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Dr. Chong CHEN

Dr. Chong CHEN

Deep-sea biologist. Malacologist. Evolutionary biologist. "Mollusc collector", photographer.

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Gallery of Publications

We carried out a comprehensive survey of the Sumisu Caldera deep-sea hot vent about 500 km southeast of Tokyo, increasing the known animal species diversity from 9 to 54 -- making it the most species-rich vent in the NW Pacific! These are key data for the conservation of these vulnerable 'oases' eyed for deep-sea mining. Just out in Aquatic Conservation, free for everyone to read (Open Access): https://doi.org/10.1002/aqc.70009<br /> <br /> Abstract: <br /> Hydrothermal vents are biodiversity hotspots on the deep seafloor powered by chemosynthetic primary production, inhabited by a specially adapted fauna whose composition varies between regions. Sumisu Caldera, located approximately 500 km south of Tokyo, hosts a hot vent with an unusual species composition among the Izu–Ogasawara Arc sites and has been suggested as a priority site for conservation in light of upcoming deep-sea mining for massive sulfides. However, this was based on just five species serendipitously recorded from geological surveys. Here, we carried out the first comprehensive biological sampling of Sumisu using two dives of the human-occupied vehicle Shinkai 6500. Together with literature records, we count a total of 54 animal species of which at least 25 are endemic to chemosynthetic ecosystems, drastically increasing the known faunal diversity—including three sponges, one cnidarian, 12 molluscs, 23 annelids, 13 arthropods, one echinoderm, and one fish. The presence of sediments facilitating the occurrence of burrowing species and three non-endemic predators contribute to the high species richness. Our findings make Sumisu the most species-rich vent community in the entire northwestern Pacific and our work serves as a prime example for detailed faunal surveys to obtain key piece of baseline data for future environmental assessments. Although the apparent lack of massive sulfide deposits means Sumisu is unlikely to be an immediate target of mining, its close distance to Bayonnaise Knoll with a major deposit and the possibility that it acts as a critical stepping-stone population for many species, as well as the presence of several endangered ones, presents a case for its protection.<br /> <br /> Chen C*, Hookabe N, Hashimoto R, Shimooka S, Shiraki S, Uyeno D, Kawagucci S (2024). Faunal composition of the Sumisu Caldera hydrothermal vent field as a key baseline for conservation in light of deep-sea mining. Aquatic Conservation: Marine and Freshwater Ecosystems, 34(11): e70009. DOI: 10.1002/aqc.70009
Our new paper In Systematic Biology uses hundreds of newly captured ultra-conserved elements (UCEs) on over 50 families of bivalve molluscs from all six major clades, revealing new topologies. Many were historical museum specimens! Link: https://doi.org/10.1093/sysbio/syae052<br /> <br /> Abstract: <br /> Despite significant advances in phylogenetics over the past decades, the deep relationships within Bivalvia (phylum Mollusca) remain inconclusive. Previous efforts based on morphology or several genes have failed to resolve many key nodes in the phylogeny of Bivalvia. Advances have been made recently using transcriptome data, but the phylogenetic relationships within Bivalvia historically lacked consensus, especially within Pteriomorphia and Imparidentia. Here, we inferred the relationships of key lineages within Bivalvia using matrices generated from specifically designed ultraconserved elements (UCEs) with 16 available genomic resources and 85 newly sequenced specimens from 55 families. Our new probes (Bivalve UCE 2k v.1) for target sequencing captured an average of 849 UCEs with 1085 bp in mean length from in vitro experiments. Our results introduced novel schemes from 6 major clades (Protobranchina, Pteriomorphia, Palaeoheterodonta, Archiheterodonta, Anomalodesmata, and Imparidentia), though some inner nodes were poorly resolved, such as paraphyletic Heterodonta in some topologies potentially due to insufficient taxon sampling. The resolution increased when analyzing specific matrices for Pteriomorphia and Imparidentia. We recovered 3 Pteriomorphia topologies different from previously published trees, with the strongest support for ((Ostreida + (Arcida + Mytilida)) + (Pectinida + (Limida + Pectinida))). Limida were nested within Pectinida, warranting further studies. For Imparidentia, our results strongly supported the new hypothesis of (Galeommatida + (Adapedonta + Cardiida)), while the possible non-monophyly of Lucinida was inferred but poorly supported. Overall, our results provide important insights into the phylogeny of Bivalvia and show that target enrichment sequencing of UCEs can be broadly applied to study both deep and shallow phylogenetic relationships. <br /> <br /> Li Y-X, Ip JC-H, Chen C, Xu T, Zhang Q, Sun Y, Ma P-Z, Qiu J-W* (2024). Phylogenomics of Bivalvia using ultraconserved elements (UCEs) reveal new topologies for Pteriomorphia and Imparidentia. Systematic Biology, Advance Article: syae052. DOI: 10.1093/sysbio/syae052 <br /> PDF: https://www.researchgate.net/publication/384077062_Phylogenomics_of_Bivalvia_Using_Ultraconserved_Elements_UCEs_Reveal_New_Topologies_for_Pteriomorphia_and_Imparidentia
We described and named Lebbeus parvirostris Komai & Chen, 2024, a new thorid shrimp species discovered from the Amami Rift deep-sea hydrothermal vent field off Amami Ōshima Island, Japan! Link to the paper in Zootaxa: https://doi.org/10.11646/zootaxa.5523.2.7<br /> <br /> Abstract: <br /> A new species of the thorid shrimp genus Lebbeus White, 1847, is described and illustrated on the basis of two specimens collected from the recently discovered Amami Rift hot vent field in the Ryukyu region in southwestern Japan, at a depth of 628 m. Lebbeus parvirostris sp. nov. is morphologically similar to L. microceros (Krøyer, 1841), L. mundus Jensen, 2006, L. saldanhae (Barnard, 1947), L. schrencki (Bražnikov, 1907), L. spongiaris Komai, 2001, and L. tosaensis Hanamura & Abe, 2003, but differs from all of them in the lack of a pterygostomial tooth on the carapace in the female. Other diagnostic characters useful in differentiating the new species from the aforementioned close relatives are also discussed. Genetic analyses using sequences of two mitochondrial markers, including cytochrome c oxidase subunit I (COI) and 16S rRNA, are also presented to provide preliminary support for the status of the new species. Lebbeus parvirostris sp. nov. is the second representative of Lebbeus known from active hydrothermal vents in the Ryukyu region. <br /> <br /> Komai T*, Chen C* (2024). A new species of the thorid shrimp genus Lebbeus White, 1847 (Decapoda: Caridea) from the Amami Rift hydrothermal vent field in the Ryukyu region, Japan. Zootaxa, 5523(2): 254-268. DOI: 10.11646/zootaxa.5523.2.7<br /> PDF: https://www.researchgate.net/publication/384904322_A_new_species_of_the_thorid_shrimp_genus_Lebbeus_White_1847_Decapoda_Caridea_from_the_Amami_Rift_hydrothermal_vent_field_in_the_Ryukyu_region_Japan
We revisited Mokuyo Seamount deep-sea vent field on the Izu-Ogasawara Arc 30 years after its discovery, finding significant changes in hydrothermal activities. Our survey also updated its faunal list from three to 18 species! Link: https://doi.org/10.1111/1440-1703.12528<br /> <br /> Abstract: <br /> Deep-sea hydrothermal vents are biological hotspots driven by microbial chemosynthetic primary production and characterized by a high proportion of endemic, specially adapted species. Vent communities can be unstable depending on the geological setting, as the underlying geofluid supply may change in location and chemical composition over a decadal timescale. Although the Izu-Ogasawara Arc in Japan is home to many vent fields within an Ecologically or Biologically Significant Marine Area (EBSA), no observations of decadal changes have been conducted. On Mokuyo Seamount, venting was first confirmed by several submersible dives between 1990 and 1993, but only fragmentary information has been published on its biodiversity. Here, we revisited Mokuyo on two dives between 2021 and 2024, three decades after its discovery. We found changes in venting activities, with the fluid supply on the northern caldera wall almost completely waned, while the northeastern face of the central cone has become increasingly active. The northwestern ridge of the central cone was covered in a dense white plume, under which xenophyophores (giant protists) thrive. The first comprehensive faunal sampling at Mokuyo greatly updated the faunal list from three to 18 species. Our results suggest vent communities on the Izu-Ogasawara Arc shift on a decadal scale, providing key baseline data for future conservation planning of the EBSA. <br /> <br /> Chen C*, Methou P, Yamamoto D, Kayamori M, Nomaki H (2024). There and there again: Hydrothermal vent communities at Mokuyo Seamount, 30 years apart. Ecological Research, 39: Early View. DOI: 10.1111/1440-1703.12528<br /> https://www.researchgate.net/publication/384395462_There_and_there_again_Hydrothermal_vent_communities_at_Mokuyo_Seamount_30_years_apart
Our new paper in PEPS measured natural radiocarbon (14C) in cold seep clams and tubeworms to reveal their carbon sources! ~9% of carbon in clams come from seep fluid vs >40% for tubeworms, likely due to different CO2 uptake mechanisms. OPEN ACCESS, read for FREE here: https://doi.org/10.1186/s40645-024-00648-5<br /> <br /> Abstract:<br /> Cold seeps, where geofluids containing methane and other hydrocarbons originating from the subseafloor seeps through the sediment surface, play important roles in the elemental and energy flux between sediment and seawater. These seep sites often harbor communities of endemic animals supported by chemolithoautotrophic bacteria, either through symbiosis or feeding. Despite these animal communities being intensively studied since their discovery in the 1980’s, the contribution of carbon from seep fluid to symbiotic microbes and subsequently host animals remains unclear. Here, we used natural-abundance radiocarbon to discern carbon sources: the ambient bottom water or the seeping geofluid. The 14C concentrations were measured for vesicomyid clams, a parasitic calamyzine polychaete, and a siboglinid tubeworm species from four different cold seep sites around Japan. We found most vesicomyid clams exhibiting 14C concentrations slightly lower than that of the ambient bottom water, suggesting up to 9% of C for chemolithoautotrophy originates from geofluid DIC. The different extent of fluid contribution across species may be explained by different routes to incorporate DIC and/or different DIC concentrations in the geofluid at each seep site. Stable nitrogen isotopic compositions further suggested N incorporation from geofluids in these clams, where the burrowing depth may be a key factor in determining their δ15N values. The siboglinid tubeworm showed a clear dependency for geofluid DIC, with a contribution of >40%. Our results demonstrate the effectiveness of 14C analyses for elucidating the nutritional ecology of cold seep animals and their symbionts, as was previously shown for hydrothermal vent ecosystems.<br /> <br /> Nomaki H*, Kojima S, Miyairi Y, Yokoyama Y, Chen C (2024). Natural 14C abundances and stable isotopes suggest discrete uptake routes for carbon and nitrogen in cold seep animals. Progress in Earth and Planetary Science, 11: 51. DOI: 10.1186/s40645-024-00648-5
We collaborated with Sony to develop a new method to evaluate organismal behaviour and particle dynamics using the Event‐based Vision Sensor (EVS)! By focusing on brightness shifts, EVS is a new type of camera sensor that can reach 10,000 fps even under low-light. Read this OPEN ACCESS paper for free: https://doi.org/10.1002/ece3.70150<br /> <br /> Abstract:<br /> The Event-based Vision Sensor (EVS) is a bio-inspired sensor that captures detailed motions of objects, aiming to become the ‘eyes’ of machines like self-driving cars. Compared to conventional frame-based image sensors, the EVS has an extremely fast motion capture equivalent to 10,000-fps even with standard optical settings, plus high dynamic ranges for brightness and also lower consumption of memory and energy. Here, we developed 22 characteristic features for analysing the motions of aquatic particles from the EVS raw data and tested the applicability of the EVS in analysing plankton behaviour. Laboratory cultures of six species of zooplankton and phytoplankton were observed, confirming species-specific motion periodicities up to 41 Hz. We applied machine learning to automatically classify particles into four categories of zooplankton and passive particles, achieving an accuracy up to 86%. At the in situ deployment of the EVS at the bottom of Lake Biwa, several particles exhibiting distinct cumulative trajectory with periodicities in their motion (up to 16 Hz) were identified, suggesting that they were living organisms with rhythmic behaviour. We also used the EVS in the deep sea, observing particles with active motion and periodicities over 40 Hz. Our application of the EVS, especially focusing on its millisecond-scale temporal resolution and wide dynamic range, provides a new avenue to investigate organismal behaviour characterised by rapid and periodical motions. The EVS will likely be applicable in the near future for the automated monitoring of plankton behaviour by edge computing on autonomous floats, as well as quantifying rapid cellular-level activities under microscopy.<br /> <br /> Takatsuka S# / Miyamoto N#, Sato H, Morino Y, Kurita Y, Yabuki A, Chen C, Kawagucci S* (2024). Milli-second-scale behaviours of plankton quantified in vitro and in situ using the Event-based Vision Sensor. Ecology and Evolution, 14: e70150. DOI: 10.1002/ece3.70150 [Preprint available on bioRxiv, DOI: 10.1101/2023.01.11.523686]
New Species Alert! 1 new genus, 11 new species, and 1 redescription/reinstatement, to be exact. Including two deep-sea hydrothermal vent gastropods contributed by myself and collaborators -- Lepetodrilus marianae and Shinkailepas gigas. The paper is OPEN ACCESS: https://bdj.pensoft.net/article/128431/<br /> <br /> The Ocean Species Discoveries (OSD) is a new publication format from @oceanspecies of concise and high-quality species descriptions that aims to accelerate the pace at which new marine invertebrate species are described and published. The species in the OSD originate from all over the globe, at depths from 5.2 to 7081 meters and were contributed by 25 researchers from 10 countries.<br /> <br /> Reducing the time it takes to get from discovering a new animal to a public species description is crucial in our era of increasing biodiversity loss. A scientific name and description help us better understand and protect animals like the deep-sea snails Lepetodrilus marianae and Shinkailepas gigas.<br /> <br /> Learn more about the OSD, the 13 new marine invertebrate taxa included, and how it helps accelerate the discovery of more species in our OPEN ACCESS paper: https://bdj.pensoft.net/article/128431/<br /> <br /> #OceanSpeciesDiscoveries<br /> <br /> Senckenberg Ocean Species Alliance (SOSA), Brandt A, Chen C, Engel L, Esquete P, Horton T, Jażdżewska AM, Johannsen N, Kaiser S, Kihara TC, Knauber H, Kniesz K, Landschoff J, Lörz A-N, Machado FM, Martínez-Muñoz CA, Riehl T*, Serpell-Stevens A, Sigwart JD, Tandberg A-H, Tato R, Tsuda M, Vončina K, Watanabe HK, Wenz C, Williams JD (2024). Ocean Species Discoveries 1-12 – A primer for accelerating marine invertebrate taxonomy. Biodiversity Data Journal, 12: e128431. DOI: 10.3897/BDJ.12.e128431
We sequenced a draft genome of the deep-sea volutid snail Fulgoraria chinoi Bail, 2000, the first genomic data for superfamily Volutoidea -- and used it to improve the existing Neogastropoda phylogeny! Out now in Zoologica Scripta: https://doi.org/10.1111/zsc.12687<br /> <br /> Abstract: <br /> Neogastropoda is a large order of predominantly marine gastropod molluscs, typically predatory or parasitic on other animals. It includes over 16,000 species representing a large post-Cretaceous radiation, but the internal phylogenetic relationships of contained taxa are far from resolved, with inconsistent results from nuclear genes, mitogenomes, and morphology. One major issue in reconstructing the molecular phylogeny is the lack of high-quality sequences for early-diverging families and superfamilies such as Volutidae (Volutoidea). Here, we examine the superfamily-level phylogenetic relationships in Neogastropoda, aided by newly sequenced draft genome and mitogenome of the volutid snail Fulgoraria chinoi from the deep sea off Japan. The genome of F. chinoi is relatively large at 1.54&amp;#x02009;Gb but exhibits low genome heterozygosity; over 54% of this genome constitutes of repeat contents, and we find evidence for active insertion of transposable elements, particularly LINEs and SINEs. A total of 50,792 protein-coding genes (PCGs) were predicted from the nuclear genome, and a circular mitogenome was also assembled and annotated. Our phylogenetic analyses using mitogenomes recovered each neogastropod superfamily as monophyletic, though also revealed inconsistent phylogenetic signals within superfamilies. Phylogenetic reconstructions using the PCGs resulted in a robust tree from different models and data matrices, recovering Volutoidea as the earliest diverging superfamily (among those for which comparable data is available) within a monophyletic Neogastropoda. Dated phylogenetic analysis revealed an early Cretaceous radiation of Neogastropoda, congruent with the fossil record. Our study provides a robust internal evolutionary framework for the speciose but genomically undersampled Neogastropoda, and expands the available genomic resources for this order. Genomic data for key missing lineages such as Mitroidea, Olivoidea, and Cancellariidae are much sought in the future for a full understanding of Neogastropoda evolution.<br /> <br /> Wang H, He X, Chen C, Gao K, Dai Y, Sun J* (2024). New insights into the phylogeny of Neogastropoda aided by draft genome sequencing of the volutid snail Fulgoraria chinoi. Zoologica Scripta, Early View. DOI: 10.1111/zsc.12687
Our paper in Marine Ecology Progress Series presents new data on alvinocaridid shrimps from deep-sea hot vents and cold seeps off Aotearoa / New Zealand, revealing their genetic connectivity and isotopic niches! We also name a new species and synonymise two names. <br /> <br /> Abstract: <br /> Chemosynthetic ecosystems off Aotearoa/New Zealand comprise both hydrothermal vents on the Kermadec Arc and methane seeps on the Hikurangi Margin which host rich communities of specialized fauna including 4 alvinocaridid shrimp species. The systematic positions of these New Zealand alvinocaridid shrimps have not been studied using genetic tools and little is known about their habitat use and feeding habits. Here, we re-evaluate the taxonomy of alvinocaridid shrimps from New Zealand using genetic barcoding and characterize their connectivity and isotopic niches across 8 localities. We describe a new species, Alvinocaris webberi sp. nov., previously confused with A. longirostris. We also show that A. alexander and A. chelys are junior synonyms of A. dissimilis, revealing a high genetic connectivity across hydrothermal vents and methane seeps from Japan to New Zealand, greatly extending its range. Finally, we find clear niche separation in co-occurring alvinocaridid shrimps, suggesting different diets and/or habitat use. Nevertheless, all species rely on chemosynthetic resources, regardless of the habitat depth, which ranges from 380 to 1650 m. <br /> <br /> Methou P*, Ogawa NO, Nomaki H, Ohkouchi N, Chen C, Schnabel K (2024). Genetic connectivity and isotopic niches of alvinocaridid shrimps from chemosynthetic habitats in Aotearoa/New Zealand, with a new Alvinocaris species. Marine Ecology Progress Series, 739: 85-109. DOI: 10.3354/meps14611
Our paper in Zoosystematics and Evolution names a new giant worm-mollusc from deep-sea cold seeps in South China Sea! Chaetoderma shenloong is the 2nd largest member of class Caudofoveata and the first aplacophoran mollusc associated with cold seeps! Its name was inspired by the magical dragon in the manga Dragon Ball. The paper is OPEN ACCESS and free to read: https://doi.org/10.3897/zse.100.125409<br /> <br /> Abstract: <br /> Caudofoveata is a class of worm-like molluscs (aplacophorans) that typically have an infaunal lifestyle, burrowing in soft bottoms in a wide range of marine habitats from shallow to deep waters. Here, we describe a very large new species of caudofoveate from South China Sea methane seeps growing up to 154 mm in length: Chaetoderma shenloong sp. nov. It is the first caudofoveate to be named from a chemosynthetic ecosystem and the first aplacophoran mollusc associated with seeps. Our new species stands out from other Pacific Chaetoderma species by its large size, a wide body relative to its length, a barely sclerotised radula, and the presence of isosceles-triangular sclerites. Phylogenetic reconstruction using the mitochondrial cytochrome c oxidase subunit I (COI) gene placed it within a paraphyletic clade comprising Chaetodermatidae and Limifossoridae, in line with a previous phylogenetic analysis. This also revealed that C. shenloong sp. nov. is conspecific with a Chaetoderma sp. whose whole genome was recently sequenced and assembled but remained undescribed until now. The most closely related species with an available COI sequence was C. felderi, the largest caudofoveate species recorded. Our discovery suggests caudofoveates may be present in other seeps globally but so far neglected; a potential example is C. felderi from the Gulf of Mexico, where seeps are abundant but whose exact habitat remains unclear. <br /> <br /> Chen C# / Liu X#, Gu X, Qiu J-W, J Sun* (2024). Integrative taxonomy of a new giant deep-sea caudofoveate from South China Sea cold seeps. Zoosystematics and Evolution, 100(3): 841-850. DOI: https://doi.org/10.3897/zse.100.125409
We published a commentary on a paper by Mao et al. (2024) in Frontiers in Marine Science., pointing out a highly problematic misidentification of their main study species -- a deep-sea hot vent barnacle. OPEN ACCESS: https://doi.org/10.3389/fmars.2023.1269411<br /> <br /> Abstract: <br /> Mao et al. (2024) recently published an article comparing the mitochondrial genome and transcriptome of the deep-sea hydrothermal vent barnacle Vulcanolepas fijiensis and the relatively shallower barnacle Scalpellum stearnsi (contradictory to the title, no new species was described). This paper concluded that the mitogenomes and key genes found in the transcriptomic analysis were subjected to positive selection related to high-temperature and high-pressure conditions, allowing V. fijiensis to adapt to the deep-sea environment. However, the neolepadid hydrothermal vent barnacle used in their study was misidentified and actually represents a different species, Neolepas marisindica. We present our evidence and reasoning for this below. Although the main conclusions presented by Mao et al. (2024) still stand because N. marisindica is also a deep-sea vent species, their misidentification has connotations on the context, interpretation, and of course future use of their data. <br /> <br /> Chan BKK, Watanabe-Kayama H, Chen C* (2024). Commentary: “Comparative omics analysis of a new deep-sea barnacle species (Cirripedia, Scalpellomorpha) and shallow-water barnacle species provides insights into deep-sea adaptation”. Frontiers in Marine Science, 11: 1374419. DOI: 10.3389/fmars.2024.1374419
We describe and name three new neomphaline limpet species from deep-sea hot vents of the SW Pacific in a new paper in the Zoological Journal of the Linnean Society! Read for FREE: https://bit.ly/CHUBACARC2<br /> <br /> Abstract: <br /> Neomphaloidean gastropods are endemic to chemosynthesis-based ecosystems ranging from hot vents to organic falls, and their diversity and evolutionary history remain poorly understood. In the southwestern Pacific, deep-sea hydrothermal vents on back-arc basins and volcanic arcs are found in three geographically secluded regions: a western region around Manus Basin, an eastern region around North Fiji and Lau Basins, and the intermediate Woodlark Basin where active venting was confirmed only recently, on the 2019 R/V L’Atalante CHUBACARC expedition. Although various lineages of neomphaloidean snails have been detected, typically restricted to one of the three regions, some of these have remained without names. Here, we use integrative taxonomy to describe three of these species: the neomphalid Symmetromphalus mithril sp. nov. from Woodlark Basin and the peltospirids Symmetriapelta becki sp. nov. from the eastern region and Symmetriapelta radiata sp. nov. from Woodlark Basin. A combination of shell sculpture and radular characters allow the morphological separation of these new species from their described congeners. A molecular phylogeny reconstructed from 570 bp of the mitochondrial cytochrome c oxidase subunit I gene confirmed the placement of the three new species in their respective genera and the superfamily Neomphaloidea. The finding of these new gastropods, particularly the ones from the Woodlark Basin, provides insights and implications on the historical role of Woodlark as a dispersing centre, in addition to highlighting the uniqueness of the Woodlark faunal community.<br /> <br /> Chen C*, Poitrimol C, Matabos M (2024). Integrative taxonomy of new neomphaloidean gastropods from deep-sea hot vents of the southwestern Pacific. Zoological Journal of the Linnean Society, Advance Access: zlae064. DOI: 10.1093/zoolinnean/zlae064<br /> PDF: https://www.researchgate.net/publication/380818411_Integrative_taxonomy_of_new_neomphaloidean_gastropods_from_deep-sea_hot_vents_of_the_southwestern_Pacific
My serendipitous (re)discovery of the "Living Fossil" monoplacophoran mollusc Neopilina galatheae off Galápagos is now out in Journal of Molluscan Studies! This is the first bona fide specimen of this legendary mollusc collected since 1959. The paper is OPEN ACCESS: https://doi.org/10.1093/mollus/eyae014<br /> <br /> Abstract: <br /> Monoplacophoran molluscs have been dubbed ‘living fossils’ due to their absence in the fossil record for about 375 million years, until Neopilina galatheae Lemche, 1957 was trawled off Costa Rica in 1952. Since then, over 35 species of living monoplacophorans have been discovered. Nevertheless, in situ observations of these rare deep-sea animals remain scant. Here, I observed and collected an intact specimen of N. galatheae using a remotely operated vehicle from 2460 m deep on the Eastern Galápagos Spreading Center. The animal was found attached to the glassy surface of solidified basalt lava flow, and no feeding trails were found near the animal. Such hard substrate is in contrast with previous records that were trawled on sand and mud, suggesting Neopilina can be found on a wide range of substrates. This is the first time this species was collected since 1959, and represents a southeast range extension of about 1000 km for the species. <br /> <br /> Chen C* (2024). In situ observation and range extension of the first discovered monoplacophoran Neopilina galatheae. Journal of Molluscan Studies, 90(2): eyae014. DOI: 10.1093/mollus/eyae014 [Preprint available on bioRxiv, DOI: 10.1101/2023.11.08.566290]
Our new paper in Marine Ecology reports the animal community in the serpentinisation-hosted cold seep on the South Chamorro Seamount, Mariana Forearc. We also found evidence that scientific drilling wiped out a lush community there in 2001 with no signs of recovery 22 years later! OPEN ACCESS: https://doi.org/10.1111/maec.12808<br /> <br /> Abstract:<br /> Deep-sea chemosynthetic ecosystems are ‘oases’ of life powered by reducing geofluids, of which serpentinite-hosted seeps are among the least studied. South Chamorro Seamount, a serpentine mud volcano on the Mariana Arc, has been known to host chemosynthesis-based assemblages since 1996, but no detailed information on the fauna was published. Here, we revisited South Chamorro to characterise its biodiversity. We located two regions of chemosynthetic communities dominated by bathymodioline mussels, vesicomyid clams, and chaetopterid parchment worms: one on the northwestern flank (‘Fryer Site’) and one on the southern summit (‘Summit Site’). We sampled a total of 20 species including 13 molluscs, five annelids, and two crustaceans – all present on the more active Summit Site but only a subset being found at Fryer Site. A mussel bed surrounding the Fryer Site was drilled by the Ocean Drilling Program in 2001 resulting in six holes, the deepest being 266 m (Hole 1200C). Cuttings ~50 cm deep still cover an approximately 60 m radius around Hole 1200C even 22 years later, and there is no sign of recovery. Low geofluid supply in serpentinite-hosted seamounts may not allow decadal recovery of animal colonies, unlike a previous drilling site in an Okinawa Trough vent.<br /> <br /> Chen C*, Watanabe HK, Sawada H, Iwamoto H, Takai K (2024). Serpentinite-hosted chemosynthetic community of South Chamorro Seamount, Mariana Forearc. Marine Ecology, Early View. DOI: 10.1111/maec.12808
We used natural-abundance radiocarbon (Δ14C) and habitat water temperature to reveal carbon sources of deep-sea hydrothermal vent animals! Closer to vent orifice means more carbon (up to 74.8%) from vent fluid CO2 -- unless one uses methane. Just out in Limnology and Oceanography, OPEN ACCESS: https://doi.org/10.1002/lno.12570<br /> <br /> Abstract: <br /> Deep-sea hydrothermal vents host exceptional ecosystems with lush animal communities primarily relying on organic matter (OM) produced by chemoautotrophic microbes. Though energy sources and food webs at vents have been extensively studied, the exact carbon sources of chemosynthetic primary production, such as methane (CH4) and carbon dioxide (CO2) in the vent fluid or bottom water, have not been elucidated quantitatively across spatial scales. Here, we investigate carbon and nitrogen sources of 12 vent animal species at the Iheya North field, Okinawa Trough inhabiting different distances from the central venting area and with various feeding ecologies using natural-abundance radiocarbon (Δ14C) in combination with conventional stable carbon and nitrogen isotope ratios (δ13C and δ15N). Our results show that generally, animals living closer to vent orifices were more depleted in 14C, indicating they assimilate more carbon from vent fluid CO2. Those relying on methanotrophs, however, exhibited low Δ14C values regardless of distance due to the lack of methane in the non-vent-influenced bottom water. Organisms with low Δ14C values also tend to exhibit low δ15N values, implying NH4+ assimilation into biomass in environments with high NH4+ concentrations. Our results demonstrate that 14C can clearly distinguish between chemoautotrophically fixed carbon originating from the vent fluid and detrital OM derived from surface primary production, and also discriminate between CO2- and CH4-based chemoautotrophy. Although vent animals rely on vent fluid energetically, our results highlight that the dependency on vent fluids as carbon source varies greatly depending on habitat, as well as carbon fixation pathways of microbial primary producers.<br /> <br /> Nomaki H*, Chen C, Ogawa NO, Miyairi Y, Ohkouchi N, Makabe A, Kawagucci S, Yokoyama Y, Shimanaga M (2024). Elucidating carbon sources of hydrothermal vent animals using natural 14C abundances and habitat water temperature. Limnology and Oceanography, Early View. DOI: 10.1002/lno.12570
We discovered a brand new deep-sea hydrothermal vent field in Japan, on the Amami Rift where Okinawa Trough and Ryukyu Arc meet! We found 29 animal species, including 19 vent specialists. Out now in Journal of the Marine Biological Association of the United Kingdom: https://doi.org/10.1017/S0025315424000304<br /> <br /> Abstract:<br /> Deep-sea hydrothermal vents host chemosynthesis-based ecosystems inhabited chiefly by specially adapted animals that do not live anywhere else, and depth has been shown to be a major driver of species composition at vents around Japan. Though the Ryukyu region in southern Japan is home to many hot vents, only two – Minami-Ensei Knoll and Yoron Hole – have been found shallower than 1000 m. Here, we report the discovery of a new vent field on the Amami Rift northwest off Amami Ōshima at 630 m deep. A total of 29 macrofaunal species were recorded from Amami Rift, including 19 vent specialists. Comparison of species composition across the three shallow Ryukyu vents revealed only three shared species, highlighting that all three display distinct community structure. Amami Rift exhibits distinct zonation patterns and is generally more similar to Minami-Ensei than Yoron Hole, but the presence of key taxa such as the sulphide worm Paralvinella and the mussel ‘Bathymodiolus’ platifrons as well as the absence of the symbiotic squat lobster Shinkaia and the limpet Lepetodrilus exemplify its difference with Minami-Ensei. Furthermore, the non-vent specific predators seen in these two sites were completely different. Overall, the Amami Rift vent field can be considered a shallow vent with a unique set of fauna, warranting future research on the mechanisms shaping disparate macrofaunal diversity between nearby shallow vents such as Amami Rift and Minami-Ensei. The unusual geological setting of Amami Rift at the converging point of Okinawa Trough and Ryukyu Arc may influence fluid chemistry to drive such differences.<br /> <br /> Chen C*, Hookabe N, Komatsu H (2024). Macrofaunal community of a new hot vent field on the Amami Rift. Journal of the Marine Biological Association of the United Kingdom, 104: e39. DOI: 10.1017/S0025315424000304<br /> <br /> PDF: https://www.researchgate.net/publication/379573502_Faunal_community_of_a_new_hot_vent_field_on_the_Amami_Rift
We revised the generic placement of two hadal thyasirid bivalves from cold seeps in the Japan Trench, including naming a new genus for Tartarothyas hadalis (new combination) -- the deepest known bivalve with chemosynthetic symbiosis at over 7400 m depth. This paper is OPEN ACCESS and freely available here: https://doi.org/10.61733/jconch/1405<br /> <br /> Abstract:<br /> The hadal bivalves from the Japan Trench originally described as Maorithyas hadalis and Parathyasira kaireiae are reassigned to the genera Tartarothyas n. gen. and Spinaxinus, respectively. The shell, anatomy, and fine structure of the ctenidia are described, and based on these the new genus Tartarothyas is introduced. Both species have modified ctenidia to host chemosymbiotic bacteria; those of Tartarothyas n. gen. is partly tubular in structure, whereas those of Spinaxinus is of fleshy lamellae.<br /> <br /> Oliver PG*, Chen C (2024). Revision of the generic placement of two hadal bivalves (Bivalvia: Thyasiridae) from the Japan Trench with the introduction of a new genus, Tartarothyas. Journal of Conchology, 45(1): 35-50. DOI: 10.61733/jconch/1405
We updated the list of animals inhabiting Galápagos Rift hydrothermal vents based on new findings from our 2023 Schmidt Ocean Institute Galápagos expedition (+literature review) -- adding 15 new records to make a total of 92 species! We also discovered a new vent field which we named "Tortugas". The paper is OPEN ACCESS in Marine Biodiversity: https://doi.org/10.1007/s12526-024-01408-w<br /> <br /> Abstract: <br /> The sighting of giant bivalves and tubeworms at the Rose Garden vent field on the Galápagos Rift in 1977 marked the discovery of hydrothermal vents, a turning point for modern biology. The following decade saw a flurry of taxonomic descriptions of vent endemic species from the first vents. With the finding of high-temperature “black smokers” on the East Pacific Rise, exploration shifted away from Galápagos. A faunal list of Galápagos vents with 65 species was published in 1991, then updated to 74 species in 2006. Since then, few expeditions returned to the Galápagos Rift. Here, we revisited several Galápagos vents including recently confirmed high-temperature sites and inactive sulfide mounds. From our collecting efforts and observations, as well as revisions from the literature, we update the faunal list to 92 species including 15 new records, restricted to obvious vent associates. Accurate regional faunal lists are important for understanding the biogeography of vent fauna, and our list will also be valuable for setting management strategies.<br /> <br /> Chen C*, Jamieson JW, Tunnicliffe V (2024). Hydrothermal vent fauna of the Galápagos Rift: updated species list with new records. Marine Biodiversity, 54: 16. DOI: 10.1007/s12526-024-01408-w [Preprint available on bioRxiv, DOI: 10.1101/2023.11.28.568903]
In a Zootaxa paper, we revised the hot vent shrimp genus Rimicaris, synonymising a number of genera with it in order to rectify the long-standing issue of its paraphyly. We also described a new species -- Rimicaris cambonae, named after Marie-Anne Cambon from IFREMER in France! Link: https://mapress.com/zt/article/view/zootaxa.5406.4.1<br /> <br /> Abstract: <br /> A new species of alvinocaridid shrimp is reported, from the Northwest Eifuku hydrothermal vent field at 1619–1667 m depth on the Mariana Arc. A comprehensive phylogenetic reconstruction of Alvinocarididae based on the mitochondrial cytochrome c oxidase subunit I (COI) gene including this new species reveals the paraphyly of the genus Rimicaris Williams & Rona, 1986 with four other genera—Alvinocaridinides, Manuscaris, Opaepele, and Shinkaicaris—nested within it. We re-examine material of these four problematic genera, and synonymise them under Rimicaris whose diagnosis has been amended, in order to maintain a monophyletic Rimicaris. Our new species, Rimicaris cambonae sp. nov. is genetically close to Rimicaris loihi (Williams & Dobbs, 1995) comb. nov. (previously Opaepele loihi) with which it co-occurs, but can be morphologically distinguished by the less elevated dorsal surface of the rostrum, this being devoid of a median carina, a stronger pterygostomial tooth on the carapace, and a blunt rather than acuminate proximolateral process on the antennular stylocerite. Species previously assigned to the above listed, synonymized genera are also discussed, with new material examined for three key species: R. loihi, R. acuminata, and R. leurokolos. Further, Alvinocaridinides formosa Komai & Chan, 2010 and Manuscaris liui Wang & Sha, 2016 are synonymized under Rimicaris leurokolos (Kikuchi & Hashimoto, 2000) comb. nov. and R. acuminata (Komai & Tsuchida, 2015) comb. nov., respectively. Revised diagnoses are presented for R. loihi, R. acuminata, and R. leurokolos. After the present revision revision, Rimicaris now consists of 15 species.<br /> <br /> Methou P*, Chen C, Komai T (2024). Revision of the alvinocaridid shrimp genus Rimicaris Williams & Rona, 1986 (Decapoda: Caridea) with description of a new species from the Mariana Arc hydrothermal vents. Zootaxa, 5406(4): 501-518. DOI: 10.11646/zootaxa.5406.4.1 PDF: https://www.researchgate.net/publication/378040507_Revision_of_the_alvinocaridid_shrimp_genus_Rimicaris_Williams_Rona_1986_Decapoda_Caridea_with_description_of_a_new_species_from_the_Mariana_Arc_hydrothermal_vents
We used amino acid nitrogen isotopes to clearly show that two cold seep copepods gain nutrition from their host animals, in the first application of this technique to parasite-host pairs in deep-sea chemosynthetic ecosystems. Out now in Marine Ecology Progress Series: https://doi.org/10.3354/meps14503<br /> <br /> Abstract: <br /> Deep-sea chemosynthetic ecosystems harbour high biomass centred around animals with chemoautotrophic symbionts. Despite being intensively studied over the last 4 decades, microscopic animals associated with and/or parasitic on dominating holobionts remain understudied. Here, we combine bulk tissue isotope analysis for carbon and nitrogen and compound-specific isotope analysis of amino acids (CSIA-AA) for nitrogen to elucidate the relationship between 2 copepod-host pairs from the Off Hatsushima hydrothermal seep in Sagami Bay, Japan: the vesicomyid clam Phreagena okutanii and Hyphalion sagamiense living on its mantle, and the tubeworm Lamellibrachia columna and Dirivultus kaiko found on its plume. Bulk tissue isotope analyses found overall large variations in δ13C and δ15N values across both associations, and did not allow conclusions on the trophic relationship between each pair. In contrast, CSIA-AA for Phreagena-Hyphalion clearly showed trophic positions (TPGlu/Phe) increasing from gill (symbiont) to adductor muscle (host tissue) to H. sagamiense. In the case of Lamellibrachia-Dirivultus, a similar increase in TPGlu/Phe was found from the plume to D. kaiko. These results show that both H. sagamiense and D. kaiko are nutritionally dependent on their respective hosts and therefore should be considered parasites despite being from copepod families that are typically not recognised as parasitic. Our CSIA-AA results represent the first use of this technique to document host-parasite relationships in chemosynthetic ecosystems. Understanding the role of parasites is of great importance in reconstructing energy flow in ecosystems, and our results underscore the promising nature of CSIA-AA in revealing their otherwise hidden relationships. <br /> <br /> Ishikawa NF*, Chen C, Hashimoto R, Ogawa NO, Uyeno D, Nomaki H (2024). Amino acid nitrogen isotopic compositions show seep copepods gain nutrition from host animals. Marine Ecology Progress Series, 727: 81-90. DOI: 10.3354/meps14503<br /> PDF: https://www.researchgate.net/publication/376659302_Amino_acid_nitrogen_isotopic_compositions_show_seep_copepods_gain_nutrition_from_host_animals
We discovered two new deep-sea snails from inactive vent chimneys on the East Pacific Rise -- described as Melanodrymia laurelin and M. telperion, named after the Two Trees of Valinor in J.R.R. Tolkien's legendarium! Link to the paper: https://www.tandfonline.com/eprint/NK6DIQX9QHTYRUAYHMAM/full?target=10.1080/14772000.2023.2294014<br /> <br /> Abstract:<br /> Since their discovery in 1977, animals specialized to life in active deep-sea hydrothermal vents have been the focus of many studies. Inactive spires in the vent periphery, however, have received little attention. Recent shifts of deep-sea mining interests from active vents to inactive sulphide deposits have led to an urgent need to characterize the inactive vent fauna. Here, we report two new species of the vent-endemic genus Melanodrymia that are apparently specific to surfaces of inactive sulphides on the East Pacific Rise. Melanodrymia laurelin sp. nov. and M. telperion sp. nov. are easily distinguished from other congeners by shell shape and sculpture; their standings as distinct species are supported by molecular analyses using the mitochondrial cytochrome c oxidase subunit I (COI) gene. They were collected together with numerous specimens of M. galeronae, another species originally described some distance away from active vents. Phylogenetic reconstruction indicates Melanodrymia species living in active vents likely evolved from ancestors specializing in inactive spires, and in turn from sunken wood. Our findings add to the growing evidence that inactive sulphides host unique species, bolstering the need to better understand these systems before any anthropogenic exploitation takes place.<br /> <br /> Chen C*, Y Li, Sun J, Beaulieu SE, Mullineaux LS (2024). Two new melanodrymiid snails from the East Pacific Rise indicate the potential role of inactive vents as evolutionary stepping-stones. Systematics and Biodiversity, 22(1): 2294014. PDF: https://www.researchgate.net/publication/377577317_Two_new_melanodrymiid_snails_from_the_East_Pacific_Rise_indicate_the_potential_role_of_inactive_vents_as_evolutionary_stepping-stones
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