Search Results (19)

The genus Sebastes comprises around 110 species of marine fish. In Japan, the Sebastes inermis complex includes three sympatric species (S. cheni, S. inermis, and S. ventricosus), and morphotypes that cannot be assigned to any of these three species. We focused on two morphotypes: (1) the ‘big red’, which is predominantly found in the Kii and Izu peninsulas and are traditionally believed to be large, older specimens of S. inermis; and (2) the ‘red white’, which is found in the Seto Inland Sea and Kagoshima and includes putative hybrids of S. cheni and S. inermis. We assessed the biological identity of both morphotypes by comparing their morphological and genetic variations with those of the three species. The meristic traits of both morphotypes overlapped with those of the three species. The ‘big red’ morphotype showed significant differences in body proportions and otolith structure, whereas the ‘red white’ morphotype differed mainly in otolith features. Phylogenetic analyses of mitochondrial and nuclear genes did not separate these morphotypes into distinct lineages. However, the ‘big red’ morphotype exhibited unique mutations at the rhodopsin gene. Analyses of microsatellite loci indicated that the divergence of both morphotypes is as large as the divergence observed between sister species within the genus. Phylogenetic analyses of genomic data placed the ‘big red’ morphotype in a basal position in relation to the three species and supported the separation of the ‘red white’ morphotype from S. cheni and S. inermis. Genomic scan analyses comparing the ‘big red’ and ‘red white’ morphotypes with S. inermis and S. cheni, respectively, indicate that genes involved in fertilization, egg hatching, immunity, and thermal resilience are under divergent selection. Overall, the results suggest that both morphotypes could represent previously undescribed cryptic species, warranting further investigation to confirm their status as independent taxa. Full article

This article focuses on ponds and reservoirs (PRs) in Sanuki, Kagawa Prefecture, Japan. Sanuki is a region in the Seto Inland Sea with low annual rainfall. In 1999, there were 14,619 PRs in the 1877 km² area. Mannō-ike, the largest PR, is said to have been constructed at the beginning of the ninth century by Kūkai, one of Japan’s most prominent Buddhist monks. Such huge man-made structures could have been achieved only through collective human labor. The motivation to build large PRs was driven by the risk of drought. However, it is important to note that there were many more small PRs managed by individuals or families than one might imagine. PRs can range in size from huge to small and in location from mountainous areas to mountain foothills and plains. Rather than hard clustering, which classifies PRs according to a single logic, this article takes a new, historically holistic approach by using soft clustering to analyze the classification mechanism by considering the “Living Spaces” the world of all living organisms, including humans, and quantifying its complex logic. Full article

Low-cost ocean monitoring systems are increasingly needed to address data gaps in coastal environments, particularly in regions where traditional research infrastructure is limited. This paper presents the design, development, and field deployment of a biophysical ocean buoy (BOB)—a compact, solar-powered autonomous buoy system capable of measuring sea surface temperature, salinity (via electrical conductivity), total dissolved solids, pH, and GPS position. The system features real-time data transmission via the Iridium satellite, local data logging, and modular sensor integration. The BOB was deployed for three missions in the Seto Inland Sea, Japan, ranging from 26–56 h in duration. The system successfully recorded high-resolution environmental data, revealing coastal gradients, diurnal heating cycles, and tidal current reversals. Over 95% of the measurements were successfully recovered, and the Iridium communications exceeded 90% reliability. The temperature and salinity data captured fine-scale variations consistent with freshwater plume interactions and tidal forcing. With a total system cost under USD 2000 and minimal deployment requirements, the BOB offers a scalable solution for distributed ocean monitoring. Its performance suggests strong potential for use in aquaculture monitoring, coastal hazard detection, and climate change research, especially in data-sparse regions. This work contributes to the growing field of democratized ocean observation, combining affordability with operational reliability. Full article

In Thailand, mangrove forests form a major component of the Andaman coastal ecosystems in the southern provinces. However, studies on their microbial assemblage largely revolved around groups of bacteria, fungi, and eukaryotic microalgae, while the diversity of cyanobacteria in these regions remains almost unknown. This taxonomic study applied the polyphasic approach to examine seven cyanobacterial strains collected from different mangrove environments (including soil crust, tree bark, wood, and rock surface) across Ranong, Phang-Nga, and Phuket provinces. The comprehensive analysis combining morphology, ecology, 16S rRNA phylogenetic relationships, genetic identity, ITS secondary structure, and ITS dissimilarity resulted in the first records of the genera Picosynechococcus, Allocoleopsis, and Sirenicapillaria in Thailand, and led to the description of a new species, Picosynechococcus mangrovensis sp. nov. This new species was differentiated from the type species P. fontinalis based on the distinct 16S rRNA gene phylogenetic position, low 16S rRNA genetic similarity, its slightly halophilic nature, and ability to form pseudo-filaments with up to 160 cells. Our research significantly expands the documented cyanobacterial diversity of Southeast Asian mangrove ecosystems, establishing a critical foundation for future ecological and biotechnological investigations in these understudied yet vital tropical habitats. Full article

The largescale blackfish, Girella punctata Gray, 1835, is important in the fishing industry and recreational fishing, and it is also cultured in East Asia. Cymothoidae (Crustacea: Isopoda) is a group of parasites that infest fish in marine, brackish, and freshwater environments. In this study, we report, for the first time, Ceratothoa arimae (Nunomura, 2001) (Cymothoidae) from the buccal cavity of G. punctata in the Seto Inland Sea, Japan. Ceratothoa arimae showed a prevalence of 29.4–66.7% in G. punctata. The morphology of the mancae of this species was also described in comparison with that of the adult female (ovigerous), transitional stage, and adult male. The manca of Ceratothoa arimae has more chromatophores than those of other Ceratothoa species from Japan, and is a candidate for a future taxonomic trait. This species may have a negative impact on cultured G. punctata, which would be important to determine in future studies. Currently, it is difficult to identify cymothoid mancae species based on their morphology, but the information provided in this study could be useful when combined with other methods developed in the future, such as molecular analysis. Full article

We have developed a free-fall type glass sphere underwater observation system with suspended cable. The developed observation system is quite simple to construct and is able to operate at deep sea because the system is structured by glass sphere. The glass sphere has high endurability. Due to no motion system like thrusters, the position of a free-fall type underwater observation system is not clear. And hence, we propose the operation of a free-fall type underwater observation system with a suspended cable like a zipline. To make the position of the system more precise, an inertial measurement unit (IMU) is installed inside the system. A router is also installed inside the system to obtain underwater pictures via a LAN cable. The observation system, which is named UWOS (Under Water Observation System), was operated in the Seto Inland Sea. It was found that the UWOS indicates the possibility of a free-fall type glass sphere underwater observation system with a suspended cable. Full article

Coastal habitats are crucial for supporting ecological processes and serve as vital ecosystems for diverse fish species, providing essential functions such as feeding, nursery provision, and reproductive habitats. Fish communities are ecologically important components of coastal ecosystems and are affected by multiple environmental factors. Despite their importance, determining the effects of environmental factors on seasonal variations in fish species diversity and community dynamics remains a challenge. The advent of environmental DNA (eDNA) technology, an environmentally conscious approach, has resulted in considerable advancements in recent years and has been progressively adopted for marine fish population monitoring. Here, we used environmental DNA metabarcoding to study seasonal variations in fish community structure on a coastal island, and we assessed the effects of environmental factors in structuring these communities. Our findings revealed a rich diversity of 72 fish species across 40 families and 23 orders in the seawater surrounding an island of the Seto Inland Sea (SIS), Western Japan. Notably, the composition of fish communities varied significantly between seasons, with seawater temperature, salinity, and dissolved inorganic phosphorus (DIP) concentration identified as important factors correlated with fish communities’ structures. In conclusion, our study provides useful information of fish diversity, and we suggest that eDNA is a valuable technique for monitoring fish diversity in coastal areas. These findings are crucial for ecological studies and the environmental monitoring of oceanic coastal environments. Full article

This study developed a coupled atmospheric–marine model using the COAWST model system for the Harima Nada area between spring 2010 and winter 2011 to evaluate the seasonal influence of the Kako River’s discharge in the sea. The Kako River is one of the largest rivers in southwest Japan, contributing almost half of the freshwater discharged in the Harima Nada region in the Seto Inland Sea. Validation was conducted for the entire period, showing a good performance for the atmospheric and marine variables selected. Multiple experiments injecting an inert tracer in the Kako River estuary were performed to simulate the seasonal river water distribution from the estuary into the sea and to analyze the seasonal differences in concentration patterns and mean residence times in Harima Nada. Because the study area is shallow, the results were evaluated at the surface and 10 m depth layers and showed significant seasonal differences in tracer distribution, circulation patterns, and mean residence times for the region. On the other hand, differences seemed to not be significant during the same season at different depths. The obtained results also agreed with the area’s natural water circulation, showing that the Kako River waters tend to distribute towards the west coast of Harima Nada in the warmer seasons but shift towards the east in winter. The influence of the Kako River in the center of the study area is seasonal and strongly dependent on the direction of the horizontal velocities more than their magnitude. The mean residence times varied seasonally from approximately 30 days in spring to 12 days in fall. The magnitude of the horizontal velocity was found to be maximum during summer when circulation patterns at the surface and 10 m depth in the central part of Harima Nada also seem to promote the strongest horizontal and vertical mixes. Full article

As methane fermentation is inhibited by ammonia derived from organic waste, anaerobic microbial communities tolerant to enriched wastewater with high concentrations of ammonia and salt must be obtained for methane fermentation. Therefore, acclimation cultures were prepared in bottles for 60–80 weeks with artificial wastewater medium added every 2 weeks, using three types of sludge from wastewater treatment plants in food factories. These cultures were maintained without substantially decreasing methanogenesis and gradually increasing NH₄-N and salt concentrations to 5 and 34 g/L, respectively, via the accumulation of ammonia and salt through anaerobic digestion and direct addition. The culture did not show the severe inhibition of methanogenesis or the accumulation of volatile fatty acids (VFAs) such as acetic and propionic acids. The analysis of bacterial consortia in the acclimated sludge based on the 16S rRNA sequence showed that hydrogenotrophic methanogenic bacteria of the genus Methanoculleus were dominant among archaea, whereas bacteria from the orders Clostridiales and Bacteroidales were dominant among eubacteria. Further, VFA-assimilating bacteria, including synthetic acetate-oxidizing bacteria coupled with hydrogenotrophic Methanoculleus to convert methane from acetate, were present to prevent the excessive accumulation of VFAs in the acclimation culture. The proposed acclimation process can enhance the anaerobic digestion of wastewater for methane production. Full article

Coastal blue carbon ecosystems are crucial to mitigating global warming. To accurately calculate the blue carbon stock, the existing amount of each species in seaweed and seagrass (SWSG) beds must be estimated to calculate the amount of CO₂ absorbed by each species. However, there exists no efficient and comprehensive method for separating SWSG species. Remote sensing techniques hold promise in addressing this issue. This study used satellite Sentinel-2 data to differentiate and map the areas in which Sargassum and Zostera flourish in the Seto Inland Sea. A two-step approach was proposed to separate these algae. First, the SWSG bed area was estimated using the bottom index method, which has been commonly used for sediment mapping. Consequently, using spectral characteristics obtained from field surveys, the Sargassum and Zostera distinguishing index was developed to efficiently separate Sargassum and Zostera. This algorithm was applied to Sentinel 2 data to create a distribution map of Sargassum and Zostera in the Seto Inland Sea. When the map was compared with SWSG bed maps, obtained using field survey-based methods, it showed high credibility, meaning that the proposed method can be used to repeatedly and easily understand seasonal changes in SWSG types in this area in the future. Full article

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. Full article

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. Full article

Groundwater dynamics near the saltwater–freshwater interface were investigated in an island of the Seto Inland Sea, using multiple tracers (δD, δ¹⁸O, Cl⁻, SF₆, and ¹⁴C) at two coastal groundwater monitoring wells at depths of 10–40 m. The groundwater recharge area and age were also estimated using these tracers. Additionally, bedrock groundwater at a depth of 40 m at the 2.7 m altitude was brackish and considered to be near the saltwater–freshwater interface, and a mixture of seawater (2–3.5%) and fresh groundwater (97–98%) was estimated by the Cl⁻ concentration. Based on the δ¹⁸O of fresh groundwater estimated from the seawater mixing ratio, the recharge area was estimated to range from near to above the summit; however, this region is unlikely to be the actual recharge area, as the groundwater may be old freshwater that was recharged during a previously colder period. Groundwater dating using SF₆ and ¹⁴C suggests that the fresh groundwater originated during the last glacial period (assumed 20,000 years ago) and that the 40 m deep bedrock groundwater is a mixture of old water (0–28%), 30 m deep groundwater (76–100%), and stagnant seawater (1–3%). Full article

Understanding the spatiotemporal environment of the ocean after a heavy rain disaster is critical for satellite remote sensing research and disaster prevention. We attempted to reproduce changes in marine debris distributions using multidate data of Landsat-8 spectral reflectance acquired immediately after a heavy rain disaster in western Japan in July 2018. Data from cleaning ships were used for screening the marine debris area. As most of the target marine debris consisted of plant fragments, a method based on the corrected floating algae index (cFAI) was applied to Landsat-8 data. Data from cleaning ships clarify that most of the marine debris accumulated in the waters in the northern part of Aki Nada, a part of the Seto Inland Sea. The spectral characteristics of the corresponding marine debris spectral reflectance obtained from the Landsat-8 data were explained by the FAI with band 5 (central wavelength: 865 nm) as the maximum value. Unlike traditional FAI, cFAI eliminated the effect of background water turbidity. The Otsu method was effective for the automatic threshold determination for cFAI. Although Landsat-8 data have limited spatial resolution and observation frequency, these data were useful for understanding marine debris distribution after a heavy rain disaster. Full article

The consumption of a pufferfish, Takifugu flavipterus or komonfugu in Japanese, formerly known as Takifugu poecilonotus, is popular in Japan. However, T. flavipterus is frequently involved in cases of tetrodotoxin (TTX) poisoning in Japan. Although victims have usually consumed inedible parts, some cases are related to consumption of flesh. To improve the risk management of pufferfish poisoning, we studied TTX level in the flesh and skin of T. flavipterus. Ninety-seven specimens obtained from the Seto Inland Sea and landed in Fukuoka Prefecture were analyzed by liquid chromatography-tandem mass spectrometry. The flesh from six specimens was toxic (>10 MU/g = 2.2 mg/kg): one was in poor condition (not freeze–thawed); three were freeze–thawed before sample preparation; and two freshly prepared and in good condition (not freeze–thawed). The fillets were divided into outer and inner portions; the TTX levels in the outer portions were notably higher. The skin of the six specimens was moderately to extremely toxic: 165 MU/g (36.3 mg/kg) in the fresh specimen not in good condition, 600–950 MU/g (132–200 mg/kg) in freeze–thawed specimens, and 4500 and 6000 MU/g (990 and 1320 mg/kg) in the two fresh specimens. We concluded that TTX in the flesh migrated from the highly toxic skin. In addition, TTX levels in the skin appeared to be regionally specific. We recommend that toxic portions of T. flavipterus are removed as soon as possible after individuals are caught, and that fish from known highly toxic areas are not consumed. Full article