East Sea Research Articles

Estimation of tidal energy potential in the Vietnam East Sea: A comprehensive analysis using semi-empirical tide models

This study assesses the tidal energy potential in the Vietnam East Sea (VES), a region with complex hydrodynamics and significant interactions with the Western Pacific Ocean. A rigorous validation of six prominent semi-empirical global ocean tide models (FES2014, DTU16, EOT20, GOT4.10c, HAMTIDE12, OSU12.V1) was conducted against an extensive network of 34 tide gauge stations in the VES region. The validation identified FES2014 as the superior model, exhibiting the closest agreement with observations due to its advanced data assimilation techniques, high-resolution grids, and robust hydrodynamic representation influenced by the complex VES bathymetry. Leveraging the FES2014 model, the influential role of the semi-diurnal component (M2) in dictating energy distribution is prominently evident. Evaluation results of tidal amplitudes revealed three emerging hotspots: the Batang Lupar estuary (Malaysia), Anpu Gang (China), and Bac Lieu (Vietnam), with tidal amplitudes up to 326.2 cm. The Anpu Gang exhibited the highest theoretical potential tidal energy of 14.90 Wh/m2, making it the most promising site for localized tidal power development. Although moderate compared to globally renowned sites, the identified VES hotspots merit consideration for small-to-medium scale projects tailored to local conditions. While limited to potential energy assessments, this study provides a crucial baseline for the VES region, highlighting opportunities for sustainable tidal energy exploitation.

Long-Term Changes in Deep Ocean Currents between Ulleung Island and Dok Island in the East Sea from 1996 to 2023

This study presents a comprehensive analysis of long-term deep ocean currents between Ulleung Island and Dok Island in the East Sea, based on data observed from the East Sea Current Measurement 1 (EC1) mooring station spanning from 1996 to 2023. The deep current at the Ulleung Interplain Gap, a trough situated between Ulleung Island and Dok Island, originates from the Japan Basin, a region where deep water formation occurs within the East Sea. The southward flow and velocity of this deep water are reflective of both regional and global climate dynamics. Understanding these dynamics is crucial for assessing environmental impact, both locally in Korea and globally. Significant trends and anomalies were identified in the zonal and meridional velocities within the 1,800 and 2,500-meter depth range. Data from 2012 to 2014 required corrections due to unit inconsistencies, which, after adjustment, revealed a deceleration of the southward bottom current, with speeds decreasing from 1.49 cm s<sup>-1</sup> in November 1996 to 1.14 cm s<sup>-1</sup> in April 2023. These changes may be linked to global climate variations and bottom water formation in the Japan Basin, influencing regional circulation patterns. The findings highlight the importance of sustained ocean monitoring and enhanced data management to ensure the accuracy and utility of long-term oceanographic datasets.

Fish Diversity of East Sea Streams in Nakdong River Region

Fish surveys were conducted near artificial structures installed in eight streams flowing from the Nakdong River region to the east coast of Korea. As a result of the survey, a total of 20,000 individuals belonging to nine orders, 17 families, and 47 species were found. The dominant species was Zacco koreanus, and the subdominant species was Pungtungia herzi. Among the surveyed fish species, endangered species were Pseudobagrus brevicorpus (rank I) and Cottus hangiongensis (rank II). In addition, migratory fish species were Oncorhynchus keta, Plecoglossus altivelis, and Tribolodon hakonensis. As a result of community analysis, the highest diversity, dominance, richness, and evenness indices were Wangpi, Chuksan, Gokgang, and Janggi Stream respectively. The highest number of species was surveyed in Gokgang Stream (25 species). Alpha diversity, the number of species at each survey point in each stream, was the highest at a survey point in Wangpi Stream (20 species), and beta diversity, species at each stream survey point that does not overlap with nearby survey point, was the highest at survey points in Gokgang Stream (12 species). As a result of the similarity analysis, surveyed streams were divided into four groups: group 1 (Chuksan, Baeknok Stream), group 2 (Uljinnamdae, Wangpi, Yungdeokosip Steam), group 3 (Gokgang Stream), and group 4 (Janggi, Hoeya Stream). This study is expected to serve as basic data for managing the aquatic ecosystem of streams flowing from the Nakdong River region to the east coast.

Assessment of high-resolution regional ocean reanalysis K-ORA22 for the Northwest Pacific

The Korea Institute of Ocean Science and Technology developed the Korea Operational Oceanographic System-Ocean Predictability Experiment for Marine Environment (KOOS-OPEM), a high-resolution (1/24°, 51 vertical levels) ocean prediction model for the Northwest Pacific Ocean that incorporates ensemble optimal interpolation. In this study, we present KOOS-OPEM ReAnalysis version 2022 (K-ORA22), which covers the period from 2011 to 2022. We conducted a comparative analysis between K-ORA22 and other high-resolution (1/10°–1/12°) global reanalyses, including the Hybrid Coordinate Ocean Model, Global Ocean Reanalysis and Simulation (GLORYS), and Bluelink ReAnalysis (BRAN), to demonstrate the reproducibility and reliability of regional characteristics. Statistical comparisons revealed that while K-ORA22 exhibited some warm biases, its sea surface temperature (SST) anomaly correlation after removing the seasonal cycle was approximately 0.87, comparable to other reanalyses. Additionally, K-ORA22 effectively reproduced coastal upwelling, which is characterized by a sharp decrease in SST, as observed by marine meteorological buoys in the Southwest of the East/Japan Sea. K-ORA22 exhibits a warm bias of approximately 0.50 °C around 200 m, slightly higher than those of GLORYS and BRAN, while maintaining a low salinity bias in the subsurface. Notably, K-ORA22 outperformed the other reanalyses in accurately reproducing the unique characteristics of North Pacific and East Sea intermediate waters, characterized by a salinity minimum layer. In addition, K-ORA22 stands out in its ability to accurately reproduce the Yellow Sea Cold Water Mass with a low-temperature root-mean-square error (RMSE) of 0.76 °C in the Yellow Sea (YS) region. However, it exhibited the highest RMSE for salinity in the YS region and Korea/Tsushima Strait, indicating a potential overestimation of river discharge from Korea and China. While the sea surface height (SSH) anomaly correlation of K-ORA22 did not surpass 0.80 in the entire region because of limitations in the background error covariance used, its ability to reproduce the Kuroshio path was comparable to those of other reanalysis datasets. In conclusion, K-ORA22 excels in reproducing the unique characteristics of Korean marginal seas. Still, it exhibits weaknesses, such as the overestimation of river discharge and a somewhat limited ability to simulate SSH variability, compared with other global reanalyses. We plan to enhance K-ORA22 by updating background error covariance, addressing biases related to river discharge and assimilating the best available in situ observations and satellite data.

Combined Effects of Fishing and Environment on the Growth of Larimichthys polyactis in Coastal Regions of China

In fisheries’ stock assessments, the concept of “growth plasticity”—the ability of organisms to modulate their growth rates in response to environmental conditions—has gained attention in recent years. Historically, the impacts of fishing activities and environmental fluctuations were considered separately, while their combined effects have recently come into focus. This study collected 834 adult small yellow croakers (Larimichthys polyactis) from the northern Yellow Sea, the central Yellow Sea, the southern Yellow Sea, and the northern East Sea by trawling during 2020–2021. Using otolith increments as a proxy for annual somatic growth, the study reconstructed otolith chronologies during 2015–2020 for these four stocks. The results of the mixed-effects modeling suggested that temperature during spawning and previous overwintering seasons had comparable importance for the annual growth of small yellow croakers, with higher temperature promoting growth. The growth of small yellow croakers was also found to be correlated with ENSO events, with a lag of 1 to 2 years. A further investigation into combined effects revealed that higher fishing pressure might inhibit the small yellow croaker’s response to favorable environmental conditions. Furthermore, considering the potential differences in growth plasticity among stocks, an analysis was conducted on the spatial variations in growth response to these factors. The analysis revealed that, compared to the stocks in the Yellow Sea, the stock from the East China Sea could exhibit higher growth, superior adaptability to temperature, and a distinctive response to fishing pressure. In conclusion, the present study, while primarily focusing on temperature, preliminarily analyzed the combined effects of fishing and environment and underscored the differences in growth plasticity between stocks in the Yellow Sea and the East China Sea. Despite the limited factors analyzed in this study, it suggests a direction for future studies, highlighting the necessity to include more environmental factors, and even population factors (e.g., the biomass of preys), for a more comprehensive understanding of the combined effects. Based on the observed differences between the two potential subpopulations, this study also provides new insights for the management of the small yellow croaker based on metapopulation dynamics.

Metazoan parasite fauna of grey mullet (Mugilidae) from the coastal waters of Vietnam

A total of 201 fishes of the family Mugilidae caught off central Vietnam (Nha Trang Bay) were examined for parasites. Eight species of Mugilidae were identified based on cytb and 16S rRNA sequences. Protozoa were not revealed. The metazoan parasites belong to six higher taxa. Myxozoa Grassé, 1970 is represented by six genera, three of which were first found in grey mullets off Vietnam. The specimens of Monogenea Van Beneden, 1858 belong to two genera: Ligophorus Euzet et Suriano, 1977 and Metamicrocotyla Yamaguti, 1953. Twelve species of the former were recorded for the first time both in the coastal waters of Vietnam and in the East Sea. Trematoda Rudolphi, 1808 is represented by the members of the four families, of which only three species, Haplosplanchnus pachysoma (Eysenhardt, 1892), Pseudohaploporus planilizum Atopkin, Besprozvannykh, Ha, Nguyen, Nguyen & Chalenko, 2019 and Spiritestis arabii Nagaty, 1948, were identified. The latter was first recorded in the East Sea. Acanthocephala Rudolphi, 1808 specimens belong to the species Neoechinorhynchus dimorphospinus Amin & Sey, 1996. Crustacea Brünnich, 1772 are represented by five families, of which only the copepod Lernanthropsis mugilii (Shishido, 1898) and the isopod Nerocila orbignyi (Guérin, 1832) were identified. Hirudinea Savigny, 1822 were not determined to genus and species level. A total of 25 species of parasites were found in the Mugilidae fishes examined in Nha Trang Bay. In general, 96 species of parasites are currently documented in these fishes in the East Sea, 55 of which occur off Vietnam. As a result of this study, carried out off central Vietnam, 16 parasite species were recorded in grey mullet for the first time in Vietnamese coastal waters and 15 for the first time in the East Sea. Thus, extending the geographical range of the studies may result in new records of parasites in these fishes.

Dark Carbon Fixation Measurements in the East Sea (Sea of Japan)

The vertical distribution patterns of daily primary production and dark carbon fixation were investigated at three stations in the East/Japan Sea (hereafter East Sea), a semi-enclosed marginal sea in the northwest Pacific Ocean. Our results displayed consistent vertical patterns of daily primary production at two of the stations, while the third station exhibited a markedly different distribution pattern, highlighting localized variations in production dynamics. In contrast, dark carbon fixations displaying varying vertical patterns among the stations are not specific enough to have much meaning. Water column-integral values showed differences in the contribution of dark carbon fixation to total primary production, ranging from 4.5% to 27.1%. These variations may reflect environmental parameters such as nutrient concentrations. However, our study is limited by the lack of direct data on the microbial community structure and chemoautotrophic activities, which are crucial for a more comprehensive understanding of these patterns. Understanding the environmental drivers of dark carbon fixation is crucial for elucidating carbon cycling dynamics in the East Sea. Notably, dark carbon fixation could contribute up to one-third of primary production in the region as an additional source of newly produced organic matter, highlighting the need for further investigation into this previously overlooked process.

Improved Bathymetry Estimation Using Satellite Altimetry-Derived Gravity Anomalies and Machine Learning in the East Sea

This study aims to improve the accuracy of bathymetry predicted by gravity-geologic method (GGM) using the optimal machine learning model selected from machine learning techniques. In this study, several machine learning techniques were utilized to determine the optimal model from the performance of depth and gravity anomalies. In addition, a tuning density contrast calculated from satellite altimetry-derived free-air gravity anomalies (FAGAs) was applied to estimate enhanced bathymetry. By comparison with shipborne depth, the accuracy of the bathymetry estimated by using satellite altimetry-derived FAGAs and machine learning was evaluated. The findings reveal that the bathymetry predicted by the optimal machine learning using the Gaussian process regression and the GGM with a tuning density contrast can enhance the accuracy of 82.64 m, showing an improvement of 67.40% in the RMSE at shipborne depth measurements. Although the tuning density is larger than 1.67 g/cm3, bathymetry using satellite altimetry-derived FAGAs and machine learning can be effectively improved with higher accuracy.

Geological implications for submarine geohazards, Ulleung Basin, East Sea

Geological implications for submarine geohazards, Ulleung Basin, East Sea

Continent‐Side Uplifted Mantle and Geological Imprints Along a Paleo Rift in the Western East Sea (Sea of Japan)

Continent‐Side Uplifted Mantle and Geological Imprints Along a Paleo Rift in the Western East Sea (Sea of Japan)

Comparing spatial differences in behavioral pattern transition of Black-tailed gull during post breeding season in the Korean peninsula

Parents adjust their foraging effort according to the chick and their own body condition and dual foraging strategy is one of the foraging tactics parents replenish their own reserves while feeding their chicks. During the post-breeding season, seabirds disperse to recover their own body condition and prepare for the next breeding season. Recently, we discovered Black-tailed gulls (Larus crassirostris) breeding around the Korean Peninsula occasionally foraging long trips during the late fledging, however, our understanding of the behavioral patterns of Black-tailed gulls during the late fledging and post-breeding, as well as its inter-colonial differences, remains considerably limited. Here, we employed 92 GPS trackers to adult Black-tailed gulls (Larus crassirostris) from six breeding colonies around the Korean peninsula (Yellow Sea—three colonies, South Sea—one colony, and East Sea—two colonies). To determine the foraging investment during the fledging, we suggested the flight efficiency in each trip as the ratio of maximum foraging distance (i.e., straight line distance) to total foraging distance (i.e., sum of all consecutive distance for each trip). Overall, the mean flight efficiency of the long foraging trips were lower than 57% (40.76 ± 13.07%) whereas that of the short foraging trips were over 74% (80.87 ± 4.03%). This may suggest that Black-tailed gulls may visited more than one foraging site during the long foraging trip while they flew directly between the foraging site and breeding colony during the short foraging trip to invest more in their juvenile. Moreover, longer maximum foraging distance with higher flight efficiency observed in the East Sea may indicate a balance between the costs (such as energy expended during foraging or food competition near breeding sites) and the benefits (quantity and quality of food obtained). Our findings revealed the flight behavior of Black-tailed gulls during the late fledging and post breeding, across six breeding colonies, which have different competition pressures and proximity to foraging site.

Biomarker reconstructions of temperature and hydroclimate variability in Vietnam during Marine Isotope Stage 3

Limited hydrological data coupled with a reliance on the monsoon rains for agriculture make Southeast (SE) Asia vulnerable to climate change. To develop a better understanding of how SE Asia responds to climatic forcings, we provide a paleoclimate perspective by reconstructing temperature and hydroclimate from a wetland outcrop in the Central Highlands of Vietnam (CHV) during Marine Isotope Stage 3 (MIS 3). Mean annual atmospheric temperatures inferred from brGDGTs (branched glycerol dialkyl glycerol tetraethers) indicate an increase from 23 to 26 °C between ∼54 and 37 cal ka BP, which follows an increase in mean annual insolation at the latitude of the site. δDwax data show a shift from a greater proportion of summer monsoon rain derived from the Bay of Bengal between 54 and 49 cal ka BP toward more autumn rain from the South China Sea (also known as the Vietnam East Sea) for most of the rest of the record. brGDGT-inferred soil pH suggests that the climate was wetter at 54 to 49 cal ka BP, then became drier, then returned to wet conditions approaching 37 cal ka BP. Both orbital forcing and changes in the exposure of the Sunda Shelf likely influenced hydroclimate in the CHV. δ13Cwax indicates that C4 plants dominate the vegetation cover during MIS 3. Comparison between our new record from the CHV with existing water isotope proxy records reveals coherent changes with nearby speleothem data, but regional differences between the history of hydroclimate in SE Asia and in the central Indian Monsoon domain. As a snapshot of glacial climate conditions, our data provide new information on the past drivers of climate in an understudied region.

Ontogenetic, Sexual, and Monthly Niche Segregation of Sepia esculenta in the Northern East China Sea Revealed by Stable Carbon and Nitrogen Isotopes.

Golden cuttlefish play a significant role in the food web of the East and Yellow Seas and are a valuable fishery resource in Chinese coastal waters. Samples of golden cuttlefish were obtained from the northern East China Sea between September 2021 and March 2022, and stable isotope methods were utilized in this study to examine the variations in the forage ecology of golden cuttlefish. Our findings reveal dynamic shifts in carbon and nitrogen stable isotopes (δ13C and δ15N), highlighting intricate foraging strategies tailored to growth and environmental changes. A notable trend emerges: an initial growth-linked rise in δ13C and δ15N enrichment, followed by seasonal fluctuations mirroring seasonal food availability. The ontogenetic niche evolution displays striking habitat shifts and trophic level escalation in small mantle length stages, transitioning to niche overlap and subtle trophic shifts later on. Sex-specific differences emerge, with females occupying higher trophic levels than males in most samples. This comprehensive study underscores the complexity and adaptability of golden cuttlefish feeding ecology, inviting further inquiry into their intricate relationships within the marine ecosystem.

Cryptic invasions of Pseudopolydora (Annelida: Spionidae), with description of a new species from Queensland, Australia

During surveys worldwide, we collected adult and larval specimens of Pseudopolydora Czerniavsky, 1881 similar to P. achaeta Radashevsky & Hsieh, 2000 and P. rosebelae Radashevsky & Migotto, 2009 far from their type localities in Taiwan and Brazil, respectively. Analysis of sequence data of five gene fragments: mitochondrial COI and 16S rDNA, nuclear 18S rDNA and 28S rDNA, and Histone 3 (3114 bp in total) of individuals from Nha Trang Bay (Vietnam), São Paulo (Brazil), Florida (USA), and the Caribbean Sea (Martinique) confirmed their conspecificity with P. achaeta from Taiwan. Based on the morphology, we also report this species for the first time for the East Sea (South Korea) and provide new records for the north-western part of the Sea of Japan (Russia). The analysis also showed the conspecificity of worms from Vietnam with P. rosebelae from Brazil. Based on the morphology, we also report P. rosebelae for the first time for the Caribbean Sea (Belize), South China Sea (Thailand), and Hawaii. Developed pelagic larvae of P. achaeta and P. rosebelae from Nha Trang Bay are described and illustrated. A worm from the Great Barrier Reef (Queensland, Australia) earlier identified as P. cf. rosebelae, is referred to the new species Pseudopolydora nivea sp. nov. Following our earlier hypothesis about the origin of Pseudopolydora in the Indo-West Pacific Ocean, we explain the occurrence of these worms, including Pseudopolydora floridensis Delgado-Blas, 2008, on the Atlantic coasts of North and South America by unintentional transportation in ballast water, followed by successful invasions. We assume that the penetration of warm waters of the East China Sea through the Korea Strait and the warming of the waters of the Sea of Japan have led to the extension of the range of tropical-subtropical P. achaeta to the north-western part of the Sea of Japan.

Long-Term Monitoring of Macroinvertebrate Community Assemblages and Species Composition on the Coast of Dokdo, East Sea of Korea

Dokdo Island’s diverse marine ecosystem requires long-term monitoring to understand the effects of rapid environmental changes, such as global warming, on macrobenthos species and communities. Current studies are often short-term and limited, highlighting the need for extended research to predict future changes to ecosystems. This study analyzed the environmental variables influencing macrobenthos through long-term monitoring. In total, 511 species (spp./23.4 m2) were identified with an abundance of 1709.9 individuals/m2 and a diversity of 2.9. Since 2020, there has been a decline in both the number of species and diversity, attributed to changes in sediment composition, particularly an increase in gravel and sand. The dominant species include the crustacean Abludomelita denticulata (17.6%), the polychaete Haplosyllis spongiphila (6.8%), the bivalve Glycymeris munda (5.6%), the polychaete Opisthodonta uraga (5.3%), and the bivalve Limatula japonica (3.8%). The macrobenthos community differs each year, as the dominant species G. munda has decreased in abundance since 2022 and L. japonica since 2021. Depth and gravel sediment strongly correlated with community variation. Site-specific analysis also showed significant differences, with depth, bottom temperature, and sediment composition as the influencing factors. These species thrive in cold water but their abundance declines with an increase in temperature. Continuous long-term monitoring is essential to understand and protect the Dokdo ecosystem amid rapid environmental changes. Long-term monitoring studies have revealed more species than have short-term studies, showing annual and site-specific environmental changes, including sediment erosion and bottom temperature increases. These changes have affected macrobenthos diversity, abundance, and community composition, necessitating ongoing research to determine the persistence of these trends and to protect the ecosystem.

Characteristics of rainfall distribution induced by tropical cyclones using GSMaP data over the Vietnam region

ABSTRACT Tropical cyclones (TCs) contribute significantly to rainfall along Vietnam's coast, yet their complex precipitation structures remain poorly resolved, hindering forecast skill. This study analyzes TC rainfall distributions over the Vietnam East Sea from 2000 to 2020. The Global Satellite Mapping of Precipitation (GSMaP) product provides precipitation estimates with 0.1° resolution at hourly intervals, enabling detailed structural characterization. Rainfall features are analyzed across TC intensities, motion vectors, landfall locations, and interactions with cold surge (CS) air masses. Results show that total coverage differences are less significant than the intensity variations in narrow inner core rainbands. Asymmetric rainfall distributions concentrate in the front-right quadrant but shift after landfall. Northern Vietnam observes higher TC frequencies, but southern regions experience heavier extreme rains. Additionally, CS intrusions substantially intensify eyewall convection and redirect TC precipitation. These structural sensitivities visible in GSMaP observations elucidate the dynamics modulating TC rainfall. Characterizing multi-scale interactions and precipitation processes aids in forecasting and impact assessment for these high-risk storms with complex regional behavior.

Spatiotemporal variation of sterols in sediment as markers of primary production and ocean sewage dumping in the southwestern East Sea (Japan Sea)

The sedimentation of organic carbon in the Ulleung Basin, in the southwestern East Sea (Japan Sea) was investigated using radiocarbon and sterols. The accumulation rates of organic carbon and the contents of brassicasterol and dinosterol were higher on the slope than in the central basin, reflecting the surface water productivity, whereas cholesterol showed similar or higher contents in the central basin. The coprostanol concentration in surface sediments reflected the dispersion of sewage dumped in this region. The vertical distribution showed that the coprostanol concentration was the highest in the top 5-cm layer near the Korea Strait, close to one of the two dumping sites. A high coprostanol concentration was also found near the coast further north, where the content peaked at ∼10 cm depth. The vertical distribution of coprostanol helped to estimate the sediment accumulation rate at sites where radiocarbon gradient was too small or the values were too variable.

Morphological and genetic diversity of Eichwald Toad, Bufo eichwaldi in marginal populations of the east and west Caspian Sea lowland

The Eichwald Toad, Bufo eichwaldi is one of the endemic amphibians distributed throughout Hyrcanian forests, marshes, wetlands, and streams in the north of Iran and the south of Azerbaijan. Populations of B. eichwaldi have previously been studied based on a few molecular and morphological data. Here, we undertake taxonomic and phylogenetic analyses based on morphological and morphometric features for 56 specimens of B. eichwaldi from Iran, and mitochondrial cyt b marker for 20 specimens from the whole species range in the west and east Caspian Sea lowland. Molecular analyses based on 794 bp of cyt b gene demonstrated two clusters: the east Caspian Sea lowland (A1) and the west Caspian Sea lowland (A2) clusters. Univariate analyses indicated six out of 25 morphometric variables in male B. eichwaldi specimens from the east (A1) are significantly different from male specimens of B. eichwaldi from the west Caspian Sea (A2; P≤0.05). Females have been also significantly different between two clusters in one character (distance between lids; P≤0.05). Sexual size dimorphism was also significantly different within and between populations in some variables. However, the PCA analyses show no differentiation among B. eichwaldi populations in the east and west Caspian Sea lowland. Based on p-distance parameter, the east and west groups showed a low level of genetic differentiation (0.2%).

Phylogenetic analysis of Ellipsomyxa species (Myxosporea) and description of Ellipsomyxa gordeyi n. sp. from the gall bladder of mullets (Mugiliformes: Mugilidae) in Nha Trang Bay of the East Sea, Vietnam

The coastal waters of Vietnam are home to a wide diversity of fishes, but the parasite diversity of these potential hosts is much less well characterized. To begin addressing this knowledge gap, we carried out surveys of myxozoan parasites in fishes collected from Nha Trang Bay in Vietnam's East Sea in 2018–2019. Mugilid fishes were collected in March–April 2018, January–February 2019, and November–December 2019, and examined for myxozoans. Myxospores consistent with those of the genus Ellipsomyxa were found in the gall bladder of four mullet species, and we thoroughly characterized those from Planiliza melinoptera. Myxospores were elliptoid and devoid of striation, with a distinct sinuous suture line. Polar capsules were pyriform and oriented toward the poles of the spore. Morphological features were compared to nominal species and this species from Vietnam was distinct. Phylogenetic analysis based on partial small subunit rDNA sequence revealed that broadly, Ellipsomyxa species split into three phylogenetic lineages, and although in some branches there are groupings by host family, habitat or locality, there are no clear phylogenetic patterns. The new species we encountered in P. melinoptera had a close sister relationship with Ellipsomyxa adlardi, with both species part of a larger subclade within the Ellipsomyxa lineage. Despite this phylogenetic similarity, these species were morphologically distinct, and partial large subunit DNA sequences were only 93% similar to each other. A combination of the morphological characteristics and molecular data suggest that this is an undescribed species and we propose the name Ellipsomyxa gordeyi n. sp.

Variability and driving effect of aquatic gross primary productivity across long-distance inter-basin water diversion project

Long-distance water diversion projects significantly affect the water resource cycle and allocation of regions. However, many unknowns still exist in water ecosystem functionality and energy flow in large-scale inter-basin water diversion projects. This study focused on the gross primary production (GPP) in the Middle-Route of the South-to-North Water Diversion Project of China (MRSNWDPC), i.e., the world's longest inter-basin water diversion project. The spatiotemporal distribution, driving factors, and pathways of GPP were comprehensively analyzed based on four years of high-frequency water quality monitoring and satellite re-analysis data from 11 national stations, coupling the Bayesian hierarchical models and multivariate statistical methods. The results showed that the daily average GPP in the main canal of the MRSNWDPC over the years was 2.650 g O2 m−2 d−1, with seasonal peak GPP occurring in summer and generally increasing with the distance along the canal. Five structural equation modeling (SEM) were built to analyze the variations of GPP, revealing the surface pressure (PS) and surface carbon dioxide concentrations (CO2) and pH value were the main driving factors in the main canal. The surface pressure showed significant negative impacts on GPP changes in the canal, while the CO2 and pH showed different direction effects in different sections. The daily average carbon equivalent GPPs in the MRSNWDPC is 0.828 g C m−2 d−1, ranging from 0.600 to 1.028 g C m−2 d−1, and close to the Yangtze River and the East Sea of China. This study provides a scientific basis for a deeper understanding and analysis of the energy flow mechanisms in water ecosystems of mega inter-basin water diversion projects.