Author: Chong Chen

Strange ‘stacking’ behaviour seen in vent snails

A short paper describing the strange behaviour of forming hanging ‘stacks’ exhibited by the vent snail genus Gigantopelta has been published in the journal Plankton and Benthos Research! This behaviour is probably related to reproduction. The paper is open access and available for view here: https://doi.org/10.3800/pbr.13.25“Mating stacks” have been widely documented in calyptraeid slipper limpets, which are protandric and exhibit sequential hermaphroditism. Gigantopelta is a genus of peltospirid snails endemic to deep-sea hydrothermal vents containing two species, one distributed on the East Scotia Ridge in the Southern Ocean and another on the Southwest Indian Ridge in the Indian Ocean. Here, we report the observation that both species form extensive (often >15 individuals) “snail chains”. These chains are potentially analogous to ‘mating stacks’ of calyptraeids, or alternatively, maybe a behaviour to facilitate spermatophore transfer. Both Gigantopelta species apparently have separate sexes and are sexually mature at a small size. However, it remains unclear whether they undergo sex change during their life.

Snail chains formed by Gigantopelta chessoia (left) and G. aegis (right)

  • Chen C*, Marsh L, Copley JT (2018). Is it sex in chains? Potential mating stacks in deep-sea hydrothermal vent snails. Plankton and Benthos Research, 13(1): 25-27.

Three new muricids from Western Pacific

A co-authored paper describing three new muricid gastropods from the western Pacific, has been published in the peer-reviewed journal The Nautilus!

Of the three muricids described in this paper, one is a Chicomurex from the Philippines and Kwajalein Atoll – Chicomurex excelsus Houart, Moe & Chen, 2017. With live-taken specimens known from 150~200 m deep (dead shells have been collected as shallow as 60 m), this species is characterised by a long siphonal canal which carries intricately webbed fronds but lacks in strong recurved spines. This unique siphonal canal sculpture, as well as a lower spire and a more angular final teleoconch whorl, separate it from C. gloriosus (Shikama, 1977), the closest congener which it co-occurs with.

Chicomurex excelsus Houart, Moe & Chen, 2017, Holotype (7-9) and Paratype CM (10-11)

The other two species described are from Fiji and in the genus Chicoreus (Triplex) – Chicoreus kaitomoei Houart, Moe & Chen, 2017 and Chicoreus aquilus Houart, Moe & Chen, 2017, both being small-sized (<40 mm) for the genus. Although C. kaitomoei has been confused with C. aculeatus (Lamarck, 1822) and C. nobilis Shikama, 1977, these two species have multispiral protoconchs implying planktotrophic development unlike C. kaitomoei which has a pausispiral protoconch implying lecithotrophic development. The teleoconch of C. kaitomoei is by very short variceal spines (except those from P1-3) and a siphonal canal with three abapically bent spines concentrated on the anterior half. This species inhabit shallow waters around 9~30 m deep and is named after Kaito Moe, son of Chris Moe.

Chicomurex kaitomoei Houart, Moe & Chen, 2017, Holotype (21-23) and Paratype CM (24-25)

Finally, C. aquilus which is only known from the holotype taken from 31~40 m deep in Fiji, is a highly distinctive species closest to C. rubescens (Broderip, 1833) and a few other species belonging to Chicoreus “group 2” (sensu Houart, 1992) but easily distinguished by differences in varice and aperture characteristics.

Chicoreus aquilus Houart, Moe & Chen, 2017, Holotype

Houart R*, Moe C, Chen C (2017). Description of three new muricids (Gastropoda: Muricidae: Muricinae) from the Philippines and Fiji. The Nautilus, 131(4): 207-216.

Unveiling the “Yokosuka” hydrothermal vent site

A new paper on the discovery of a new hydrothermal vent field has been published in the peer-reviewed Open Access journal Royal Society Open Science! I acted as the corresponding author. Read for free here: http://rsos.royalsocietypublishing.org/content/4/12/171570

We report, in this paper, the discovery of the “Yokosuka” site – the deepest and hottest hydrothermal vent field in the Okinawa Trough, Japan. At 2190 m deep, this new vent field is highly active and exhibit vigorous focused venting from ‘black smoker’ chimneys, the highest temperature recorded being 364°C.

Vent chimneys in the “Yokosuka site”

Fauna and microbiota in the new site were generally similar to other Okinawa Trough vents, although with some different characteristics. For fauna, the dominance of the deep-sea mussel Bathymodiolus aduloides is surprising given other nearby vent sites are usually dominated by B. platifrons and/or B. japonicus, and a sponge field in the periphery dominated by Poecilosclerida is unusual for vents in this region. In terms of microbiota, the H2-rich vent fluids in one of the chimneys resulted in the dominance of hydrogenotrophic chemolithoautotrophs such as Thioreductor and Desulfobacterium. In terms of vent fluid, notable Cl depletion (130 mM) and high concentrations of both H2 and CH4 (~10 mM) probably result from subcritical phase separation and thermal decomposition of sedimentary organic matter. Our insights from the Yokosuka site implies that although the distribution of vent animal species may be linked to depth, the constraint is perhaps not water pressure and resulting chemical properties of the vent fluid but instead physical properties of the surrounding seawater.

Overview of the “Yokosuka site”

We named the new vent site after R/V Yokosuka, the supporting vessel of DSV Shinkai6500 and AUV URASHIMA.

R/V Yokosuka, which caught the first signs of the “Yokosuka site” using a Multi-Beam Echo Sounder

  • Miyazaki J, Kawagucci S, Makabe A, Takahashi A, Kitada K, Torimoto J, Matsui Y, Tasumi E, Shibuya T, Nakamura K, Horai S, Sato S, Ishibashi J, Kanzaki H, Nakagawa S, Hirai M, Takaki Y, Okino K, Watanabe HK, Kumagai H, Chen C* (2017). Deepest and hottest hydrothermal activity in the Okinawa Trough: Yokosuka site at Yaeyama knoll. Royal Society Open Science, 4: 171570. http://dx.doi.org/10.1098/rsos.171570

First Columbellidae snail from deep-sea vent

Lead-authored paper published in Zootaxa today! This paper describes Astyris thermophilus Chen, Watanabe, Araya, 2017, the first Columbellidae species discovered from deep-sea hydrothermal vent ecosystems. Its Japanese name literally means “columbellid from the underworld”. It was found at the Natsu site, Iheya North hydrothermal field, Okinawa Trough, just shy of 1100m depth. http://www.mapress.com/j/zt/article/view/zootaxa.4363.4.13

Astyris thermophilus. A–D. Holotype (UMUT RM32644). E. Paratype #1 (NSMT Mo 78990). F. Paratype #2(UMUT RM32645), periostracum removed to show spiral striae. G. Protoconch of paratype #6, a juvenile specimen (UMUT RM32646). H. Operculum of paratype #2 (UMUT RM32645). I. Radula of paratype #2, UMUT RM32645). Scale bars = 2 mm (A–F),500 μm (G, H), 20 μm (I).

  • Chen C*, Watanabe HK, Araya JF (2017). First columbellid species (Gastropoda: Buccinoidea) from deep-sea hydrothermal vents discovered in Okinawa Trough, Japan. Zootaxa, 4363(4): 592-596. DOI: 10.11646/zootaxa.4363.4.13

Two new vent snails from 2.8km deep in the Indian Ocean!

New lead-authored paper, announcing the discovery of two new peltospirid vent snails, has been published in the peer-reviewed Open Access journal Frontiers in Marine Science! Read for free here: https://doi.org/10.3389/fmars.2017.00392

This paper describes two new species of small gastropods, belonging to the hydrothermal vent endemic family Peltospiridae, from the Longqi hydrothermal vent field (~2785 m deep) on the Southwestern Indian Ridge, Indian Ocean; a new genus was erected to house one of them. The descriptions are based on shell (protoconch, teleoconch, periostracum, shell microstructure), radula, as well as anatomical characters.

Lirapex politus Chen et al., 2017 (~4.5 mm shell height) is the first Indian Ocean representative of genus Lirapex which is also known from eastern Pacific and mid-Atalantic vents, and differs from the other known congeners by its lack of obvious axial sculpture (hence ‘politus’, smooth), as well as a narrower umbilicus and the final 0.5 whorl of the teleoconch being less detached.

Lirapex politus n. sp., scale bars = 1 mm.

Dracogyra subfuscus Chen et al., 2017 (~7 mm shell diameter) is a depressed, globular, coiled peltospirid with a dark periostracum; the genus Dracogyra Chen et al., 2017 was established for this species. It is most similar to Depressigyra globulus Warén & Bouchet, 1989 known from the eastern Pacific, but easily separated from it by a lack of basal notch in the aperture and a more depressed shell with narrower umbilicus. Furthermore, the radula of D. subfuscus is highly characteristic with the central tooth being very wide and compressed.

Dracogyra subfuscus n. gen., n. sp., scale bars = 1 mm.

A Bayesian phylogeny using the mitochondrial COI barcoding gene confirmed the placement of the two new species in clade Neomphalina and family Peltospiridae. The two new species co-occur with two giant holobiont peltospirids including the scaly-foot Chrysomallon squamiferum Chen et al., 2015 and Gigantopelta aegis Chen et al., 2015, and are sometimes found on their body surface. The two new species do not host endosymbiotic bacteria and gut contents suggest that they probably feed on microbial film on chimney surfaces, as well as epibionts of the two larger peltospirids.

  • Chen C*, Zhou Y, Wang C, Copley JT (2017). Two new hot-vent peltospirid snails (Gastropoda: Neomphalina) from Longqi hydrothermal field, Southwest Indian Ridge. Frontiers in Marine Science, 4: 392. DOI: 10.3389/fmars.2017.00392

Two rare gastropods from two new vents!

Lead-authored paper reporting the unexpected discovery of two very rare snails in two new hydrothermal vent sites is now published in the peer-reviewed Open Access journal PeerJ! Read for free at: https://peerj.com/articles/4121/

In this paper, we report the discovery of two very rare gastropods – the calliostomatid Otukaia ikukoae Sakurai, 1994 and the muricid Abyssotrophon soyoae (Okutani, 1959) in newly located hydrothermal vent sites in the Okinawa Trough, Japan. One of the two new sites is named the “Fukai” site after the poisonous forest of the same name in the Studio Ghibli film “Nausicaä of the Valley of the Wind” (1984)! The discovery of these snails represent the second record of Calliostomatidae and the third Muricidae from vents, and also represent range extensions of both species to the southwest, by about 700 km in the case of O. ikukoae. Based on radular characteristics, O. ikukoae is returned to genus Otukaia from Tristichotrochus.

Specimens of the two gastropods collected from hydrothermally influenced areas.(A–D) Tristichotrochus ikukoae from Fukai site, Higashi-Ensei. (E–J) Abyssotrophon soyoae from Crane site, Tarama Hill; (E–H) Specimen #1, (I, J) Specimen #2. Scale bars: (A–D) 1 cm, (E–J) 0.5 cm.

Although this is the first time either species are observed in their natural habitat, both are considered to be occasional invaders of vent ecosystems from surrounding regular sea bottom and not vent endemics given their other records from non-vent environment as well as the fact that they were found in weak diffuse flow venting areas and not focused venting areas. Nevertheless, it is clear that they are able to tolerate, to a certain extent, environmental stresses associated with vents (e.g., raised heavy metal and hydrogen sulfide concentrations). This enables them to access to rich food supplies supported by chemosynthesis primary production, and suggest that vent periphery likely play a key role in the evolution of biological adaptation to hydrothermal vent environment.

The Fukai site (above) and the Crane site (below).

  • Chen C*, Watanabe HK, Miyazaki J, Kawagucci S (2017). Unanticipated discovery of two rare gastropod molluscs from recently located hydrothermally influenced areas in the Okinawa Trough. PeerJ, 5: e4121. http://dx.doi.org/10.7717/peerj.4121/

New paper on diversity of Mollusca at a shallow vent

Lead-authored paper on shallow water hydrothermal vent molluscs published in journal Marine Biodiversity! Read online for free here: http://rdcu.be/wKVR

Mar Biodiv, doi:10.1007/s12526-017-0804-2

This paper reports diversity of molluscs inhabiting shallow water (10-30m deep only!) hydrothermal vent ecosystem off Kueishan Island, Taiwan. Unlike deep-sea hydrothermal vents no endemic molluscs were found, and the species present were a subset of species present in surrounding areas that are apprently able to tolerate the ‘extreme’ environment. We report a total of 13 core species including 12 gastropods and one chiton, and discuss their ecology at the shallow vents.

Representative specimens of the 13 mollusc species collected from shallow hydrothermal vents off Kueishan Island, Taiwan

New paper characterises microbes associated with Antarctic vent snail

New co-authored paper published in the peer-reviewed journal “Polar Biology“! The article can be read for free via the following link: http://rdcu.be/tWBe .

In this paper, we characterised microbes associated with the recently discovered Antarctic vent snail Gigantopelta chessoia Chen et al., 2015. It has been known that this snail hosts endosymbionts in an much enlarged oesophageal gland, but the details about the symbiont’s phylogenetic position has not been published. We show that the endosymbiont is a Gammaproteobacteria related to sulfur-oxidising bacteria from cold seeps and other animals living in chemosynthetic ecosystems. Also revealed is a more diverse epibiont community on the gill surface, including members belonging to Gamma, Epsilon and Deltaproteobacteria. Interestingly, the endosymbiont Gammaproteobacteria strain was also found on the gill surface but not in the surrounding water column. Given that juveniles of this species is regularly recovered from within the adults’ mantle cavity, this suggests they may acquire the symbionts directly from the gills of adult snails.

Gigantopelta chessoia and its associated microbial community

New paper presents a new deep-sea fluid sampler

New co-authored paper (with Shinsuke Kawagucci and other colleagues) is now officially published in the Open Access journal Frontiers in Earth Sciences! Available from: http://journal.frontiersin.org/article/10.3389/feart.2017.00045/full/

Long story short, we developed a new water sampler for collecting hydrothermal fluid and other geofluids in the deep-sea. This new sampler, the “WHATS-III”, is capable of pressure-tight, flow-through sampling of four independent geofluids per submersible dive. We also present real data collected during field tests carried out in hydrothermal vents of the Indian Ocean and Okinawa Trough.

Overview of the WHATS-3 Sampler

  • Miyazaki J, Makabe A, Matsui Y, Ebina N, Tsutsumi S, Ishibashi J, Chen C, Kaneko S, Takai K, Kawagucci S (2017). WHATS-3: An improved flow-through gas-tight fluid sampler for deep-sea geofluid research. Frontiers in Earth Science, 5: 45. https://doi.org/10.3389/feart.2017.00045

New paper shows a vent squat lobster actively cultivates its epibionts!

A co-authored paper about the mechanism of symbiosis in a deep-sea vent crustacean is now published in the journal “Deep Sea Research Part I”: https://authors.elsevier.com/c/1Vm3k3RueHIHRB . Shinkaia crosnieri Baba & Williams, 1998 is a vent-endemic squat lobster with dense setae / hair on its ventral surface. Much like its distant (convergently evolved) cousin, the “yeti-crab” Kiwa, these setae are full of epibiotic bacteria. Recently, S. crosnieri became the first vent animal where the nutritional reliance on epibiotic bacteria was experimentally demonstrated. In this study, we take a step further and show that S. crosnieri actively utilises and produces water current that significantly increases the productivity (chemosynthetic activity) of its epibionts. This means the squat lobster is actively cultivating / farming its own food — the first example of such behavioural adaptation demonstrated among epibiont-hosting animals inhabiting chemosynthetic ecosystems.

Dense ventral setae of S. crosnieri (left) and epibionts on the setae (right)

Through a series of experiments measuring the rate of chemosynthesis (sulfide consumption rate), it was revealed that the rate in epibionts significantly increased when water current was produced. Then, living S. crosnieri individuals were shown to produce an endogenous water flow to the ventral setae through elegant current visualisation using fluorescent particles. Finally, behavioral experiment indicated that S. crosnieri likely exhibit rheotaxis in its natural habitat, meaning it uses existing water current in addition to self-generated ones to increase the productivity of its epibionts = food.

Endogenous water flow generated by S. crosnieri, left: artist’s impression (by Emi Hada) and right: visualisation of the actual current speed generated

Watsuji T, Tsubaki R, Chen C, Nagai Y, Nakagawa S, Yamamoto M, Nishiura D, Toyofuku T, Takai K (2017). Cultivation mutualism between a deep-sea vent galatheid crab and chemosynthetic epibionts. Deep-Sea Research Part I: Oceanographic Research Papers, 127: 13-20. DOI: 10.1016/j.dsr.2017.04.012