Korea Strait Research Articles

Ethnic fermented foods of the world: an overview

AbstractThe origins of traditional fermented foods and the types and characteristics of fermented foods by region are reviewed. Fermented foods are classified into alcohol fermentation, acid fermentation, carbon dioxide (bread) fermentation, and amino acid/peptide fermentation, and related fermentation technologies for each region are introduced. The raw materials, microorganisms involved, and usage of ethnic fermented foods are reviewed and compared one another. The beginning of food fermentation technology is related to the invention and use of earthenware, and Northeast Asia is presumed to be one of the birth places. During the period of primitive pottery culture (8000–3000 BCE) on the Korean Peninsula and the coastal region of Korea Strait, boiling technology of food materials using pottery and salt manufacturing technology from seawater were developed, and at the same time, alcohol fermentation using grains and salt-fermentation of fish and vegetables emerged. In the West, where people were nomads, a roasting/grilling culture was continued for a long time, and technologies for fermenting fruit wine and milk products such as cheese and yogurt were developed. As a result, fermentation was mainly used for enhancing the taste of plant foods in the East, while for extending the shelf life of animal foods in the West. The production of salty and meaty flavors from soybeans and marine products by fermentation in East Asia is a technology that increases the value of low-quality proteins.

Drying trend in land and sea in East Asia during the warm season over the past four decades

Abstract The East Asian region is typically characterized by warm and humid conditions from late spring to summer. However, in recent decades, this region has experienced an increase in severe drying conditions, deviating from historical climatological patterns. This study investigated the precipitation-evaporation (P-E) trends across land and sea regions in East Asia (EA) during the extended summer season (April to September) from 1980 to 2022, and the key physical processes driving these trends through moisture budget decomposition and numerical experiments. The results reveal pronounced drying trends in southeastern China and the Yellow Sea and parts of the Korea Strait and Korean Peninsula over the past 43 years. The underlying physical processes driving these drying conditions differ between land and sea in EA. In southeastern China, the drying is driven by dynamic processes, particularly moisture divergence related to wind changes. This is linked to anomalous strengthening of descending motion due to the Indo-Pacific warm pool warming induced by both anthropogenic global warming and natural Pacific Decadal Oscillation-like sea surface temperature (SST) patterns. Conversely, drying in the Yellow Sea and adjacent areas is influenced by thermodynamic moisture advection. The altered humidity distribution due to global warming-induced SST patterns, which are higher over the Northwest Pacific marginal sea and lower in inland China, drives dry air transport from inland China to the Yellow Sea via background southwesterly wind. These findings enhance our understanding of the drying trend and their distinct processes in EA’s land and sea areas during the extended summer.

The Ecological Changes of Macrozoobenthos to the Sand Excavation Activities in the Southern Continental Shelf of the Korea Strait

The Ecological Changes of Macrozoobenthos to the Sand Excavation Activities in the Southern Continental Shelf of the Korea Strait

Comparison of Summer Coastal Currents off the East Coast of Korea in 2021 and 2022

This study investigates the variability of coastal currents off the east coast of Korea, specifically in the Wangdolcho area of the East/Japan Sea, from June 2021 to October 2022. The observations revealed significant fluctuations in depth-averaged current velocity, with a peak of 0.81 m/s in August 2021 and a minimum of −0.05 m/s in August 2022. These year-to-year variations highlight the complex dynamics of coastal currents influenced by regional wind patterns and mesoscale eddies. In the summer of 2021, the development of offshore eddies, coupled with variable alongshore wind stress, led to increased current velocities and alternating upwelling and downwelling conditions, resulting in abrupt changes in current intensity. Conversely, in the summer of 2022, the negative vorticity in the Korea Strait and negative wind stress curl along the coast likely caused the East Korean Warm Current to shift further offshore, resulting in a weakened southward flow along the coast. This study emphasizes the need for long-term monitoring to better understand the coastal current dynamics and their environmental impacts. The anticipated completion of the Wangdolcho Ocean Research Station is expected to greatly improve monitoring capabilities, providing continuous and comprehensive data that will enhance our understanding of coastal currents and their broader impacts on the marine environment.

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.

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.

Hidden underlying mechanisms for changes in mesozooplankton communities: Transport and eddy driven changes

Mesozooplankton communities have been used extensively as reliable climate change indicators, mainly because of their rapid growth and sensitivity to environmental changes. This study explored the modifications in the taxonomic composition of the mesozooplankton community and the associated physical changes of transport-driven, eddy-driven, and marine heatwaves in the summers of the last 14 years (2009–2022) within the mixed layer of the Ulleung Basin in the East Sea/Japan Sea, where surface waters have rapidly warmed in recent decades. A slight increase was observed in the abundance of mesozooplankton from 2009 (3709 inds.m−3) to 2022 (4231 inds.m−3), with two notable peaks in 2015 (11,377 inds.m−3) and 2020 (11,184 inds.m−3), which was mainly attributed to the prevalence of Noctiluca scintillans. The first peak in 2015 showed thaliaceans to be the next dominant taxa, in which the southward direction of meandering in East Korea Warm Current (EKWC), presence of the Ulleung warm eddy, lower volume of the Western Channel (V-west) of the Korea Strait, and marine heatwaves (MHWs) did not occur. In contrast to the first peak, the second peak in 2020 showed Pyrocystis pseudonoctiluca to be the next dominant species, which may have been transported and advected by the strong V-west and eastward direction of the EKWC and the occurrence of MHWs that allowed the persistence of the subtropical species P. pseudonoctiluca. Overall, the significant increases in the second dominant mesozooplankton taxa appeared to be affected by physical changes, including transport or eddy-driven changes, along with the occurrence of strong V-west, the direction of the EKWC, and the occurrence of MHWs, which may synergistically influence the increase in the second dominant taxa during summer. This study highlights the complex interplay between notable variations in mesozooplankton communities and environmental factors, highlighting the potential consequences of different physical changes (transport-driven and eddy-driven) in this regional ocean.

Influence of warm surface water originating from the East China Sea on surface water temperature off the south coast of Korea in summer

Surface seawater temperature in the southwestern coast of Korea suddenly rose in the summer of 2017. This rapid temperature rise event occurred simultaneously with a change in wind direction in the Korea Strait from northwesterly to southeasterly due to the approach of typhoon Noru. To identify the causes of the abrupt rise in surface temperature, the variations of the surface currents and temperature were investigated using a three-dimensional ocean circulation model. Warm and less saline surface water, a mixed shelf water of the Changjiang Diluted Water and saline water from an onshore branch of the Kuroshio in the East China Sea (ECS), flowed northeastward to the west and south of Jeju Island, proceeding eastward through the Jeju and Korea Straits. While westerly winds prevailed, wind-driven ageostrophic currents flowed southeastward, moving away from the south coast of Korea, due to Ekman transport. The shallow coastal region was occupied by cool and saline surface water (T < 22 °C, S > 32.5 psu). However, after the wind shifted to an easterly direction, the surface ageostrophic currents realigned northwestward, and the warm and less saline water moved into the shallow coastal region. In a passive tracer dispersal experiment, dyes injected from the ECS flowed to the west of Jeju Island and through the Jeju Strait via geostrophic currents. These dyes did not affect the shallow southern coastal region of Korea while the westerly winds dominated. However, during the easterly wind event, the dyes were advected toward the coast by the coastward Ekman transport. An analysis of temperature data observed at Cheongsando over 16 years and the tracer experiment revealed that the abrupt temperature rise in the summer of 2017 was a marine heatwave event generated by the advection of warm and less saline surface water from the ECS to the southwestern coast of Korea through the Jeju Strait.

Sedimentary evolution of the Nakdong River deposits on the Korea Strait shelf since the Last Glacial Maximum

We investigated the development of depositional systems and the evolution of the depositional sequence in the Korea Strait shelf deposits since the Last Glacial Maximum (LGM), integrating a dense grid of seismic data and multiple long-core datasets from the delta plain to offshore. This depositional sequence includes the lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST) over an incised valley sequence boundary. These tracts developed discrete depositional environments in both the bay and the open shelf area demarcated by the island arc. The evolution of these tracts can be delineated into five distinct phases based on the sea-level curve for the Korea Strait since the LGM. First, in the LST (the LGM lowstand; 25–17 kyr BP), fluvial deposits with upward-fining characteristics were observed in bedrock-incised valleys within the bay, while amalgamated fluvial deposits were identified in unconfined incised valleys over Pleistocene sequences on the open shelf. A shelf-margin delta was also detected along the continental shelf break. The TST is composed of three subunits: the lower, middle, and upper TSTs. In the lower TST (the post-LGM transgression; 17–13 kyr BP), estuarine deposits were occupied in the bay, while a broad sand sheet with a few moribund sand ridges was present on the open shelf. In the middle TST (the Younger Dryas (YD) event; 13–12 kyr BP), bay barrier islands were observed growing along the island arc, but a mid-shelf delta and a sand ridge developed on the open shelf. In the upper TST (the Early to Mid-Holocene transgression; 12–6 kyr BP), the fining-upward retrogradational bayhead delta–estuarine complex within a bay encircled by barrier islands developed toward the head of the estuary. Finally, in the HST (the Late Holocene highstand; 6–0 kyr BP), the coarsening-upward delta was prograding seaward, with its prodelta initially distributed off the river mouth and later as a mud belt along the eastern coast. The TST deposits, encompassing diverse sedimentary systems that make up a substantial portion of the depositional sequence on the shelf, were significantly influenced by a combination of topographical characteristics limiting the discharge of sediment from the river into the open shelf and the displacement of accommodation space with stepwise sea-level rise.

Development of a prediction system for precipitation- and wind-causing typhoons affecting the Korean peninsula using observational data

Introduction: When the forecasted typhoon track differs from the numerical model’s prediction, the estimated precipitation and wind from the model may not be reliable. Typically, forecasters receive numerical model forecasts with a delay of 4 h or more in calculation time. However, a more timely reference of precipitation and wind forecasts is required in an emergency with an approaching typhoon. Analyses of the observational data of typhoon-related characteristics, such as heavy rainfall and strong winds, from 1997 to 2021 revealed that their distribution areas are considerably affected by typhoon tracks. In this study, we developed a precipitation and wind prediction system based on the observational data of the typhoons that affected the Korean Peninsula.Methods: Typhoon tracks were categorized into west-coast landfalls, southeast landfalls, and those passing the Korea Strait. Each category affects the Korean Peninsula differently in terms of rainfall and wind. We devised a system that predicts these patterns based on incoming typhoon tracks. We can make forecasts by comparing the approaching typhoons to previous instances and analyzing their center, movement direction, and size. Observations from these past typhoons were averaged to produce a forecast grid for each new typhoon.Results: Our system, validated from 2019 to 2022, showed a wind speed root-mean-square error of 3.37 m/s and a precipitation accuracy index of 0.72. For comparison, traditional numerical models yielded 5.04 m/s and 0.75, respectively. This indicates that our system is comparably efficient and computationally less demanding.Discussion: Our system’s strength is its ability to offer real-time typhoon forecasts, often faster than numerical models. However, its dependence on historical data limits its predictive power for atypical weather scenarios. It is essential to consider integrating ensemble models with these observations for enhanced accuracy. Since 2022, this system has been operational at the Korea Meteorological Administration, showing consistent reliability in forecasting.

Comparative ontogeny and phylogenetic relationships of eight lizardfish species (Synodontidae) from the Northwest Pacific, with a focus on Trachinocephalus monophyly.

Lizardfish (Aulopiforms: Synodontidae), distributed broadly in temperate to tropical waters, are represented globally by 83 species across four genera, with 10 species in Korea. Despite these numbers, few studies have been conducted on the early life history of lizardfishes compared to their adult counterparts. Thus, we conducted molecular identification of 123 Synodontidae larvae collected from the Northwest Pacific (Korea Strait, Yellow Sea, East China Sea, and East Sea) between June 2017 and July 2021, using mitochondrial DNA COI and 16S rRNA sequences. Significant morphological differences were observed in the larvae and juvenile, including variation in melanophore, count, morphometric characteristics, and body shape. The morphological traits of eight species (Harpadon nehereus, Saurida macrolepis, Saurida wanieso, Saurida sp., Synodus hoshinonis, Synodus kaianus, Synodus macrops, and Trachinocephalus trachinus) served as vital data for interpreting the phylogenetic relationships within the Northwest Pacific Synodontidae. Ultimately, the identification key revealed by this study will enable accurate identification of Synodontid larvae and juveniles, and further facilitate our understanding of the phylogenetic relationships within this family.

Geoacoustic model based on physical property characterization of the southeastern shelf sediments (Korea Strait) of Korea

Deep-core samples collected from the southeastern shelf (Korea Strait) of Korea were used to characterize physical properties of the area with respect to burial depth. Laboratory analyses of the acoustic and physical properties of the samples were conducted and shear-wave velocity, velocity ratio, and Poisson’s ratio were calculated. Geoacoustic and physical property data at the two sites were in correlation with the lithological units alternating between sandy mud and muddy sand at sedimentary depth. Geoacoustic units (GAUs) identified from sites 19ESDP-104 and 21ESDP-203 were divided into 6 and 15 units with sedimentary depth, respectively, and geoacoustic models were developed for the sedimentary layers around these sites. This suggests that the physical properties are not only controlled by lithology and compaction caused by dewatering with burial depth but also by different sedimentary environments after deposition. Based on the velocity ratio and velocity anisotropy (particularly at site 21ESDP-203), clay particles within the sediment layers had a greater effect on compaction owing to the overburden pressure with burial depth.

피란수도 부산의 극장 운영에 관한 일 고찰

Busan Theaters Street was built during the Japanese colonial period. This Busan Theaters Street was a gathering place for multi-purpose theaters that staged plays and films and held various events. he reason why this place is particularly noteworthy is that it was the road where Japanese performing groups and external contents were first performed across the border(Korea Strait) and spread throughout the Korean Peninsula. After independence, this theater district(Busan Theaters Street) played a role in accommodating Korean(Choseon) content and promoting cultural exchange between the region and the center. Then, the Korean War broke out and many cultural and artistic artists flocked to Busan. In 1950, theater operation and content performance were restricted, but after 1951, each theater became a center of new creation and restored the role of producing, viewing, and distributing a lot of content at the same time. Busan Theaters Street is again home to cultural innovation, art distribution and creative activities. This phenomenon continued until the time of ‘Hwando’, and after ‘Hwando’ it acted as a driving force that gave new vitality to the development and distribution of Korean contents.

Sedimentary Facies and Environments of the SSDP-101 Long-core in a Submarine Sand Ridge in the Korea Strait

Sedimentary Facies and Environments of the SSDP-101 Long-core in a Submarine Sand Ridge in the Korea Strait

Sources and behaviors of particulate organic carbon, iron, and manganese in the bottom nepheloid layer of the southwestern East Sea (Japan Sea)

The sources and behaviors of particulate organic carbon (POC) and particulate iron and manganese (pFe and pMn, respectively) in the bottom nepheloid layer (or benthic nepheloid layer, BNL) of the southwestern East Sea, also known as the Japan Sea, along a transect from the shelf to the central Ulleung Basin were investigated. The fluxes of POC, pFe, and pMn from the BNL to the seafloor on the shelf and in the basin were determined based on thorium-234 (234Th). The influence of resuspended sediment on POC was quantified using radiocarbon isotope ratio of POC (Δ14C). Sources and behaviors of pFe and pMn in the BNL were investigated by comparison to those of particulate aluminum (pAl). The stable carbon isotope ratios mainly indicated the marine origin of the POC, and the Δ14C values indicated that the majority of the POC in the BNL (68% ± 22%) was supplied by sediment resuspension. pAl and pFe were lithogenic in origin, whereas pMn was mainly authigenic (89–100%). The deficiency of 234Th activity relative to that of 238U increased toward the seafloor in the BNL, implying the efficient removal of 234Th by adsorption to the resuspended sediment particles. The 234Th-based settling fluxes of POC, pAl, pFe, and excess Mn (pMnxs) to the seafloor in the central basin agreed with the results previously obtained from a sediment trap study in the Ulleung Basin. The settling flux of pAl and pFe in the central basin was 2–8% of the lateral transport from the Korea Strait, implying that the transported lithogenic particles mostly settled on the slope before reaching the central basin. In contrast, the settling flux of pMn in the central basin was much larger than that of pMn in the shelf, implying that pMn is further transported toward the central basin or supplied from the local sediments.

Incised-valley filling sedimentation in a small river valley of a wave-dominated, embayed coast in response to Holocene sea level rise, Yeongil Bay, Southeastern Korea

Incised-valley infill deposits are closely related to sea level changes during the post-glacial period of the late Quaternary and are an important topic in sea level history. In Asia, there are many large river basins that receive large amounts of sediment from the land, and the infilling deposits of incised valley systems have been well studied. Yeongil Bay is a semi-enclosed, funnel-shaped topographic feature on the east coast of the Korean Peninsula, located in the southwestern part of the East Sea (Sea of Japan). The Hyeongsan River, a small river flowing into Yeongil Bay, is flows perpendicular to the East sea. During the last glacial maximum (LGM), when the sea level was >120–130 m lower than at present in the Korea Strait, inflowing river processes are thought to have formed incised valleys. In this study, the sediment depositional patterns of incised valley fill since the LGM were examined by analyzing the sedimentary facies, optically stimulated luminescence (OSL) dates, and radiocarbon dates by accelerated mass spectrometry (AMS) of three sediment cores in Yeongil Bay. The infilling sequence consists of sediments from channel lag (>12 ka) and meandering river (12–10 ka), wave-dominated estuary (12–7.8 ka), and wave-dominated delta (7.8–0 ka) systems in ascending order. The barrier appear only in the outer part of Yeongil Bay. The barrier emerged from eroding estuary systems at 8.5 ka. Millennial-scale isochrons based on OSL and radiocarbon dates showed that fluvial and estuary systems were deposited in retrogradation and delta systems were deposited in progradation since LGM. The modern delta of the Asian large rivers were initiated by a decreasing rate of sea level rise during the mid-Holocene, and consideration of this is important for RSL. This study emphasizes the importance of accommodation capacity as much as sediment discharge as a factor in the timing of delta initiation. This study provides important insights into the incised-valley infill deposits and past environmental conditions, and may help to gain a better understanding of how coastal environments have changed with sea level changes.

Bathymetric trends of the deep-sea meiobenthos distributed on the continental shelf, slope, and deep floor of the Ulleung Basin, East Sea

Understanding bathymetric patterns of deep-sea meiofauna is important for elucidating the influence of environmental variables on the characteristics of meiofaunal community structures. Depth-dependent meiobenthic community structures were investigated on the continental shelf, slope and deep basin of the Ulleung Basin in the southeastern East Sea. Meiobenthic samples were collected at 29 stations (water depth: 74–2155 m) from the continental shelf near the Korea Strait to the southern slope and basin areas of the Ulleung Basin during the summer cruise of R/V Eardo (June 2006). In total, 15 meiobenthic taxa (between two and nine taxa at each station) were identified. Nematodes formed the most abundant taxon (53–80%), followed by benthic foraminifera (7–39%). Meiobenthic abundance varied from 295 to 3697 ind. 10 cm−2 (nematodes, 106–3319 ind. 10 cm−2) at each station. The distribution of meiobenthic animals in the Ulleung Basin showed considerable spatial trends, with higher densities on the southern slope (1083 ± 249 ind. 10 cm−2) of the Ulleung Basin than the shelf (650 ± 220 ind. 10 cm−2) or deep basin (459 ± 214 ind. 10 cm−2) regions. Among the environmental parameters, TOC (total organic carbon) concentration was significantly correlated with meiobenthic abundance (r2=0.297), indicating that high food supply promotes meiobenthic abundance. Meiobenthic community structures showed depth-related trends from the continental shelf to the deep basin, with several meiobenthic taxa (e.g., amphipods, bivalves, harpacticoids, kinorhynchs, nauplius, nematodes, ostracods and polychaetes) contributing to these variations in the meiofauna.

Palynological implications for the paleoclimate and paleoceanographic reconstruction of the East Sea since the early Pleistocene at IODP site U1430

Palynomorphs, including pollen and dinoflagellate cysts from marine sediments, can provide a history of paleoclimate and paleoceanography. We present new palynological profiles based on a core from the Integrated Ocean Drilling Program Site U1430, which was drilled in the Ulleung Plateau East Sea. This core covers the past 2 Ma and spans the Mid-Pleistocene Transition (MPT, 1.2–0.8 Ma) and Mid-Brunhes Event (MBE, ∼0.43 Ma). Terrestrial and marine palynomorph records indicate orbital-scale variations in paleoclimate and paleoceanography, reflecting changes in the interconnections between vegetation, climate, and the ocean. Before the MPT, the high pollen taxa ratio and abundant temperate pollen suggest a relatively warm temperature associated with astronomical forcing-induced insolation changes. At ca. 1.3 Ma, boreal coniferous pollen increased, suggesting intensification of the East Asian winter monsoon (EAWM). The long-term trend of boreal coniferous pollen concentration was similar to that of benthic δ18O. This orbital scale boreal conifer pollen assemblage variation indicates Quaternary EAWM evolution controlled by changes in global ice volume and climatic cooling. The marine palynological data reflect the ocean circulation history of the study area, where sea level fluctuations and tectonic activity played important roles around the marginal sea. The abundance of warm-water dinoflagellate species after ca. 1.9 Ma, including Tuberculodinium vancampoae, indicates Tsushima Warm Current intrusion related to the expansion of the Korea (Tsushima) Strait. Nematosphaeropsis labyrinthus and other cold-water species increased markedly during the MPT, suggesting a low sea surface temperature and weakened vertical mixing of the East Sea due to the cooled climate and sea ice during the MPT. The marked sea level fluctuation associated with the glacial–interglacial cycling after the MBE resulted in an assemblage composition shift from cold to warm water species. Tsuga and Betula thrived during mild winters, primarily influenced by winter insolation. These genera were particularly prosperous in the early Pleistocene, coinciding with a strong intrusion of the Tsushima Warm Current (TWC). Our findings should be considered in developing a comprehensive understanding of the paleoclimate and paleoceanographic history of northern East Asia across the major climate transitions of the Pleistocene.

Water mass structure determine the prokaryotic community and metabolic pattern in the Korea Strait during fall 2018 and 2019

Water mass structure determine the prokaryotic community and metabolic pattern in the Korea Strait during fall 2018 and 2019

Protistan community structure and the influence of a branch of Kuroshio in the northeastern East China Sea during the late spring

The northeastern East China Sea is an ecologically important marine ecosystem influenced by warm water derived from the Kuroshio Current. However, relatively little is known about the spatial variation of protist communities and their regulating factors from this region’s ecosystem during the spring season. Here, we investigated protistan community structures using a complementary approach combining 18S rRNA gene amplicon sequencing and light microscopy cell counts at nine stations from the northeastern East China Sea to the west of Jeju Island. The vertical profiles of physicochemical properties revealed that the Jeju Warm Current water mass, flowing from the southeast towards the northwest, created a thermohaline front dividing the region in two. These two regions had similar planktonic biomass, but the protistan communities differed significantly: dinoflagellates accounted for higher proportions of the protistan communities in the warm and saline waters, particularly at stations E35, E44, and E45, while the relative abundances of diatoms and picochlorophytes were higher in the low-density water of the western stations (E32 and E42). Furthermore, higher species richness and Shannon Diversity Index values in the warm and saline waters suggests that the Jeju Warm Current, a branch of the Kuroshio, increases protistan taxonomic diversity in the northeastern East China Sea during the late spring. Seed populations of harmful algal bloom-causing species were discovered in the warm and saline water originating from the Kuroshio, which is particularly important as it indicates that these waters could introduce harmful species that may spread to the Yellow Sea and Korea Strait. Taken together, the study suggests that potential changes to the current systems in the region could dramatically alter the structure of its protistan community.