extremely understudied and contains major unknowns for evaluating mining impacts. 3. Management objectives, regulations and management actions need to prevent the creation of a persistent regional scale “haze” (enhanced suspended particle concentrations) in pelagic midwaters. Such a haze would very likely cause chronic harm to deep midwater ecosystem biodiversity, structure and function. 4. Effort is needed to craft suitable standards, thresholds, and indicators of harmful environmental effects that are appropriate to pelagic ecosystems. In particular, suspension feeders are very important ecologically and are likely to be very sensitive to sediment plumes. They are a high priority for study. 5. Particularly noisy mining activities such as ore grinding at seamounts and hydrothermal vents is of concern to deep diving marine mammals and other species. One way to minimize sound impacts would be to minimize activities in the sound-fixing-and-ranging (SOFAR) channel (typically at depths of ~1000 m) which transmits sounds over very long distances. 6. A Lagrangian (drifting) perspective is needed in monitoring and management because the pelagic ecosystem is not a fixed habitat and mining effects are likely to cross spatial management boundaries. For example, potential broad-scale impacts to pelagic ecosystems should be considered in the deliberations over preservation reference zones, the choice of stations for environmental baseline and monitoring studies and other area-based management and conservation measures. 7. Much more modeling and empirical study of realistic mining sediment plumes is needed. Plume models will help evaluate the spatial and temporal extent of pelagic (as well as benthic) ecosystem effects and help to assess risks from different technologies and mining scenarios. Plume modeling should include realistic mining scenarios (including duration) and assess the spatial-temporal scales over which particle concentrations exceed baseline levels and interfere with light transmission to elucidate potential stresses on communities and ecosystem services. Models should include both near and far field-phases, incorporating realistic near field parameters of plume generation, flocculation, particle sinking, and other processes. It is important to note that some inputs to these models such as physical oceanographic parameters are lacking and should be acquired in the near-term. Plume models need to be complemented by studies to understand effects on biological components by certain particle sizes and concentrations.

This study is a quantitative assessment of the role fish-induced bio-resuspension plays in the silica cycle of coastal waters. We used new, published and archived oceanographic data to construct a comprehensive silica budget for Saanich Inlet (Vancouver Island, Canada), a highly productive Northeast Pacific fjord, where siliceous diatoms dominate primary productivity. Anoxia in the deep water of the inlet persists during most of the year, precluding animal life, whereas abundant groundfish continuously rework and resuspend bottom sediments in the shallower, oxygenated margins. This resuspension transfers settled biogenic silica fragments from the sediment, where they are immersed in porewater that is rich with dissolved silica, to the overlying water, where the much lower concentrations accelerate their dissolution rate. The budget shows that Saanich Inlet sediments constitute a sink for approximately 250 × 106 mol Si y−1. Most of this Si enters the inlet in advected, siliceous phytoplankton. Sediment resuspension by groundfish in the oxygenated margins of Saanich Inlet generates about 50% of the total flux of dissolved silica from the inlet seafloor. This resuspension also facilitates a massive transport of biogenic silica from the margins to the anoxic basin, where approximately 90% of all the biogenic silica is buried. The excess dissolution caused by fish activity reduces the burial efficiency of biogenic silica in the entire inlet sediments by about 20%. This case study emphasizes the link between the silica cycle and groundfish activity. Based on this study and because biological resuspension occurs in most regions of the ocean, we recommend that it will be taken into account when budgeting the silica cycle, and potentially other geochemical cycles, in marine environments.

Decades of exploration for venting sites along spreading ridge crests have produced global datasets that yield estimated mean site spacings of ∼ 12 – 220 km . This conclusion demands that sites where hydrothermal fluid leaks from the seafloor are improbably rare along the 66 000 km global ridge system, despite the high bulk permeability of ridge crest axes. However, to date, exploration methods have neither reliably detected plumes from isolated low-temperature, particle-poor, diffuse sources, nor differentiated individual, closely spaced (clustered within a few kilometers) sites of any kind. Here we describe a much lower mean discharge spacing of 3–20 km, revealed by towing real-time oxidation–reduction–potential and optical sensors continuously along four fast- and intermediate-rate (>55 mm/yr) spreading ridge sections totaling 1470 km length. This closer spacing reflects both discovery of isolated sites discharging particle-poor plumes (25% of all sites) and improved discrimination (at a spatial resolution of ∼1 km) among clustered discrete and diffuse sources. Consequently, the number of active vent sites on fast- and intermediate-rate spreading ridges may be at least a factor of 3–6 higher than now presumed. This increase provides new quantitative constraints for models of seafloor processes such as dispersal of fauna among seafloor and crustal chemosynthetic habitats, biogeochemical impacts of diffuse venting, and spatial patterns of hydrothermal discharge.

11 pages, 10 figures, 1 table, supplementary data https://dx.doi.org/10.1016/j.jmarsys.2015.09.005, The use of small-scale space by benthos and its variation over the seasons in transiently hypoxic zones is poorly known. In this study, we examined the reciprocal spatial dispersion of the squat lobster (. Munida quadrispina) and the slender sole (. Lyopsetta exilis) according to oxygen concentrations at a VENUS platform of Ocean Networks Canada (ONC). This platform is located in a seasonally hypoxic zone at 96. m depth in the fjord of Saanich Inlet (British Columbia, Canada). We counted and located small as well as large squat lobsters and slender soles in digital still images during 1 year (2012-2013) also concomitantly obtained oxygen data. Images were subdivided in a squared grid to obtain relative density maps as a proxy for surface occupation and spatial autocorrelation. Pearson's chi-squared tests at a yearly scale, along with Dixon's spatial segregation index (S) for each possible pair among the studied groups, showed a significant absence of overlap. The same analyses by month and cross-correlation between oxygen and S showed that while the dispersion patterns of the large squat lobsters seemed to be driven mainly by the morphology of the seafloor, an effect of hypoxia was found in the small squat lobsters and the slender soles levels of aggregation. Small squat lobster sought seabed protrusions, such as sponges, to reach more oxygenated water. The slender sole's space occupation decreased significantly, being forced to retreat when the squat lobsters' abundance peaked as a result of what appeared to be a seasonal reproduction event in early summer. Our results contribute to the understanding of the ways in which oxygen levels modulate substrate use by benthic species in the framework of a global expansion of hypoxia in coastal and ocean areas, RITFIM project (ref. CTM2010-16274) of the Spanish national RTD program funded this work without any further involvement in the preparation of the article. Jacopo Aguzzi is a Research Fellow of the Ramon y Cajal Program (MINECO)

Deep seabed mining is a major new intersection of human enterprise and deep-ocean ecosystems. This paper reviews the concept and process for a holistic approach to planning environmental management in the deep sea based on Strategic Environmental Goals and Objectives. Strategic planning around the environment can establish a vision for the future condition of the ocean floor for which the International Seabed Authority (ISA) can draw on a wealth of precedents and experience. By engaging stakeholders and applying current knowledge of deep ecosystems, the ISA can build meaningful strategic environmental goals and objectives that give guidance to its own operation and those of its contractors. This framework builds understanding of the organization’s aspirations at global, regional and contractor levels. Herein, some examples are suggested, but we focus on the process. To operationalize these goals and objectives, progress must be measurable; thus, targets are set, reports are assessed, and appropriate responses are awarded. Many management tools and actions are applicable for achieving environmental goals. To date, the ISA has considered marine spatial planning largely around the current exploration contract blocks. Other elements of environmental management, including the requirements for baseline studies, impact assessment, post-impact monitoring and the treatment of harmful effects and serious harm need to be implemented to support well-defined environmental goals and objectives. We suggest that this planning be executed for scales larger than individual blocks, through a Strategic Environmental Management Plan, to ensure sustainable use of ocean resources across the Area.

As global ocean deoxygenation proceeds and the frequency of extreme low-oxygen (hypoxic) events increases, seafloor ecosystems will inevitably be affected. Our study examines how benthic community responses scale with the severity and spatial extent of hypoxia. Saanich Inlet is a natural model system for testing the effects of hypoxic conditions that determine the benthic megafaunal community structure during annual deoxygenation and reoxygenation. In 2016, an anomalously severe and widespread hypoxic event occurred in the fjord after a decade of oxygen decline at a rate of 0.07 mL L −1 y −1 as measured by a cabled seafloor observatory. We use a living ecological time-series generated from remotely operated vehicle surveys to assess how the benthic megafaunal community disassembled in response to this extreme hypoxic event. Three benthic surveys at similar times in 2013 and 2016 reveal large increases in the area of seafloor bathed in anoxic and hypoxic waters in the latter year. Both bottom oxygen and species depth distributions shoaled from 2013 to 2016, accompanied by a 56% overall decline in megafauna. The abundant habitat-forming pennatulacean octocoral, Halipteris willemoesi , decreased in abundance by 92.3% from fall 2013 to fall 2016, and pandalid shrimp disappeared from the community. Hypoxia-tolerant species experienced milder losses, and two new species occurred in 2016 – one a predator on the coral. Co-occurrence analyses revealed loss of significant community segregation from 2013 to 2016, and a re-mix of pairwise species co-occurrences in the latter year. The loss of oxygenated habitat compressed species into narrower depth ranges and led to disassembly probably through niche space constriction, while decimation of some populations eliminated key community associations. Community fragmentation and disruption of interactions is a possible outcome for many marine benthic ecosystems as marine hypoxia intensifies.

Highlights • Active hydrothermal vent ecosystems are extremely rare. • Vent ecosystems are recognized as vulnerable by international organizations. • Mineral resources at active vents would not contribute significantly to the global metal supply. • Effective networks that protect representative active vents cannot be ensured. • A prohibition on mining active vents is consistent with obligations for conservation. Abstract There is increasing interest in mining minerals on the seabed, including seafloor massive sulfide deposits that form at hydrothermal vents. The International Seabed Authority is currently drafting a Mining Code, including environmental regulations, for polymetallic sulfides and other mineral exploitation on the seabed in the area beyond national jurisdictions. This paper summarizes 1) the ecological vulnerability of active vent ecosystems and aspects of this vulnerability that remain subject to conjecture, 2) evidence for limited mineral resource opportunity at active vents, 3) non-extractive values of active vent ecosystems, 4) precedents and international obligations for protection of hydrothermal vents, and 5) obligations of the International Seabed Authority under the UN Convention on the Law of the Sea for protection of the marine environment from the impacts of mining. Heterogeneity of active vent ecosystems makes it extremely challenging to identify “representative” systems for any regional, area-based management approach to conservation. Protection of active vent ecosystems from mining impacts (direct and indirect) would set aside only a small fraction of the international seabed and its mineral resources, would contribute to international obligations for marine conservation, would have non-extractive benefits, and would be a precautionary approach.

Cobb Seamount lies at 46" 46' N, 130" 48' W in the northeast Pacific 5 10 km due west of the Oregon coast. The isolated seamount rises 3000 m in a current field flowing from west to east. The seamount supports dense populations of fish and benthos. Collections and submersible observations of the benthic community pro- duced a list of 117 species representing 13 phyla. The organisms present can nearly all be found on the North American Pacific coast, but the diversity is low. This paper presents an analysis of the larval dispersal modes of the benthos at Cobb Seamount. This remote seamount is dominated by species with either a short-lived or no planktonic larval phase. The preponderance of such larval strategies and the observation of abundant drifting kelp near the seamount suggest that rafting of adults may be an effective dispersal mode. The presence of a recirculating flow in the form of a modified Taylor cap appears im- portant for trapping short-lived larvae on the seamount. However, because the water mass is replaced about every 17 days, medium and long-lived larvae would not be re- tained. The interplay between local currents, available dispersal vectors, and life-history strategies cannot be overlooked in the interpretation of marine biogeographic patterns.

Current pressures to mine polymetallic sulfide deposits pose threats to the animal communities found at deep-sea hydrothermal vents. Management plans aimed at preserving these unusual communities require knowledge of historical and contemporary forces that shaped the distributions and connectivity of associated species. As most vent research has focused on the eastern Pacific and mid-Atlantic ridge systems less is known about Indo-Pacific vents, where mineral extraction activities are imminent. Deep-sea mussels (Bivalvia: Mytilidae) of the genus Bathymodiolus include the morphotypic species B. septemdierum, B. brevior, B. marisindicus, and B. elongatus which are among the dominant vent taxa in western Pacific back-arc basins and the Central Indian Ridge. To assess their interpopulational relationships, we examined multilocus genotypes based on DNA sequences from four nuclear and four mitochondrial genes, and allozyme variation encoded by eleven genes. Bayesian assignment methods grouped mussels from seven widespread western Pacific localities into a single cluster, whereas the Indian Ocean mussels were clearly divergent. Thus, we designate two regional metapopulations. Notably, contemporary migration rates among all sites appeared to be low despite limited population differentiation, which highlights the necessity of obtaining realistic data on recovery times and fine-scale population structure to develop and manage conservation units effectively. Future studies using population genomic methods to address these issues in a range of species will help to inform management plans aimed at mitigating potential impacts of deep-sea mining in the Indo-Pacific region.

Glass sponges are conspicuous members of the deep-sea fauna, but in the northeastern Pacific they form unusual reefs covering kilometers of seafloor. Individual sponges in fjords can process up to 10 m3 water d−1 osculum−1; sponge reefs must therefore process considerable volumes and could significantly affect local water properties. We measured, in situ, the flux of carbon and nitrogen through Aphrocallistes vastus, the dominant reef-building species on Fraser Ridge reef, and calculated the energetics of feeding for all reefs in the Strait of Georgia, British Columbia. Sponges removed up to 90% of bacteria from the water and released ammonium. Because of the high density of sponges, high volumetric flow rates (up to 210 ± 35 m3 m−2 d−1, mean ± standard error, 95% confidence interval (CI) 132–288 m3 m−2 d−1), and the efficient extraction of bacteria, we calculate a grazing rate of 165 ± 29 m3 m−2 d−1 (95% CI 102–228 m3 m−2 d−1) for sponge reefs, the highest benthic grazing rate of any suspension-feeding community measured to date. Reefs of A. vastus extract seven times more carbon (3.4 ± 1.4 g C m−2 d−1) than can be supported by vertical flux of total carbon alone and therefore require productive waters and steady currents to sustain their strong grazing. We calculate that modern sponge reefs in the northeastern Pacific remove 2.27 × 105 ± 0.91 × 105 kg of bacterial carbon daily, nearly an order of magnitude less than the 1.38 × 106 ± 0.55 × 106 kg removed by past sponge reefs estimated to have covered the continental shelf.

Large symbiont-hosting snails of the genus Alviniconcha (Gastropoda: Abyssochrysidae) are among the dominant inhabitants of hydrothermal vents in the Western Pacific and Indian oceans. The genus was originally described as monotypic, but unique DNA sequences for mitochondrial genes revealed six distinct evolutionary lineages that we could not distinguish based on external morphology. Subsumed under the name Alviniconcha hessleri Okutani & Ohta, the distinct allopatric and sympatric lineages have been assigned placeholder epithets that complicate scientific communications. Based on the present multi-gene sequence data, we hereby describe five Alviniconcha species (in the order of their discovery) – A. kojimai sp. nov., A. boucheti sp. nov., A. marisindica sp. nov., A. strummeri sp. nov. and A. adamantis sp. nov. Thus, we restrict application of the name A. hessleri to specimens that are genetically similar (≥95% for COI) to those found at localities in the Mariana Trough. Single distinct Alviniconcha speci...

Flatfish are a major component of the hydrothermal vent community on three seamounts of the northern Mariana Volcanic Arc in the northwest Pacific. Nikko, Kasuga-2 and Daikoku seamounts host vent fields between 375 and 480 m depth where high temperature vents release molten sulphur. The small cynoglossid tonguefish, Symphurus thermophilus Munroe and Hashimoto, is ubiquitous in all vent habitats observed on these seamounts: among extensive fields of tubeworms and mussels and on solid sulphur surfaces on Nikko; on sulphur-rich sediments and barnacle-covered boulders on Kasuga-2; and on recent sulphur flows and on broad areas of loose and semi-consolidated sediments on Daikoku. We recorded repeated forays by individuals onto flows of molten sulphur as these surfaces cooled. Based on observations using ROVs, the mean density is 90 fish/m 2 with maximum counts over 200 fish/m 2 on Daikoku sediments. Compared to collected tonguefish from Daikoku and Kasuga-2, those from Nikko have significantly greater lengths and, on average, six times the mass. Otolith data indicate upper ages of 13 years with Nikko tonguefish growing significantly faster. Diets of tonguefish on the three seamounts reflect the different habitats and prey availability; in Daikoku specimens, small crustaceans and polychaetes are most common while on Nikko, gut contents are predominantly larger shrimp. We made the unusual observation of stunned midwater fish falling to the seafloor near the vents where S. thermophilus immediately attacked them. This tonguefish has a wide diet range and foraging behaviour that likely influence the differing growth rates and sizes of fish inhabiting the different vent sites. Limited genetic data suggest that larval exchange probably occurs among sites where the common habitat factor is high levels of elemental sulphur forming hard and partly unconsolidated substrata. Here, in the northern range of the Mariana Trench Marine National Monument, S. thermophilus , despite having an unusually broad habitat association, may be restricted in its overall range to this region of isolated volcanoes with active hydrothermalism.

A novel video survey method measures small-scale seafloor bottom roughness in fragile and deep-sea habitats called microtopographic laser scanning (MiLS). Using a controlled submersible platform, an attached downward- facing video camera with a single optical laser can return imagery to detail the bottom profile at a resolution of ~1–2 cm. The method compares the position of the underlying substratum and laser dot between successive video frames to determine distance traveled in the forward direction and substratum height. The video imagery is processed using photogrammetry to calculate small-scale topography (horizontal and vertical axes). MiLS is adaptable for most aquatic habitats as it can be executed using any platform that can move forward with a constant slope over the desired transect. Traditional techniques of measuring small-scale roughness are largely restricted to easily accessible habitats and often yield measurements that are relative and not comparable among different habitats and studies. Quantifying roughness in ways that permit comparisons is critical to understanding effects of bottom roughness and would benefit many fields of aquatic science. With its versatility, ability to access remote locations and output of quantified measurements, MiLS has the potential to fill this need. It is also likely this method will be useful in subaerial habitats such as wetlands. Here, we describe the MiLS equipment, theory, and method in detail, and then demonstrate its application in a lab trial and in a field study in a deep-sea (≤450 m depth) sponge and coral habitat where its high resolution, accuracy, and precision is made evident.

The seafloor of the Molucca and Celebes Seas, Indonesia, was investigated using a remotely operated vehicle with high-definition video during 18 dives to depths of 280 to 3200 m. Irregular slopes and rocky substrata supported abundant megabenthos, including stalked crinoids. Video zoomed on many individuals provided enough details to assign 770 stalked crinoids to major taxa and many to species level. These taxa included Guillecrinus neocaledonicus, Ptilocrinus cf. amezianeae, three species of Hyocrinus, an unknown phrynocrinid, Naumachocrinus hawaiiensis, Proisocrinus ruberrimus, Endoxocrinus alternicirrus, seven phenotypes in the Subfamily Metacrininae and one taxon of unknown affiliation. A novel observation of a juvenile Endoxocrinus included the attachment disk to a rocky surface. Taxa usually considered rare were well represented on hard substrata, thus expanding knowledge of their depth distributions. Mostly, stalked crinoids were sparsely distributed in low densities (to 186 individuals per km), except for occasional single-species clusters. Metacrinins and P. cf. amezianeae dominated at depths of 250–600 m, while E. alternicirrus and G. neocaledonicus were the most abundant species at a depth range of 1000–1400 m. The largest peak of species richness (with nine of the 17 taxa identified) occurred at 1000 to 2000 m. Many specimens altered their feeding posture with current intensity, but a balloon-like crown posture is common in low or non-existent currents. The postures of several mobile metacrinin individuals suggest an active role of arms and cirri in slow crawling movements. The possible origin of some taxa from either Gondwanaland or Eurasian margins is discussed using biogeographical and paleontological data. The location of the Wallace line cannot be delimited only using extant stalked crinoid distribution.

The Canadian Healthy Oceans Network (CHONe) research program formed to unite leading academic and government researchers with managers from Canada's national resource agencies to address an urgent need for better scientific information on marine biodiversity in Canada's Atlantic, Pacific, and Arctic waters. Specifically, the network is producing diverse scientific products to inform policy commitments in conservation and sustainable use of marine biodiversity resources. A common disconnect between science-driven research and policy application results in a dearth of science information relevant to specific decisions that cannot wait for knowledge to accumulate. To narrow this gap, CHONe research structures around three interlinking and integrated themes of marine biodiversity, ecosystem function, and population connectivity. CHONe products span from baseline maps, databases, and barcodes as tools to understand processes and monitor future change; spatial and temporal predictive tools to maximize ...

Learmonth Bank in northern British Columbia sustains an active trawl fishery that returns large bycatches of deep-sea sponges and corals. To examine effects of biogenic structures on the distribution of fish, we examined nearly 30 km of high-definition imagery from a remotely oper- ated vehicle and documented locations of 2770 scorpaenid fish. The 2 local genera have similar abun- dances, averaging about 1.2 individuals 100 m -2 , but have different spatial abundance patterns: shortspine thornyhead Sebastolobus alascanus are randomly distributed on featureless substrata and their abundance increases with depth. Rockfish Sebastes spp. associate with higher seafloor relief nonrandomly and select for sponges and corals over the inert substrata alone; 95% of the rockfish occurred on 27% of the seafloor surveyed. Sponges (Demospongia and Hexactinellida) were abun- dant on the bedrock and boulders of the bank and adjacent moraine and covered 30 to 55% of the seafloor compared with 1% of the sediment and aggregates of the surrounding basin. The majority of rockfish (80%) occurred with sponges ≥50 cm in height, and even beds of short sponges attracted 4 times as many rockfish than did substrata with no large epifauna. While over half of primnoid corals over 30 cm tall had associated rockfish, less than 2% of the seafloor had large coral, and small coral had no associated rockfish. On the adjacent seafloor with past trawling activity, Primnoa pacifica was 13 times less abundant, and large corals and sponges were rare. Thornyhead abundance doubled but rockfish had a 3-fold reduction in numbers. Our study indicates that degradation of biogenic struc- tures is a long-term detriment to rockfish species and, although the mechanism remains unclear, our data suggest it occurs through the destruction of a habitat that is more effective for shelter than rough inert seafloor.

Hydrothermal vents near the summits of seamounts in Western Pacific volcanic arcs foster dense populations of flatfishes, a group otherwise unknown at vents. We examined genetic divergence among populations of a symphurine tonguefish described as Symphurus thermophilus Munroe & Hashimoto from sites up to 6000 km apart in the Western Pacific to explore connectivity patterns among seamounts. Average genetic divergence between individuals from the Mariana Arc and the Tonga-Kermadec Arcs was 14.2% (COI) and 9.0% (16S), whereas within-arc divergences were

Global expansion of oxygen-deficient (hypoxic) waters will have detrimental effects on marine life in the Northeast Pacific Ocean (NEP) where some of the largest proportional losses in aerobic habitat are predicted to occur. However, few in situ studies have accounted for the high environmental variability in this region while including natural community-assembly dynamics. Here, we present results from a 14-month deployment of a benthic camera platform tethered to the VENUS cabled observatory in the seasonally hypoxic Saanich Inlet. Our time series continuously recorded natural cycles of deoxygenation and reoxygenation that allowed us to test whether a community from the NEP showed hysteresis in its recovery compared to hypoxia-induced decline, and to address the processes driving temporal beta diversity under variable states of hypoxia. Using high-frequency ecological time series, we reveal (i) differences in the response and recovery of the epibenthic community are rate-limited by recovery of the sessile species assemblage; (ii) both environmental and biological processes influence community assembly patterns at multiple timescales; and (iii) interspecific processes can drive temporal beta diversity in seasonal hypoxia. Ultimately, our results illustrate how different timescale-dependent drivers can influence the response and recovery of a marine habitat under increasing stress from environmental change.

Hydrothermal vents harbor dense aggregations of invertebrate fauna supported by chemosynthesis. Severe tectonic events and volcanic eruptions frequently destroy vent communities and initiate primary succession at new vents on ridge-crest submarine lava flows. An eruption on Axial Volcano (∼1500 m depth), a seamount on the Juan de Fuca Ridge (JdFR) in the northeast Pacific Ocean, occurred in January 1998, which created new substratum and vents. This study examines the development of the macrofaunal vent assemblages associated with tubeworms (Ridgeia piscesae) at eight diffuse flow vents over the following 3 years. Biological collections by suction of lava surfaces also characterized “pre-tubeworm assemblages”. Coupled fluid sampling showed an overall decrease in temperature, sulphide, and sulphide-to-heat ratios over 3 years as well as large spatial variability across the new vents. We examined collections of pre-eruption diffuse flow vent assemblages at Axial Volcano to compare the stages of new community development to “mature” vents. Mature vent assemblages are characterized by two major community types dominated by limpets (Lepetodrilus fucensis) and alvinellid polychaetes (Paralvinella pandorae and/or P. palmiformis). The following post-eruption succession patterns emerged. First, R. piscesae tubeworms took up to 3 years to establish aggregations at the new vents, and the majority of pre-tubeworm assemblages were dominated by grazing polychaetes. Second, species colonized quickly and by 30 months after habitat creation >60% of Axial's species pool had arrived at the new vents; abundance at mature vents predicted colonization success with some notable exceptions. Third, shifts in species dominance occurred rapidly and by Year 3 new vent assemblages resembled mature, pre-eruption communities. In general, tubeworm assemblages were dominated by alvinellid polychaetes (P. pandorae and P. palmiformis) in the first 2 years post-eruption, with limpets (L. fucensis) becoming more numerous in Year 3. Fourth, successional trajectories corresponded to four habitat variables: the timing of R. piscease recruitment, vent age, maximum vent fluid sulphide-to-heat ratios, and maximum vent fluid temperatures. The two mature community types (dominance by limpets or alvinellid polychaetes) seem to relate in part to vent differences in fluid properties, with limpets more prevalent than alvinellids at diffuse vents with lower maximum sulphide-to-heat ratios and temperatures. We present a general model of post-eruption succession for Juan de Fuca Ridge diffuse flow vents. The model incorporates potential abiotic and biotic drivers of community development and identifies six successional stages: a pre-tubeworm assemblage, four tubeworm assemblage states determined by the relative dominance of alvinellid polychaetes and the limpet, and a final senescent stage when venting wanes. Future eruptions will allow for this model to be tested through direct observation and experimentation.

Increasing atmospheric carbon dioxide levels are causing ocean acidification, compromising the ability of some marine organisms to build and maintain support structures. An analysis of mussels from a submarine volcano setting with natural low-pH conditions shows low shell thicknesses and growth rates, but survival over up to four decades. Increasing atmospheric carbon dioxide levels are causing ocean acidification1,2, compromising the ability of some marine organisms to build and maintain support structures3 as the equilibrium state of inorganic carbon moves away from calcium carbonate4. Few marine organisms tolerate conditions where ocean pH falls significantly below today’s value of about 8.1 and aragonite and calcite saturation values below 1 (refs 5, 6). Here we report dense clusters of the vent mussel Bathymodiolus brevior in natural conditions of pH values between 5.36 and 7.29 on northwest Eifuku volcano, Mariana arc, where liquid carbon dioxide and hydrogen sulphide emerge in a hydrothermal setting. We find that both shell thickness and daily growth increments in shells from northwest Eifuku are only about half those recorded from mussels living in water with pH>7.8. Low pH may therefore also be implicated in metabolic impairment7. We identify four-decade-old mussels, but suggest that the mussels can survive for so long only if their protective shell covering remains intact: crabs that could expose the underlying calcium carbonate to dissolution are absent from this setting. The mussels’ ability to precipitate shells in such low-pH conditions is remarkable. Nevertheless, the vulnerability of molluscs to predators is likely to increase in a future ocean with low pH.

We quantify sediment resuspension due to groundfish activity in a partly anoxic basin using acoustic backscatter sensors, transmissometers, and remotely operated cameras on stationary and mobile platforms. Where these fish were present, a distinct benthic nepheloid layer (BNL) devel- oped despite minimal bottom currents ( 100 disturbances m -2 d -1 resulting in complete surface reworking every 2.5 d and a daily resuspension of 1.3 ± 0.7 l bulk sediment m -2 d -1 . Preliminary geochemical measurements suggest substantial impact of fish resuspension activity, the immediate effect being an instantaneous increase in nutrient concentration in the benthic boundary layer and a drop in oxygen concentration. Over longer time scales (hours to days), the freshly exposed organic matter is oxidized and additional nutrients (silica, ammonium, phosphate) are regenerated and released to the water. The increase in benthic oxygen demand suggests that fish activity reduces organic carbon sequestration by 9 ± 5 mmol C m -2 d -1 , equivalent to ~40% of its downward flux in this basin. To date, these processes are missing from geochemical models and require further investigation, particularly considering the depletion of groundfish stocks and the likely effects on global biogeochemical cycles.

Intraoceanic arcs of the world are dominated by submarine volcanoes, many of which host active hydrothermal systems. A considerable number of the morphological features common to subaerial volcanoes are also present on the submarine edifices, including summit craters. Surprisingly, some of the craters, such as at Daikoku and Nikko volcanoes of the Mariana Arc, and Macauley Cone of the Kermadec Arc, are host to lakes of molten sulfur, both ancient and modern. These lakes, up to ~200 m in diameter, act as condensers of gases that derive from the underlying magmas. Volcanic vents beneath these lakes provide a steady outflow of hot gases that continuously generate molten sulfur. At Daikoku, an extraordinary lake of liquid sulfur is in constant convective and gas escape-driven motion. Smaller pools of molten sulfur occur on Nikko, and there is evidence of older, larger lakes on both this volcano and Macauley, based on the accumulation of large quantities of sulfur in the subsurface. The elemental S at these sites is produced largely by the reaction 2H2S + SO2 = 3S + 2H2O and the disproportionation of magmatic SO2. Anomalous concentrations of Au and Cu in the lakes are most likely transported by vapor.

Zooplankton and nekton at 2000 m depth in the axial valley of Endeavour Segment, Juan de Fuca Ridge, show marked variability in abundances in a plane at 20 m above bottom. A remotely operated vehicle flew a gridded rectangle 3.2×0.5 km that included two large high-temperature and two small low-temperature vent fields. Numbers of zooplankton, jellyfish, shrimp and fish were recorded with a video camera, and the abundance patterns were examined with the program SADIE © . Each organism group displayed a distinctive distribution pattern. Abundance gaps over the high-temperature fields were significant and, for the more abundant copepods, were related to the locations of individual smokers. Pelagic shrimp and macrourid fish abundances were correlated and concentrated around the northern high temperature field. Distinct aggregations of zooplankton and nekton were correlated with the fluid indicators from both the low temperature diffuse effluent and the focused high temperature vents. Patterns were likely established by organism choice that forms aggregations and gaps, and by physical processes that entrain passive particles near vigorous smoker plumes. While enhanced plankton and nekton numbers were not observed over the vent fields, overall abundances in the axial valley may be sustained by production transported from the vent fields on the seafloor.

Three-quarters of the Earth's volcanic activity is submarine, located mostly along the mid-ocean ridges, with the remainder along intraoceanic arcs and hotspots at depths varying from greater than 4,000 m to near the sea surface. Most observations and sampling of submarine eruptions have been indirect, made from surface vessels or made after the fact. We describe here direct observations and sampling of an eruption at a submarine arc volcano named NW Rota-1, located 60 km northwest of the island of Rota (Commonwealth of the Northern Mariana Islands). We observed a pulsating plume permeated with droplets of molten sulphur disgorging volcanic ash and lapilli from a 15-m diameter pit in March 2004 and again in October 2005 near the summit of the volcano at a water depth of 555 m (depth in 2004). A turbid layer found on the flanks of the volcano (in 2004) at depths from 700 m to more than 1,400 m was probably formed by mass-wasting events related to the eruption. Long-term eruptive activity has produced an unusual chemical environment and a very unstable benthic habitat exploited by only a few mobile decapod species. Such conditions are perhaps distinctive of active arc and hotspot volcanoes.

We examine the nature of variation in a hot vent tubeworm, Ridgeia piscesae, to determine how phenotypes are maintained and how reproductive potential is dictated by habitat. This foundation species at northeast Pacific hydrothermal sites occupies a wide habitat range in a highly heterogeneous environment. Where fluids supply high levels of dissolved sulphide for symbionts, the worm grows rapidly in a ‘‘short-fat’’ phenotype characterized by lush gill plumes; when plumes are healthy, sperm package capture is higher. This form can mature within months and has a high fecundity with continuous gamete output and a lifespan of about three years in unstable conditions. Other phenotypes occupy low fluid flux habitats that are more stable and individuals grow very slowly; however, they have low reproductive readiness that is hampered further by small, predator cropped branchiae, thus reducing fertilization and metabolite uptake. Although only the largest worms were measured, only 17% of low flux worms were reproductively competent compared to 91% of high flux worms. A model of reproductive readiness illustrates that tube diameter is a good predictor of reproductive output and that few low flux worms reached critical reproductive size. We postulate that most of the propagules for the vent fields originate from the larger tubeworms that live in small, unstable habitat patches. The large expanses of worms in more stable low flux habitat sustain a small, but long-term, reproductive output. Phenotypic variation is an adaptation that fosters both morphological and physiological responses to differences in chemical milieu and predator pressure. This foundation species forms a metapopulation with variable growth characteristics in a heterogeneous environment where a strategy of phenotypic variation bestows an advantage over specialization.

The polychaete annelid Paralvinella pandorae Desbruyeres and Laubier 1986 is endemic to hydrothermal vents in the northeast Pacific, and is found at almost all vents sites along the 500-km long Juan de Fuca ridge (JdF) system. The sperm morphology of P. pandorae indicates that fertilization occurs internally or in the worm's tube, and the maximum observed oocyte size of 215 lm sug- gests that a dispersive larval phase is short or non-existent. Size frequency ana- lyses of populations of P. pandorae suggest continuous or semi-continuous recruitment of juveniles. Given our limited knowledge of the species' life his- tory, we predicted that populations of P. pandorae would exhibit a decline in genetic similarity with increasing distance among populations along the JdF. While our attempts to use amplified fragment length polymorphisms to test this prediction were not successful, our analysis of cytochrome oxidase I gene sequences provided insights into the phylogeography of the species. For 31 individuals from five sites along the JdF there is little sequence variation among individuals and no phylogeographic pattern among haplotypes from popula- tions separated by distances of up to 210 km. These results indicate that gene flow occurs among all sites in the analyses, i.e. despite the very limited disper- sal potential inferred from life history characteristics of this worm, there is no evidence for isolation-by-distance across the geographical scale of the study. Demersal larvae dispersed by near-bottom currents might explain the gene flow among sites, as well as the establishment of populations of P. pandorae at new vents within a year.

Habitat selection by 3 Juan de Fuca Ridge gastropod species relates to their thermal environment. Both collections and images taken along transects document the small-scale abundance patterns of each species with respect to temperature and distance from vent flows. Lepetodrilus fucensis and Depressigyra globulus were most abundant at distances from vent flows of 0 to 25 cm in warm fluids with high temperature variability (10 ± 5°C) over several time scales. Both species were also abundant at 26 to 50 cm, where temperatures were lower with less variability (4 ± 1°C). Provanna variabilis was most abundant from 51 to 75 cm, where temperatures were stable (3 ± 0.5°C). All species were absent where maximum fluid temperatures reached 18°C and their substratum coverage was related to temperature. When presented with a choice in vent fluids from 10 to 2°C, L. fucensis and D. globulus moved to areas with temperatures above 5°C, while P. variabilis showed no preference. In species-specific temperature preference experiments, L. fucensis and D. globulus aggregated between 5 and 13°C, while P. variabilis occupied areas with significantly lower temperatures from 4 to 11°C. These experimental temperature preferences correspond with their thermal environments. Upper temperature limits are moderate; extreme abiotic variability in higher temperature fluids may constrain these 3 species. We conclude thermal conditions are a primary determinant of habitat selection, thereby driving gastropod abundance patterns. However, other factors likely contribute. Space competition nearest vent flows may result in the displacement of individuals of these species to low quality habitats.