In this study, we present the first thorough trophic characterization of cold seep macrofaunal communities on the Gulf of Mexico lower continental slope (> 1000 m depth). We analyzed tissue delta C-13, delta N-15, and delta S-34 of vestimentiferan tubeworms, bathymodiolin mussels, vesicomyid clams, and their associated macrofaunal communities from discrete collections made across the entire lower slope. Over half of macrofauna associated with mussels and about half associated with vestimentiferans had delta C-13 values below -45%. We also observed high spatial variability in the delta C-13 values of entire local communities, and the delta C-13 of associated fauna were significantly correlated with the delta C-13 compositions of the symbiotic species from the same location. These data indicate widespread incorporation of methane-derived carbon in mussel and vestimentiferan communities. This finding was particularly surprising in communities associated with older vestimentiferans, given the low rates of seepage observed in similar communities on the upper slope. On average, delta N-13 values in mussels and their associates were significantly more depleted and more variable than vestimentiferans, clams, and their associates, and there was a significant linear relationship between tissue delta N-15 values of mussels and their associated communities. The tissue delta S-34 values in macrofauna associated with vestimentiferans were more variable and significantly more depleted than mussel associates (delta S-34 = -16.8 to + 19.1% for vestimentiferan associates and delta S-34 = -3.1 to + 20.8% for mussel associates), consistent with higher isotopic fractionation during sulfate reduction in vestimentiferan habitats and a potentially higher nutritional contribution of sulfide-derived organic sulfur in vestimentiferan communities.

Patterns of succession in Lau Basin hydrothermal vent communities determined with high‐resolution imagery and in situ physico—chemical data collected over 4 yr and analyzed within a Geographic Information System show that Alviniconcha snails are a pioneering group, the snail Ifremeria nautilei is a mid‐successional species, and the heat‐intolerant mussel Bathymodiolus brevior dominates when venting declines. The associated fauna also changes as communities progress through the successional stages, and eventually non‐vent—endemic deep‐sea species appear when venting has mostly subsided. This is a unique example of primary succession in which the primary producers form symbiotic associations with mobile animals, resulting in successional patterns not observed in other systems. I. nautilei dominates newly formed substrates or venting sources where both I. nautilei and Alviniconcha spp. are already established (e.g., by migration), while Alviniconcha spp. seem to be better at colonizing newly active vents (e.g., by settlement) that are remote from colonized vents. Thus, on the scale of a 5–39 m2 diffuse flow area or a single edifice, the mid‐successional species dominates new substrates instead of the pioneering group. These communities are remarkably stable over long time periods relative to other hydrothermal vent regions. In addition to the sequential replacements of species as sites age and overall conditions change, Lau vent animals track changes in vent fluids and relocate themselves when local hydrothermal plumbing changes over small spatial scales.

We analyzed the tissue carbon, nitrogen, and sulfur stable isotope contents of macrofaunal communities associated with vestimentiferan tubeworms and bathymodiolin mussels from the Gulf of Mexico lower continental slope (970-2800 m). Shrimp in the genus Alvinocaris associated with vestimentiferans from shallow (530 m) and deep (1400-2800 m) sites were used to test the hypothesis that seep animals derive a greater proportion of their nutrition from seeps (i.e. a lower proportion from the surface) at greater depths. To account for spatial variability in the inorganic source pool, we used the differences between the mean tissue δ(13)C and δ(15)N of the shrimp in each collection and the mean δ (13)C and δ(15)N values of the vestimentiferans from the same collection, since vestimentiferans are functionally autotrophic and serve as a baseline for environmental isotopic variation. There was a significant negative relationship between this difference and depth for both δ(13)C and δ(15)N (p=0.02 and 0.007, respectively), which supports the hypothesis of higher dependence on seep nutrition with depth. The small polychaete worm Protomystides sp. was hypothesized to be a blood parasite of the vestimentiferan Escarpialaminata. There was a highly significant linear relationship between the δ(13)C values of Protomystides sp. and the E. laminata individuals to which they were attached across all collections (p < 0.001) and within a single collection (p = 0.01), although this relationship was not significant for δ(15)N and δ(34)S. We made several other qualitative inferences with respect to the feeding biology of the taxa occurring in these lower slope seeps, some of which have not been described prior to this study.

Hydrothermal vent sulfide edifices contain some of the most extreme thermal and chemical conditions in which animals are able to live. As a result, sulfide edifices in the East Pacific Rise, Juan de Fuca Ridge, and Mid Atlantic Ridge vent systems often contain distinct faunal assemblages. In this study, we used high-resolution imagery and in-situ physico-chemical measurements within the context of a Geographic Information System (GIS) to examine community structure and niche differentiation of dominant fauna on sulfide edifices in the Eastern Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR) in the Western Pacific Ocean. Our results show that ELSC and VFR sulfide edifices host two distinct types of communities. One type, that covers the majority of sulfide edifice faces, is overall very similar to nearby lava communities and biomass is dominated by the same chemoautotrophic symbiont-containing molluscs that dominate lava communities, namely the provannid gastropods Alviniconcha spp. and Ifremeria nautilei and the mytilid bivalve Bathymodiolus brevior. The spatial distribution of the dominant molluscs is often a variation of the pattern of concentric rings observed on lavas, with Alviniconcha spp. at the tops of edifices where exposure to vent flow is the highest, and I. nautilei and B. brevior below. Our physico-chemical measurements indicate that because of rapid dispersion of vent fluid, habitable area for symbiont-containing fauna is quite limited on sulfide edifices, and the realized niches of the mollusc groups are narrower on sulfide edifices than on lavas. We suggest that competition plays an important role in determining the realized distributions of the mollusc groups on edifices. The other habitat, present in small patches of presumably hot, new anhydrite, is avoided by the dominant symbiont-containing molluscs and inhabited by crabs, shrimp and polynoids that are likely more heat tolerant. The ratio of sulfide concentration to temperature anomaly of vent fluids was significantly different between sulfide edifice sites and lava sites in the southern vent fields but not in the northern vent fields. We suggest that this is due to increased sulfide consumption by a large microbial consortium associated with the more friable andesitic lava substrates in the south.

Deep-sea hydrothermal vents are populated by dense communities of animals that form symbiotic associations with chemolithoautotrophic bacteria. To date, our understanding of which factors govern the distribution of host/symbiont associations (or holobionts) in nature is limited, although host physiology often is invoked. In general, the role that symbionts play in habitat utilization by vent holobionts has not been thoroughly addressed. Here we present evidence for symbiont-influenced, regional-scale niche partitioning among symbiotic gastropods (genus Alviniconcha) in the Lau Basin. We extensively surveyed Alviniconcha holobionts from four vent fields using quantitative molecular approaches, coupled to characterization of high-temperature and diffuse vent-fluid composition using gastight samplers and in situ electrochemical analyses, respectively. Phylogenetic analyses exposed cryptic host and symbiont diversity, revealing three distinct host types and three different symbiont phylotypes (one ε-proteobacteria and two γ-proteobacteria) that formed specific associations with one another. Strikingly, we observed that holobionts with ε-proteobacterial symbionts were dominant at the northern fields, whereas holobionts with γ-proteobacterial symbionts were dominant in the southern fields. This pattern of distribution corresponds to differences in the vent geochemistry that result from deep subsurface geological and geothermal processes. We posit that the symbionts, likely through differences in chemolithoautotrophic metabolism, influence niche utilization among these holobionts. The data presented here represent evidence linking symbiont type to habitat partitioning among the chemosynthetic symbioses at hydrothermal vents and illustrate the coupling between subsurface geothermal processes and niche availability.

The Lau Integrated Study Site (ISS) has provided unique opportunities for study of ridge processes because of its back-arc setting in the southwestern Pacific. Its location allows study of a biogeographical province distinct from those of eastern Pacific and mid-Atlantic ridges, and crustal compositions along the ridge lie outside the range of mid-ocean ridge crustal compositions. The Lau ISS is located above a subduction zone, at an oblique angle. The underlying mantle receives water and other elements derived from the downgoing lithospheric slab, with an increase in slab influence from north to south. Water lowers the mantle melting temperature and leads to greater melt production where the water flux is greater, and to distinctive regional-scale gradients along the ridge. There are deeper faulted axial valleys with basaltic volcanism in the north and inflated axial highs with andesites in the south. Differences in igneous rock composition and release of magmatic volatiles affect compositions of vent fluids and deposits. Differences in vent fluid compositions and small-scale diffuse-flow regimes correlate with regional-scale patterns in microbial and megafaunal distributions. The interdisciplinary research effort at the Lau ISS has successfully identified linkages between subsurface processes and deep-sea biological communities, from mantle to microbe to megafauna.

On the otherwise low-biomass seafloor of the Gulf of Mexico (GoM) continental slope, natural oil and gas seeps are oases of local primary production that support lush animal communities. Hundreds of seep communities have been documented on the continental slope, and nutrition derived from seeps could be an important link in the overall GoM food web. Here, we present a uniquely large and cohesive data set of δ(13)C, δ(15)N, and δ(34)S compositions of the vestimentiferan tubeworms Escarpia laminata and Lamellibrachia sp. 1, which dominate biomass at GoM seeps and provide habitat for hundreds of other species. Our sampling design encompassed an entire region of the GoM lower slope, allowing us for the first time to assess spatial variability in isotope compositions and to robustly address long-standing hypotheses about how vestimentiferans acquire and cycle nutrients over their long lifespan (200+ years). Tissue δ(13)C values provided strong evidence that larger adult vestimentiferans use their buried roots to take up dissolved inorganic carbon from sediment pore water, while very small individuals use their plume to take up carbon dioxide from the seawater. δ(34)S values were extremely variable among individuals of the same species within one location (<1 m(2) area), indicating high variability in the inorganic sulfur pools on a very small spatial scale. This finding supports the hypothesis that vestimentiferans use their roots to cycle sulfate and sulfide between their symbionts and free-living consortia of sulfate-reducing archaea in the sediment. Finally, consistent differences in δ(15)N between two cooccurring vestimentiferan species provided the first strong evidence for partitioning of inorganic resources, which has significant implications for the ecology and evolution of this taxonomic group.

The sulfide (H2S/HS−) that is emitted from hydrothermal vents begins to oxidize abiotically with oxygen upon contact with ambient bottom water, but the reaction kinetics are slow. Here, using in situ voltammetry, we report detection of the intermediate sulfur oxidation products polysulfides [\( {\text{S}}_{\text{x}}^{2 - } \)] and thiosulfate [\( {\text{S}}_{ 2} {\text{O}}_{ 3}^{ 2- } \)], along with contextual data on sulfide, oxygen, and temperature. At Lau Basin in 2006, thiosulfate was identified in less than one percent of approximately 10,500 scans and no polysulfides were detected. Only five percent of 11,000 voltammetric scans taken at four vent sites at Lau Basin in May 2009 show either thiosulfate or polysulfides. These in situ data indicate that abiotic sulfide oxidation does not readily occur as H2S contacts oxic bottom waters. Calculated abiotic potential sulfide oxidation rates are <10−3 μM/min and are consistent with slow oxidation and the observed lack of sulfur oxidation intermediates. It is known that the thermodynamics for the first electron transfer step for sulfide and oxygen during sulfide oxidation in these systems are unfavorable, and that the kinetics for two electron transfers are not rapid. Here, we suggest that different metal catalyzed and/or biotic reaction pathways can readily produce sulfur oxidation intermediates. Via shipboard high-pressure incubation experiments, we show that snails with chemosynthetic endosymbionts do release polysulfides and may be responsible for our field observations of polysulfides.

Stable isotope compositions of cold-seep bivalves can illuminate processes that affect the chemical and isotopic compositions of seeping fluids along the continental slope of the Gulf of Mexico as well as provide insight into the physiological ecology of these species. Carbon and nitrogen isotope compositions were analyzed in mussels and clams from 14 seep sites spanning a depth range of 1000 to 2800m along the lower Louisiana slope of the Gulf of Mexico. Mussels of three species found on the lower slope, Bathymodiolus childressi, B. brooksi, and B. heckerae, showed site-specific differences in tissue δ13C, reflecting differences in the local methane pool. Mussels from sites on the lower slope sitting atop the contiguous salt sheet generally had tissue δ13C values that reflected a stronger biogenic methane signal (−70.8 to −58.8‰) than mussels on the upper slope or seaward of the Sigsbee Escarpment (−67.3 to −40.4‰). Clams (Calyptogena ponderosa and Calyptogena sp. nov.) had a narrow range of δ13C values between −37.0 and −34.4‰, indicating that their thiotrophic symbionts are fixing primarily seawater-dissolved organic carbon. The most depleted tissue δ15N values yet published for both mussels and clams are reported in this study at −23.7 and −9.2‰, respectively. These depleted values have implications for the assimilation of inorganic nitrogen by these symbioses and the concentrations of particular inorganic nitrogen sources in the local environment.

To investigate interactions between ferroportin (FPN) an iron exporter and hephaestin (Heph) a copper‐bound ferroxidase, we performed experiments using fluorescence energy transfer (FRET). We prepared appropriate fluorescent probes by attaching cyan fluorescent protein (CFP) to the N‐terminus of Heph and yellow fluorescent protein (YFP) to the N‐terminus of FPN. In cells stably expressing Heph‐CFP, we first assessed CFP fluorescence, pixel by pixel. In cells stably expressing both Heph‐CFP and FPN‐YFP, we then reassessed fluorescence of each pixel at the CFP donor emission wavelength. An YFP‐induced decrease in CFP emission suggests that the two proteins are associated. We found that an FPN‐YFP induced the decrease of Heph‐CFP emission suggesting the association of these two proteins on the basolateral membrane of human intestinal Caco‐2 cells. Our FRET experiments show that the distance of FPN‐YFP from Heph‐CFP is ~ 5 nm. Our FRET studies also indicate that neither FPN nor Heph is associated with TfR1 on the basolateral membrane of the enterocyte, although we showed the colocalization of these two proteins with TfR1 on the basolateral membrane of the enterocyte.

A pattern of succession has been demonstrated at Gulf of Mexico cold seeps proceeding from a high‐biomass endemic community dominated by grazers to a diverse community of endemic and nonendemic species in multiple trophic levels to a low‐biomass community comprising primarily nonendemic predatory species. We test the hypothesis that these shifts in community structure are due to a decline in the availability and reliance on local chemosynthetic productivity. Isotopic signatures were measured in 134 individuals from 34 different species in three tubeworm aggregations in different stages of succession. The average stable isotope delta values of the fauna were more positive in the older aggregations, suggesting a decreased reliance on local chemosynthetic productivity. These trends were also apparent in the species that were present in all three aggregations and for the grazer trophic group as a whole. The proportion of biomass in the lower trophic levels declined in the older aggregation. Food webs were reconstructed on the basis of variable trophic shifts and included the error in stable isotope measurements. The majority of potential trophic links supported by carbon and nitrogen isotopes alone were rejected when sulfur stable isotope values were included. Food webs consisted of relatively few trophic links overall, with the most complex food web in the more diverse community of the middle aggregation. These results suggest that many of the species in the tubeworm aggregations are generalists, and these species may feed on prey outside the aggregation, especially in the older aggregation, where few trophic links could be detected.

Efforts to understand and preserve the seep communities of the deep Gulf of Mexico (GOM) begin with a comprehensive survey of the biodiversity of these communities. Previous studies have provided a conceptual model of the physiology, population, and community ecology of upper continental slope seeps. However, seeps at water depths below 1000m in the Gulf of Mexico remain relatively unknown. In this study, data from 47 samples of tubeworm- and mussel-associated communities at depths of 1005–2750m are examined. Other than tubeworms and mussels, 66 taxa of macro- and megafauna were collected, 43 of which appear to be restricted to water depths of over 1000m, and 39 that have not been reported previously from the Gulf of Mexico. Diversity in mussel beds was highest at mid-slope depths, but tubeworm-associated communities did not show clear bathymetric trends in diversity. Diversity was higher in tubeworm aggregations at the alpha level (per sample), but higher in mussel beds at the beta level (species turnover among collections). Although both community types were often numerically dominated by the endemic shrimp Alvinocaris muricola, broad differences in the communities hosted by tubeworm aggregations and mussel beds were apparent. The most important factors explaining community similarity within community type were the depth, relative abundance of different mussel species in a bed, and the average size of tubeworms in an aggregation. The high proportion of deep-seep species that were found for the first time in the Gulf of Mexico emphasizes the importance of conservation efforts for these patchy communities.

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

We have used solid-state Au/Hg voltammetric electrodes to understand redox and biogeochemical processes in hot spring and deep sea hydrothermal environments. These electrodes are non-specific and have the capability of measuring simultaneously a suite of chemical species including several of the principal redox species involved in early diagenesis (O-2, Mn2+, Fe2+, H2S/HS-, and I-) as well as some Fe species (FeS and Fe3+) and sulfur species (S-x(2-) and S2O32-). Here we demonstrate how in situ data obtained in complex environments can be used to study specific iron and sulfur reactions and processes at (sub)millimeter to centimeter resolution and over short time scales. Examples include the oxidation of Fe2+ by O-2 produced by cyanobacterial mats in Yellowstone National Park hot springs and the formation of S2O32- in diffuse flow waters from the hydrothermal vents at Lau Basin. In one example, profiles of redox species in cyanobacterial mats from Yellowstone National Park hot springs show that in the light dissolved Fe2+ is completely removed from the source waters as cyanobacterial mats produce O-2 and oxidize the Fe2+. Performing kinetic experiments in the dark and light at the depth of maximum O-2 production indicates that the decay of Fe2+ follows a zero order rate law consistent with photosynthesis as the source of 0, These dynamic environments show how kinetic data can be obtained in situ and be used to understand the interactions between biology and chemistry. We know of no other analytical technique that can provide this information in both clear and turbid waters on the time scales (seconds) observed.

Habitat formation by foundation species is a major ecological force affecting community structure in numerous systems. On the upper continental slope of the Gulf of Mexico, the cold-water scleractinian coral Lophelia pertusa creates complex habitat on cold seep-associated carbonates. In this study, the communities associated with the cold-water coral L. pertusa are described from the Gulf of Mexico for the first time. A total of 68 taxa was identified in close association with the coral framework. Three species with specific relationships to L. pertusa were identified: Eunice sp., a polychaete which may facilitate colony formation in L. pertusa; Coralliophila sp., a species of corallivorous gastropod ; and Stenopus sp., a decapod crustacean which may act in a cleaner shrimp role in these habitats. Similarity among coral-associated communities was best explained by similarity in depth of collection and the proportion of live coral in the collections. These variables were somewhat confounded with location as the sites to the east were both shallower and contained higher proportions of live coral; however, distance between collections per se was not as significant in the analyses. The coral-associated communities also showed a low degree of similarity to communities inhabiting vestimentiferan tubeworm aggregations that occur nearby at the same sites. The increased habitat heterogeneity in the coral structure, differences in the niches constructed by the two foundation species, and different direct interspecific interactions between foundation species and members of the associated community contributed to the presence of dissimilar communities in these two biogenic habitats.

Many of the world's productive deepwater hydrocarbon basins experience significant and ongoing vertical migration of fluids and gases to the modern seafloor. These products, which are composed of hydrocarbon gases, crude oil, formation fluids, and fluidized sediment, dramatically change the geologic character of the ocean floor, and they create sites where chemosynthetic communities supported by sulfide and hydrocarbons flourish.Unique fauna inhabit these sites, and the chemosynthetic primary production results in communities with biomass much greater than that of the surrounding seafloor.

We have used solid‐state Au/Hg voltammetric electrodes to understand redox and biogeochemical processes in hot spring and deep sea hydrothermal environments. These electrodes are non‐specific and have the capability of measuring simultaneously a suite of chemical species including several of the principal redox species involved in early diagenesis (O 2 , Mn 2+ , Fe 2+ , H 2 S/HS − , and I − ) as well as some Fe species (FeS and Fe 3+ ) and sulfur species (S x 2− and S 2 O $\rm{ _3^{2 - } )}$ . Here we demonstrate how in situ data obtained in complex environments can be used to study specific iron and sulfur reactions and processes at (sub)millimeter to centimeter resolution and over short time scales. Examples include the oxidation of Fe 2+ by O 2 produced by cyanobacterial mats in Yellowstone National Park hot springs and the formation of S 2 O $\rm{ _3^{2 - } }$ in diffuse flow waters from the hydrothermal vents at Lau Basin. In one example, profiles of redox species in cyanobacterial mats from Yellowstone National Park hot springs show that in the light dissolved Fe 2+ is completely removed from the source waters as cyanobacterial mats produce O 2 and oxidize the Fe 2+ . Performing kinetic experiments in the dark and light at the depth of maximum O 2 production indicates that the decay of Fe 2+ follows a zero order rate law consistent with photosynthesis as the source of O 2 . These dynamic environments show how kinetic data can be obtained in situ and be used to understand the interactions between biology and chemistry. We know of no other analytical technique that can provide this information in both clear and turbid waters on the time scales (seconds) observed.

The kinetics of the reaction of NO3 radicals with rive alkenes was investigated at room temperature in a discharge fast flow system with mass spectrometric detection. NO3 radicals were produced by hydrogen abstraction from HNO3 With F atoms. The 1:1 stoichiometry of the reactions was confirmed. Rate constants were determined by measuring the decay of NO3 and/or of alkene under pseudo-first-order conditions. The following values of rate constants are reported: trans-2-butene (3.9 +/- 0.3) - 10(-13), cis-2-butene (3.8 +/- 0.2) . 10(-13), iso-butene (3.9 +/- 0.4) . 10(13), 2-methyl-2-butene (8.4 +/- 0.6) - 10(-12), 2,3-dimethyl-2-butene (4.1 +/- 0.4) . 10(-11) in units of cm3 molecule-1 s-1. The results are compared with literature data.