Japanese Coast Research Articles

Difference in the stable nitrogen isotope ratio of Sargassum piluliferum (Phaeophyceae: Fucales) associated with fish and pearl oyster aquaculture facilities

In order to estimate the nitrogen loading from fish aquaculture facilities, we studied the nitrogen and carbon stable isotope ratios (δ15N and δ13C, respectively) in the brown macroalga Sargassum piluliferum and small amphipod crustaceans Caprella spp., both of which are lower trophic level biota found at fish and pearl oyster aquaculture facilities situated along the eastern coast of the Uwa Sea, Japan. This coastal region is one of the least populated areas along the Japanese coast. The mean concentrations of chlorophyll a, dissolved inorganic nitrogen, dissolved inorganic phosphate, and dissolved silicate-Si were 1.5- to 2-fold higher in samples from the fish aquaculture facilities than in those from the pearl oyster aquaculture facilities, indicating that the fish aquaculture facilities were associated with nitrogen loading. The δ15N abundance level in S. piluliferum collected from the fish aquaculture facilities was significantly higher (1.3‰) than that in macroalga collected at the pearl oyster aquaculture facilities, whereas that in Caprella spp., primary consumers, was only slightly higher (0.3‰). The feeding style of Caprella spp., which depends on suspended particulate organic matter and attached microalgae, is considered to the primary causal factor for the lack of a significant difference in δ15N abundance level between the two types of aquaculture facilities. Based on these results, we conclude that S. piluliferum found in close proximity of aquaculture facilities is a suitable organism for monitoring nitrogen loading from fish aquaculture facilities, through the analysis of δ15N.

Modeling of marine litter drift and beaching in the Japan Sea

Characteristics of drift and beaching of floating marine litter in the Japan Sea are examined numerically using the reanalysis data of the Japan Sea Forecasting System of Kyushu University. The residence time of model marine litter deployed uniformly over the surface of the Japan Sea strongly depends on the buoyancy ratio. However, almost all litter beaches or flows out through straits within 3years. Experiments with inputs of litter imposed at large cities and the Tsushima Straits as well as river basins of the Japan Sea exhibit a good agreement with beach surveys with regard to country ratios of beached litter along the Japanese coast in cases of lighters. In a case of lighter, almost all lighters originating from Japan beach along the Japanese coast, while almost all lighters originating from a country surrounding the Japan Sea except Japan beach along the coast of that country and the Japanese coast.

Coast guards and maritime piracy: sailing past the impediments to cooperation in Asia

Despite the efforts of the past decade, maritime piracy remains of international concern today. Countries need to cooperate actively at both the regional and international levels to eradicate the problem effectively. In particular, the nature of the threat in the Asia-Pacific region suggests that coastal states – countries that possess sovereignty over the pirate-infested waters but lack the law-enforcement resources – have to turn to resource-rich extra-regional powers for assistance. Unfortunately, cooperation between such disparate countries has traditionally been impeded by sovereignty sensitivities, as best exemplified by Malaysia's and Indonesia's hostile responses to the United States' Regional Maritime Security Initiative in 2003. Faced with this apparent dilemma, a new phenomenon has emerged. National coast guard agencies, instead of their military naval counterparts, have become attractive alternatives for promoting international cooperation against non-traditional security threats, such as maritime piracy. Spearheaded by the Japanese Coast Guard (JCG), coast guards from various countries have imparted training expertise, conducted joint exercises, hosted low-publicity multilateral meetings, and even transferred security equipment across international borders. Together they have succeeded in promoting cooperation without arousing the sovereignty sensitivities often associated with such cooperation. This article analyzes the evolution of coast guard cooperation in Asia, highlighting in particular the Japanese Coast Guard's success in this endeavor. With the general alignment of regional and global power interests in Southeast Asia, coast guard agencies hold promise for extra-regional powers wishing to help eradicate maritime piracy in the region.

Multi-scale modeling of CO2 dispersion leaked from seafloor off the Japanese coast

A numerical simulation was conducted to predict the change of pCO2 in the ocean caused by CO2 leaked from an underground aquifer, in which CO2 is purposefully stored. The target space of the present model was the ocean above the seafloor. The behavior of CO2 bubbles, their dissolution, and the advection–diffusion of dissolved CO2 were numerically simulated. Here, two cases for the leakage rate were studied: an extreme case, 94,600t/y, which assumed that a large fault accidentally connects the CO2 reservoir and the seafloor; and a reasonable case, 3800t/y, based on the seepage rate of an existing EOR site. In the extreme case, the calculated increase in ΔpCO2 experienced by floating organisms was less than 300ppm, while that for immobile organisms directly over the fault surface periodically exceeded 1000ppm, if momentarily. In the reasonable case, the calculated ΔpCO2 and pH were within the range of natural fluctuation.

Scattering of near‐inertial internal waves along the Japanese coast of the Japan Sea

The scattering of near‐inertial internal waves (NIIWs) induced at the tips of landmasses was investigated by mooring observations using current meters and thermometers in the surface layer along peninsulas and an island located along the Japanese coast of the Japan Sea during the fall of 2006. Signals of NIIWs were found in alongshore currents and in temperatures recorded near the seasonal thermocline. The signals appeared after wind stress had reached a maximum, and they lasted for more than 2 days. Relatively high current energy regions due to NIIWs were localized around the northern parts of the peninsulas and island. The phase lag of the temperature fluctuations increased in the southern regions along the eastern coasts of the peninsulas and island. The generation and propagation of NIIWs were investigated by numerical experiments that used a multilayer level model with realistic topography. Model results showed that NIIWs induced by the wind struck the tips of landmasses and scattered and that NIIWs were trapped by the coast and propagated with characteristics of coastal‐trapped waves (CTWs) and then rapidly attenuated. The CTWs had a distorted current structure at landmass tips because of periodic beam‐like current structures from the seafloor. These signals show that CTWs radiate energy away from the shore as internal waves originating from topographical scattering, which is considered to cause the rapid attenuation of the CTWs.

Modeling of the branches of the Tsushima Warm Current in the Eastern Japan Sea

The branches of the Tsushima Warm Current (TWC) are realistically reproduced using a three-dimensional ocean general circulation model (OGCM). Simulated structures of the First Branch and the Second Branch of the TWC (FBTWC and SBTWC) in the eastern Japan Sea are mainly addressed in this study, being compared with measurement in the period September–October 2000. This is the first numerical experiment so far in which the OGCM is laterally exerted by real volume transports measured by acoustic Doppler current profiler (ADCP) through the Tsushima Straits and the Tsugaru Strait. In addition, sea level variation measured by tide-stations along the Japanese coast as well as satellite altimeters is assimilated into the OGCM through a sequential data assimilation method. It is demonstrated that the assimilation of sea level variation at the coastal tide-stations is useful in reproducing oceanic conditions in the nearshore region. We also examine the seasonal variation of the branches of the TWC in the eastern Japan Sea in 2000. It is suggested as a consequence that the FBTWC is continuous along northwestern Honshu Island in summertime, while it degenerates along the coast between the Sado Strait and the Oga Peninsula in other seasons. On the other hand, a mainstream of the SBTWC exists with meanders and eddies in the offshore region deeper than 1000 m to the north of the Sado Island throughout the year.

High water temperature tolerance in photosynthetic activity of Zostera japonica Ascherson & Graebner seedlings from Ago Bay, Mie Prefecture, central Japan

Photosynthetic activity of Zostera japonica seedlings was measured using a gas volumeter at 0 and 6 days in culture under eight light (0–800 μmol photons/m2/s) and ten water temperature conditions (5–35°C). Seedlings from Ago Bay, Mie Prefecture were cultured in incubators accurately controlled at each test temperature for 1 week. After 1 week, maximum gross photosynthesis (P maxg) appeared at 29°C and most seedlings cultured at 30–35°C bleached and withered. At the same time, the light compensation point (I c) increased only at 30°C during the culture period. As a result, the upper critical water temperature for survival was 29°C in Z. japonica seedlings, which agrees well with that for the southern boundary of Z. japonica around Japanese coast. It is necessary to monitor this species around this boundary as a bio-indicator for seawater warming.

Modeling the effects of atmospheric nitrogen input on biological production in the Japan Sea

The effects of atmospheric nitrogen input on biological production in the Japan Sea have been investigated using a coupled physical-ecosystem model. Comparison between the cases with and without nitrogen deposition shows a relatively large effect on primary production in the southern Japan Sea during summer to autumn, when nitrogen deposition is high and nutrient is depleted in the surface layer. The atmospheric nitrogen deposition supports > 10% of the annual export production in the nearshore region along the Japanese coast. The importance of atmospheric input as a new nutrient will grow steadily with increasing deposition into the Japan Sea.

Hydroides dianthus (Polychaeta: Serpulidae), an alien species introduced into Tokyo Bay, Japan

Calcareous tube polychaetes (family Serpulidae) are notorious biofoulers that are easily transported and introduced to allochthonous habitats. Here we report the recent introduction of Hydroides dianthus (Verrill, 1873) to eastern Japan as its first occurrence in East Asia, probably from European or American coasts. Specimens had been found on artificial hard substrata together with congeners H. ezoensis, H. exaltatus and H. fusicolus in Tokyo Bay, Japan in 2006. The origin, vector, source of introduction and possible impact of H. dianthus on Japanese coasts is discussed from a perspective based on worldwide Hydroides transport.

Dissolved iron(II) in the Pacific Ocean: Measurements from the PO2 and P16N CLIVAR/CO 2 repeat hydrography expeditions

The redox speciation of dissolved iron in seawater was evaluated at 121 locations in the Pacific Ocean at depths of 15-1000 m, using the method of luminol chemiluminescence. The results indicate that reduced iron, Fe(II), is ubiquitous in surface seawater with a relatively consistent pattern of occurrence. Surface maxima were present in most profiles, with median concentrations of 25-30 pM representing 12-14% of the total dissolved iron. Concentrations decreased monotonically with depth to<12 pM within the upper euphotic zone. This pattern was observed during both day and nighttime sampling events, which suggests that non-photochemical production mechanisms can produce photochemical-like signatures. Further, if theoretical rates of Fe(II) oxidation are applicable to the open ocean, then the employed sampling methods precluded assessment of photochemically-produced Fe(II), regardless of ambient light conditions. For this and other reasons, the concentrations reported here for the upper water column likely represent lower limits of labile iron concentration, and suggest that dissolved iron may be more available for uptake than previously believed. Deeper in the water column, Fe(II) was also frequently detected, though it constituted a small fraction of the total dissolved iron. Possible source mechanisms at these depths include thermal (dark) reduction of Fe(III) organic complexes or remineralization of sinking biogenic particles containing Fe(II). In the northern Philippine Sea between the Japanese coast and the Izu-Bonin volcanic arc system, Fe(II) concentrations were found to be atypically high, possibly because of high atmospheric dust deposition near the surface and transport of sediment-derived iron at depth.

Seasonal upwelling underneath the Tsushima Warm Current along the Japanese shelf slope

Seasonal upwelling variations are examined in the eastward coastal boundary branches of the Tsushima Warm Current (TWC). The climatological pattern and the fundamental hydrographic structure of the seasonal appearance of cold water are revealed by analyzing the temperature profile data around the Japanese shelf area. Seasonal maps of temperature at the intermediate layer around 200 m depth show the rise of the main pycnocline along the Japanese coast due to seasonal subsurface cooling from May to September. The cold water areas appear around the strong curvature in the continental shelf break. These areas are confined to the south of the TWC thermal front, i.e., to the coastal boundary region. The seasonal appearance of the localized cooling areas implies that the seasonal upwelling is induced by horizontal variations in shelf topography and the intensifying TWC from May to September.

Particle filtering with path sampling and an application to a bimodal ocean current model

This paper introduces a recursive particle filtering algorithm designed to filter high dimensional systems with complicated non-linear and non-Gaussian effects. The method incorporates a parallel marginalization (PMMC) step in conjunction with the hybrid Monte Carlo (HMC) scheme to improve samples generated by standard particle filters. Parallel marginalization is an efficient Markov chain Monte Carlo (MCMC) strategy that uses lower dimensional approximate marginal distributions of the target distribution to accelerate equilibration. As a validation the algorithm is tested on a 2516 dimensional, bimodal, stochastic model motivated by the Kuroshio current that runs along the Japanese coast. The results of this test indicate that the method is an attractive alternative for problems that require the generality of a particle filter but have been inaccessible due to the limitations of standard particle filtering strategies.

Geographical genetic structure and phylogeography of the Sargassum horneri/filicinum complex in Japan, based on the mitochondrial cox3 haplotype

The genetic structure and phylogeography of the brown seaweed Sargassum horneri/filicinum complex in Japan were studied based on the mitochondrial cox3 haplotype. The cox3 haplotypes found were divided into three clades in a statistical parsimony network, among which there were large numbers of steps. Contrary to the reported large amount of drifting S. horneri along the Japanese coast, the three clades were dividedly distributed on the Japanese coast: the northern Pacific, the central Pacific, and western Japan. The western Japan S. horneri had haplotypes that were phylogenetically closer to those of S. filicinum than to the northern and central Pacific S. horneri populations. The S. filicinum populations were included within the western Japan clade and grouped together with the S. horneri samples from western Japan. Taken together with the unstable morphological diagnosis, this result suggests that S. filicinum should be reduced into a synonymy of S. horneri. The TMRCA analysis suggested that the divergence time of each clade may go back to the last interglacial period and a skyline plot suggested that the last glacial maximum had only a small effect on the population size of S. horneri. The geographic subdivision of the three groups, in spite of a large amount of drifting mats, suggests a limited contribution of drifting mats to gene flow on a large geographic scale. On a small geographic scale, a small number of haplotypes were shared between S. horneri-type and S. filicinum-type populations. This result suggests that populations of these two types are partially, though not completely, isolated from each other, possibly by selfing in S. filicinum-type populations or by a difference in peak reproduction.

Erratum to: Comparisons of genetic population structures in four intertidal brachyuran species of contrasting habitat characteristics

Genetic population structures along the Japanese coast, analyzed by sequence data from the mitochondrial DNA COI region, were determined for four intertidal brachyuran species in the superfamily Thoracotremata (Ocypode ceratophthalma, Gaetice depressus, Chiromantes dehaani and Deiratonotus japonicus), which were characterized by different habitat requirements. O. ceratophthalma (seashore; supratidal sand) and C. dehaani (estuarine; supratidal marsh) showed no significant genetic differentiation among Japanese populations. The Japanese populations of O. ceratophthalma, however, were found to genetically differentiated from the Philippine population. G. depressus (seashore; intertidal cobbles) exhibited significant genetic differentiation between the Amami-Ohshima population and other local populations. D. japonicus (estuarine; intertidal cobbles) showed significant genetic differentiation among many local populations separated by about 30–1,200 km. The different patterns of genetic population structure recorded for the four species, thus, do not simply correspond to habitat type.

Excitation of Resonant Modes along the Japanese Coast by the 1993 and 1983 Tsunamis in the Japan Sea

We observed seiches at 55 ports in Japan facing the Japan Sea and obtained dominant periods from their maximum spectral amplitudes. These periods were mostly determined ranging from 10 to 40 minutes. They were compared with dominant periods of the 1993 Hokkaido Nansei-oki tsunami and the 1983 Nihonkai Chubu-oki tsunami at the same ports. As a result, relations of dominant periods between seiches and tsunamis are classified into three types. The first one is fundamental mode excitation, the second is higher mode excitation and the third is no excitation. Plotting the maximum spectral amplitude normalized at an epicentral distance of 50 km versus the ratio of the tsunami dominant period to the seiche dominant period, we obtained resonance curves having maxima at one. This fact shows a contribution of resonance to the amplification. Thus it is recognized that the dominant period of seiching is an important factor in interpreting amplification and resonance of tsunami.

炭素・窒素安定同位体比を用いた大阪湾の人工干潟における食物連鎖網の解析

Four years after the construction of an artificial tidal flat in Osaka Bay, Japan, the food web structure was analyzed using stable isotope ratios of nitrogen and carbon. The nitrogen stable isotope ratios (δ15N) ranged from 8.8±0.3‰ in Chondrus giganteus f. flabellatus (macroalga) to 15.2‰ in Repomucenus beniteguri (fish), whereas the carbon stable isotope ratios (δ13C) ranged from -18.6±0.2‰ in POM (particulate organic matter) to -10.5±1.1‰ in Ulva sp. (macroalga). The food web structure of the artificial tidal flat was estimated to be composed of three trophic levels. Moreover, it was thought that fishes inhabiting this ecosystem are dependent on POM and macroalgae (and/or benthic microalgae) for their carbon source, whereas crustaceans and mollusks are likely to be dependent on macroalgae (and/or benthic microalgae), not on POM. These results indicate that the food web structure of the artificial tidal flat resembles those of natural estuaries along the Japanese coasts. A temporal analysis of the food web structure of an artificial tidal flat and a comparison of such a structure to that of closely situated natural tidal flats using stable isotope analysis will contribute significantly to the evaluation of the structure and function of artificial tidal flats.

D212 マルチスケールモデルを用いた日本沿岸海底から漏洩したCO_2拡散のシミュレーション(OS12 温暖化対策とCO2削減技術)

A numerical simulation was conducted to predict the change in pCO_2 in seawater off a Japanese coast caused by the leakage of CO_2, which is originally stored in a sub-seabed aquifer to sequester CO_2 from the atmosphere. The behaviour of CO_2 bubbles, their dissolution, and the advection-diffusion of dissolved CO_2 were numerically simulated. As a result, it was suggested that the leaked CO_2 bubbles all dissolve in the seawater before spouting up to the atmosphere. The calculated increase of ΔpCO_2 experienced by floating organisms in an extreme case, in which the leakage rate was 94600 t/year, was less than 300 ppm, meanwhile that for immobile organisms right on the fault surface exceeded 500 ppm instantaneously and periodically. In a realistic case, in which the leakage rate was 3800 t/year, ΔpCO_2 and pH experienced by both floating and immobile organisms were in the range of natural fluctuation.

Phylogenetic relationship of two Mola sunfishes (Tetraodontiformes: Molidae) occurring around the coast of Japan, with notes on their geographical distribution and morphological characteristics

Phylogenetic analyses were conducted using complete nucleotide sequences of the D-loop in the mitochondrial genome of Mola specimens, collected mainly in Japanese waters, to clarify the genetic features and distribution patterns of Mola sunfishes. Two significantly distinct groups (designated A and B) were present in the genus, with a considerable net nucleotide sequence divergence between the two (8.4%). The two groups occurred sympatrically around the Japanese coast, as previously suggested by Sagara et al. (2005). Group A occurred mostly on the Pacific coast of eastern Japan, while group B was widely distributed along the Kuroshio Current, strongly suggesting different migration routes for each group. The morphological characteristics of the two group specimens were differentiated via the head bump, body proportions and shape of the clavus. Through the addition of Mola sequence data taken from outside Japan to our phylogenetic analyses, three independent groups, including groups A and B, were found, each with a wide geographical distribution, which suggests the presence of at least three independent species within the genus Mola.

Satellite evidence of wintertime atmospheric boundary layer responses to multiple SST fronts in the Japan Sea

We present satellite evidence of wintertime atmospheric boundary layer responses to multiple sea surface temperature (SST) fronts in the Japan Sea under cold‐air outbreak during 22–28 December 2005. It is found that the lower atmosphere adheres to the stepwise SST variations, focusing on a wind trajectory from the Eurasian continent to the northern Japan, which goes through the meandering Polar Front and the Tsushima Warm Current. Wind speed anomaly and wind divergence are linearly related to the SST anomaly and downwind SST gradient, respectively. Vertically uniform layers of potential temperature are accomplished when reaching the Polar Front and Tsushima Warm Current. Variations of water vapor mixing ratio and the resulting surface turbulent heat fluxes show also stepwise increases. Little wind vertical shear on the Japanese coast suggests that well‐mixed boundary layer is eventually formed.

Time Trends and Transplacental Transfer of Perfluorinated Compounds in Melon-Headed Whales Stranded Along the Japanese Coast in 1982, 2001/2002, and 2006

As a result of the phase-out of production of perfluorooctanesulfonyl-based compounds by a major producer, concentrations of perfluorooctanesulfonate (PFOS) in marine mammals from North American and European coastal waters have been declining since the early 2000s. Nevertheless, temporal trends in perfluorochemical (PFC) concentrations in marine mammals from Asian coastal waters have not been examined. In this study, PFCs were determined in livers of melon-headed whales (Peponocephala electra) collected along the coast of Japan, from three mass strandings that occurred during the past 25 years. Concentrations of nine PFCs were determined in livers of 48 melon-headed whales that were collected during strandings in 1982, 2001/2002, and 2006. In addition, concentrations in liver tissues obtained from two pregnant females and their fetuses were compared for determination of transplacental transfer rates of PFCs during gestation. PFOS and perfluorooctanesulfonamide (PFOSA) were the predominant PFCs found in livers of melon-headed whales collected in 1982 (n = 22). PFOS, PFOSA, perfluoroundecanoate (PFUnDA), perfluorododecanoate (PFDoDA), perfluorodecanoate (PFDA), and perfluorononanoate (PFNA) were found in whales collected in 2001/2002 (n = 21) and in 2006 (n = 5). Concentrations of PFOS and PFOSA were approximately 10-fold higher in 2001/2002 than in 1982. Whereas concentrations of PFOSA then declined by 2-fold from 2001/ 2002 to 2006, concentrations of PFOS and perfluorocarboxylates did not decline after 2001/2002. Conversely, concentrations of PFNA and PFDA increased significantly from 2001/2002 to 2006. The proportion of perfluoroalkylsulfonates in total PFC concentrations decreased from 75% in 1982 to 51% in 2006. Conversely, the contribution of perfluorocarboxylates to total PFC concentrations increased from 25% in 1982 to 49% in 2006. PFUnDA was the major perfluorocarboxylate found in whale livers collected after 2000. Analysis of paired samples of mother-fetus demonstrated that the transplacental transfer rates of PFCs were higher than those for PCBs and PBDEs.