BPT08-01

Japan Geoscience Union Meeting 2016

Microbialites in chemosynthetic ecosystems*Tomoyo Okumura1
1.Japan Agency for Marine-Earth Science & Technology
Microbialites are macroscopically identifiable the earliest evidence of life, which are formed withassociation of benthic microbial communities and some environmental factors (1). Most microbialites
consist of carbonate, but also consist of silica, phosphate, iron- and manganese-oxides, ironsulfides (2), and magnesium hydroxide (3). Previous investigations for microbialites in terrestrial(rivers, lakes, and hot springs) and shallow marine settings revealed that photosynthetic microbes
such as cyanobacteria and algae play an important role for microbialite formation (2). However,microbialites are also occurred in some chemosynthetic ecosystems at subsurface and deep-sea
settings. Due to the sample availabilities, reports and descriptions of such unusual microbialites
were limited so far. Here, I summarize the studies on microbialites at the dark environments, andintroduce characteristics on a microbialite that have newly found on 2013 at the Shinkai Seep
Field, Southern Mariana.
Some carbonates at deep-sea methane seep sites (4, 5) and in pipeline at the landfill sites (6, 7)
contained microbialite textures. Carbon isotope ratio of the carbonates and biomarkers indicatedthe association of methanogen and/or methane-oxidizer for making microbialite textures. Some ironsulfide deposits near deep-sea hydrothermal vents also exhibited microbialite textures, which havebeen interpreted as organosedimentary structures associated with various chemosynthetic microbes. A
newly discovered chimney at the Shinkai Seep Field consisted of magnesium hydroxide and calcium
carbonates, which were interpreted as a product of serpentinite-associated alkaline fluid.
Microbialite textures were locally found in the chimney and only consisted of magnesium hydroxide.
Scales of microbialites at the chemosynthetic ecosystems were ranged from several mm to cm. In
addition, some of them occurred with bivalves and tubeworms. On the other hand, microbialites atthe photosynthetic ecosystems occur larger scales at a maximum of several km (2). Further studies
for understanding microbialites at the chemosynthetic ecosystems will provide useful information
for reconstruction on early life from ancient microbialites.
Acknowledgements: The chimney samples of the Shinkai Seep Field were obtained through thecooperative efforts of the captain and crews of the support ship R/V Yokosuka and the operationteam of the DSV Shinkai 6500. In addition, the scientific party on the cruise YK13-08, YK14-11, andYK15-11 lead by Dr. Yasuhiko Ohara provided the chimney samples and tireless supports during thecruises. I would like to thank all these relevant persons.
References: [1] Brune and Moore (1987) Palaios 2, 241-245. [2] Riding (2011) Encyclopedia of
Geobiology pp. 635-654. [3] Nothdurft et al. (2005) Geology 33, 169-172. [4] Greinert et al. (2002)
International Journal of Earth Sciences 91, 698-711. [5]Reitner et al. (2005) Facies 51, 66-79. [6]Maliva et al. (2000) Geology 28, 931-934. [7] Feng & Chen (2015) Environmental Earth Sciences 74,
4839-4851. [8] Georgieva et al. (2015) Geobiology 13, 152-169. [9] Li and Kusky (2007) Gondwana
Research 12 84-100.
Keywords: microbialite, chemosynthetic ecosystems©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-01 -BPT08-02

Japan Geoscience Union Meeting 2016

Decomposition of the plant in the ocean of the Late Cretaceous-Focused on the Upper Cretaceous Yezo Group distributed in Nakagawa Town, Hokkaido, Japan*Yuma Yamamoto1, Robert Jenkins2
1.Division of Environmental Science and Engineering, Graduate School of Natural Science andTechnology, Kanazawa University, 2.School of Natural System, College of Science and Engineering,
Kanazawa University
Land plants, mainly composed of cellulose and lignin, are an important carbon reservoir on theearth. However, those organic compounds are relatively difficult to decompose for most organisms.
In modern marine environments, wood-boring bivalves, which have symbiotic microbes to decompose
cellulose, can mechanically break up the wood by their shells and consume cellulose. Then,decomposed organic compounds are useful for benthic organisms which have no ability to decompose
original wooden material. Based on such degraded organic matter and other chemical compounds
produced during decay of woods, sunken-wood communities will be established. Thus, it is important
to know role of wood-boring bivalves through the ages. The wood-boring bivalves have appeared in
the Early Jurassic and diversified in late Cretaceous. However, degradation process of the wood byboring bivalves in the Cretaceous ocean hasn’t been fully revealed. Thus, the current study aim toreveal the degradation process of the wood in the ocean using the fossils from the Cretaceous Yezo
Group distributed in Nakagawa Town, Hokkaido, Japan.
Totally 67 carbonate concretions were collected from the localities where Cretaceous deposits were
exposed. Surface of the observation, cut polished surface and thin section of the observation,
X-ray CT imaging, such as the cleaning of containing invertebrate fossils were carried out in thelaboratory. Within the sample, ca. 70 % of concretions contained wooden trunk fossils. Within theconcretions contained wooden fossils, about 34 % were bored by wood-boring bivalves. Detailed
observations of borings suggest that the all bore holes were made by xylophagous wood-boringbivalves which are known as deep-sea wood borers. Within the bore holes, aggregations of framboidal
pyrites, indicating activity of sulfate reducing bacteria were frequently found, and pyrites
accumulated within the wood and around the wooden fossils. Fecal pellets, sometimes contain wood
fragments, were also accumulated around the woods. It indicates that it was revealed that at least
about 30% of the wood is degraded by deep-sea wood-boring bivalves and sulfate reducing bacteria inthe deep sea zone of Yezo basin of the Cretaceous.
Keywords: Wood-boring bivalves, Sulfate reducing bacteria, Cretaceous©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-02 -BPT08-03

Japan Geoscience Union Meeting 2016

Influence of cold seep methane on the forming of echinoderm skeletons*Moe Kato1, Tatsuo Oji2, Kotaro Shirai3, Tatsuya Unuma4
1.Graduate School of Environmental Studies, Nagoya University, 2.Nagoya University Museum,
3.Atmosphere and Ocean Research Institute, The University of Tokyo, 4.Hokkaido National Fisheries
Research Institute,Fisheries Research Agency
Recently, a few modern species of echinoderms have been reported as a member of the chemosynthetic
community organisms, and at least two fossil species of echinoderms have been found from cold seep
deposits (Pawson and Vance, 2004; Gaillard et al., 2011; Landman et al., 2012). In order tounderstand how these echinoderms from cold seep environment take carbon to form their skeletons,
two analyses were done; 1) stable carbon isotope analysis of the fossil skeletons, and 2) stablecarbon isotope analysis of a living sea urchins in aquaria under environments of controlled stablecarbon isotope ratios (δ13C).
The fossil echinoderms have been collected and studied from two cold seep areas; the Upper
Cretaceous (Campanian) in South Dakota, USA and the coeval formation in Hokkaido, Japan. The bothcrinoids from South Dakota and Hokkaido have clearly lower δ13C values than normal echinoderms,
suggesting their skeletons were influenced by cold seep methane which has extremely low δ13C values(Kato and Oji, 2015). However, it was still unknown how these crinoids formed their skeletons withsuch low δ13C values.
A lot of marine organisms such as many mollusks, are considered to precipitate their skeletons inequilibrium with the ambient sea water in regards to their carbon isotope (Epstein et al., 1951).
For example, bivalves shells from a chemosynthetic community show ±5‰ δ13C values (e.g. Mae et al., 2007). However, echinoderm skeletons, even from a normal (non-seep) environment, are known to beformed not in isotopic equilibrium, and the δ13C values of the echinoderms skeletons are different
depending on the classes or species (e.g. Weber, 1968). Thus, in echinoderm biomineralization, an
isotope fractionation due to vital effect or some carbon sources other than from sea water should
be possible.
In order to clarify the cause of inequilibrium of the δ13C value in the skeletons of echinoderms
and to estimate degree of isotope fractionation in forming skeletons, specimens of modern echinoid(Strongylocentrotus intermedius) have been raised in two experiments; 1) the echinoids has beenraised under three types of sea water with differently controlled δ13C value of DIC (dissolved
inorganic carbon), and 2) with two different types diets (a kelp (Saccharina longissima) and aland plant (Fallopia sachalinensis)) with different δ13C value.
Compared with the controlled case of culture with normal sea water with seaweed diet, δ13C value ofthe echinoid test changed in both cases (in waters with high δ13C value, and with different diets.
Thus, it suggests that skeletons δ13C of this echinoid, are influenced by isotope ratio of both sea
water and foods. This result clearly shows that the process of isotope fractionation and forming
skeletons of echinoderms should be different from those of most of mollusks. It is thought that theechinoderms in cold seep environment depend on bacteria mat for their diet, or detritus that havelow δ13C.
Keywords: cold seep, echinoderms, chemosynthetic community, biomineralization©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-03 -BPT08-04

Japan Geoscience Union Meeting 2016

Mass occurrence of the enigmatic gastropod Elmira in the Late Cretaceous Sada Limestone
seep deposit in southwestern Shikoku, Japa
*Takami Nobuhara1, Daigaku Onda1, Takuya Sato1, Hidemi Aosawa1, Toyoho Ishimura2, Akira Ijiri3, Urumu
Tsunogai4, Naoki Kikuchi5, Yasuo Kondo6, Kiel Steffen7
1.Science Education (Geology), Faculty of Education, Shizuoka University, 2.Department of Chemistry
and Material Engineering, National Institute of Technology, Ibaraki College, 3.Kochi Institute forCores Sample Research, JAMSTEC, 4.Graduate School of Environmental Studies, Nagoya University,
5.Museum of Nature and Human Activities, Hyogo, 6.Sciences Unit, Natural Sciences Cluster, Kochi
University, 7.Department of Palaeobiology, Naturhistoriska riksmuseet, Stockholm

Elmira is a medium- to large-sized gastropod genus, which has so far been recorded only from apresumably Eocene methane-seep deposit in Cuba, and its systematic affinity and paleoecology are
unknown. We report a mass occurrence of Elmira sp. from a Late Cretaceous seep deposit in Shikoku,
Japan, called Sada Limestone, with its mode of fossil occurrence, carbonate petrology, and stablecarbon isotope analyses. Sada Limestone is characterized by the dominant occurrence of alarge-sized thyasirid bivalve "Thyasira" hataii and serpulid worm tubes. The mass occurrence ofElmira sp. occurs as a lens-shaped carbonate body, 6.5 m in length and less than 2 m in thickness,intercalated in the thyasirids-rich limestone. The Elmira-rich lens body has a flat top and aconcave base, and consists of multiple shell accumulation layers, which were formed by winnowing
and filling of a depression in slope mud. The rare occurrence of Elmira sp. elsewhere in the Sada
Limestone suggests that it lived in local aggregations in the vicinity of the depression. The
matrix of the Elmira mass occurrence is rich in dolomite and ankerite and is less depleted in 13C(δ13C values of calcite: –5.3 to –2.4‰; of dolomite: –8.3‰) than the calcitic matrix of thesurrounding limestones. This suggests that the Elmira mass occurrence was cemented below thesulfate reduction zone and thus with little influence of anaerobic methane oxidation. It is,therefore, difficult to consider that Elmira sp. harbor chemosymbiotic bacteria. As some trochiform
gastropods do in seep sites, Elmira sp. was maybe a bacteria grazer gregarious on bacteria mats
and/or hard bottoms.
Keywords: chemosynthesis, cold seep, Gastropods, Cretaceous, Shikoku©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-04 -BPT08-05

Japan Geoscience Union Meeting 2016

Meiofaunal community compositions around hydrothermal vents in three seamounts in NW
Pacific –Vent copepods want to stay with vent polychaetes?
*Motohiro Shimanaga1,2, Reina Senokuchi1, Yuki Uejima1, Hidetaka Nomaki2, Hiromi Kayama WATANABE2,
Tomo Kitahashi2
1.Kumamoto University, 2. Japan Agency for Marine-Earth Science and Technology
In contrast to specific large benthic invertebrates in chemosynthetic ecosystems around deep-sea
hydrothermal vents, meiofaunal communities in such habitats have only recently been investigated.
This is especially true in the Northwest Pacific Ocean, even though there are many seamounts withactive hydrothermal vents in their calderas. We studied the variations in meiofaunal composition
around hydrothermal vents on chimney structures (vent chimneys) and in the adjacent non-vent fields
in the calderas of three neighboring seamounts (Bayonnaise Knoll, Myojin Knoll, and Myojin-sho
Caldera), in Izu-Ogasawara Arc, NW Pacific. A typical meiofaunal composition (nematodes as the mostabundant taxon; harpacticoid copepods as the second) was observed in the sediments on sea-floor in
the non-vent (control) fields, and even in the sediment at the base of chimneys. On the surfaces ofvent chimneys, on the other hand, copepods and their nauplii were the most abundant. There weresignificant differences in copepod compositions on vent chimneys between the three seamounts, andeven between different substrates on the same chimneys. Stygiopontius (Dirivultidae,
Siphonostomatoida), a typical vent copepod group, was abundant and often predominant on the densemats of tubes of Paralvinella polychaetes living in the closest proximity to vent fluids among ventmetazoan macrofauna. These copepods, however, showed the lower density on the beds of Neoverruca
barnacles although their beds were adjacent to Paralvinella mats at cm scales. No significant
genetic difference was observed among local populations of Stygiopontius, suggesting they are thesame species. Furthermore, stable carbon and nitrogen stable isotopic ratios and radiocarbon
abundances in meiofaunal soft tissues revealed the dirivultids utilized mainly
chemolithoautotrophic microbes at vents. These results show that Stygiopontius copepods prefer

Paralvinella mats as their habitats or have similar environmental preferences (such as higher watertemperature or existence of chemolithoautotrophic microbes) to Paralvinella.
Keywords: hydrothermal vent, meiofauna, community compositions©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-05 -BPT08-06

Japan Geoscience Union Meeting 2016

Nutrition sources of meiofauna revealed by stable carbon and nitrogen isotope ratios andnatural radiocarbon abundances explain meiofaunal distribution patterns at hydrothermalvent fields*Hidetaka Nomaki1, Yuki Uejima2, Nanako O Ogawa1, Masako Yamane1, Hiromi Kayama WATANABE1, Reina
Senokuchi2, Tomo Kitahashi1, Yusuke Yokoyama3,1, Naohiko Ohkouchi1, Motohiro Shimanaga2,1
1.Japan Agency for Marine-Earth Science and Technology, 2.Kumamoto University, 3.The University ofTokyo
Deep-sea hydrothermal vents host unique marine ecosystems which mainly rely on organic matters
produced by chemolithoautotrophic microbes. Although there are abundant meiofauna at thehydrothermal vent field, studies on their distributional patterns and nutritional sources are still
limited due to their small body sizes. In this study, we investigated dietary sources of meiofauna
at hydrothermal vent fields in the western Pacific using stable carbon and nitrogen isotope ratios(d13C, d15N) and natural radiocarbon abundances (D14C). Based on these data, we evaluated how much do
the hydrothermal vent meiofauna gain their nutrition from the chemolithoautotrophic microbes andhow does it related to their distributional patterns around hydrothermal vent fields. Bacterialmats of the hydrothermal vent chimney typically exhibited heavy d13C values (up to -10‰) anddepleted D14C values (~600‰). The d13C and D14C values of Dirivultidae, an endemic copepod family
inhabiting hydrothermal vent chimney, exhibited similar values to the bacterial mat but distinct
from those of sediments at surrounding area or water column plankton, suggesting that theyexclusively rely on bacterial mat at the vent chimney. Other copepods at the vent chimneys may also
rely on bacterial mat to some extent. To the contrary, d13C values of nematodes at vent chimneys
were -26.6 and 23.2‰, which were similar ranges to those at non-vent sites, suggesting ventnematodes did not gain their nutrition from the chemolithoautotrophic microbes. Those nutritional
facts obtained from isotopic compositions explain well about distributional patterns of thesemeiofauna; while dirivultid copepods exclusively distribute at vent chimneys and other copepods are
more abundant at vent chimneys than in non-vent sediments, nematodes showed similar abundances
between vent chimney and non-vent sediments.
Keywords: Hydrothermal vent ecosystem, meiofauna, feeding habit, stable isotope ratios, naturalradiocarbon abundance©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-06 -BPT08-P01

Japan Geoscience Union Meeting 2016

Species diversity of vesicomyid bivalves from the middle Miocene seep carbonates in the
Bessho Formation, Nagano Prefecture, Japan*Yusuke Miyajima1, Takami Nobuhara2, Hakuichi Koike3
1.Graduate school of Science, Kyoto University, 2.Faculty of Education, Shizuoka University,
3.Shinshushinmachi Fossil Museum
Vesicomyid bivalves have been dominant animals in submarine cold seeps through the Cenozoic age.
Although coexistence of two or more vesicomyid species in a modern single seep site is considered
to be due to different preferences in sulfide flux, salinity, and water temperature among species(Barry et al., 1997; Watanabe et al., 2013), co-occurrence of two or more vesicomyid species andits cause have rarely been discussed for ancient seeps. The middle Miocene Bessho Formation in
Nagano Prefecture, central Japan is composed of slope mudstone deposited at a back-arc basin andcontains many seep carbonates in various sizes. Two fossil vesicomyid species, Adulomya

uchimuraensis and “Calyptogena” akanudaensis, were previously recorded from the Bessho Formation.
This study makes genus reassignment of “C”. akanudaensis and newly reports two vesicomyid species,
Pliocardia sp. and Adulomya sp. and notes that relative abundance of the four vesicomyid species
depends on carbonate size. The large seep-carbonate mounds more than 20 m in diameter ischaracterized by abundant occurrence of A. uchimuraensis with rare occurrences of “C”.
akanudaensis and Pliocardia sp. From the smaller, about 1 m in diameter carbonate body, “C”.
akanudaensis dominantly occur in association with A. uchimuraensis. The siltstone containing
several cm-sized small carbonate concretions yields abundant shells of Adulomya sp. in scatteredoccurrence. The difference of carbonate size suggests that of fluid flux and/or longevity, and thespecies diversity of vesicomyid clams in the Bessho Formation might be caused by variation of seep
activities among sites.
Keywords: Pliocardia, Adulomya, Vesicomyidae, Middle Miocene, Cold seep©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-P01 -BPT08-P02

Japan Geoscience Union Meeting 2016

Reconstruction of seepage history in the Eocene Poronai Formation, Hokkaido, Japan*Takami Nobuhara1, Yuriko Shirotori1, Shintaro Hitomi1, Toyoho Ishimura2, Akira Ijiri3
1.Science Education (Geology), Faculty of Education, Shizuoka University, 2.Department of Chemistry
and Material Engineering, National Institute of Technology, Ibaraki College, 3.Kochi Institute forCores Sample Research, JAMSTEC
The Eocene Poronai Formation, central Hokkaido, is known to mark the oldest fossil records ofvesicomyid bivalves in Japan. This study made an outcrop mapping of lithology, mode of fossils
occurrence, and stable isotopic analyses to make clear the seep-habitats in initial stages ofvesicomyid diversification through the Cenozoic age.
A series of irregular-shaped seep-carbonate rocks, about 1-2 m in diameter, vertically piled up in
the outcrop section of massive siltstone. The carbonate rocks and the surroundings yield abundant
shells of chemosynthetic bivalves, Hubertschenkia ezoensis and Conchocele bisecta. Their modes offossil occurrences are divided into two types, 1) shell-concentrated lens and 2) sporadic patches
and scattering, which alternate each other in the vertical section. The shell-concentrated lenses
are mainly recognized in siltstone, whereas the scattering type is encompassed in the carbonate
bodies.
It is noteworthy that all the shell-concentrated lenses were associated with calcitic concretions
partly containing fluidized texture just below them. The fluidized part consists of mixture of 1)
white-colored detrital micrite depleted in δ13C (–38.05 to -22.91‰), 2) gray-colored micrite notdepleted in δ13C (4.87 to 9.01‰) and 3) black-colored sparitic cements with widely ranging valuesof δ13C (-42.09 to 1.88‰). Detail lithological mapping show that such fluidized texture tends to beformed avoiding shell-rich part. These suggest that the alternating pattern of two modes of fossil
occurrences was controlled by intermittent fluidizing events as follows. Sporadic biofacies wasformed under the diffusive phase resulting in gradual rise of pore-water pressure. Over thecritical point of pore-water pressure, fluidization was triggered in unconsolidated parts not richin buried shell remains, which acted as a nucleus of precursor concretions. Such local fluidization
caused a focused flow fostering shell-concentrated mode.
Keywords: chemosynthetic, Vesicomyidae, methane seepage, Poronai Formation, Eocene©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-P02 -BPT08-P03

Japan Geoscience Union Meeting 2016

Succession of whale-fall ecosystems at shallow waters: mainly based on one year monitoringof deployed whale carcasses in aquarium tank and natural environments in Tsukumo Bay,
Ishikawa, Japan
Kazuhiro Moriya2, *Robert Jenkins1, Toshio Sekiguchi3, Nobuo Suzuki3
1.School of Natural System, College of Science and Engineering, Kanazawa University, 2.Graduate
School of Natural Science and Technology, Kanazawa University, 3.Noto Marine Laboratory, Instituteof Nature and Environmental Technology, Kanazawa University
A whale carcass which sank into the sea-floor supports unique ecosystem called "whale-fallcommunity" (Smith, 1989, Nature). Some of the communities are supported by microbial activities
during degradation of organic matter within the bones. The community is thought to be change in its
community structure over time through degradation process of carcass (Smith and Baco, 2003). Those
whale-fall communities are well known in deep-sea environments and such schematic faunal succession
has been proposed based on research in the deep-sea. Because of technical limitation ofobservations in the deep-sea, changes of microbial mat hasn’t been fully analyzed. In addition,
whale-fall community in the shallow waters are also not well known so far.
So, we tried experiments on deployed whale bones in aquarium tank. Fresh sea water continuously
flow into the tank. In addition, we put whale-bones at 11 m in depth in Tsukumo Bay, Ishikawa,Japan.
As a result, the whale bones floated within few days after deployment. Many bubbles of gas,probably hydrogen sulfides, gushed out from the bones. A week later, green algae and white giant
bacteria appeared on the bones. Two to three weeks after the deployment, the chemosynthetic
cilliate (Zoothamnium niveum) and Hyalogyrinidae gastropod (Xenoskenea sp.) iappearred in thetanks. X. sp. grazed on both microbial mats, white bacterial mat and green algal mat. Afterappearance of those biota, abundance of those changed through a year. The green algae and thegastropods decreased in the winter and flourished in summer. Whale bones deployed in the naturalenvironments, ca. 11 m deep, more than 1.5 years had encrusting animals such as barnacles, and very
few area of the bone surface were covered by microbial mats.
We succeed to make a whale-fall community from fresh bone in aquarium tank with continuous supplyof fresh sea water. It allow more detailed observations. Based on the observations, the shallow
water whale-fall communities including chemosynthetic biota have establish within few weeks.
Keywords: Whale-fall community, ecosystem, reduced environment©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-P03 -BPT08-P04

Japan Geoscience Union Meeting 2016

Population connectivity of benthic copepods in deep-sea chemosynthetic communities*Hiromi WATANABE1, Reina Senokuchi2, Yuki Uejima2, Hidetaka Nomaki1, Tomo Kitahashi1, Motohiro
Shimanaga2, Hiroyuki Yamamoto1
1.Japan Agency for Marine-Earth Science and Technology, 2.Kumamoto University
Meiobenthos are small (<1mm) benthic animals living on seafloor. Although their considerable
diversity in marine environment, only less attention is paid for meiobenthos than macro- andmega-benthos. Copepod is the most abundant crustacean in meiobenthos in deep-sea hydrothermal ventenvironment, and a copepod family Dirivultidae is one of the most successful vent taxa. However,
only little is known about ecology and evolution of dirivultids. In the present study, we examined
efficiencies of several DNA extraction methods available for copepods, and estimate population
connectivity of dirivultid copepods of the genus Stygiopontius in the western Pacific hydrothermalvent fields. DNA extraction efficiency was increased when the morphology of copepod was destructed.
However, even the DNA extraction with the lowest concentration (~5ng/μL) was sufficient to obtain
sequence data by Sanger sequencer. Genetic diversities of Stygiopontius copepods were different
among oceanographic regions, higher in back-arc basins in the southern Pacific than in volcanicarc. In both regions, local populations were not significantly separated genetically based onpartial mtCOI sequence. The present result contributes to our knowledge of ecology of meiobenthos,and establishment of environmental assessment tool using meiobenthos in deep-sea hydrothermal vent
fields.
Keywords: hydrothermal vent, environmental assessment, meiobenthos©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-P04 -BPT08-P05

Japan Geoscience Union Meeting 2016

Evaluation of nutrient sources of the biological community in the Shinkai Seep Field,
Southern Mariana Forearc using C, N and S stable isotopes*Yuji Onishi1, Toshiro Yamanaka1, Hiromi WATANABE2, Yasuhiko OHARA2,3
1.Okayama University, 2.JAMSTEC, 3.Hydrographic and Oceanographic Dept. of JapanThe Shinkai Seep Field (SSF), located in the inner trench slope of the southern Mariana Trench, ~80
km northeast of the Challenger Deep, is a serpentinite-hosted chemosynthesis-based community
composed mainly of Calyptogena bivalves. It has been considered that the community is supported by
the following mechanism; serpentinization of mantle peridotite produces CH4-rich fluids, andanaerobic oxidation of CH4 by sulfate-reducing bacteria (SRB) generates H2S. Then,sulfide-oxidizing bacteria (SOB) oxidize the H2S in order to obtain energy and produce organic
matter (Ohara et al., 2012). However, there have been no geochemical studies on the energy andnutrient sources supporting this community. Therefore, the purpose of this study is to elucidate
nutrient sources of the community in SSF using C, N, and S isotope analyses.
Nine animal species and particulate organic matter (POM) obtained around the colony and sediments
obtained beneath the colony by Shinkai 6500 during YK13-08 cruise were analyzed. The animal samples
were used to measure C, N, and S isotopes of their soft tissues, and the POM and sediment samples
were measured total organic carbon (TOC) and total nitrogen (TN) and their isotope ratios. Acid
volatile sulfide (AVS) was extracted from the sediment samples to measure its concentration andsulfur isotopic ratio.
TOC and AVS concentration increased with decreases in their isotopic ratios, suggesting that SOB
produces organic matter using H2S derived from SRB activity in sediment beneath the colony. Because
isotopic ratios of POM are within the range of the common marine phytoplankton, it is thought that
the POM was produced within the phobic zone by photosynthesis.
δ13C value of Calyptogena bivalves within the range of a typical chemosynthesis-based animals
relying on SOB for a nutrient source, while δ34S value is approximately equal to that of AVS in thesediment. Thus, the energy source supporting the bivalves is H2S derived from SRB activity. Also,
isotopic composition of the amphipod, polychaete, and anthozoan samples show intermediate values
between the POM and sedimentary organic matter, suggesting that the nutrient sources of theseorganisms are organic matter derived from both photosynthetic and chemosynthetic productions. The
sibogrinid has clearly different isotope composition, implying that this organism relies on SOB
using the different carbon fixation pathway and/or methanotroph as nutrient sources.
Keywords: isotopic composition©2016. Japan Geoscience Union. All Right Reserved.

- BPT08-P05 -