Western Coast Of Japan Research Articles

Cryptic diversity in the inshore hagfish, Eptatretus burgeri (Myxinidae, Pisces) from the northwest Pacific

The fishery of inshore hagfish (Eptatretus burgeri) is particularly important from the perspective of the eel-skin leather industry in the northwest Pacific. In order to reveal the genetic diversity and population structure of E. burgeri in the northwest Pacific, we analyzed partial nucleotide sequences of three mitochondrial DNA regions (523 bp in COI, 712 bp in ND4 and 617 bp in Cytb) based on specimens collected from six locations in Korea and Japan. The genetic diversities of E. burgeri were higher in Korean locations compared to Japanese ones. AMOVA showed that E. burgeri was completely separated into two groups (group A: southern coast of Korea and western coast of Japan vs. group B: eastern coast of Japan). Furthermore, groups A and B were divided into each two lineages (lineage I: west southern coast of Korea, lineage II: east southern coast of Korea and western coast of Japan, lineage III and IV: eastern coast of Japan). Our molecular results suggest that these two groups and lineages of E. burgeri may be different evolutionary significant unit and management unit, respectively.

Direct Measurement of Adhesion Force of Individual Aerosol Particles by Atomic Force Microscopy

A new method, namely, force–distance curve mapping, was developed to directly measure the adhesion force of individual aerosol particles by atomic force microscopy. The proposed method collects adhesion force from multiple points on a single particle. It also takes into account the spatial distribution of the adhesion force affected by topography (e.g., the variation in the tip angle relative to the surface, as well as the force imposed upon contact), thereby enabling the direct and quantitative measurement of the adhesion force representing each particle. The topographic effect was first evaluated by measuring Polystyrene latex (PSL) standard particles, and the optimized method was then applied on atmospherically relevant model dust particles (quartz, ATD, and CJ-1) and inorganic particles (ammonium sulfate and artificial sea salt) to inter-compare the adhesion forces among different aerosol types. The method was further applied on the actual ambient aerosol particles collected on the western coast of Japan, when the region was under the influence of Asian dust plume. The ambient particles were classified into sea salt (SS), silicate dust, and Ca-rich dust particles based on individual particle analysis (micro-Raman or Scanning Electron Microscope/Energy Dispersive X-ray Spectroscopy (SEM-EDX)). Comparable adhesion forces were obtained from the model and ambient particles for both SS and silicate dust. Although dust particles tended to show smaller adhesion forces, the adhesion force of Ca-rich dust particles was larger than the majority of silicate dust particles and was comparable with the inorganic salt particles. These results highlight that the original chemical composition, as well as the aging process in the atmosphere, can create significant variation in the adhesion force among individual particles. This study demonstrates that force–distance curve mapping can be used as a new tool to quantitatively characterize the physical properties of aerosol particles on an individual basis.

Reinstatement of Myelophycus caespitosus (Scytosiphonaceae, Phaeophyceae) from Japan

SUMMARYReinstatement of Myelophycus caespitosus Kjellman (Ectocarpales s.l., Phaeophyceae) described from western Japan is proposed based on the comparisons of DNA sequences of Japanese Myelophycus specimens, the type specimen of Chordaria simplex and lectotypified specimen of Myelophycus caespitosus. In the genetic analyses using mitochondrial cox1 and cox3, chloroplast atpB, psbA and rbcL DNA sequences, the specimens morphologically referable to M. simplex formed two distinct clades (clade‐1 and clade‐2) supported by high statistical values. Clade‐1 was distributed on the western coast of Japan (Honshu, Shikoku and Kyushu) from the Kii Peninsula to Tsushima and the Pacific coast of Aomori, northeastern Honshu, and clade‐2 on the Pacific coast of central Honshu from Sanriku to the Kii Peninsula. Based on the cox3 DNA sequences and the location of the type locality at Shimoda, Izu Peninsula, clade‐2 was concluded to correspond to true M. simplex. There were no recognizable differences in the representative morphological features (height and diameter of sporophytes and gametophytes, number of cells comprising cortical, subcortical and medullary layers, thickness of plurilocular gametangia, or length and diameter of unilocular zoidangia) between the specimens included in the two taxa. Analyses of the specimens of the two taxa, including sympatric populations on the Kii Peninsula, using a nuclear genetic marker ocm3 did not suggest any genetic exchanges between the two taxa. On the other hand, cox3 gene sequence of the voucher specimen of Myelophycus caespitosus collected from Goto, Kyushu, western Japan housed in the UPS herbarium was included in clade‐1. In conclusion, we propose the reinstatement of M. caespitosus and to lectotypify the specimen in UPS. Korean Myelophycus specimens reported from Cheju Island and Wando were considered to belong to M. caespitosus based on the reported rbcL sequences.

Holocene changes in flooding frequency in South Korea and their linkage to centennial-to-millennial-scale El Niño–Southern Oscillation activity

AbstractTo trace past changes in flooding frequency, we investigated fluvial sediments in the middle reach of the Nakdong River, South Korea. Sediments with larger grain size, lower total organic carbon percentage, and depleted δ13C values in the recovered sediment cores were interpreted as periods of more frequent flooding. Patterns of decreased long-term flooding frequency and vegetation changes during the early to late Holocene were similar to the decreasing regional summer monsoon intensity. Multicentennial frequent flooding periods in the study area (2900–3400 cal yr BP, 3600–3900 cal yr BP, 4600–5300 cal yr BP, and 5800–6400 cal yr BP) corresponded to stronger El Niño–Southern Oscillation (ENSO) activity periods. Based on previous studies showing that high-frequency tropical typhoon-driven coastal inundation along the western coast of Japan during the middle to late Holocene was coupled with stronger ENSO activity, it is likely that the observed centennial-to-millennial-scale flood frequency change in South Korea was influenced mainly by changes in the genesis and tracks of tropical typhoons at centennial-to-millennial time scales. This suggests that the centennial-to-millennial-scale hydrologic changes in East Asia were linked to the remote atmospheric-oceanic circulation changes represented by an ENSO-like pattern.

Building Damage Assessment Using Scenario Based Tsunami Numerical Analysis and Fragility Curves

A combination of a deterministic approach and fragility analysis is applied to assess tsunami damage caused to buildings. The area selected to validate the model is Imwon Port in Korea. The deterministic approach includes numerical modeling of tsunami propagation in the East Sea following an earthquake on the western coast of Japan. The model is based on the linear shallow-water equations (LSWE) augmented with Boussinesq approximation to account for dispersion effects in wave propagation, and coastal wave run-up is modeled by non-linear shallow-water equations (NLSWE). The output from the deterministic model comprises inundation depth. The numerical output is used to perform fragility analysis for buildings vulnerable to flooding by tsunamis in the port area. Recently developed fragility curves—based on the ordinal regression method—are used for damage probability estimates. The extent of structural damage in the areas under a tsunami hazard is identified by the numerical modeling of tsunami features. Our numerical model offers high bathymetric resolution, which enables us to capture flow features at the individual structure level and results in improved estimation of damage probability. This approach can serve as a measure of assessing structure vulnerability for areas with little or no records of tsunami damage and provide planners with a better understanding of structure behavior when a tsunami strikes.

Simulation of the impact of climate change on the egg and larval transport of Japanese anchovy (Engraulis japonicus) off Kyushu Island, the western coast of Japan

AbstractIn order to investigate the impact of climate change on egg and larval transport of Japanese anchovy (Engraulis japonicus) off Kyushu Island western Japan, we conducted particle‐tracking simulations on transport success/failure to fishing grounds from 1960 to 2007. The modeled transport success since the mid‐1990s increased and decreased in the offshore and coastal zones, respectively, compared with the 1960s and 1970s. The estimated northward shift of the spawning ground and weakened Tsushima Warm Current contributed to increase in modeled transport success to the offshore zone. Conversely, the weakening trend of the modeled onshore current in the Goto‐Nada Sea combined with the northward shift of the spawning ground resulted in unsuccessful larval transport. These results suggest that fluctuations in juvenile and subadult anchovy catches in this area may be attributable to changes in the physical environment. The present study showed that changes in transport success induced by oceanographic fluctuations related to climate change, have the potential to affect anchovy recruitment off the western coast of Japan.

Discovery of two novel viruses expands the diversity of single-stranded DNA and single-stranded RNA viruses infecting a cosmopolitan marine diatom.

Recent studies have suggested that diatom viruses are an important factor affecting diatom population dynamics, which in turn are important in considering marine primary productivity. The marine planktonic diatom Chaetoceros tenuissimus Meunier is a cosmopolitan species and often causes blooms off the western coast of Japan. To date, two viruses, C. tenuissimus DNA virus (CtenDNAV) type I and CtenRNAV type I, have been identified that potentially affect C. tenuissimus population dynamics in the natural environment. In this study, we successfully isolated and characterized two additional novel viruses (CtenDNAV type II and CtenRNAV type II). This paper reports the basic characteristics of these new viruses isolated from surface water or sediment from the Hiroshima Bay, Japan. The physiological and morphological characteristics of the two new viruses were similar to those of the previously isolated viruses. However, the amino acid sequences of the structural proteins of CtenDNAV type II and CtenRNAV type II were clearly distinct from those of both type I viruses, with identity scores of 38.3% and 27.6%, respectively. Our results suggest that at least four genetically distinct viruses sharing the same diatom host are present in western Japan and affect the population dynamics of C. tenuissimus. Moreover, the result that CtenRNAV type II lysed multiple diatom species indicates that RNA viruses may affect various diatom populations in the natural environment.

Decadal sea‐level variability along the coast of Japan in response to ocean circulation changes

Decadal sea‐level variability along the coast of Japan and its relation to large‐scale ocean circulation changes from 1993 to 2010 was investigated using tide‐gauge and satellite‐derived sea‐level data. A singular value decomposition (SVD) analysis is performed between coastal sea levels of Japan and sea levels in the western North Pacific. The first SVD mode reveals that the northward shifts of the Kuroshio Extension (KE) jet and the Kuroshio southeast of Japan accompany the coastal sea‐level rise in the early 2000s and 2010, and their southward shifts accompany the coastal sea‐level fall in the late 1990s and the late 2000s. The shifts of the KE jet are induced by westward propagating Rossby wave from the eastern North Pacific, which is concentrated along the KE jet axis as jet‐trapped Rossby waves. The resulting sea‐level changes along the coast of Japan show a strong spatial contrast. The sea‐level fluctuation is quite large along the southeastern coast of Japan that is under the direct influence of the jet‐trapped Rossby waves, and also large in the western coast of Japan, probably due to coastal waves that are excited by the incoming Rossby waves, but is small north of the KE jet latitude. Hence, the nature of the wave trapped by the KE jet produces an “active zone” and a “shadow zone” of coastal sea‐level variability of Japan. Our results indicate that the correct representation of western boundary currents is necessary for reliable prediction of future coastal sea‐level changes.

Analysis of evacuation system on tsunami disaster prevention in Korea

Kim, D.S., Hong, S.J and Park, H.S., 2013. Analysis of evacuation system on tsunami disaster prevention in Korea.The purpose of this study is to develop tsunami hazard maps by analyzing the coastal inundation characteristics on the eastern coast of Korea. The Korean peninsula is mistakenly considered to be a country safe from tsunamis as it is located next to Japanese islands which are believed to act as a barrier in various disaster situations. However, in reality, it is rather disaster-prone as it is located in the seismic zone along the western coast of Japan in the East Sea. To date, five tsunamis have affected Korea, including the Kanpo tsunami in 1741, the Shankotan tsunami in 1940, the Niigata tsunami in 1964, the Central East Sea tsunami in 1983, and the Hokkaido south western tsunami in 1993, of which the Central East Sea tsunami and Hokkaido south western tsunami resulted in casualties and caused property damages, especially in the Gangwon province. In this study, future tsunamis with a high probability of occurrence are investigated through an analysis of the seismic zone in the East Sea. For the analysis, hypothetical tsunami scenarios are developed to examine the inundation characteristics and create tsunami hazard maps of the eastern coast of Korea; tsunami inundation characteristics are analyzed for the subject areas based on the numerical simulation results using different scenarios. According to the analysis, tsunamis tend to land in the eastern coastal areas of the Korea peninsula due to bathymetric features of the East Sea. Furthermore, tsunami heights are calculated to be up to twelve meters above mean sea level (MSL). Finally, the tsunami hazard maps are developed based on the inundation analyses of the study areas. By developing tsunami hazard maps, inundation areas, evacuation routes, and shelters can be easily predicted, established, and selected. In non-emergency situations, tsunami hazard map can be used for education and promotion purposes and as a reference for risk assessment and disaster prediction.

Dynamics of diatom viruses on the western coast of Japan

Diatoms are prominent primary producers that play an important role in global carbon cycles. Diatom dynamics are, therefore, important for biogeochemistry, fisheries and earth science. Viral infection is now assumed to be one of the most significant factors affecting diatom dynamics. However, few studies, based on practical field data, have focused on the relationship between diatoms and viruses in natural waters. To elucidate on this relationship, we assessed the temporal change in the abundance of diatoms and their viruses on the western coast of Japan from 2004 to 2009. Three species of diatoms were used as hosts to enumerate viruses in water and sediment sam- ples: Chaetoceros debilis, C. tenuissimus and C. salsugineum. Diatom viruses in the water column rapidly increased during C. debilis and C. tenuissimus blooms, maintaining a high abundance throughout the blooming period. These data suggest the potential importance of viruses in control- ling the population dynamics of diatoms in natural environments. The number of viruses in sediments fluctuated considerably, even during non-blooming periods, which suggests that virus-infected diatom cells were supplied to the sediments from water-column populations throughout the year. This process might be an important strategy to reduce the impact of viruses on diatom populations. Because diatom populations are thought to have an intimate relationship with their viruses in natural waters, further studies of diatom dynamics should include the effects of viral infections.

Resistance of the fish-killing dinoflagellate Cochlodinium polykrikoides against algicidal bacteria isolated from the coastal sea of Japan

Noxious red tides of the dinoflagellate Cochlodinium polykrikoides tend to be long lasting and cause mass mortalities of cultured and natural fish and invertebrates along the western coast of Japan and the southern coast of Korea. In order to assess the tolerance of C. polykrikoides to attack by algicidal bacteria, the effects of algicidal bacteria strains on the growth of three C. polykrikoides strains were examined in laboratory culture experiments. Algicidal bacteria used were two strains of Cytophaga (J18/M01 and AA8-2, direct attack type and wide prey range), three strains of Alteromonas (S, K, D) and one strain of Pseudoalteromonas (R, indirect attack type), which were all isolated by using Chattonella antiqua as a prey organism. Neither Cytophaga strain showed any algicidal activity. In the cases of Alteromonas and Pseudoalteromonas, some cultures of C. polykrikoides were killed, but at least 10 days or more were required for the death of this dinoflagellate. C. polykrikoides survived in the presence of algicidal bacteria in concentrations up to 10 6–10 7 cells ml −1, which is enough for other red tide microalgae to be killed. On the contrary, the algicidal effects of bacteria on C. antiqua were detected clearly within a few days. These results imply that C. polykrikoides is resistant to the six algicidal bacteria examined, which may reflect the capacity for mixotrophy. This resistance of C. polykrikoides to algicidal bacteria could provide a selective advantage for survival compared to other microalgae susceptible to attack by algicidal bacteria and hence prolong red tides caused by this harmful dinoflagellate.