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Introduction: Methane seeps influence surrounding benthic communities in different ways from slight changes in benthic abundance and biomass to major altering the species composition. Materials and Methods: We studied benthic communities of 14 methane seep flares in Laptev and East Siberian seas with comparative analysis of species composition and abiotic parameters at the nearby areas not affected by methane seeps. The species diversity was comparable at seep and non-seep sites varying from 3.9 to 39.6 taxa per 100 individuals and from 4.5 to 34.8 taxa per 100 individuals, correspondingly. Results: The Laptev Slope community corresponds with the Polychaeta-community, encircling the upper continental slope area of the entire Siberian Arctic. The Lower Shelf community described in this study apparently corresponds with the Ophiocten sericeum community identified in the shelf areas of the Kara, Laptev and East Siberian seas. The Upper Shelf community is mostly inhabited by the bivalves species such as Portlandia arctica, Ennucula tenuis and Astarte montagui communities. The Estuarine community, which is the poorest by diversity but has high values of abundance and biomass is directly influenced by the Lena River runoff in terms of lower salinities and higher sedimentation rates. Discussion: Throughout the study area, the differences between the Estuarine, Upper Shelf Lower Shelf and Laptev Slope communities exceeded the differences between the seep and background non-seep areas. Several taxa demonstrated correlations with different environmental factors, including the latitude, depth, temperature, salinity, pH and methane content, not depending on the revealed benthic community. Eight taxa demonstrated correlations with the methane content measured at different sediment depths. Two siboglinids taxa demonstrated high abundances at stations with highest methane content deep in the sediment. At the Siberian shelf, our geochemical data for siboglinid habitats are the first to be published so far. [ABSTRACT FROM AUTHOR]

IntroductionMethane seeps influence surrounding benthic communities in different ways from slight changes in benthic abundance and biomass to major altering the species composition.Materials and MethodsWe studied benthic communities of 14 methane seep flares in Laptev and East Siberian seas with comparative analysis of species composition and abiotic parameters at the nearby areas not affected by methane seeps. The species diversity was comparable at seep and non-seep sites varying from 3.9 to 39.6 taxa per 100 individuals and from 4.5 to 34.8 taxa per 100 individuals, correspondingly.ResultsThe Laptev Slope community corresponds with the Polychaeta-community, encircling the upper continental slope area of the entire Siberian Arctic. The Lower Shelf community described in this study apparently corresponds with the Ophiocten sericeum community identified in the shelf areas of the Kara, Laptev and East Siberian seas. The Upper Shelf community is mostly inhabited by the bivalves species such as Portlandia arctica, Ennucula tenuis and Astarte montagui communities. The Estuarine community, which is the poorest by diversity but has high values of abundance and biomass is directly influenced by the Lena River runoff in terms of lower salinities and higher sedimentation rates.DiscussionThroughout the study area, the differences between the Estuarine, Upper Shelf, Lower Shelf and Laptev Slope communities exceeded the differences between the seep and background non-seep areas. Several taxa demonstrated correlations with different environmental factors, including the latitude, depth, temperature, salinity, pH and methane content, not depending on the revealed benthic community. Eight taxa demonstrated correlations with the methane content measured at different sediment depths. Two siboglinids taxa demonstrated high abundances at stations with highest methane content deep in the sediment. At the Siberian shelf, our geochemical data for siboglinid habitats are the first to be published so far.

Abstract Frenulate species were identified from a high Arctic methane seep area on Vestnesa Ridge, western Svalbard margin (79°N, Fram Strait) based on mitochondrial cytochrome oxidase subunit I (mtCOI). Two species were found: Oligobrachia haakonmosbiensis, and a new, distinct, and undescribed Oligobrachia species. The new species adds to the cryptic Oligobrachia species complex found at high latitude methane seeps in the north Atlantic and the Arctic. However, this species displays a curled tube morphology and light brown coloration that could serve to distinguish it from other members of the complex. A number of single tentacle individuals were recovered which were initially thought to be members of the only unitentaculate genus, Siboglinum. However, sequencing revealed them to be the new species and the single tentacle morphology, in addition to thin, colorless, and ringless tubes indicate that they are juveniles. This is the first known report of juveniles of northern Oligobrachia. Since the juveniles all appeared to be at about the same developmental stage, it is possible that reproduction is either synchronized within the species, or that despite continuous reproduction, settlement, and growth in the sediment only takes place at specific periods. The new find of the well‐known species O. haakonmosbiensis extends its range from the Norwegian Sea to high latitudes of the Arctic in the Fram Strait. We suggest bottom currents serve as the main distribution mechanism for high latitude Oligobrachia species and that water depth constitutes a major dispersal barrier. This explains the lack of overlap between the distributions of northern Oligobrachia species despite exposure to similar current regimes. Our results point toward a single speciation event within the Oligobrachia clade, and we suggest that this occurred in the late Neogene, when topographical changes occurred and exchanges between Arctic and North Atlantic water masses and subsequent thermohaline circulation intensified.

Pogonophora or siboglinid tubeworms (Annelida, Siboglinidae) have been found in the East Siberian Sea for the first time. On the basis of the results of molecular phylogenetic analysis, the found specimens are presumably assigned to the genus Oligobrachia. The stations where the siboglinid tubeworms have been found are located in the area of methane seeps. This confirms the previously stated hypothesis about relationship of siboglinid tubeworm distribution with the areas of underwater methane seeps. [ABSTRACT FROM AUTHOR]

Frenulate species were identified from a high Arctic methane seep area on Vestnesa Ridge, western Svalbard margin (79°N, Fram Strait) based on mitochondrial cytochrome oxidase subunit I (mtCOI). Two species were found: Oligobrachia haakonmosbiensis, and a new, distinct, and undescribed Oligobrachia species. The new species adds to the cryptic Oligobrachia species complex found at high latitude methane seeps in the north Atlantic and the Arctic. However, this species displays a curled tube morphology and light brown coloration that could serve to distinguish it from other members of the complex. A number of single tentacle individuals were recovered which were initially thought to be members of the only unitentaculate genus, Siboglinum. However, sequencing revealed them to be the new species and the single tentacle morphology, in addition to thin, colorless, and ringless tubes indicate that they are juveniles. This is the first known report of juveniles of northern Oligobrachia. Since the juveniles all appeared to be at about the same developmental stage, it is possible that reproduction is either synchronized within the species, or that despite continuous reproduction, settlement, and growth in the sediment only takes place at specific periods. The new find of the well‐known species O. haakonmosbiensis extends its range from the Norwegian Sea to high latitudes of the Arctic in the Fram Strait. We suggest bottom currents serve as the main distribution mechanism for high latitude Oligobrachia species and that water depth constitutes a major dispersal barrier. This explains the lack of overlap between the distributions of northern Oligobrachia species despite exposure to similar current regimes. Our results point toward a single speciation event within the Oligobrachia clade, and we suggest that this occurred in the late Neogene, when topographical changes occurred and exchanges between Arctic and North Atlantic water masses and subsequent thermohaline circulation intensified. [ABSTRACT FROM AUTHOR]

Siboglinid tubeworms of the genus Oligobrachia that thrive in obligatory association with endosymbionts have been predominantly observed in Arctic and high-latitude Atlantic cold seeps. Metabolic features of endosymbionts provide fundamental understanding for the survival strategy of tubeworms in cold seeps. However, no information on the bacterial endosymbionts of tubeworms from the Canadian Beaufort Sea has been available until now. In this study, we investigated the phylogeny and metabolic potential of a bacterial endosymbiont of siboglinid tubeworms from an active mud volcano in the Canadian Beaufort Sea using Illumina MiSeq sequencing of 16S rRNA gene amplicons. The siboglinid tubeworm shared 99.9% 18S rRNA gene sequence similarity with Oligobrachia haakonmosbiensis and 99.7–99.8% mitochondrial cytochrome C oxidase subunit I gene similarity with members of Oligobrachia sp. CPL-clade and was designated 'Oligobrachia sp. BS1.' The endosymbiont of Oligobrachia sp. BS1, which belongs to the Gammaproteobacteria, was most closely related to endosymbionts of Oligobrachia sp. CPL-clade, revealing the close relationships between the endosymbionts and their hosts. The bacterial endosymbiont of Oligobrachia sp. BS1 contained the key gene required for sulfur oxidation, aprA gene encoding the α-subunit of adenosine 1,5-phosphosulfate reductase, suggesting that this endosymbiont is capable of using sulfide as an energy source. The bacterial endosymbiont of an Oligobrachia species from an active mud volcano in the Canadian Beaufort Sea presented here expands our knowledge of the identities and thiotrophic metabolism of endosymbionts that are associated with hosts that dominate a wide range of methane seep habitats in the Arctic. [ABSTRACT FROM AUTHOR]

The present study is based on new material ofOligobrachia haakonmosbiensisfrom the Arctic and Northeast Atlantic. The species redescribed here is shown to have a wider distribution than previously known. The investigation of well-preserved specimens ofO. haakonmosbiensisrevealed longitudinal glandular patches on the forepart, which previously have not been observed due to inadequate fixation. In addition, the opisthosome is described. The presence of glandular patches confirms the closest morphological affinity betweenO. haakonmosbiensisandO. webbi, the two North Atlantic pogonophorans of the genusOligobrachia. These two species are unique amongOligobrachiaspecies in possessing cuticular plaques on the anterior (metameric) part of the trunk and in lacking pinnules on the tentacles. The description ofO. dogieliis supplemented with a few important details. Key characters of all species of the genusOligobrachiaare given in a table. It is suggested that the family Oligobrachiidae includes four genera:Oligobrachia,Nereilinum,UnibrachiumandPolarsternium; their species are listed and diagnoses reviewed. The peculiar characters ofCrassibrachiaandBirsteiniawhich allow me to exclude these genera from the family are listed. Two keys are provided to the oligobrachiid genera and to the known world species of the genusOligobrachia. [ABSTRACT FROM PUBLISHER]