Like hydrothermal vents along oceanic ridges, cold seeps are patchy and isolated ecosystems along continental margins, extending from bathyal to abyssal depths. The Atlantic Equatorial Belt (AEB), from the Gulf of Mexico to the Gulf of Guinea, was one focus of the Census of Marine Life ChEss (Chemosynthetic Ecosystems) program to study biogeography of seep and vent fauna. We present a review and analysis of collections from five seep regions along the AEB: the Gulf of Mexico where extensive faunal sampling has been conducted from 400 to 3300m, the Barbados accretionary prism, the Blake ridge diapir, and in the Eastern Atlantic from the Congo and Gabon margins and the recently explored Nigeria margin. Of the 72 taxa identified at the species level, a total of 9 species or species complexes are identified as amphi-Atlantic. Similarity analyses based on both Bray Curtis and Hellinger distances among 9 faunal collections, and principal component analysis based on presence/absence of megafauna species at these sites, suggest that within the AEB seep megafauna community structure is influenced primarily by depth rather than by geographic distance. Depth segregation is observed between 1000 and 2000m, with the middle slope sites either grouped with those deeper than 2000m or with the shallower sites. The highest level of community similarity was found between the seeps of the Florida escarpment and Congo margin. In the western Atlantic, the highest degree of similarity is observed between the shallowest sites of the Barbados prism and of the Louisiana slope. The high number of amphi-atlantic cold-seep species that do not cluster according to biogeographic regions, and the importance of depth in structuring AEB cold-seep communities are the major conclusions of this study. The hydrothermal vent sites along the Mid Atlantic Ridge (MAR) did not appear as “stepping stones” for dispersal of the AEB seep fauna, however, the south MAR and off axis regions should be further explored to more fully test this hypothesis.
Citation: Olu K, Cordes EE, Fisher CR, Brooks JM, Sibuet M, et al. (2010) Biogeography and Potential Exchanges Among the Atlantic Equatorial Belt Cold-Seep Faunas. PLoS ONE 5(8): e11967. doi:10.1371/journal.pone.0011967
Editor: Anna Stepanova, Paleontological Institute, Russian Federation
Received: January 25, 2010; Accepted: July 6, 2010; Published: August 5, 2010
Copyright: © 2010 Olu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The Gulf of Guinea seeps off Congo, Angola and Gabon were investigated during the Biozaire program, partially funded by Total (P.I. M. Sibuet for Ifremer). Ifremer and Total oil company have supported the work in the Gulf of Guinea through a scientific partnership. Total contributed to finance data acquisition during oceanographic cruises. TDI-Brooks International were responsible for the collections of the scientific seep samples from the Nigerian margin. Data processing is supported by the French project ANR DeepOases (ANR06 BDV005) (https://aap.agencerecherche.fr/) and by Ifremer. Work at cold seeps in the Gulf of Mexico was supported by: US National Oceanic and Atmospheric Administration (NOAA) Mineral Management Service, and National Science Foundation (NSF) OCE 0117050. COML/ChEss (http://www.noc.soton.ac.uk/chess/) supported scientific exchanges (workshops) and publishing costs. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: Total oil company has partially funded the work in the Gulf of Guinea (collaboration Ifremer-Total: program “Biozaire”). The company TDI-Brooks International was responsible for the collections of the scientific seep samples from the Nigerian margin. The funding from these commercial sources does not alter the authors' adherence to all the PLoS ONE policies on sharing data and materials.
Since the discovery of lush communities of specialized animals associated with deep-sea vents  and cold-seeps  the question of biogeography of the inhabitants of these isolated chemosynthesis-based ecosystems has been one of the major persistent questions , , , , , , , , , . Studies of the hydrothermal vent fauna have defined several biogeographic provinces (EPR, Northern Pacific, MAR…) based on faunal composition and patterns of endemicity which are consistent with historical geological events. The latest analysis, which included hydrothermal vent fauna from 63 vent fields, supported the presence of 6 major biogeographic provinces . Meanwhile cold seeps have been discovered worldwide along continental margins and have also been grouped into several biogeographic provinces (Gulf of Mexico, Atlantic, Mediterranean, East Pacific and West Pacific) . However, high estimated rates of gene flow among disjunct populations of various species (reviewed by , ,  and the genetic similarity of several groups of widely distributed vent and seep endemic taxa ,  suggest high capacities of dispersal within and potentially among these seep and vent biogeographic provinces. One striking example is the siboglinid tubeworm Escarpia spicata Jones, 1985, which inhabits cold seeps and whale falls off southern California, seeps on the Pacific margin of Costa Rica and sedimented hydrothermal vents in the Gulf of California, which is thus-far genetically indistinguishable from Escarpia laminata Jones, 1985 living at cold seeps in the Gulf of Mexico ,  and Escarpia southwardae Andersen et al. 2004, from the Gulf of Guinea . Reproductive strategies may explain high dispersal capacities for some species, as for the seep mytilid Bathymodilus childressi Gustafson et al., 1998, which have broadcast spawning and produce numerous long-lived planktotrophic larvae , . The high number of seep sites may also favour dispersal along continental margins of non planktotrophic taxa such as vesicomyid bivalves .
Depth has also been shown to influence the distribution of vent and seep organisms, as it has for the general deep-sea fauna in all ocean basins along margins . Difference in depth has been hypothesized as a barrier to successful colonization of organisms along the Mid-Atlantic Ridge ,  and in seeps on continental margins , , , , .
Luxurious cold-seep communities are known from both sides of the equatorial Atlantic ocean between 32°29′N (Blake Ridge) and 05°47′S latitude (Regab pockmark) and between 350m and 3300m depth. They have been extensively studied in the northern Gulf of Mexico, a broad area of hydrocarbon seepage resulting from salt tectonics. The first seep communities were described from the Florida Escarpment at 3300 m depth , , and others were soon discovered at shallower depths , , . Numerous additional seep sites were discovered and more detailed community-level characterizations followed, both on the upper slope above 800 m , , , , , , ,  and the lower slope at greater depths , , , . Cold-seep communities in the western Atlantic have also been described from a few dives on mud volcanoes and diapirs between 1000 and 5000m depth in the Barbados accretionary prism area , ,  and from the Blake ridge diapir off North Carolina . More recently seep communities have been discovered in the eastern Atlantic, on a giant pockmark cluster in the Gulf of Guinea near the Congo deep channel , , also on other pockmarks of the Congo margin , Gabon margin  and Nigeria margin  and in the Gulf of Cadiz . All revealed dense invertebrate communities associated with mytilid mussels, vesicomyid clams, and/or siboglinid tubeworm aggregations. The similarities in landscape, habitat and dominant taxa of many of these cold-seep sites located on both sides of the Atlantic ocean led to the selection of the Atlantic equatorial belt (AEB) as an area to more closely examine the biogeography of deep chemosynthetic ecosystems in the Census of Marine Life ChEss project .
The first taxonomic investigations provided evidence for strong affinities at least at the genus level between the cold-seep fauna of the Barbados seeps in the Caribbean region and Gulf of Mexico , the Blake ridge and Florida escarpment , and more recently between Congo and west Atlantic equatorial cold seeps . A comparison of tubeworms, mussels, and associated megafauna communities among sites of the different West Atlantic seep sites, suggested a broadly distributed community structured primarily by depth rather than by distance . Hypotheses of recent genetic connections among seep taxa on the two sides of the Atlantic ocean were confirmed by genetic studies of Bathymodiolinae mussels, which revealed a high degree of genetic similarity between two species from Nigerian margin cold seeps and B. childressi and Bathymodiolus heckerae Gustafson et al., 1998, from the Gulf of Mexico (). A study combining morphology and genetics supported two species complexes of amphi-Atlantic cold-seep mussels : a first including Bathymodiolus boomerang Cosel & Olu, 1998 from Barbados, B. heckerae from the Gulf of Mexico, and Bathymodiolus aff. boomerang from the Gulf of Guinea, and a second one, the B. childressi complex, including species from the Louisiana slope, Barbados, Congo and Nigerian margin seeps. Another species from the Gulf of Cadiz attributed to Bathymodiolus mauritanicus Cosel, 2002 may belong to the B. childressi complex . There also appears to be segregation by depth of these complexes, with species of the B. boomerang complex living deeper than those of the B. childressi complex .
In this paper we review the recent studies of fauna inhabiting West and East Atlantic cold seeps and present a new analysis of similarity among faunal collections, which includes a large number of additional Gulf of Mexico seep sites and sites in the Gulf of Guinea. In this intra- and inter-regional comparison, depth and geographic distance are compared as factors influencing large-scale distribution of seep species. Other abiotic and biotic factors likely to influence the structure of seep communities and the dispersal capacity of the deep chemosynthetic fauna are discussed, and further exploration of potential dispersal “stepping stones” are proposed.
A list of taxa was established from a literature review of Equatorial Atlantic cold-seep community composition , , , , , , , , , , , ,  and taxonomic papers , , , , , , , . The AEB cold-seep sites explored up to now form 4 regions: the Gulf of Mexico, the Barbados prism, the North Carolina margin (Blake Ridge) and the Gulf of Guinea (Fig. 1; Table 1). Because of many cold-seep sites sampled along the Louisiana Slope, it was divided into upper slope (<1000 m), mid-slope (1000–2000 m), and lower slope (2000–3000 m), while the Florida Escarpment sites are at 3200m depth. Records from the Nigerian margin where cold seeps were sampled by box cores by both American  and French teams (unpubl.) were included in the list of taxa but not in the statistical analyses due to limited sampling effort and absence of submersible dives. We also omitted in some later analyses the Guiness site off Gabon (600m depth), and the Barbados trench mud volcanoes (4900m depth), although explored and sampled by ROV, because of the absence at both site of any known shared species with any of other Atlantic sites.
Gulf of Mexico: ULS, MLS, LLS: upper, middle and lower Louisiana slope, FE: Florida Escarpment; BR: Blake Ridge diapir; Barbados prism: OR: Orenoque A & B sectors, EP: El Pilar sector, BT: Barbados trench; Gulf of Guinea: REG: Regab pockmark, GUI: Guiness area, NIG: Nigerian slope. For depths and references refer to Table 1. The Nigerian slope sites have been only partially sampled.
Because of large differences in sampling efforts among sites, in particular between Barbados and Gulf of Mexico sites, only sampled megafaunal taxa, and bivalve commensals were included in statistical analyses (comparable to ). Only taxa identified to the species level (named or known as new species) were included; e.g. we omitted records as Lamellibrachia sp. or Escarpia sp. that were reported from 3 different sites of the GoM or Barbados, but used Calyptogena cf. kaikoi from Barbados trench based on molecular comparisons to specimens from the Florida escarpment and Mid-Atlantic Ridge . The species complexes of Bathymodiolinae were considered as a single record (as a species) in the similarity analyses. Finally, the taxa morphologically indistinguishable from described species, but lacking molecular confirmation of their identity, were reported as affinis (e.g. Phymorhynchus cingulatus, Chiridota heveva) and considered to be the same species for these analyses. A total of 72 species (19 symbiont-bearing and 53 associated species) were associated in the multivariate analyses. Similarity between sites based on their faunal composition was analysed using clustering analysis and ordination (PCA). Nine sites were included in this analysis (Table 1). In the Gulf of Guinea, only the REGAB pockmark and those from the GUINESS area were sufficiently surveyed and sampled to be compared with the other sites. The Barbados trench mud volcanoes (BT) and the Guiness pockmarks (Gui) from the Gabonese margin were excluded as sharing only one (Gui) or no (BT) species with the other sites. Their inclusion in the dataset do not change the relationships among the other sites in both Similarity and PCA analyses. Both Hellinger distance and Bray-Curtis similarity, based on species presence-absence data, were used for the cluster analysis based on “Ward” linkage. Ward's method, like the Group-Average method, is an agglomerative technique that uses the squared Euclidean Distance (or here the Hellinger distance) measured between the cluster centroids , . The PCA ordination represents Hellinger distance based on species presence-absence data.The Hellinger distance is another technique for clustering or ordination of species abundance data that allows representation in an ordination space that conserves metric distances and does not consider double absence as an indicator of similarity between samples . All analyses were performed using the Vegan package in R .
Variability among cold-seep communities in the Gulf of Guinea
Preliminary investigations along the African Margin from 600 to 3300m depth and along Congo-Angola, Gabon and Nigeria margins, have revealed a relatively high degree of dissimilarity among the different areas investigated, which further demonstrates the variability of seep communities at this spatial scale (100–1000 km). The Astrid pockmark, and other pockmarks described from the Congo basin around 3000m depth (Hydrate Hole, Black Hole and Worm Hole) were explored by only one ROV dive or TV-guided grab each but revealed similarities in the largest megafauna, symbiont-bearing (vesicomyids and mytilid bivalves, escarpid tubeworms) or associated taxa (alvinocarid shrimps, galatheids and synaptid holothurids) within this small area (Table S1). The Guiness pockmarks located at 650 m depth along the Gabon margin are characterised by low seep emissions and are colonised only by patchy beds of small vesicomyids. The associated megafauna consist of a small number of species compared to the fauna associated with the different habitats of the other pockmark sites. The Nigerian margin cold seeps have not been yet comprehensively sampled, but seem to have higher similarity to the Regab site off Congo than to the Guiness pockmarks. One striking peculiarity of the Nigeria slope compared to other known African sites is the presence of large Cladorhizidae sponges, resembling to those of the Barbados trench seeps.
Comparison among seep communities in the Atlantic equatorial belt
The highest similarities among the regions encompassed by the AEB, in terms number of shared megafauna species, were found in the west Atlantic between the Gulf of Mexico and the Barbados prism with 10 species found so far, followed by the Gulf of Mexico and Gulf of Guinea with 8 or 9 species (Tables 2, 3). The Blake Ridge diapir showed a lower similarity with other regions but affinities with all three other regions. The highest number of shared taxa between two sites of different regions was found between east and west Atlantic cold seep sites of the Florida escarpment and Regab pockmark, with 7 shared species identified so far (Table 2), and a high level of similarity in the families of polychaetes at the two sites (Table S1). Nigerian margin seeps also may have a high degree of similarity with West Atlantic seeps (Table S1). In the Gulf of Guinea, the shallow and less active Guiness pockmark communities appeared very different from those of the deep Regab site and did not share any species with other AEB cold-seep sites.
The Bathymodiolinae species or complexes of species are the most widespread. The B. boomerang complex is found at the Florida escarpment site, the Blake Ridge diapir, the Barbados prism and the Regab site of Congo. The B. childressi complex is also widely distributed along the AEB from the Gulf of Mexico across to the Nigerian Margin, although not on the Regab or Blake ridge sites. The commensal polynoid, Branchipolynoe seepensis is another of the species shared by more than 2 regions (GoM, GoG and Barbados). Other species with distributions extending from the eastern to western Atlantic are: the gastropods Phymorhynchus cingulatus Warén & Bouchet, 2009, Cordesia provannoides Warén & Bouchet, 2009, the shrimp Alvinocaris muricola Williams, 1988, the galatheids Munidopsis geyeri Pequegnat & Pequegnat, 1970 and Munidopsis livida Perrier, 1886 and probably the holothurid Chiridota heheva Pawson & Vance, 2004.
Similarity analyses performed using both distance indices (Bray Curtis and Hellinger), on the 9 sites indicated higher similarity among sites according to depth than to geographic distance (Table 2, Fig. 2). The Regab site clustered with the Blake Ridge diapir and with the deepest sites in the Gulf of Mexico (Florida Escarpment and lower Louisiana slope>2000m). The shallower Barbados prism communities (El Pilar 1300m, Orenoque 1700–2000m) grouped with shallow sites in the Gulf of Mexico: the upper and middle Louisiana slopes (Hellinger distance) or the upper slope only (Bray Curtis). The difference in the placement of the MLS is due to the inclusion of double absence by the Bray Curtis analysis and the exclusion of these data in the Hellinger analysis of similarity between samples. Indeed there are more ULS species absent from both MLS and LLS (11) than LLS species absent from MLS and ULS (7). Nevertheless the number of shared species between MLS and LLS is also higher (11) than between ULS and MLS (9) (Table 2), which is consistent with BC clustering.
Analysis based on species presence-absence at 9 AEB cold-seep sites including: the Louisiana Slope: ULS (<1000m), MLS (1000–2000m), LLS (>2000m), Florida Escarpment (FE, 3300m), south of Barbados prism: El Pilar (EP, 1300m), Orenoque A (OA, 1700m), Orenoque B (OB, 2000m), Blake ridge (BR, 2150m), Regab pockmark (3150m). The distance measuring dissimilarity between sites are the Bray Curtis distance (left) or Hellinger distance (right).
In the ordination of the 9 sites (PCA based on Hellinger distance) the sites were distributed along the first axis (24% of variance) primarily according to depth, with sites deeper than 2000m at the positive end of the axis and those <2000m at the negative one (Fig. 3). The second PCA axis (18%) separated the Gulf of Mexico sites from all other ones. The species that explain the majority of the variance along the first axis are, at the negative end (shallowest sites) the B. childressi complex, the gastropods Bathynerita naticoidea Clarke, 1989 and Cataegis meroglypta McLean & Quinn, 1987, Phascolosoma turnerae Rice, 1985 while A. muricola, M. geyeri, C. provannoides, P. cingulatus, C. heheva at the positive end separate the deepest sites towards the positive end of the axis. The GOM communities contain high abundance of Hesiocaeca methanicola Desbruyères & Toumond, 1998, Munidopsis curviristra Whiteaves, 1874 and Ophienigma spinilimbatum Stöhr & Segonzac, 2005 that are absent from other regions.
Species data have been transformed using Hellinger distance. The first axis explains 24% of the variance, the second one 18%.
Segregation by depth
Depth stratification in the west Atlantic cold-seep fauna is first observed at regional scale in the Gulf of Mexico with known sites and communities described all along the depth gradient analysed in the present study (500–3300m). It is also highlighted by the low number of shared taxa among the shallowest sites in the El Pilar region (1000–1300m) and those of the Orenoque A/B sectors (1700–2000m) and by the absence of any shared species with the deepest mud volcanoes located at 4900 m depth in the northern part of the prism (Table S1).
Depth boundaries seem to be particularly evident for the well sampled symbiont-bearing taxa. In the Gulf of Mexico and on the Barbados prism, the B. childressi complex of species occur at all shallower sites but are replaced at the deeper sites by B. heckerae observed up to 3300m. These two species have never been found to co-occur in the GoM and an additional species, B. brooksi is present at intermediate depths whose distribution overlaps with both B. childressi and B. heckerae at the two ends of its bathymetric range. However both species complexes have been found at intermediate depths between 1700 to 2200m in the Gulf of Mexico and on the Barbados prism. The same depth pattern is observed along the West Africa margins, where B. boomerang is the only species found at the Regab pockmark (3170m) while both species complexes co-occur at mid-depth sites along the Nigerian margin (1600 to 2200m). Empty shells of B. childressi and B. boomerang have also been sampled on a pockmark in the Congo basin at 1900m (unpubl. data). Vesicomyidae bivalve species are also segregated by depth within each region of the AEB. In the Gulf of Mexico, Calyptogena ponderosa Boss, 1968 and Vesicomya cordata Boss, 1968 are present on the upper and middle Louisiana slopes while another Calyptogena sp. occurs at the deeper Florida escarpment. Similarly, different species have been collected from the Barbados trench (Calyptogena sp.) compared to the nearby Orenoque/El Pilar shallower sites (Laubiericoncha myriamae Cosel & Olu, 2008), and from the Regab pockmark and the Guiness area (Table S1).
Depth influence on cold-seep fauna composition
The analysis of cold-seep megafauna communities along the AEB revealed relatively high degrees of similarity among sites found in similar depth ranges, even across large geographic distances. The cold-seep sites in the eastern equatorial Atlantic shared almost 30% of the megafauna taxa with sites from similar depths in the western Atlantic, despite distance. Although few of the total number of examined species are shared among the sites, the similarity analysis based on their faunal composition, the Atlantic equatorial belt sites clustered within regions and according to depth ranges (Fig. 2), a result that is reinforced by the principal component analysis. These analyses suggest that seep community structure, at least for megafauna, is strongly controlled by depth, at the scale of the AEB.
In the analyses based on Hellinger distance, the depth separation between the two groups of sites is around 2000m. A second bathymetric segregation is observed on the PCA plot between 1300 and 1700m with the shallowest Barbados prism sites (El Pilar) clustering with the shallowest ones in the GoM (upper Louisiana slope). The highest species richness is observed at intermediate depths (between 1700 to 2000m) with species of both deeper and shallower communities. The differences among Bray-Curtis and Hellinger distance analyses suggest that there may be a gradual transition in this depth range and a mixing among the fauna of these two bathymetric zones between 1000 and 2000 m. In the study of west Atlantic cold-seep similarity , rapid replacement was also suggested at intermediate depths (1300–1700m). Similar patterns are found in the non-seep fauna of the Gulf of Mexico as well as in other ocean basins (e.g. , , ) with the maximum of alpha diversity at mid-slope depths (1500–2500m) for both mega- and macrofauna , . Causes of depth zonation on continental margins have been attributed to physico-chemical parameters (temperature, water-masses, pressure), food availability, and biotic interactions (predation and competition)  and export POC flux was recently evidenced as the major factor explaining (macro-) faunal depth zonation patterns, as independent of the depth effect itself, for mid- or lower slopes in the GOM .
In contrast, export POC is not likely to be the main factor explaining depth patterns at seeps due to their primary reliance on local chemosynthetic productivity. Nevertheless, seep communities include non-endemic taxa, background species that are colonists (such as galatheids) or vagrant species (not included in this study) that would be expected to follow general depth zonation patterns driven by food availability, temperature, pressure or water masses. Additional depth-related factors structuring cold-seep communities include biotic interactions. Predation pressure is likely higher at the shallowest seeps , ,  and may help explain differences observed between the shallow (above 1000m) and deep sites in Gulf of Mexico . Similarly, large crustaceans (Lithodidae and Majidae) have been observed on the El Pilar mussel beds, as well as on the Guinesss pockmarks but not in the deepest sites of the Barbados prism or of the deep Gulf of Guinea.
The bathymetric zonation of the shallower B. childressi and the deeper B. boomerang species complexes of the AEB are more broadly supported by the global distributions of related bathymodiolin mussels. A combined phylogenetic analysis of three genes support the existence of a “childressi” clade including shallow water species from the west Pacific, while B. heckerae and B. boomerang cluster with the majority of the vent species that tend to live at deeper sites , . Seep vestimentiferans tend to be more widely distributed than hydrothermal vent species, based on combined morphological descriptions and COI sequence data , and can have very large geographic ranges within bathymetric zones. Indeed the three described Escarpia species, are all very closely related morphologically and genetically ,  but appear to be restricted to depths greater than 1300 m , . Nevertheless, other siboglinids in the Escarpia clade, including Seepiophila jonesi and an undescribed Escarpia species, are found at shallower sites in the GoM and Atlantic seeps , . Different vesicomyid species occur at shallow Louisiana slope sites and Florida escarpment . Although depth ranges may be influenced by sampling bias, the six vesicomyid species described from seeps in the Gulf of Guinea seem to be distributed either shallower or deeper than 2000–2500m with a transition depth zone at in this depth range . Apparent depth segregation of vesicomyids has been reported at seeps along other continental margins off Japan and Peru , . Calyptogena pacifica occurs over a remarkably restricted depth range despite high dispersal capacities , with also a bathymetric segregation at the intra-specific level  like B. childressi .
It is important to remember that other seep environmental factors (geologic settings, seep chemistry and flow rates, substrate types) may vary with depth in the regions studied and, as discussed in the next section these factors are critical not only for the types of communities present, but even for the existence of seep macro- and megafauna. For example, fluid chemistry, depth related, was found to be a strong factor structuring distinct faunal islands (instead of biogeographical provinces), differing in species composition, along the Mid-Atlantic Ridge , .
Variation within regions and depth ranges
The present analysis provides evidence for depth as a structuring factor of AEB megafauna seep communities, but this factor only explains part (42%) of the variation in the communities observed in different areas. Local communities in the deep sea in general may be composed of species that exist as metapopulations whose regional distribution depends on a balance among global-scale, landscape-scale, and small-scale dynamics . Variation in the type and magnitude of fluid venting will have a first order effect on presence of different types of seep foundation fauna and the level of chemoautotrophic primary production from both symbiont containing species and free living microbes in the site. Biogenic habitats created by microbial mats and the symbiotic species contribute to create heterogeneity in structural complexity (Fig. 4), habitat geochemistry, nutrient sources, and inter-specific interactions enhancing beta diversity of associated fauna .
A. Mussel bed (Bathymodiolus brooksi) from Atwater Valley at 2200m depth in the Gulf of Mexico, B. Mussel bed (Bathymodiolus childressi) on the El Pilar area, Barbados prism (1300m) (©Ifremer, Diapisub 1992), C. Mussels and tubeworms along with Alvinocaris muricola from Atwater Valley at 2200m depth in the Gulf of Mexico. (A. & C.: © MMS-NOAA OER Chemosynthetic Ecosystems study). D. Bathymodiolus aff. boomerang bed on the Regab pockmark off Congo associated with other amphi-Atlantic species (Alvinocaris muricola, Chiridota aff. heheva), and the Siboglinidae Escarpia southwardae. E. Vesicomyidae Calyptogena valdiviae and microbial mats on the Guiness area off Gabon (D. & E. ©Ifremer, Biozaire 2001). F. Vesicomyidae Calyptogena aff. kaikoi aggregate and sponges Cladorhiza methanophila in the Barbados trench. (©Ifremer, Manon 1992).
In the Gulf of Mexico, over 90 seep sites have been visited by submersible . Although broad similarities among sites within depth ranges were apparent in our analyses, individual sites within a depth range may vary with respect to the associated communities, the higher taxa of foundation fauna at species level (e.g. relative abundance of the different mussel species in a bed ). Some of these differences may be attributed to succession processes related to the age of the site and substratum evolution , the age of tubeworm aggregations , , and even this pathway of succession may differ from site to site .
As demonstrated for the export POC flux for detritus-based benthic communities , the fluid flow is also a limiting factor for seep communities. Methane and oxygen concentrations have been identified as important factors influencing the communities in seep mussel beds , , as has been sulphide concentration in tubeworm aggregations . Highly variable methane concentrations above the pockmarks in the Gulf of Guinea ( and Charlou, Caprais, pers.com.) could explain the absence of any mytilid in the majority of explored pockmarks. The presence of multiple symbionts likely favours B. heckerae, B. boomerang and B. brooksi at sites where sulphide is more available than methane. This may convey competitive advantage to these species at some sites as observed for B. heckerae  or for B. boomerang which may be able to utilize reduced compounds from pore waters, by burrowing in sediments at low activity sites , . Vesicomyid distribution is also likely to be influenced by specific adaptations to sulphide or oxygen concentrations, which can be correlated to methane fluxes in some environments , , ,  and adaptations to specific geochemical environments has been suggested to have driven the evolution of co-existing vesicomyid genera . Finally, the rare occurrence of Cladorhizidae sponges, in the Barbados trench  and on the Nigeria margin may be favoured by high methane fluxes but another unknown factor limits their distribution to other AEB seep sites. Further investigations of their habitat preferences and the environmental conditions at all of the sites are required to explain the distribution of these sponges.
Potential for long distance larval dispersal
Considerable mixing among populations of vent organisms along ridge segments , and the lack of genetic structure that has been observed for numerous vent taxa over oceanic ridge scales  argue for long dispersal capacities of hydrothermal vent taxa. The relatively high degree of community similarity among AEB cold-seep regions suggests recent exchanges among the Gulf of Mexico, the Caribbean, and the Gulf of Guinea. The Blake Ridge diapir communities also share taxa with other regions but to a lower degree. Different deep and shallow currents have been suggested to provide connections for propagules between the Gulf of Mexico, the Barbados prism and Blake Ridge . The longitudinal flow of the North Atlantic Deep Water, enhanced by equatorial intermediate jets, could theoretically provide a connection eastward to the west Africa margins or westward from these sites, but the relatively low velocities of these deep currents may not be sufficient to transport even long lasting propagules across the Atlantic . Propagule transport by surface currents, which could produce crossing times of a few months, would be a more realistic time frame for many seep animals, assuming the larvae could persist at shallow depths.
Cold-seep amphi-Atlantic species represent various taxonomic groups differing in reproductive strategies. Possessing a planktotrophic larval form does not appear to be a prerequisite for long-distance dispersal, as lecitotrophic larvae may disperse over longer distance than planktotrophs in oligotrophic waters , . Decrease of developmental and metabolic rates with temperature may also extend dispersal potential for lecitotrophic larvae in the cold deep sea . Variable buoyancy of propagules can change the vertical dispersal of a larva in the water column (e.g. ). Thus, larvae can be transported by different water currents at different depths and subsequent divergent trajectories at different times during their development. Larvae of the gastropod Cordesia provannoides, or a very similar species, has been collected 0–100m below the surface in the tropical East Atlantic overlying a total water depth of 4570 m . Teleplanic larvae (long-distance dispersing) have been demonstrated for several shallow water gastropods (e.g. ). Lengthy developmental period, long-lasting (>60 day) larvae and ontogenic vertical migration have also been shown for Bathynerita naticoides , found at both GOM and Barbados seeps. The gametogenic periodicity correlated with surface production demonstrated for B. childressi can enhance survival of its planktotrophic larvae and therefore long-range dispersal . B. childressi larvae may be teleplanic and, according to known settlement times and spawning seasons, spend more than a year in the plankton  The small size of Alvinocaris muricola embryos also suggested planktotrophic larvae and the capacity for extended larval development , . Consistently, phylogenetic analyses of the hydrothermal vent shrimps indicate that the Alvinocaris species do not cluster according to biogeographic regions .
Amphi-atlantic distribution at seeps also concerns taxa with potentially lecitotrophic larvae like the galatheid Munidopsis geyeri found at the deepest sites. Some galatheid species have very large egg sizes that apparently give them broad dispersal capabilities . Several deep-sea galatheids appear to have an amphi-Atlantic distribution , as has been shown for a number of deep-sea decapods. However, additional genetic and larval biology studies are needed to verify these findings for the present species and understand the mechanisms sustaining this broad distribution. The giant isopod Bathynomus giganteus despite brooding eggs also has a broad distribution from GoM to GoG (Rowe pers com).
Genetic similarities between populations separated by long geographic distances may also result of low rates of evolution in the mitochondrial genes analysed rather than very recent genetic exchange between the various regions, hypothesis suggested for seep siboglinids , . Although morphologically distinct, E. southwardae, E. laminata and E. spicata are genetically undistinguishable and could represent a single polymorphic species with extremely widespread distribution . This is supported by a significant capacity for larval dispersal for Escarpia and Lamellibrachia with positively buoyant lecitotrophic larvae that can spend at least three weeks up in the water column . However, there is unlikely to be significant gene flow between at least E. laminata and E. spicata, since the Panama Isthmus closure 3 million years ago. On the contrary, molecular analyses of Vesicomyidae suggest these clams have generally more restricted geographic and bathymetric distributions, and it has been suggested that an older radiation favoured higher diversification . Geographic isolation but also physiological adaptations to geochemical environments are major factors for speciation within the genus Calyptogena . Nonetheless, molecular studies support the view that some vesicomyid clams spread easily along continental margins and trans-Pacific migrations have been suggested for several species by molecular studies .
More than 80% of Atlantic marine invertebrates that possess a planktotrophic larval form appear to have an amphi-Atlantic distribution, and 30% of molluscs of the eastern or western Atlantic are amphi-atlantic . While some of these species may be capable of dispersing all the way across the Atlantic Ocean with long-distance planktonic larvae, other coastal species more likely use islands as ‘stepping stones’. For species associated with chemoautotrophic ecosystems, the occurrence of contemporary gene flow across the Atlantic equatorial belt via planktonic larvae could be sustained by larval exchanges along a continuum of seep sites, sunken wood and whale carcasses . With the possible exceptions of the seep mussel commensal Branchipolynoe seepensis, which is also associated with the hydrothermal Bathymodiolinae all along the Mid Atlantic Ridge, and the shrimp Alvinocaris muricola, that may occur at the Logatchev vent site , the hydrothermal vent communities of the Mid Atlantic Ridge do not seem to serve as major stepping stones for AEB cold seep communities. A third species, the brittle star Ophioctenella acies, is shared between West Atlantic cold seeps and MAR vents, but has not yet been found at West Africa seeps.
Though some DNA evidence suggests that B. heckerae may have derived recently from Bathymodiolus azoricus , a recent phylogeny based on COI suggested colonization pathways of the seeps of the AEB appear distinct from those that led to the colonization of the MAR and the emergence of B. azoricus and B. puteoserpentis , and B. brooksi from the Gulf of Mexico appears to be basal to all of these groups . Reports of shared vesicomyids among seeps on the West Florida escarpment, the Barbados accretionary prism and the Logatchev vent field on the Mid-Atlantic Ridge ,  await further genetic investigations and the current revision of the vesicomyids , , . Regardless, the MAR does not appear to be a consistent stepping stone for the fauna of the AEB seeps, but further exploration of low temperature vents or seeps and along transform faults may reveal potential favourable sites for seep taxa. In addition, as most of the known amphi-Atlantic AEB seep species are associated with the sites deeper than 2000m, investigations of the deeper MAR sites and transform faults, in particular the on the inter-tropical area, will provide important data to test the seep to vent stepping-stone hypothesis.
Sunken woods, whale carcasses or other sources of organic matter may also serve as stepping stones for seep species such as C. provannoides also found on wood falls . Siboglinid tubeworms were brought to the surface from a shipwreck full of coffee beans and fruits lying at 1200 m of water off the north-western coast of Spain . Clearly this is not the natural habitat for this seep species, however it demonstrates the ability of seep fauna to colonize diverse habitats where reducing chemicals are present in sufficient concentrations to support chemoautotrophic primary production.
Conclusion, future directions
The similarity analyses presented in this paper suggest that the seep megafauna along the Atlantic equatorial belt do not primarily cluster according to biogeographic regions, as strongly structured by depth. This pattern is particularly evident for endemic seep fauna, and is supported by phylogenetic studies for some species. Different hypotheses may explain these broad geographic distributions, including present-day larval exchanges facilitated by extended larval durations of some seep taxa. Larval tracking in the vicinity of cold seep sites or along transects across the AEB could be used to address this hypothesis. It is also possible that many of the apparently shared species may in fact be cryptic species or species that are distinguishable morphologically but lack apparent genetic differentiation. The development of more molecular markers and population genetic studies are needed to better understand the genetic connections among regions and populations. A recent study demonstrated the power of nucleotide polymorphism in mitochondrial COI and coalescence analyses for tracing historical demographic events, genetic exchanges and population isolation in the case of hydrothermal vent species .
Exploration of new areas, such as the Amazon fan and other potential hydrocarbon seep areas off southern Brazil, potential seep sites off of the east coast of the U.S. and the Laurentian fan where chemosynthetic communities are known deeper than 3500m, and shallower sites in the Gulf of Guinea are need to further assess the role of depth as dominant factor structuring seep communities. Use of comparable sampling strategies and devices, increase of faunal collections in all regions, and collections of comparable environmental data sets are also needed to facilitate these comparisons and better understand the role of abiotic and biotic factors in structuring Atlantic cold-seep communities.
List of macro- and megafaunal taxa identified in the AEB cold-seep sites. For abbreviations, see Table 1. Shared taxa are identified as followed: *: amphi-Atlantic species or species complex, ** species shared between at least 2 regions of the West A.
(0.51 MB DOC)
We are grateful to the chief scientists of the BIOZAIRE cruises (M. Sibuet, A. Khrippounoff), and to the NERIS cruise (M. Voisset), and to the captains and the crews of the N.O. L'Atalante and VICTOR 6000 team. This work was done with the support of the ANR Deep Oases (ANR06 BDV005) project. CRF acknowledges NSF OCE 0117050 and many years of support from the US National Oceanic and Atmospheric and Administration and Mineral Management Service for work at the cold seeps in the Gulf of Mexico.
This collaborative paper was initiated in the framework of the COML/ChEss program, and benefited greatly from the exchanges during the workshop on AEB chemosythesis-based ecosystems held in Barcelona in 2006. We thank Eva Ramirez-Llorda and Maria Baker for organizing the workshop and for organizing the PLoS collection and Census of Marine Life for covering publishing costs.
We are grateful to Gilbert Rowe and another anynomous reviewer for their helpful comments improving the manuscript.
Conceived and designed the experiments: EEC CRF MS. Performed the experiments: KO EEC CRF. Analyzed the data: KO. Wrote the paper: KO. Contributed to writing the paper (corrections): EEC CRF. Supplied some of the W African collections analyzed and was the lead on the deep water Chemo project in the GoM, where a bunch of the original data for those analyses came from: JMB. Project leader for Congo and Gabon margins: MS. Leader of ChEss project “Atlantic Equatorial Belt communities”: DD.
- 1. Lonsdale PF (1977) Clustering of suspension-feeding macrobenthos near abyssal hydrothermal vents at oceanic spreading centers. Deep-Sea Research 24: 857–863.
- 2. Paull CK, Hecker B, Commeau R, Freeman-Lynde RP, Neumann C, et al. (1984) Biological communities at the Florida escarpment resemble hydrothermal vent taxa. Science 226: 965–967.
- 3. Desbruyères D, Almeida A, Biscoito M, Comtet T, Khripounoff A, et al. (2000) A review of the distribution of hydrothermal vent communities along the northern Mid-Atlantic Ridge: dispersal vs. environmental controls. Hydrobiologia 440: 201–216.
- 4. Desbruyères D, Biscoito M, Caprais JC, Colaço A, Crassous P, et al. (2001) Variations in deep-sea hydrothermal vent communities on the Mid-Atlantic Ridge when approaching the Azores plateau. Deep-Sea Research II 48: 1325–1346.
- 5. Kojima S (2002) Deep-sea chemoautosynthesis-based communities in the Northwestern Pacific. Journal of Oceanography 58: 343–363.
- 6. Sibuet M, Olu K (1998) Biogeography, biodiversity and fluid dependence of deep-sea cold-seep communities at active and passive margins. Deep-Sea Research II 45: 517–567.
- 7. Tunnicliffe V (1988) Biogeography and evolution of hydrothermal-vent fauna in the eastern Pacific Ocean. Proceedings of the Royal Society of London, B 233: 347–366.
- 8. Tunnicliffe V, McArthur AG, McHugh D (1998) A biogeographical perspective of the deep-sea hydrothermal vent fauna. Advances in Marine Biology 34: 353–442.
- 9. Tyler PA, German CR, Ramirez-Llodra E, Van Dover C (2003) Understanding the biogeography of chemosynthetic ecosystems. Oceanologica Acta 25: 227–241.
- 10. Van Dover CL (2000) The Ecology of Deep-Sea Hydrothermal Vents. Princeton New Jersey: Princeton University Press. 424 p.
- 11. Van Dover CL, German CR, Speer KG, Parson LM, Vrijenhoek RC (2002) Evolution and biogeography of deep-sea vent and seep invertebrates. Science 295: 1253–1257.
- 12. Cordes EE, Carney SL, Hourdez S, Carney RS, Brooks JM, et al. (2007) Cold seeps of the deep Gulf of Mexico: Community structure and biogeographic comparisons to Atlantic equatorial belt seep communities. Deep Sea Research Part I: Oceanographic Research Papers 54: 637–653.
- 13. Bachraty C, Legendre P, Desbruyères D (2009) Biogeographic relationships among deep-sea hydrothermal vent faunas at global scale. Deep Sea Research I 56: 1371–1378.
- 14. Vrijenhoek RC (1997) Gene flow and genetic diversity in naturally fragmented metapopulations of deep-sea hydrothermal vent animals. Heredity 88: 285–293.
- 15. Won Y, Young CR, Lutz RA, Vrijenhoek RC (2003) Dispersal barriers and isolation among deep-sea mussel populations (Mytilidae: Bathymodiolus) from eastern Pacific hydrothermal vents. Molecular Ecology 12: 169–184.
- 16. Jollivet D (1996) Specific and genetic diversity at deep-sea hydrothermal vents: an overview. Biodiversity and Conservation 5: 1619–1653.
- 17. Peek AS, Gaut BS, Feldman RA, Barry JP, Kochevar RE, et al. (2000) Neutral and nonneutral mitochondrial genetic variation in deep-sea clams from the family Vesicomyidae. Journal of Molecular Evolution 50: 141–153.
- 18. Black MB, Halanych KM, Maas PAY, Hoeh WR, Hashimoto J, et al. (1997) Molecular systematics of vestimentiferan tubeworms from hydrothermal vents and cold-water seeps. Marine Biology 1–9.
- 19. McMullin ER, Hourdez S, Schaeffer SW, Fisher CR (2003) Phylogeny and biogeography of deep sea vestimentiferan tubeworms and their bacterial symbionts. Symbiosis 34: 1–41.
- 20. Andersen AC, Hourdez S, Marie B, Jollivet D, Lallier FH, et al. (2004) Escarpia southwardae sp. nov., a new species of vestimentiferan tubeworm (Annelida, Siboglinidae) from West African cold seeps. Canadian Journal of Zoology 82: 980–999.
- 21. Eckelbarger KJ, Young CM (1999) Ultrastructure of gametogenesis in a chemosynthetic mytilid bivalve (Bathymodiolus childressi) from a bathyal, methane seep environment (northern Gulf of Mexico). Marine Biology 135: 635–646.
- 22. Tyler P, Young CM (1999) Reproduction and dispersal at vents and cold seeps. Journal of Marine Biology Association of UK 79: 193–208.
- 23. Krylova EM, Sahling H (2006) Recent bivalve molluscs of the genus Calyptogena (Vesicomyidae). Journal of Molluscan Studies 72: 359–395.
- 24. Carney RS (2005) Zonation of deep biota on continental margins. Oceanogr Mar Biol Ann Rev 43: 211–278.
- 25. Van Dover CL, Desbruyères D, Segonzac M, Comtet T, Saldanha L, et al. (1996) Biology of the Lucky Strike hydrothermal field. Deep-Sea Research 43: 1509–1529.
- 26. Olu K, Duperret A, Sibuet M, Foucher JP, Fiala-Médioni A (1996a) Structure and distribution of cold seep communities along the Peruvian active margin: relationship to geological and fluid patterns. Marine Ecology Progress Series 132: 109–125.
- 27. Sahling H, Galkin SV, Salyuk A, Greinert J, Foerstel H, et al. (2003) Depth-related structure and ecological significance of cold-seep communities–a case study from the Sea of Okhotsk. Deep Sea Research Part I: Oceanographic Research Papers 50: 1391–1409.
- 28. Sibuet M, Olu-Le Roy K (2002) Cold Seep Communities on Continental Margins: Structure and Quantitative Distribution Relative to Geological and Fluid Venting Patterns. In: Wefer DB G, Hebbeln D, Jorgensen BB, Van Weering T, editors. Ocean Margin Systems. Berlin: Springer Verlag. pp. 235–251.
- 29. Hecker B (1985) Fauna from a cold sulfur-seep in the gulf of Mexico : comparison with hydrothermal vent communities and evolutionary implications. Bulletin of the Biological Society of Washington 6: 465–473.
- 30. Brooks JM, Kennicutt MC II, Fisher CR, Macko SA, Cole K, et al. (1987) Deep-sea hydrocarbon seep communities: Evidence for energy and nutritional carbon sources. Science 238: 1138–1142.
- 31. Brooks JM, Wiesenburg DA, Roberts H, Carney RS, MacDonald IR, et al. (1990) Salt, seeps and symbiosis in the Gulf of Mexico. A preliminary report of deepwater discoveries using DSV Alvin. Eos, Transactions, American Geophysical Union 71: 1772–1773.
- 32. Kennicutt MC II, Brooks JM, Bidigare RR, Fay RR, Wade TL, et al. (1985) Vent-type taxa in a hydrocarbon seep region on the Louisiana slope. Nature 317: 351–353.
- 33. Bergquist DC, Fleckenstein C, Knisel J, Begley B, MacDonald IR, et al. (2005) Variations in seep mussel bed communities along physical and chemical environmental gradients. Marine Ecology Progress Series 293: 99–108.
- 34. Bergquist DC, Ward T, Cordes EE, McNelis T, Howlett S, et al. (2003) Community structure of vestimentiferan-generated habitat islands from Gulf of Mexico cold seeps. Journal of Experimental Marine Biology and Ecology 289: 197–222.
- 35. Carney RS (1994) Consideration of the oasis analogy for chemosynthetic communities at Gulf of Mexico hydrocarbon vents. Geo-Marine Letters 14: 149–159.
- 36. Cordes EE, Bergquist DC, Predmore BL, Jones C, Deines P, et al. (2006) Alternate unstable states: Convergent paths of succession in hydrocarbon-seep tubeworm-associated communities. Journal of Experimental Marine Biology and Ecology 339: 159.
- 37. Cordes EE, Hourdez S, Predmore BL, Redding ML, Fisher CR (2005) Succession of hydrocarbon seep communities associated with the long-lived foundation species Lamellibrachia luymesi. Marine Ecology Progress Series 305: 17–29.
- 38. MacDonald IR, Boland GS, Baker JS, Brooks JM, Kennicutt MC II, et al. (1989) Gulf of Mexico hydrocarbon seep communities II. Spatial distribution of seep organisms and hydrocarbons at Bush Hill. Marine Biology 101: 235–247.
- 39. MacDonald IR, Callender WR, Burke RA Jr, McDonald SJ, Carney RS (1990a) Fine-scale distribution of methanotrophic mussels at a Louisiana cold seep. Progress in Oceanography 24: 15–24.
- 40. Cordes EE, Becker EL, Hourdez S, Fisher CR (In press) Influence of foundation species, depth, and location on diversity and 3 community composition at Gulf of Mexico lower slope cold seeps. Deep Sea Research II.
- 41. MacDonald IR, Sager WW, Peccini MB (2003) Gas hydrate and chemosynthetic biota in mounded bathymetry at mid-slope hydrocarbon seeps: Northern Gulf of Mexico. Marine Geology 198: 133–158.
- 42. Turnipseed M, Jendkins CD, Van Dover C (2004) Community structure in Florida Escarpment seep and Snake Pit (Mid-Atlantic Ridge) vent mussel beds. Marine Biology 145: 121–132.
- 43. Jollivet D, Faugères JC, Griboulard R, Desbruyères D, Blanc G (1990) Composition and spatial organization of a cold seep community on the south Barbados accretionary prism: tectonic, geochemical and sedimentary context. Progress in Oceanography 24: 25–45.
- 44. Olu K, Lance S, Sibuet M, Henry P, Fiala-Medioni A, et al. (1997) Cold seep communities as indicators of fluid expulsion patterns through mud volcanoes seaward of the Barbados Accretionary Prism. Deep Sea Research 44: 811–841.
- 45. Olu K, Sibuet M, Harmegnies F, Foucher J-P, Fiala-Medioni A (1996b) Spatial distribution of diverse cold seep communities living on various diapiric structures of the southern Barbados prism. Progress in Oceanography 38: 347–376.
- 46. Van Dover C, Aharon P, Bernhard JM, Caylor E, Doerries M, et al. (2003) Blake Ridge methane seep: characterization of a soft-sediment, chemosynthetically based ecosystem. Deep-Sea Research I 50: 281–300.
- 47. Olu K, Caprais JC, Galéron J, Causse R, Cosel R von, et al. (2009) Influence of seep emission on the non-symbiont-bearing fauna and vagrant species at an active giant pockmark in the Gulf of Guinea (Congo-Angola margin). Deep Sea Research Part II: Topical Studies in Oceanography 56: 2380–2393.
- 48. Olu-Le Roy K, Caprais JC, Fifis A, Fabri MC, Galéron J, et al. (2007a) Cold seep assemblages on a giant pockmark off West Africa: spatial patterns and environmental control. Marine Ecology 28: 115–130.
- 49. Sahling H, Bohrmann G, Spiess V, Bialas J, Breitzke M, et al. (2008) Pockmarks in the Northern Congo Fan area, SW Africa: Complex seafloor features shaped by fluid flow. Marine Geology 249: 206–225.
- 50. Sibuet M, Vangriesheim A (2009) Deep-sea environment and biodiversity of the West African Equatorial margin. Deep Sea Research Part II: Topical Studies in Oceanography 56: 2156–2168.
- 51. Genio L, Johnson SB, Vrijenhoek RC, Cunha MR, Tyler P, et al. (2008) New record of “Bathymodiolus” mauritanicus Cosel 2002 from the Gulf of Cadiz (NE Atlantic) mud volcanoes. Journal of Shellfish Research 27: 53–61.
- 52. Olu-Le Roy K, Cosel R von, Hourdez S, Carney SL, Jollivet D (2007b) Amphi-Atlantic cold-seep Bathymodiolus species complexes across the equatorial belt. Deep Sea Research Part I: Oceanographic Research Papers 54: 1890–1911.
- 53. Menot L, Galéron J, Olu K, Caprais JC, Crassous P, et al. (2010) Spatial heterogeneity of macro-infaunal communities in and near a giant pockmark area in the deep Gulf of Guinea. Marine Ecology 31: 78–93.
- 54. Cosel R von, Olu K (2008) A new genus and new species of Vesicomyidae (Mollusca: Bivalvia) from cold seeps on the Barbados accretionary prism, with comments on other species. Zoostystema 30: 929–944.
- 55. Komai T, Segonzac M (2005) A revision of the genus Alvinocaris Williams and Chace (Crustacea: Decapoda: Caridea: Alvinocaridea), with descriptions of a new genus and a new species of Alvinocaris. Journal of Natural History 39: 1111–1175.
- 56. Komai T, Shank T, Van Dover C (2005) A new species of Alvinocaris (Crustacea: Decapoda: Caridea: Alvinocarididae) and a new record of A. muricola from methane seeps on the Blake Ridge Diapir, Northwestern Atlantic. Zootaxa 1019: 27–42.
- 57. Macpherson E, Segonzac M (2005) Species of the genus Munidopsis (Crustacea, Decapoda, Galatheidae) from the deep Atlantic Ocean, including cold-seep and hydrothermal vent areas. Zootaxa 1–60.
- 58. Warén A (2001) Gastropoda and Monoplacophora from hydrothermal vent and seeps; New taxa and records. The Veliger 44: 116–231.
- 59. Warén A, Bouchet P (2009) New gastropods from deep-sea hydrocarbon seeps off West Africa. Deep Sea Research Part II: Topical Studies in Oceanography 56: 2326–2349.
- 60. Cosel R von, Olu K (2009) Large Vesicomyidae (Mollusca: Bivalvia) from cold seeps in the Gulf of Guinea off the coasts of Gabon, Congo and northern Angola. Deep Sea Research Part II: Topical Studies in Oceanography 56: 2350–2379.
- 61. Legendre P, Legendre L, editors. (1998) Numerical Ecology, second english edition. Amsterdam: Elsevier Science. 853 p.
- 62. Ward JH (1963) Hierachical grouping to optimize an objective function. Journal of American Statistician Association 58: 236–244.
- 63. Legendre P, Gallagher ED (2001) Ecologically meaningful transformations for ordination of species data. Oecologia 129: 271–280.
- 64. Oksanen J, Kindt R, Legendre P, O'Hara B, Simpson GL, et al. (2008) vegan: Community Ecology Package. R package version 1.15. http://cran.r-project.org/, http://vegan.r-forge.r-project.org/.
- 65. Chase MR, Etter RJ, Rex MA, Quattro JM (1998) Bathymetric patterns of genetic variation in a deepsea protobranch bivalve, Deminucula atacellana. Marine Biology 131: 301–308.
- 66. Gooday A, Holzmann M, Guiard J, Cornelius N, Pawlowski J (2004) A new monothalamous foraminiferan from 1000 to 6300m water depth in the Weddell Sea: morphological and molecular characterization. Deep-Sea Research II 51: 1603–1616.
- 67. McClain CR, Etter RJ (2005) Mid-domain models as predictos of sepcies diversity patterns: bathymetric diversity gradinets in the deep-sea. Oikos 109: 555–566.
- 68. Rex MA (1983) Geographic patterns of species diversity in the deep-dea benthos. In: Rowe GT, editor. The Sea. New-York: J. Wiley & sons. pp. 453–472.
- 69. Carney RS, Haedrich RL, Rowe G (1983) Zonation of fauna in the deep sea. In: Rowe G, editor. Deep-Sea Biology. pp. 371–398. Wiley-Interscience, New York ed.
- 70. Wei CL, Rowe GT, Hubbard GF, Scheltema AH, Wilson GDF, et al. (2010) Bathymetric zonation of deep-sea macrofauna in relation to export of surface phytoplankton production. Marine Ecology Progress Series 399: 1–14.
- 71. Jones WJ, Won YJ, Maas PAY, Smith PJ, Lutz RA, et al. (2006) Evolution of habitat use by deep-sea mussels. Marine Biology 148: 841–851.
- 72. Jones ML (1985) On the Vestimentifera, new phylum: six new species, and other taxa, from hydrothermal vents and elsewhere. Biol Soc Wash Bull 6: 117–158.
- 73. Miglietta MP, Hourdez S, Fisher CR (In press) Species boundaries of Gulf of Mexico vestimentiferans inferred from unclear and mitochondrial genes. Deep-Sea Research II.
- 74. Goffredi SK, Hurtado LA, Hallam S, Vrijenhoek RC (2003) Evolutionary relationships of deep-sea vent and cold seep clams (Mollusca: Vesicomyidae) of the “pacifica/lepta” species complex. Marine Biology 142: 311–320.
- 75. Carney SL, Formica MI, Divatia H, Nelson K, Fisher CR, et al. (2006) Population structure of the mussel “Bathymodiolus” childressi from Gulf of Mexico hydrocarbon seeps. Deep Sea Research Part I: Oceanographic Research Papers 53: 1061.
- 76. Levin LA, Etter RJ, Rex MA, Gooday AJ, Smith CR, et al. (2001) Environmental influences on regional deep-sea species diversity. Annual Revue of Ecology and Systematics 32: 51–93.
- 77. Cordes EE, Cunha MR, Galéron J, Mora C, Olu - Le Roy K, et al. (2010) The influence of geological, geochemical, and biogenic habitat heterogeneity on seep biodiversity. Marine Ecology 31: 51–65.
- 78. Fisher CR, Roberts H, Cordes EE, Bernard B (2007) Cold seeps and associated communities of the Gulf of Mexico. Oceanography 20:
- 79. Cordes EE, Bergquist DC, Fisher C (2009) Macro-Ecology of Gulf of Mexico Cold Seeps. Annuual Review of Marine Sciences 1: 143–168.
- 80. Charlou JL, Donval JP, Fouquet Y, Ondreas H, Knoery J, et al. (2004) Physical and chemical characterization of gas hydrates and associated methane plumes in the Congo-Angola Basin. Chemical Geology 205: 405.
- 81. Duperron S, Sibuet M, MacGregor BJ, Kuypers MMM, Fisher CR, et al. (2007) Diversity, relative abundance and metabolic potential of bacterial endosymbionts in three Bathymodiolus mussel species from cold seeps in the Gulf of Mexico. Environmental Microbiology 9: 1423–1438.
- 82. Cosel R von, Olu K (1998) Gigantism in Mytilidae. A new Bathymodiolus from cold seep areas on the Barbados accretionary Prism. Comptes Rendus de l'Académie des Sciences de Paris, Série II 321: 655–663.
- 83. Barry JP, Kochevar RE, Baxter CH (1997) The influence of pore-water chemistry and physiology in the distribution of vesicomyid clams at cold seeps in Monterey Bay : implications for patterns of chemosynthetic community organization. Limnology and Oceanography 42: 318–328.
- 84. Goffredi SK, Barry JP (2002) Species-specific variation in sulfide physiology between closely related Vesicomyid clams. Marine Ecology Progress Series 225: 227–238.
- 85. Kojima S, Ohta S (1997) Calyptogena okutanii n. sp., a sibling species of Calyptogena soyoae Okutani, 1957 (Bivalvia: Vesicomyidae). Venus: Japanese Journal of Malacology 56: 189–195.
- 86. Vacelet J, Boury-Esnault N, Fiala-Médioni A, Fisher CR (1995) A methanotrophic carnivorous sponge. Nature 377: 296.
- 87. Arhan M, Mercier H, Bourlès B, Gouriou Y (1998) Hydrographic sections across the Atlantic at 7°30N and 4°30S. Deep Sea Research I 45:
- 88. Tyler PA, Young CM (1999) Reproduction and dispersal at vents and cold seeps. Journal of the Marine Biological Association of the UK 79: 193–208.
- 89. Young CM, Tyler OA, Fenaux L (1997) Potential for deep sea invasion by Mediterranean shallow water echinoids: pressure and temperature as stage-specific dispersal barriers. Marine Ecology Progress Series 154: 197–209.
- 90. Young CM (2003) Reproduction, development and life-history traits. In: Tyler PA, editor. pp. 381–426. Ecosystems of the Deep Oceans: Elsevier, Amsterdam.
- 91. Mullineaux LS, Mills SW, Sweetman AK, Beaudreau AH, Metaxas A, et al. (2005) Vertical, lateral and temporal structure in larval distributions at hydrothermal vents. Marine Ecology Progress Series 293: 1–16.
- 92. Scheltema RS (1966) Evidence for trans-Atlantic transport of gastropod larvae belonging to the genus Cymatium. Deep-Sea Res 13: 83–95.
- 93. Van Gaest AL, Young CM53 p. Development and arval ecology of the cold seep gastropod Bathynerita naticoidea; 2005; Scripps Institution of Oceanography, La Jolla (USA), September12–16, 2005.
- 94. Tyler P, Young CM, Dolan E, Arellano SM, Brooke SD, et al. (2007) Gametogenic periodicity in the chemosynthetic cold-seep mussel “Bathymodiolus” childressi. Marine Biology 150: 829–840.
- 95. Arellano SM, Young C (2009) Spawning, Development, and the Duration of Larval Life in a Deep-Sea Cold-Seep Mussel. Biological Bulletin 216: 149–162.
- 96. Ramirez Llodra E, Segonzac M (2006) Reproductive biology of Alvinocaris muricola (Decapoda: Caridea: Alvinocarididae) from cold seeps in the Congo Basin. J Mar Biol Ass UK 86: 1347–1356.
- 97. Shank TM, Black MB, Halanych KM, Lutz RA, Vrijenhoek RC (1999) Miocene radiation of deep-sea hydrothermal vent shrimp (Caridea: Bresiliidae): Evidence from mitochondrial Cytochrome oxidase Subunit I. Molecular Phylogenetics and Evolution 13: 244–254.
- 98. Van Dover CL, Factor JR, Williams AB, Berg CJ (1985) Reproductive patterns of decapod crustaceans from hydrothermal vents. In: Jones ML, editor. pp. 223–227. The Hydrothermal vents of the Eastern Pacific: an overview: Bulletin of the Biological Society of Washington.
- 99. Halanych KM (2005) Molecular phylogeny of sigoglinid annelids (a.k.a. pogonophorans): a review. Hydrobiologia 535/536: 297–307.
- 100. Young CM, Vazquez E, Metaxas A, Tyler PA (1996) Embryology of vestimentiferan tube worms from deep-sea methane/sulphide seeps. Nature 381: 514–516.
- 101. Little CTS, Vrijenhoek RC (2003) Are hydrothermal vent animals living fossils? Trends in Ecology & Evolution 18: 582.
- 102. Krylova EM, Janssen R (2006) Vesicomyidae from Edison Seaomunt (South West Pacific:Papua New Guinea: New Ireland fore-arc basin). Arch Molluskenkunde 135: 231–261.
- 103. Kojima S, Fujikura K, Okutani T (2004) Multiple trans-Pacific migrations of deep-sea vent:seep-endemic bivalves in the family Vesicomyidae. Molecular Phylogenetics and Evolution 32: 396–406.
- 104. Vermeij GJ (2005) From Europe to America: Pliocene to Recnet trans-Atlantic axpansion of cold-water North Atlantic molluscs. Proceedings of the Royal Society of London, B 272: 2545–2550.
- 105. Won YJ, Maas PAY, Van Dover C, Vrijenhoek RC (2002) Habitat reversal in vent and seep mussels: Bathymodiolus heckerae, derived from vent ancestors. Cahiers de Biologie Marine 43: 387–390.
- 106. Dando PR, Southward AJ, Southward EC, Dixon DR, Crawford A, et al. (1992) Shipwrecked tube worms. Nature 356: 667.
- 107. Plouvier S, Shank T, Faure B, Daguin-Thiébaut C, Viard F, et al. (2009) Comparative phylogeography among hydrothermal vent species along the East Pacific Rise reveals vicariant processes and population expansion in the South. Molecular Ecology 18: 3903–3917.