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Information on genetic divergence and migration patterns of vent‐ and seep‐endemic macrobenthos can help delimit biogeographical provinces and provide scientific guidelines for deep‐sea conservation under the growing threats of anthropogenic disturbances. Nevertheless, related studies are still scarce, impeding the informed conservation of these hotspots of deep‐sea biodiversity. To bridge this knowledge gap, we conducted a population connectivity study on the galatheoid squat lobster Shinkaia crosnieri – a deep‐sea foundation species widely distributed in vent and seep ecosystems in the Northwest Pacific. With the application of an interdisciplinary methodology involving population genomics and oceanographic approaches, we unveiled two semi‐isolated lineages of S. crosnieri with limited and asymmetrical gene flow potentially shaped by the geographic settings, habitat types, and ocean currents – one comprising vent populations in the Okinawa Trough, with those inhabiting the southern trough area likely serving as the source; the other being the Jiaolong (JR) seep population in the South China Sea. The latter might have recently experienced a pronounced demographic contraction and exhibited genetic introgression from the Okinawa Trough lineage, potentially mediated by the intrusion of the North Pacific Intermediate Water. We then compared the biogeographic patterns between S. crosnieri and two other representative and co‐occurring vent‐ and seep‐endemic species using published data. Based on their biogeographical subdivisions and source‐sink dynamics, we highlighted the southern Okinawa Trough vents and the JR seep warrant imperative conservation efforts to sustain the deep‐sea biodiversity in the Northwest Pacific. [ABSTRACT FROM AUTHOR]

Whelks in the sister-genera Enigmaticolus and Thermosipho (Gastropoda: Buccinidae) commonly inhabit deep-water hydrothermal vents and hydrocarbon seeps. Thermosipho desbruyeresi , originally described from the Lau Basin, was thought to occur in vents across the western Pacific, with Eosipho desbruyeresi nipponensis described from the Okinawa Trough treated as its junior synonym. However, new material collected from vents in the Okinawa Trough and seeps in the South China Sea exhibit key characteristics of Enigmaticolus. Re-examination of the types revealed that Eosipho d. nipponensis is actually morphologically distinct from Thermosipho desbruyeresi. A molecular phylogeny reconstructed using the cytochrome c oxidase subunit I (COI) gene confirmed the placement of both taxa in Enigmaticolus and supported their distinctiveness at the species level. We, therefore, rehabilitate E. d. nipponensis as Enigmaticolus nipponensis comb. nov. and transfer T. desbruyeresi to the same genus, as Enigmaticolus desbruyeresi comb. nov. Our results also revealed that Enigmaticolus monnieri described from east Africa and E. inflatus described from the South China Sea are in fact conspecific with E. nipponensis. We discuss the distribution and biogeography, as well as morphological variability, of Enigmaticolus in the light of these new findings. Thermosipho is then left with only its type species, T. auzendei from the East Pacific vents. We have revised the diagnosis for the two genera, as well as the species included in them. [ABSTRACT FROM AUTHOR]

Site F, an active cold seep situated on the northeastern continental slope of the South China Sea (SCS), has not been systematically surveyed since its first discovery in 2007. Here we report the results of a ROV transect survey of this cold seep conducted in 2018, which mapped the distribution of the substrates and quantified epifauna along parallel dive tracks. The site, measuring 180 m × 180 m, is characterized by a central part of authigenic carbonate outcrops with crevices releasing gas bubbles, which support high densities of bathymodiolin mussels Gigantidas platifrons (up to 273 individuals m−2) and galatheid squat lobsters Shinkaia crosnieri (up to 300 individuals m−2). On more condensed carbonate crusts, G. platifrons and the munidopsid squat lobsters Munidopsis spp. are present at low densities. The outskirts of the site are dominated by soft sediment, with bacterial mats and sparsely distributed G. platifrons and their shells, as well as the vestimentiferan tubeworm Paraescarpia echinospica. Sampling in various locations of the cold seep yields 10 new records of epibenthic animals as determined by watching the captured videos, morphological analysis as well as sequencing the COI and 16S rRNA gene sequences. Stable isotope analysis showed that biogenic methane is the main carbon source for most of the macrobenthos in this community. Many of these SCS cold seep macrobenthos have been reported from hydrothermal vents of the Okinawa Trough, indicating high connectivity between the two chemosynthesis-based communities in the Western Pacific. Image 1 • We conducted an ecological survey of a cold seep in the South China Sea. • This community is dominated by deep-sea mussels and squat lobsters. • Molecular analyses revealed new records of epifauna on rocks. • This community is very similar with vent communities in the Okinawa Trough. • Stable isotope analyses revealed the food-web structure. [ABSTRACT FROM AUTHOR]