Marine Ecology Research Institute

Onjuku, Japan

Marine Ecology Research Institute

Onjuku, Japan
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Kusakabe M.,Marine Ecology Research Institute | Inatomi N.,Marine Ecology Research Institute | Takata H.,Marine Ecology Research Institute | Ikenoue T.,Marine Ecology Research Institute
Journal of Oceanography | Year: 2017

Radioactivity has been monitored in seafloor sediments off Fukushima and nearby prefectures regularly. During the initial monitoring period (May–September 2011), 137Cs concentrations in the surface sediments (0–3 cm) generally increased to 8–580 Bq/kg. Subsequently, concentrations decreased at variable rates. In the latest data, from February 2016, concentrations were still higher at 0.8–141 Bq/kg than the pre-accident level. The geometric mean concentration declined steadily from 47 Bq/kg in September 2011 to 13 Bq/kg in February 2016. The 137Cs abundance (Bq/m2) in the surface sediment at each station decreased similarly. The rate of decrease of surface abundance varied spatially by almost one order of magnitude, ranging from 1.1 × 10−4 to 1.7 × 10−3/day, equivalent to halving times of 16–1.1 years, respectively. The rate of decrease was related to the median sediment grain size at each station. In addition, bottom-water dynamics, through the redistribution of bottom sediments, may have caused spatial variability in the rate of decrease, whereas vertical profiles of 137Cs concentrations in the sediment suggest that vertical migration of 137Cs was not a major mechanism reducing the surface 137Cs concentration. From September 2011 to February 2016, the overall halving time of 137Cs in the surface sediment in the monitoring area, excluding the area inside a 30-km radius from the Fukushima Dai-ichi Nuclear Power Plant, was 2.3 years. Thus, 76% of the originally deposited 137Cs (46 × 1012 Bq) in the surface sediment was transported out of the area during that period. © 2017 The Author(s)

Kato A.,Hiroshima University | Baba M.,Marine Ecology Research Institute | Suda S.,University of Ryukyus
Phycological Research | Year: 2013

The nongeniculate species Neogoniolithon brassica-florida (Harvey) Setchell et Mason is circumscribed as a polymorphic species with various gross morphologies due to it being synonymized with several previous species. However, small subunit rDNA and cox1 analyses showed that N.brassica-florida was polyphyletic, and strongly imply that crustose species lacking any protuberances such as Neogoniolithon fosliei (Heydrich) Setchell et Mason and species with protuberances or branches such as N.brassica-florida and N.frutescens (Foslie) Setchell et Mason should be treated as genetically different groups (species). Therefore, we propose the resurrection of N.frutescens. We also confirmed that N.trichotomum was distinguished from N.frutescens by slender uniform diameter branches, a conceptacle with a prominent ostiole, and large cox1 interspecific sequence differences. Male and female reproductive structures of N.trichotomum were illustrated for the first time. Neogoniolithon fosliei, was divided into three clades, each of which was recognized as a species complex based on interspecific level sequence differences within clade and morphological differences. Therefore, we treated the clade most similar to N.fosliei as N.fosliei complex (Clade B), and the other clades as respective complexes of N. cf. fosliei with yellow conceptacles (Clade A) or N. cf. fosliei with large conceptacles (Clade C). Of two species complexes (Clade A and B) were morphologically consistent with two entities of N.fosliei previously reported in the Ryukyu Islands, Japan, which is supported by their niche partitioning. DNA barcoding research of nongeniculate corallines can promote the finding of more reliable taxonomic characters and the understanding of their biological aspects. © 2013 Japanese Society of Phycology.

Kato A.,University of Ryukyus | Kato A.,Hiroshima University | Baba M.,Marine Ecology Research Institute | Suda S.,University of Ryukyus
Journal of Phycology | Year: 2011

The subfamily Mastophoroideae (Corallinaceae, Rhodophyta) is characterized by species possessing nongeniculate, uniporate tetrasporangial conceptacles without apical plugs, the presence of cell fusions, and the absence of secondary pit connections. However, molecular phylogenetic studies not including the type genus Mastophora indicated that the Mastophoroideae was polyphyletic. Our molecular phylogenetic analysis of the subfamily including the type genus using DNA sequences of SSU rDNA and plastid-encoded gene of PSII reaction center protein D1 (psbA) revealed that Mastophora formed a robust clade only with Metamastophora. The other mastophoroid genera were divided into six lineages within the family Corallinaceae. Five supported lineages-(i) Pneophyllum; (ii) Hydrolithon gardineri (Foslie) Verheij et Prud'homme, Hydrolithon onkodes (Heydr.) Penrose et Woelk., and Hydrolithon pachydermum (Foslie) J. C. Bailey, J. E. Gabel et Freshwater; (iii) Hydrolithon reinboldii (Weber Bosse et Foslie) Foslie; (iv) Spongites; and (v) Neogoniolithon-were clearly distinguished by the combination of characters including the presence or absence of palisade cells and trichocytes in large, tightly packed horizontal fields and features of tetrasporangial and spermatangial conceptacles. Therefore, we amend the Mastophoroideae to be limited to Mastophora and Metamastophora with a thin thallus with basal filaments comprised of palisade cells, tetrasporangial conceptacles formed by filaments peripheral to fertile areas, and spermatangia derived only from the floor of male conceptacles. This emendation supports Setchell's (1943) original definition of the Mastophoroideae as having thin thalli. We also propose the establishment of three new subfamilies, Hydrolithoideae subfam. nov. including Hydrolithon, Porolithoideae subfam. nov. including the resurrected genus Porolithon, and Neogoniolithoideae subfam. nov. including Neogoniolithon. Taxonomic revisions of Pneophyllum and Spongites were not made because we did not examine their type species. © 2011 Phycological Society of America.

Takata H.,Japan National Institute of Radiological Sciences | Takata H.,Marine Ecology Research Institute | Aono T.,Japan National Institute of Radiological Sciences | Tagami K.,Japan National Institute of Radiological Sciences | Uchida S.,Japan National Institute of Radiological Sciences
Estuarine, Coastal and Shelf Science | Year: 2012

Influence of dissolved organic matter (DOM) on particle-water interactions of trace metals (Co, Cu, and Cd) between particulate (>0.2 μm) and dissolved (≤0.2 μm) phases has been investigated along a salinity gradient using samples from the estuarine area of northern Sagami Bay, Japan. Partitioning experiments were performed by mixing riverine suspended particles with the mixtures of different proportions of river and marine end-members and determining concentrations of Co, Cu and Cd in particulate and dissolved phases. Concentrations and distribution coefficients (K ds) between particulate and dissolved phases of Co and Cu were dependent on the presence of DOM. The K ds of Co and Cu in the mixtures in the presence of DOM were lower than those in mixtures that had been ultraviolet-irradiated (UV-irradiated) (absence of DOM), throughout the salinity gradient. In addition, speciation calculations estimated that a greater fraction of Co and Cu in the dissolved phase was present in organic form throughout the salinity gradient, while the seawater ion concentrations and ligand competition (e.g., competition from Ca and Mg and formation of stable and soluble chloro-, sulphato-, and carbonato complexes) had a small effect on the speciation of Co. These results indicate that DOM may play an important role in controlling the speciation and the particle-water interactions of Co and Cu in the estuarine waters. As for Cd, the effect of DOM on the interactions of this metal was less intense than for Co and Cu. Seawater ions appeared to act as an important variable for controlling the particle-water interactions of Cd in the estuarine waters. © 2012 Elsevier Ltd.

Takata H.,Japan National Institute of Radiological Sciences | Takata H.,Marine Ecology Research Institute | Aono T.,Japan National Institute of Radiological Sciences | Uchida S.,Japan National Institute of Radiological Sciences
Estuarine, Coastal and Shelf Science | Year: 2012

Concentrations of the trace metals Co, Cu and Cd in dissolved (<0.2 μm) and particulate (>0.2 μm) phases in surface waters were determined to test whether DOC, which is an indicator of dissolved organic matter (DOM), and organic matter (OM) in suspended particulate matter (SPM) act as important estuarine variables controlling the distributions of these metals in the estuarine zone. Although the dissolved metals in the surface waters from the Sagami River to northern Sagami Bay had different behaviors in June, August, and November, 2008, concentrations of dissolved Co and Cu linearly correlated with DOC concentration, but with different slopes for fresh (salinity of ≤0.1) and estuarine (salinity of >0.1) waters. This difference in the water regime between those two metals and the DOC in Sagami Bay indicates that there are differences in composition between riverine and estuarine DOM, due to change of the composition by biogeochemical processes and the presence of additional sources, or that seawater cations are competing for binding sites of DOM during the estuarine mixing. As for particulate phase, there was no relationship between the concentrations of particulate metals and that of OM in SPM at low river flows (i.e., June and November surveys). It is thought that change of the OM composition by the additional SPM sources (anthropogenic discharge and resuspension from the seabed) contributes to the affinity of trace metals for sorption sites on the surfaces of the SPM, thereby making the evaluation of importance of OM in SPM difficult. On the other hand, at high river flow (August survey), riverine SPM significantly contributed to the estuarine SPM and it entered northern Sagami Bay with negligible composition change; however, there were weak correlation coefficients of particulate Co and Cd to OM in SPM, and there was no linear relationship between particulate Cu and OM in SPM. This can be attributed to the imbalanced competition between particle sorption and organic/inorganic complexation for Co and Cd, and prevention of particle sorption by binding Cu more strongly to dissolved organic ligands. © 2012 Elsevier Ltd.

Kita J.,Marine Ecology Research Institute | Kikkawa T.,Marine Ecology Research Institute | Asai T.,Nagasaki University | Ishimatsu A.,Nagasaki University
Marine Pollution Bulletin | Year: 2013

We investigated the effects of elevated pCO2 in seawater both on the acute mortality and the reproductive properties of the benthic copepod Tigriopus japonicus and gastropod Babylonia japonica with the purpose of accumulating basic data for assessing potential environmental impacts of sub-sea geological storage of anthropogenic CO2 in Japan. Acute tests showed that nauplii of T. japonicus have a high tolerance to elevated pCO2 environments. Full life cycle tests on T. japonicus indicated NOEC=5800μatm and LOEC=37,000μatm. Adult B. japonica showed remarkable resistance to elevated pCO2 in the acute tests. Embryonic development of B. japonica showed a NOEC=1500μatm and LOEC=5400μatm. T. japonicus showed high resistance to elevated pCO2 throughout the life cycle and B. japonica are rather sensitive during the veliger stage when they started to form their shells. © 2013 Elsevier Ltd.

Kusakabe M.,Marine Ecology Research Institute | Oikawa S.,Marine Ecology Research Institute | Takata H.,Marine Ecology Research Institute | Misonoo J.,Marine Ecology Research Institute
Biogeosciences | Year: 2013

Spatiotemporal distributions of anthropogenic radionuclides in marine surface sediments off Miyagi, Fukushima, and Ibaraki Prefectures were analyzed on the basis of data collected during the monitoring program launched by the Japanese Ministry of Education, Sports, Science and Technology in 2011 right after the Fukushima Dai-ichi Nuclear Power Plant accident began. Concentrations of 137Cs in the surface sediments varied spatially by two orders of magnitude, from 1.7 to 580 Bq kg-dry-1, and there was no obvious correlation between 137Cs concentration and the proximity of the sampling location to the accident site. The total inventory of 137Cs accumulated in the upper 3 cm of surface sediments in the monitoring area was estimated to be 3.78 × 1013 Bq, that is, 0.1-2% of the total 137Cs flux from the plant to the ocean as a result of the accident (the percentage depends on the model used to estimate the total flux). The spatial variations of 137Cs concentration and inventory depended on two main factors: the 137Cs concentration in the overlying water during the first several months after the accident and the physical characteristics of the sediments (water content and bulk density). The temporal variations of the concentrations of other anthropogenic radionuclides ( 90Sr, 95Nb, 110mAg, 125Sb, 129Te, and 129mTe) in the sediments were also investigated. Activity ratios of these nuclides to 137Cs suggest that the nuclides themselves were not homogenized before they were removed from seawater to the sediments. © 2013 Author(s).

Yamamoto Y.,Hokkaido University | Yamamoto Y.,Marine Ecology Research Institute | Shibata H.,Hokkaido University | Ueda H.,Hokkaido University
Zoological Science | Year: 2013

Many attempts have been made to identify natal stream odors for salmon olfactory homing. It has recently been hypothesized that odors are dissolved free amino acids; however, it is unknown whether these odors change on a seasonal or annual basis. We analyzed dissolved free amino acid (DFAA) concentration and composition of water from the Teshio River in Hokkaido, Japan, where chum salmon (Oncorhynchus keta) returned for spawning, during juvenile downstream migration in spring and adult upstream migration in autumn with a 4-year difference. Among the 19 amino acids found in the Teshio River water, DFAA concentrations fluctuated largely, but 5-7 stable DFAA compositions (mole %) were found between the spring and autumn samples over a 4-year span. Two kinds of artificial stream water (ASW) were prepared using the same DFAA concentration in the Teshio River during the time of juvenile imprinting in spring (jASW) and adult homing in autumn (aASW), after a 4-year period. In behavioral experiments of upstream selective movement in a 2choice test tank, 4-year-old mature male chum salmon captured in the Teshio River showed significant preference for either jASW or aASW when compared to control water, but did not show any preference with respect to jASW or aASW. In electro-olfactogram experiments, adults were able to discriminate between jASW and aASW. Our findings demonstrate that the long-term stability of the DFAA compositions in natal streams may be crucial for olfactory homing in chum salmon. © 2013 Zoological Society of Japan.

Suwa R.,Kyoto University | Suwa R.,Marine Ecology Research Institute | Kataoka C.,Toyo University | Kashiwada S.,Toyo University
Marine Environmental Research | Year: 2014

In this study, the effects of silver nanocolloids (SNCs) on the early life stages of the reef-building coral Acropora japonica were investigated. The tolerance of this species to SNC contamination was estimated by exposing gametes, larvae, and primary polyps to a range of SNC concentrations (0, 0.5, 5, 50, and 500 μg l-1). Pure SNCs were immediately ionized to Ag+ in seawater and concentrations of ≥50 μg l-1 SNC had a significant detrimental effect on fertilization, larval metamorphosis, and primary polyp growth. Exposure to 50 μg l-1 SNC did not significantly affect larval survival; however, the larvae were deformed and lost their ability to metamorphose. At the highest concentration (500 μg l-1 SNC), all gametes, larvae, and primary polyps died. These experiments provide the first data on the effects of silver-nanomaterial-contaminated seawater on cnidarians, and suggest that silver nanomaterials can influence the early development of corals through anthropogenic wastewater inputs. © 2014 Elsevier Ltd.

Oikawa S.,Marine Ecology Research Institute | Watabe T.,Marine Ecology Research Institute | Takata H.,Marine Ecology Research Institute
Journal of Environmental Radioactivity | Year: 2015

A radioactivity measurement survey was carried out from 24 April 2008 to 3 June 2011 to determine the levels of plutonium isotopes and 240Pu/239Pu atom ratios in the marine environments off the sites of commercial nuclear power stations around the Japanese islands; the sampling period extended to two months after the Fukushima Dai-ichi Nuclear Power Station accident. In our previous study (Oikawa etal., 2015), data on Pu isotopes and 241Am in sediments have already been reported. In this study, we report those on Pu isotopes in seawater as well as sediments, and the characteristics of sediments in addition (e.g., ignition loss and biogenic opals). Concentrations of 239+240Pu in seawater and bottom sediments remained nearly constant at all sampling locations during the survey period. In addition, no regional differences were observed in the 239+240Pu concentrations in surface waters. Higher 239+240Pu concentrations were found in bottom waters at deeper sampling locations, but the 240Pu/239Pu atom ratios were nearly constant regardless of the water depth. Higher 239+240Pu concentrations were also found in bottom sediments at deeper sampling locations, but vice versa for 240Pu/239Pu atom ratios as reported in the previous report. The sediments samples from deeper locations showed the higher percentage of ignition loss as well as the higher content of biogenic opal. There was likely to be some driving force participating in the transfer of Pu isotopes associated with biogenic substances to the deeper seabed. The present survey showed that the accident at the Fukushima Dai-ichi Nuclear Power Station did not contribute much to the inventory of Pu isotopes in the adjacent sea area. © 2015 Published by Elsevier Ltd.

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