Habitat associations in gastropod species at East Pacific Rise hydrothermal vents (9 degrees 50'N)

At deep-sea hydrothermal vents on the East Pacific Rise (9 degrees 50'N), distinct megafaunal assemblages are positioned along strong thermal and chemical gradients. We investigated the distribution of gastropod species to determine whether they associate with specific megafaunal zones and to determine the thermal boundaries of their habitats. Gastropods colonized a series of basalt blocks that were placed into three different zones characterized by vestimentiferan tubeworms, bivalves, and suspension-feeders, respectively. Additional gastropods were collected on selected blocks from higher temperature vestimentiferan habitat and from grab samples of alvinellid polychaetes. On the blocks, gastropod species clustered into a "Cool" group (Clypeosectus delectus, Eulepetopsis vitrea, Gorgoleptis spiralis, and Lepetodrilus ovalis) whose species tended to be most abundant in the suspension-feeder zone, and a "Warm" group (Lepetodrilus cristatus, L. elevatus, L. pustulosus, and Cyathermia naticoides) whose species all were significantly more abundant in the vestimentiferan zone than elsewhere. The temperature ranges of Cool species were generally lower than the ranges of Warm ones, although both groups were present at 3 to 6 degrees C; also present was Bathymargarites symplector, which clustered with neither group. Three additional species, Rhynchopelta concentrica, Neomphalus fretterae, and Nodopelta rigneae, co-occurred with Warm-group species on selected blocks from hotter habitats. Although a few species were found only in alvinellid collections, most species were not exclusive to a specific megafaunal zone. We propose that species in the Cool and Warm groups occupy specific microhabitats that are present in more than one zone.     

Novel uncultured Epsilonproteobacteria dominate a filamentous sulphur mat from the 13 degrees N hydrothermal vent field, East Pacific Rise

Rapid growth of microbial sulphur mats have repeatedly been observed during oceanographic cruises to various deep-sea hydrothermal vent sites. The microorganisms involved in the mat formation have not been phylogenetically characterized, although the production of morphologically similar sulphur filaments by a Arcobacter strain coastal marine has been documented. An in situ collector deployed for 5 days at the 13 degrees N deep-sea hydrothermal vent site on the East Pacific Rise (EPR) was rapidly colonized by a filamentous microbial mat. Microscopic and chemical analyses revealed that the mat consisted of a network of microorganisms embedded in a mucous sulphur-rich matrix. Molecular surveys based on 16S rRNA gene and aclB genes placed all the environmental clone sequences within the Epsilonproteobacteria. Although few 16S rRNA gene sequences were affiliated with that of cultured organisms, the majority was related to uncultured representatives of the Arcobacter group (< or = 95% sequence similarity). A probe designed to target all of the identified lineages hybridized with more than 95% of the mat community. Simultaneous hybridizations with the latter probe and a probe specific to Arcobacter spp. confirmed the numerical dominance of Arcobacter-like bacteria. This study provides the first example of the prevalence and ecological significance of free-living Arcobacter at deep-sea hydrothermal vents.     

Two new species of hydrothermal vent crabs of the genus Bythograea from the southern East Pacific Rise and from the Galapagos Rift (Crustacea Decapoda Brachyura Bythograeidae)

Two new species of Bythograea Williams, B. vrijenhoeki n. sp. and B. galapagensis n. sp., are described based on morphology and mitochondrial DNA comparisons. B. vrijenhoeki was collected on the southern East Pacific Rise, south of the Easter Microplate and B. galapagensis from the Galapagos Rift, from where B. intermedia de Saint Laurent was also described. Our analyses indicate that B. vrijenhoeki is the sister species of B. laubieri Guinot and Segonzac, and B. galapagensis is the sister species of B. thermydron Williams. Bythograea is now composed of six described species, all endemic to hydrothermal vents along the East Pacific Rise and from the Galapagos Rift.     

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

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

Comparative phylogeography among hydrothermal vent species along the East Pacific Rise reveals vicariant processes and population expansion in the South

The use of sequence polymorphism from individual mitochondrial genes to infer past demography has recently proved controversial because of the recurrence of selective sweeps acting over genes and the need for unlinked multilocus data sets. However, comparative analyses using several species for one gene and/or multiple genes for one species can serve as a test for potential selective effects and clarify our understanding of historical demographic effects. This study compares nucleotide polymorphisms in mitochondrial cytochrome oxidase I across seven deep-sea hydrothermal vent species that live along the volcanically active East Pacific Rise. Approximate Bayesian Computation (ABC) method, developed to trace shared vicariant events across species pairs, indicates the occurrence of two across species divergence times, and suggests that the present geographical patterns of genetic differentiation may be explained by two periods of significant population isolation. The oldest period dates back 11.6 Ma and is associated with the vent limpet Lepetodrilus elevatus , while the most recent period of isolation is 1.3 Ma, which apparently affected all species examined and coincides with a transition zone across the equator. Moreover, significant negative Tajima's D and star-like networks were observed for all southern lineages, suggesting that these lineages experienced a concomitant demographic and geographical expansion about 100 000–300 000 generations ago. This expansion may have initiated from a wave of range expansions during the secondary colonization of new sites along the Southern East Pacific Rise (founder effects below the equator) or recurrent bottleneck events because of the increase of eruptive phases associated with the higher spreading rates of the ridge in this region.     

Bacterial and archaeal phylotypes associated with distinct mineralogical layers of a white smoker spire from a deep-sea hydrothermal vent site (9 degrees N, East Pacific Rise)

A diffusely venting chimney spire from the East Pacific Rise (9 degrees N) was analysed by petrographic thin sectioning and 16S rRNA gene cloning and sequencing in parallel, to correlate microbial community composition with mineralogy and inferred in situ conditions within the chimney mineral matrix. Both approaches indicated a zonation of the chimney spire into distinct microhabitats for different bacteria and archaea. The thermal gradient inferred from the mineral composition and porosity of the chimney was consistent with the distribution of bacterial and archaeal phylotypes in the chimney matrix. A novel phylogenetic lineage of euryarchaeota was found that co-occurred with clones related to cultured hyperthermophilic archaea. A few phylotypes related to mesophilic bacteria were found in the hot core of the chimney, indicating that seawater influx during retrieval and cooling of these highly porous structures can entrain microorganisms into chimney layers that are not their native habitat.     

A new species of Acontiophorus Brady, 1880 (Copepoda: Siphonostomatoida) from Ushuaia,Argentina

A new species of Acontiophorus belonging to the family Asterocheridae was found in Ushuaia, Patagonia, southern Argentina. The new species is distinctive in having 9-segmented antennule, five setae on terminal endopodal segment of leg 1, seven elements on terminal segment of leg 1 and leg 4 exopods, and characteristic setation on maxillule lobes. This combination of characteristic features does not occur in any other species of the genus. The genus Acontiophorus is recorded for the first time from the South Atlantic.     

Two new species of Cardiodectes Wilson (Copepoda: Siphonostomatoida)

Summary Two new species of pennellid copepods are described, Cardiodectes boxshalli from Nicholsina usta (Valenciennes, 1839) off Jamaica and C. spiralis from Anthias tuka (Herre, 1927) off the Massas Islands, New Guinea. A key to all known species of the genus is provided.Work completed during a period of secondment from the University of Bath.Work completed during a period of secondment from the University of Bath.     

New Aegisthidae (Copepoda: Harpacticoida) from western Pacific cold seeps and hydrothermal vents

Hyperbenthic harpacticoid samples from Japanese hydrothermal vents in the Okinawa Trough and cold seep sites in Sagami Bay were examined and resulted in the discovery of four new species belonging to three new genera of Aegisthidae (Copepoda: Harpacticoida). Females of Nudivorax todai gen. et sp. nov. possess a large area of flexible integument between the cephalosome and the first pedigerous somite which is suggestive of a gorging feeding strategy. Main diagnostic characters separating the new genus from other Aegisthidae are provided by the unusually short caudal rami, the complete lack of intcgumcntal surface lamellae, and the presence in the male of a linear array of pores along the rostral margin which appears to be sensory in function. Scabrantenna yooi gen. et sp. nov. displays several similarities with Aegisthus aculeatus Giesbrecht, 1891 but is highly distinctive in its male morphology which includes extremely atrophied mouthparts and a unique prehensile antenna. Jamstecia terazakii gen. et sp. nov. is only known from a single female caught in the Okinawa Trough. Jamstecia gen. nov. is most closely related to Andromastax Conroy-Dalton & Huys, 1999 but can be distinguished on the basis of the elongate antennules, the antennary morphology, the absence of lateral spinous processes on the cephalosome and swimming legs 2–4, and differences in the mandibular palp and armature of the maxilliped. Andromastax cephaloceratus sp. nov. differs from the type species A. muricatus Conroy-Dalton & Huys, 1998 primarily in the presence of long spinous processes on the cephalosome and the absence of the inner seta on the female P5.     

Expansion of the geographic distribution of a novel lineage of epsilon-Proteobacteria to a hydrothermal vent site on the Southern East Pacific Rise

The diversity associated with a microbial mat sample collected from a deep-sea hydrothermal vent on the Southern East Pacific Rise was determined using a molecular phylogenetic approach based on the comparison of sequences from the small subunit ribosomal RNA gene (16S rDNA). The DNA was extracted from the sample and the 16S rDNA was amplified by PCR. Sixteen different phylotypes were identified by restriction fragment length polymorphism analysis; four phylotypes were later identified as putative chimeras. Analysis of the 16S rDNA sequences placed all the phylotypes within the Proteobacteria. The majority of the sequences (98%) were most closely related to a new clade of epsilon-Proteobacteria that were initially identified from an in situ growth chamber deployed on a deep-sea hydrothermal vent on the Mid-Atlantic Ridge in 1995. The similarity between phylotypes identified from Atlantic and Pacific deep-sea hydrothermal vent sites indicates that this new clade of Proteobacteria may be endemic to and widely distributed among deep-sea hydrothermal vents.     

A New Archaeogastropod (Rhipidoglossa, Trochacea) from Hydrothermal Vents on the East Pacific Rise

Melanodrymia aurantiaca gen. et sp.n., a conispiral archaeogastropod of trochacean affinities, occurs on chimneys and stacks of polymetallic sulphide deposits at hydrothermal vents on the abyssal ocean floor at 21°N Latitude off Baja California, Mexico. The shell is unique in its combination of reflexed growth lines, strongly prosocline aperture, discordant sculpture, discoidal geometry and pattern of apertural angulations. The similarity in form with Paleozoic euomphalaceans and pleurotomariceans is considered superficial and the unusual shell form and simplification of shell microstructure are interpreted as evolutionary correlates of small size. The radula is unusual, but it shares many features with the rhipidoglossan radulae of four undescribed limpet-shaped species from hydrothermal vents on the East Pacific Rise. It is hypothesized that the adaptive radiation occurred in situ , late in the Tertiary or Quaternary, and from a coiled ancestor.     

New genus and species of brachyuran crab from the southern East Pacific Rise (Crustacea Decapoda Brachyura Bythograeidae)

A new genus and species of a brachyuran crab, Allograea tomentosa n. gen. and n. sp., of the family Bythograeidae, collected at a hydrothermal vent locality south of the Easter Microplate (31 degrees 09'S) on the southern East Pacific Rise, is described. The genus Allograea is distinguished by lacking modifications of the fronto-orbital region, and by the absence of coloured fields and setal patches on the carapace and chelipeds. The body and legs are smooth but densely covered by a brown tomentum, the eyestalks are not reduced, but the cornea is unfaceted and unpigmented. Comparison of mitochondrial DNA sequences among all known bythograeid genera confirms the novelty of this taxon.     

A new species of Caligus (Copepoda, Siphonostomatoida) from the plankton of the Caribbean coast of Venezuela with a key to species

During a survey of the zooplankton community of Bahía Amuay, Venezuelan Caribbean, specimens of an undescribed species of Caligus Müller were collected. It resembles Caligus xystercus Cressey and Caligus ocyurus Cressey, both known only from the Caribbean Sea. The new species can be distinguished from these and other congeners by a combination of characters including the armature of legs 1 and 4, but mainly by its unique female genital complex. This is the first species of Caligus described from Venezuela. The species is described in full and a key to the species of the genus recorded in Venezuela is provided.     

Two new Artotrogids (Copepoda: Siphonostomatoida) from Madeira Island,Portugal

Two new artotrogids are recorded from Madeira Island. A new species of Cryptopontius, associated with algae, differs from its congeners in the number of antennular segments, setation of the antennal exopod, setation and length of the maxillule lobes, and setation of both rami of the first and fourth legs. The second new artotrogid belongs to Dyspontius.It was associated with Gerardia savagliae Lacaze-Duthiers, 1864 (Cnidaria: Zoanthidea) and differs from its congeners in cephalothorax shape, siphon length and setation of the maxillule lobes.     

Four new species of Provanna Dall (Prosobranchia,Cerithiacea?) from East Pacific hydrothermal sites

Four new species of Provanna Dall, 1918 are described from East Pacific hydrothermal sites: Provanna ios sp.n., P. goniata sp.n., P. echinata sp.n. and P. variabilis sp.n. The type species of Provanna, P. Iomana Dall, 1918 and Trichotropis (Cerithioderma) pacifica Dall, 1908. which here is transferred to Provanna , are the only additional species known of the genus. Results of some preliminary anatomical investigations are given and a tentative position in the Cerithiacea is suggested. The four new species were collected by manned submersibles from sites of hydrothermal activity; P. Iomana has been dredged on two occasions only. from an area known for hydrothermal activity and we assume that the type- and only known locality for P. pacifica also is affected by hydrothermal acitivity.     

New records for Dinemoura ferox (Copepoda: Siphonostomatoida: Pandaridae) from Pacific sleeper sharks captured in waters off eastern Taiwan

Four of the 27 Pacific sleeper sharks (Somniosus pacificus Bigelow and Schroeder) captured in the western North Pacific Ocean off eastern Taiwan between 19 March and 18 May 2002 hosted the parasitic copepod Dinemoura ferox (Kr?yer, 1838) on their body surface including the fins. This report documents a new host record as well as a new ocean record for D. ferox, which until now has only been reported from the benthopelagic sharks, Somniosus microcephalus (Bloch and Schneider) and Centrophorus squamosus (Bonnaterre), occurring in the north Atlantic Ocean off Greenland and Iceland.