Seto Inland Sea Research Articles

Food habits of fishes in salt marsh estuaries in the western Seto Inland Sea, Japan

Food habits of fishes in salt marsh estuaries in the western Seto Inland Sea, Japan

Geographic, seasonal and ontogenetic variations of δ15N and δ13C of Japanese sardine explained by baseline variations and diverse fish movements

Understanding and predicting variability in the stable isotope ratios of nitrogen and carbon (δ15N and δ13C, respectively) of small pelagic fish is crucial to enable isotopic studies of a variety of marine predators that feed on them. However, because the isotope ratios reflect plastic feeding habits and fish migration in addition to baseline variation, their predictions require a mechanistic understanding of how each factor contributes. Here, we investigated the habitat-wide variability of δ15N and δ13C of the Japanese sardine Sardinops melanostictus in the western North Pacific and its marginal seas (the East China Sea and the Sea of Japan). By combining this with the archived particulate organic matter (POM) dataset as a baseline, we aimed to understand how ecological processes and baseline fluctuations affect isotope ratios of the sardine. Both δ15N and δ13C of sardine showed significant geographical and seasonal trends, with higher values in southern nearshore areas, including the Seto Inland Sea, intermediate values in marginal seas and lower values in Pacific offshore areas. As the variations were largely consistent with the geographic trend and the temporally integrated seasonal trend of isotope ratios of POM, respectively, the baseline variations are the main determinant of sardine isotope composition. The trophic positions of sardine are therefore not significantly different between regions, with possible minor increases in the southern nearshore area. Adults showed less geographic variation than larvae and juveniles, likely due to slower turnover periods and wider migration ranges. Although larval and juvenile isotope ratios in marginal seas mostly reflected the local baseline, those in the Pacific offshore often reflected the baseline in the neighbouring southern region, suggesting contrasting juvenile movements between regions. Our results suggest that the δ15N and δ13C of Japanese sardine strongly reflect baseline variations, but can also be influenced by life-stage- and region-dependent fish movements, thereby demonstrating both the possibility and difficulty of mechanistically modelling the isoscapes of lower trophic position species.

Current Status of Antifouling Biocides Contamination in the Seto Inland Sea, Japan.

A monitoring survey of antifouling biocides was conducted in the Harima Nada Sea and Osaka Bay of the Seto Inland Sea, Japan to assess contamination by organotin (OT) compounds and alternative biocides. The concentrations of tributyltin (TBT) compounds in surface water ranged from 1.0 to 2.8ng/L, and the detected TBT concentrations in the bottom water layer were higher than those in the surface water. The concentrations of TBT compounds in sediment samples ranged from 2.0 to 28ng/g dry weight (dw), respectively. The concentrations of alternative biocides in the water and sediment were lower than those before the banning of TBT by the International Maritime Organization (IMO). Although triphenyltin (TPT) compounds were not detected in water samples, TPT compounds were detected in the range of < 0.1-2700ng/g dw in sediment samples. Their concentrations in the water samples were as follows: diuron, < 1-53ng/L; Sea-Nine 211, < 1-1.8ng/L; Irgarol 1051, < 1-4.0ng/L; dichlofluanid, < 1-343ng/L; and chlorothalonil, < 1-1ng/L, and the ranges of these alternative compounds in sediment samples were diuron, 32-488ng/g dw; Sea-Nine 211, 47-591ng/g dw; Irgarol, 33-128ng/g dw; dichlofluanid, 67-8038ng/g dw; and chlorothalonil, 31-2975ng/g dw. Thus, the OTs and alternative biocides have still been detected in water and sediment samples from closed sea areas.

Contribution of the open ocean to the nutrient and phytoplankton inventory in a semi-enclosed coastal sea

Abstract. The semi-enclosed coastal seas serve as a transition zone between land and the open ocean, and their environments are therefore affected by both. The influences of land were noticed but that of the open ocean were usually neglected. The Seto Inland Sea (SIS), which is connected to the Pacific Ocean, is a typical representative of semi-enclosed seas. To quantitatively assess the inventory of nutrients originating from land and the open ocean, as well as their supported phytoplankton in the SIS, we developed a three-dimensional coupled hydrodynamic–biogeochemical model and embedded a tracking technique in it. Model results showed that the open ocean contributes 61 % and 46 % to the annual inventory of dissolved inorganic nitrogen (DIN) and phytoplankton in the SIS, respectively. This proportion has apparent spatial variations, being highest near the boundary with the open ocean, decreasing from there towards the interior area of the SIS, and being lowest in the nearshore areas. The open ocean imports 799 mol s−1 of DIN to the SIS, 25 % of which is consumed by biogeochemical processes and 75 % of which is delivered again to the open ocean. Such a large amount of oceanic nutrient input and its large contribution to the inventory of DIN and phytoplankton suggest the necessity of considering the impact of open-ocean variabilities in the management of the land loading of nutrients for the semi-enclosed seas.

Changes and Challenges in Agriculture and Farmland on the Remote Islands of the Seto Inland Sea

Changes and Challenges in Agriculture and Farmland on the Remote Islands of the Seto Inland Sea

Exploring the perceptions and attitudes of residents at modern art festivals: The effect of social behavior on support for tourism

This study examines the extent to which residents' perceptions and attitudes regarding a modern art festival influence their support for the event. Tourism events can affect residents' quality of life and lead to diverse levels of support among the local population. Few studies have used residents' social behavior as a variable. Exchange-based variables, such as the interaction between residents and visitors and their involvement in events, have rarely been employed in Social Exchange Theory-based research. The study identifies four clusters depending on diverse levels of exchange and support for a tourism event using exchange variables and the perceived regional revitalization, perceived impact of proximity, and support for continuing the event, as well as a variable for thought change which is specific to this study. Data were collected from residents of the twelve islands in the Seto Inland Sea of Japan where the art festival took place. The quantitative data was complemented by text-mining analysis to investigate the reasons for residents’ perceptions and attitudes.

Public perception and acceptance of nutrient supply from factories and sewage treatment plants to mitigate coastal oligotrophication: A case study in Japan

Coastal nutrient management often aims to reduce nutrients to avoid eutrophication; however, nutrient supply (i.e., enrichment) is an emerging issue in the post-eutrophication era when certain areas face oligotrophication. For example, part of Japan's Seto Inland Sea (SIS) faces oligotrophication, causing fish catch decline and bleaching of cultured nori (Piropia yezoensis). Hyogo Prefecture has implemented a nutrient management plan that includes five nutrient supply measures. However, concerns regarding public support for the plan existed because the key measure utilizes factories and sewage treatment plants (FSTP) to supply nutrients that may be associated with the negative preconception of “polluting the coastal sea.” Successful management needs public understanding and support for the measure. Therefore, understanding public perception and contriving measures to gain public support is a critical management issue. Using five online questionnaire surveys in a before–after information design with 3200 residents in Hyogo Prefecture, this study revealed public perception and acceptance of the measures with a focus on nutrient supply from FSTP and discussed management implications. The respondents were unfamiliar with the plan and measures. Contrary to the concerns, the nutrient supply from FSTP was positively perceived and accepted, although it was the least favored in all aspects. A lack of knowledge and misunderstandings led to negative comments, and information provision effectively improved the affective evaluation of the five measures. The respondents with a stronger connection to the SIS tended to have a better knowledge of the oligotrophication of the SIS. Trust in responsible actors varied. Five management implications (i.e., overall support for nutrient supply measures, raising awareness of problems, education, trust building, and strengthening the connectedness of people with nature) were discussed to improve public support for the plan and measures.

Distribution characteristics of vegetation on the drift lines at small beaches in the coastal area of the Seto Inland Sea

Distribution characteristics of vegetation on the drift lines at small beaches in the coastal area of the Seto Inland Sea

Wastewater treatment plants elevating microplastic abundances, ecological risks, and loads in Japanese rivers: a source-to-sink perspective.

Little were certain about how wastewater treatment plants (WWTPs) affected the Japanese riverine microplastic contamination. This study explored the influences of WWTPs on microplastic pollution, assessed ecological risks, and looked at the sources-to-sinks phenomenon (WWTPs-to-rivers-to-marine) in riverine settings in Japan's Yamaguchi prefecture. Fifty surface water samples from the five selected rivers (Koya, Saba, Shimaji, and Fushino, Nishiki) and 11 effluent samples from WWTPs in the rivers' catchment were examined. Microplastics were analyzed using filtration, wet-peroxidation, density-separation, and attenuated reflectance-Fourier transform infrared spectroscopy techniques. Results suggested that the less populated and rural river (Nishiki) was less contaminated compared to the WWTPs and urban areas affected rivers (Koya, Saba, Shimaji, and Fushino). The WWTPs increased microplastic abundance twofold in the downstream regions compared to upstream stations. Microplastic characterization showed that the smaller microplastics < 500µm, fiber-shaped, transparent, blue, and green color particles were major. Polymer identification demonstrated that the polyethylene, polypropylene, and polyethylene terephthalate were prevalent both for the rivers and WWTP effluents. There was a significant emission of microplastics from WWTPs to rivers (4.671 billion pieces per day; 71.8kg per day) and rivers to Seto Inland Sea (0.13/billion pieces per day/km2; 7.1kg per day). The per capita MP emissions to the rivers via WWTPs ranged from 0.02 to 6.49g per day, which was approximately 2% of per capita single-use plastic wastes in Japan. An assessment of ecological risks showed that the WWTPs posed high ecological risks to rivers, and built up the pollution hotspots to their downstream areas by releasing higher number of microplastics and highly toxic polymers. Overall, the WWTPs influenced the rivers through both abundances and characteristics (shapes-size-color-polymers), increased the complexity of microplastic compositions as well as elevated ecological risks in the rivers. This study contributed to bridging the knowledge gaps about microplastic sources-to-sinks, ecological risks, and pollution management in Japan and beyond.

Characteristics of PM2.5-bound metals in Japan over six years: Spatial distribution, health risk, and source analysis

Air sampling campaigns were conducted at 100 survey sites across Japan from April 2014 to February 2020, and a comprehensive database of atmospheric particles was obtained. In this study, the characteristics of PM2.5 and 26 metals were investigated in depth. Spatially, the concentration of PM2.5 gradually increased from the northeast to the southwest of Japan. The pollution in Kitakyushu City was the most serious, reaching 19.8 μg m−3. As an important particle component, metals did not show obviously spatial variation in Japan, with a sum concentration of 0.4 μg m−3. Anthropogenic metals only accounted for about 8% of the total metals, but they could pose a serious threat to public health. For children, the non-carcinogenic risk and carcinogenic risk due to exposure to anthropogenic metals could not be neglected in Japan; the corresponding HI and CR values at 100 survey sites ranged from 2.7 to 15.0 and 4.1 × 10−5 to 3.4 × 10−4, respectively. Adults faced lower health risks than children, with HI values ranging from 0.2 to 2.0 and CR values ranging from 2.0 × 10−5 to 1.6 × 10−4. The integrated health risk assessment results showed that the coastal region of the Seto Inland Sea and the north Tohoku Region were the most heavily polluted areas of Japan; in this study, 20 survey sites were finally determined to be high-risk sites, among which pollution control for Niihama City, Kitakyushu City, Hachinohe City, and Shimonoseki City were of first priority. With further combination with a positive matrix factorization model, it can be known that these four cities mainly had five to seven metal sources, and their heavy pollution was mainly caused by ship emissions, industrial emissions, biomass burning, and coal combustion. Overall, our study comprehensively revealed the regional patterns of PM2.5-bound metal pollution across Japan, which can help in making cost-effective risk management policies with limited national/local budgets.

Variations in echolocation click characteristics of finless porpoise in response to day/night and absence/presence of vessel noise.

Small odontocetes produce echolocation clicks to feed and navigate, making it an essential function for their survival. Recently, the effect of vessel noise on small odontocetes behavior has attracted attention owing to increase in vessel activities; however, the effects of the surrounding environmental factor, vessel noise, and day/night on echolocation click characteristics have not been well studied. Here, we examined the effects of vessel noise and day/night on variations in echolocation clicks and click trains parameters. Passive acoustic monitoring of on-axis echolocation clicks produced by free-ranging finless porpoises (Neophocaena asiaeorientalis sunameri) was performed at two sites in Japan, Seto Inland Sea and Mikawa Bay, in June-September 2021 and March-August 2022, using A-tag and SoundTrap 300HF. Generalized Linear Model was used to elucidate the effect of vessel noise, day/night, and surrounding environmental factors (water temperature, synthetic flow velocity, and noise level) on echolocation click and click train parameters. Echolocation click and click train parameters were strongly affected by day/night, whereas the absence/presence vessel noise did not exhibit statistically significant influence. Particularly, -3 dB bandwidth was wider, click duration was shorter, and inter-click intervals in a train were shorter at night, which may facilitate information processing at night, thereby compensating for the lack of visual information. The interaction between day/night and the absence/presence of vessel noise affected the source level of finless porpoises, with higher levels observed in the absence of vessel noise during the daytime compared to other conditions at the site with low vessel traffic. Overall, these results suggest that echolocation clicks by finless porpoise were likely to fluctuate to adapt with surrounding complex environmental conditions, especially day/night.

The effects of sea-bottom plowing on phytoplankton assemblages: a case study of northern Hiroshima Bay, the Seto Inland Sea of Japan

Sea-bottom plowing is originally a method used to oxidize sediment by stirring the bottom with a trawl fishing tool, and its effect in increasing primary productivity of the water column was investigated in the western part of the Seto Inland Sea of Japan. Preliminary field sampling showed that diatom resting stage cells were abundant in the sediment of the tested area at 1.5–2.6 × 105 MPN g-1 wet sediment. When the sediment was added to filtered seawater, diatom cells emerged from the sediment after one day and increased more drastically under a light level corresponding to sunny weather than cloudy weather. In the actual trials of sea-bottom plowing on the field for a continuous period of 4 years, dissolved inorganic nutrients increased at the bottom layer after the plowing and promoted photosynthetic activities of the phytoplankton communities in 2018 and 2021. Chlorophyll a concentration at the middle layers increased 1.06–2.15 times after plowing throughout the trials for 4 years. Diatoms contributed to 67–99% of this chlorophyll a concentrations and included the genera Skeletonema and Chaetoceros, which formed resting-stage cells in the sediment. Pseudo-nitzschia spp. often increased after the plowing, which was assumed to be of seawater origin. Estimated primary productivities of the middle layers dropped once the following day due to turbid water caused by the plowing but increased 2.03–4.41 times after two or five days in 2018, 2019, and 2021. These results suggest that sea-bottom plowing has an enrichment effect on diatoms and could be a possible measure to fertilize the sea.

Unstructured Grid-Based River–Coastal Ocean Circulation Modeling towards a Digital Twin of the Seto Inland Sea

As computational techniques advance, the scope of digital twins (DTs) is expanding to encompass entire cities, oceans, or even the Earth. Digital twins of oceans can provide highly comprehensive insights and predictions, thus enabling better-informed decision-making regarding ocean-related activities and management. Here, a numerical model of the Seto Inland Sea (SIS), Japan, was built as a basis to establish a digital twin of the SIS. Spatially varying filtering parameters and grid resolutions were applied to facilitate the robust and accurate simulation of coastal and oceanic processes even under varying extreme conditions. The modeling results were validated using observational datasets from forty-two tidal stations, one mooring system, and thirteen water thermometers. The results represented tidal variations, with NRMSE values below 0.15 and R2 values exceeding 0.87 at all tidal stations. The NRMSE and R2 values for currents were approximately 0.14 and 0.76, respectively. The model reproduced the extreme storm surge event causing a sea level rise of 1.5 m near Osaka City resulting from Typhoon Jebi in 2018. The model was shown to enable analyses of complex circulations and hazards in the SIS by accurately replicating barotropic and baroclinic processes. After additional modules are added, this model will serve as a basis for constructing a digital twin of the SIS.

Short-term effects of the chemical components of fine particulate matter on pulmonary function: A repeated panel study among adolescents

The effects of the chemical components of fine particulate matter (PM2.5) have been drawing attention. However, information regarding the impact of low PM2.5 concentrations is limited. Hence, we aimed to investigate the short-term effects of the chemical components of PM2.5 on pulmonary function and their seasonal differences in healthy adolescents living on an isolated island without major artificial sources of air pollution. A panel study was repeatedly conducted twice a year for one month every spring and fall from October 2014 to November 2016 on an isolated island in the Seto Inland Sea, which has no major artificial sources of air pollution. Daily measurements of peak expiratory flow (PEF) and forced expiratory volume in 1 s (FEV1) were performed in 47 healthy college students, and the concentrations of 35 chemical components of PM2.5 were analyzed every 24 h. Using a mixed-effects model, the relationship between pulmonary function values and concentrations of PM2.5 components was analyzed. Significant associations were observed between several PM2.5 components and decreased pulmonary function. Among the ionic components, sulfate was strongly related to decreases in PEF and FEV1 (−4.20 L/min [95 % confidence interval (CI): −6.40 to −2.00] and − 0.04 L [95 % CI: −0.05 to −0.02] per interquartile range increase, respectively). Among the elemental components, potassium induced the greatest reduction in PEF and FEV1. Therefore, PEF and FEV1 were significantly reduced as the concentrations of several PM2.5 components increased during fall, with minimal changes observed during spring. Several chemical components of PM2.5 were significantly associated with decreased pulmonary function among healthy adolescents. The concentrations of PM2.5 chemical components differed by season, suggesting the occurrence of distinct effects on the respiratory system depending on the type of component.

Ecomorphology of three closely related Sebastes rockfishes with sympatric occurrence in Seto Inland Sea, Japan

Ecomorphology of three closely related Sebastes rockfishes with sympatric occurrence in Seto Inland Sea, Japan

Abnormal high tides and flooding induced by the internal surge in Hiroshima Bay due to a remote typhoon

The Itsukushima Shrine is located in northern Hiroshima Bay in the Seto Inland Sea (SIS). This structure of great cultural value is preserved as one of the World Heritage Sites in Japan. The shrine was built seaside, 30 cm above the highest tide, to prevent it from submerging. However, from 2011 to 2019, the shrine was submerged four times during September due to internal surges. To study the abnormal tide event on 29 September 2011, a high-resolution numerical ocean circulation model was established using Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM). Observed subtidal components of surface elevation in the northern part of the bay decreased due to northerly winds when the typhoon passed east off the bay. After 7–8 days of typhoon passage, the component increased abnormally in the northern part of the bay. Simulation results revealed that a destabilized density stratification by the typhoon winds most likely caused bay-scale internal waves. The internal wave developed after the typhoon passed and was caught from the kinetic energy filtered in the possible internal wave periods. The internal wave propagated southward after the typhoon passage and returned to the northern bay, causing the subtidal component to increase after 7–8 days. Sensitivity tests with various scales of the typhoon were performed, and the test results exhibited a positive relationship between the abnormal tide level and typhoon intensity to some extent. The results can be generally applied to a semi-closed bay or closed water body for internal wave generation and propagation under specific meteorological conditions for coastal protection and disaster prevention.

A Study of Landscape Features in the Coastal Area of the Seto Inland Sea Based on Landscape Paintings.

Landscape paintings provide an abundant and objective representation of good and distinctive local scenery, which is widely used in local landscape analysis, so the comprehensive research of landscape paintings is fundamental and necessary for the subsequent landscape planning work. Landscape paintings include both planar information and spatial information. However, there has been little previous work on landscape paintings from both a three-dimensional and planar perspective, and the landscape features of landscape paintings have not yet been comprehensively clarified. Therefore, this paper, taking the Seto Inland Sea area as a case study, aims to comprehensively clarify the landscape features of the paintings and provide a valuable index of "good and characteristic landscapes" in this area based on the two planar features of element configuration and color, along with one spatial feature (element arrangement). To deeply clarify the typical landscape features of paintings, we attempt to propose a classification method by combining the similarity of features in different attributions. The results indicate that Sky, Green, and Sea are the most essential landscape elements, and yellow (orange), blue, and green hues are the most used in the paintings. In addition, the paintings were classified into eight typical landscapes, and seascape and field landscapes were the most significant presented in the landscape paintings in this area. This study presents a method to clarify the landscape features from both planar and spatial perspectives, providing more comprehensive guidance and data support for the subsequent landscape planning work and analysis-especially in regional landscape exploration-and for the development of tourism landscape resources in urban planning.

NOx should be recycled by stoping of NOx elimination by ammonia. Waste water purification center should be closed

Global warming is caused by the lack of N and P and decrease of CO2 assimilation and decrease of CO2 fix and decrease of heat absorption. Lack of N and P is caused by the elimination of NOx and NP in waste water. Fish production at Seto inland sea decreased 90% by the lack of N and P. Global warming will stop if developed countries stop the elimination of NOx and NP. CO2 assimilation will be activated and Global warming will stop. The author presented petition to stop the elimination of NOx by ammonia and to close waste water purification center. If developed countries stop the elimination of NOx by ammonia and close waste water purification. CO2 assimilation is activated and Global warming will stop

July 2020 heavy rainfall in Japan: effect of real-time river discharge on ocean circulation based on a coupled river-ocean model

In July 2020, a stationary atmospheric front over Japan caused persistent, nearly continuous rain for most of the month that resulted in new historical highest rainfall records in several areas and caused serious river floods, landslides, and debris-flow events. An existing hindcast and forecast ocean circulation model that includes climatological discharge information of major rivers failed to represent the extreme river discharge under heavy rainfall. New experiments were conducted using real-time river discharge information based on Today's Earth CaMa-Flood simulation that includes 368 rivers in Japan. The inclusion of real-time river discharge improved the salinity bias in the near-surface waters. The differences were significant compared to the observations in the heavy rain region (i.e., Ariake Bay and Tosa Bay), and insignificant at offshore stations. The ensemble experiments of real-time river discharge cases suggested the difference between the climatological and the real-time river discharge experiments was not random, but was robust. The freshening water changed the shelf circulation, and its far-reaching effect appeared hundreds of kilometers away from the shore. Passive particle tracking was conducted for examining the cross-shelf exchange. More particles released from Bungo Channel went offshore in near-surface water when the real-time river discharge was used compared to using the climatology discharge. Particles released in Tosa Bay, Seto Inland Sea, and Kii Channel showed the opposite tendency. The real-time river discharge not only changed the modeled coastal salinity distribution, but also the coastal and offshore currents. The role of the real-time river discharge on modeling normal flow periods or drought events, and its influence on a longer time scale model simulation remain to be explored.

Influence of Vegetation Coverage on Dissolved Oxygen Concentration in Seagrass Bed in the Seto Inland Sea: Possible Effects on Fish Nursery Function

Influence of Vegetation Coverage on Dissolved Oxygen Concentration in Seagrass Bed in the Seto Inland Sea: Possible Effects on Fish Nursery Function