Background:Air-breathing marine slugs of the family Onchidiidae inhabit intertidal environments worldwide, but their diversity and distribution remain poorly documented in Korean tidal flats, particularly in upper intertidal and supralittoral habitats such as saltmarsh vegetation. New information:The following report documents the first confirmed record of Onchidium reevesii from Korea, based on specimens collected from saltmarsh vegetation in the upper intertidal and supralittoral zones of Korean tidal flats at three localities: Jindo, Muan and Suncheon. Species identification was facilitated by an integrative taxonomic approach, incorporating external morphology, radular characters and mitochondrial COI and 16S rRNA sequence analyses. The Korean specimens closely matched the diagnostic morphological features described for Chinese specimens in previous studies. Furthermore, molecular analyses revealed a high degree of sequence similarity, which supports a close phylogenetic affinity with reported sequences of O. reevesii. This record constitutes the first genetic confirmation of O. reevesii on the Korean Peninsula, thereby extending the known geographic distribution of the species across the Yellow Sea in East Asia.

Marine ecosystems in semi-enclosed Gyeonggi Bay (Yellow Sea, Korea) were surveyed at 23 stations arrayed along four discharge transects to evaluate how sediment texture and contaminants influence macrobenthic communities. A total of 186 species were recorded, yet richness tends to decrease at innermost stations. Highly simplified communities were dominated by two opportunistic species, Capitella capitata and Heteromastus filiformis. Community composition was strongly influenced by sorting and contaminants, particularly copper, cadmium, total organic carbon, and polycyclic aromatic hydrocarbons rather than distance from potential pollution sources. Diversity-based metrics tracked organic enrichment, whereas tolerance-weighted scores aligned with persistent toxic substances, revealing the risk of misclassification when a single index is used. Macrobenthic communities serve as indicators of pollution and inform integrated coastal monitoring strategies. Integrating complementary indices with chemical data therefore provides a clearer "fingerprint" of environmental stress and a stronger basis for station-scale management of patchy pollution in coastal embayment.

Wind-induced currents are the major forces responsible for sediment resuspension and transport in micro-tidal bays. The hydrodynamics and sediment transport mechanisms were investigated in Onsan Bay, a heavily contaminated, micro-tidal area on the southeastern coast of Korea, designated as a “Special Management Coastal Zone” due to severe pollution. At two mooring stations (M1: central part of the bay; M2: entrance of the bay), in-situ measurements using acoustic Doppler current profilers (ADCPs) were conducted to examine the impact of wind-induced residual currents on the sediment flux over four weeks. During the mooring period, residual currents (ū) in both stations showed classical estuarine circulation characterized by seaward (landward) flows at the surface (bottom) layers. The suspended sediments at both stations were transported seaward (landward) at the surface (bottom) layer mainly through the residual currents (mean-flow flux Fmean: > 70% of the total flux). Under northerly winds, the bottom ū at M1 and M2 strengthened, with a higher increment at M1. This result implies that the intrusion of alongshore currents through the bottom layer strengthened under northerly winds. The landward Fmean at M1 (M2) was 1.4 (1.2) times higher under northerly winds than southerly winds, resulting in the quadruple “intensification” of net sediment flux. This observation was attributed to the enhanced landward water transport and the weak sediment resuspension by wind-induced residual currents. This suggests that the northerly winds might be a primary factor intensifying the landward sediment fluxes, potentially resulting in the increased sediment deposition into the bay. The findings provide insights into managing sedimentation in contaminated coastal bays and highlight the importance of wind effects on sediment transport in micro-tidal bays.

An acoustic Doppler current profiler (ADCP) is widely used to measure current velocity and estimate suspended particulate matter (SPM) through echo intensity. However, acoustic signals are affected by diverse scatterers, including sediments, zooplankton, and vessel-induced bubbles, which can alter data reliability. This study evaluates the influence of these scatterer types on mean volume backscattering strength (MVBS) and Percent Good (PG) using moored observations in Onsan Bay, Korea. The analysis revealed that PG and data reliability followed the order: suspended sediments > vessel-induced bubbles > zooplankton. Sediment-dominated periods maintained high PG (> 89

Wind-induced currents are the major forces responsible for sediment resuspension and transport in micro-tidal bays. To reveal the impact of wind-induced residual currents on the sediment flux, in-situ measurements using acoustic Doppler current profilers (ADCPs) were conducted at two mooring stations in a heavily contaminated, micro-tidal Onsan Bay. During the mooring period, the suspended sediments at both stations were transported seaward (landward) at the surface (bottom) layer mainly through the residual currents (mean-flow flux Fmean: > 70 % of the total flux). Under northerly winds, the landward bottom residual currents at both stations strengthened, resulting in the “intensification” of landward Fmean. This suggests that the northerly winds might be a primary factor intensifying the landward sediment fluxes, potentially resulting in the increased sediment deposition into the bay. The findings provide insights into managing sedimentation in contaminated coastal bays and highlight the importance of wind effects on sediment transport in micro-tidal bays.

This study aims to understand population dynamics and secondary production of a nereid polychaete Hediste diadroma in the Bongam tidal flat. Samples were collected on a monthly basis over two distinct periods: from May 2015 to April 2016 and from March 2018 to February 2019. The annual mean values for temperature, sand content, and total organic carbon in surface sediments were 18.1±9.6 ℃, 79.8±12.4% and 0.53±0.36%, respectively. Relationships between parameters such as body length (BL) versus the width of the third setiger (WS3), and dry weight (DW) versus WS3 were analyzed using a sample group of 56 intact individuals. The resulting equations were determined as BL=(28.575×WS3)-7.6462 with an R2 value of 0.93, and DW=1.3435×WS33.252 with an R2 value of 0.83. There was a notable decrease in annual mean density observed in 2018 (1,096±901 ind. m-2) compared to 2015 (1,938±1,724 ind. m-2), which could be attributed to higher temperatures and interspecies competition in 2018. Recruitment events were singular within each year, occurring in June 2015 and July 2018. The estimated secondary production (P) was 8.40g DW m-2 yr-1 with a mean biomass (B̅) of 5.18g DW m-2 (P/B̅= 1.6) from May 2015 to April 2016, and P= 3.38g DW m-2 yr-1 with B̅= 1.97g DW m-2 (P/B̅= 1.7) from March 2018 to February 2019. Based on these findings, it is suggested that the contribution of H. diadroma to energy flows in the benthic ecosystem of the study area accounts for approximately 3% (1.7gC m-2 yr-1) of the total energy flows (54.5gC m-2 yr-1).

Moorings and axial surveys using acoustic Doppler current profilers in microtidal Masan Bay were conducted to reveal impacts of coastal seiches on sediment behaviors. The hydrodynamic circulation in the bay was dominated by sluggish tidal and residual currents, with which the coastal seiches with a 1-h period were detected. The coastal seiches velocity (useiche) accounted for approximately 30% of the total velocities, causing back-and-forth water motions along the channel. This was insufficient to resuspend bed sediments without external forcings. Nevertheless, it influenced the suspended sediment concentration (SSC) of turbidity maximum (~40 mg l−1) at the central part of bay, showing SSC anomaly of 8 mg l−1. Although the seiche-induced sediment fluxes were only 1% of the total fluxes due to offsetting effect of bidirectional flows, they reached up to 0.040×10−3 kg m−2 s−1 at each pulse of coastal seiches. Repetitive coastal seiches lifted the sediment particles to the upper layer where they would not have risen if not for seiche vertical motion. However, the distance that the coastal seiches can transport the suspended sediments was too short compared to their transportable amounts. Even if sediment particles within turbidity maximum were advected by coastal seiches, they could not leave the region. This process was intensified toward the land because the useiche slowed down the further as it moved away from the node. As long as the bed sediments were resuspended, the coastal seiches were expected to enhance the potential for water pollution by causing repetitive sediment redistribution.

For four decades, cordgrass (Spartina alterniflora) has invaded salt marshes in the Yellow Sea, altering physical, biogeochemical, and biological processes. Here, we investigated the ecological effects of S. alterniflora invasion on benthic environments compared to native halophytes. S. alterniflora contributed to higher carbon accumulation rates compared with bare tidal flat in sediments (3.4 times), through greater primary production and root biomass, compared to Suaeda japonica (2.5 times) and Phragmites australis (2.4 times) over the given period. The results showed that S. alterniflora eradication treatments inhibited its growth but did not significantly affect the benthic communities. Compared to P. australis and bare tidal flats, S. alterniflora invasion resulted in lower greenhouse gas emission and higher contributions to macrobenthos nutrition, and increased sediment stability and carbon burial. Overall, these multiple lines of evidence provide new insights on S. alterniflora invasion, suggesting that the current eradication policy would be carefully reviewed.

The structure of 9-year time series data for Sea Surface Temperature (SST), Chlorophyll a (Chl-a) and Total Suspended Solids (TSS), derived from the Visible Infrared Imaging Radiometer Suite (VIIRS), was examined in this study. Authors found that there exists strong seasonality among the three variables with spatial heterogeneity along the Korean South Coast (KSC). In specific, SST was in phase with Chl-a, but out of phase with TSS by six months. A strong inversed spectral power with six-month phase-lag was found between Chl-a and TSS. This could be attributed to different dynamics and environmental settings. For example, Chl-a concentration seemed to have strong positive correlation with SST indicating typical seasonality of marine biogeochemical processes such as primary production; while a strong negative correlation between TSS and SST might have been influenced by changes in physical oceanographic processes, such as stratification and monsoonal wind-driven vertical mixing. In addition, the strong east-west heterogeneity of Chl-a suggests that the marine coastal environments are predominantly governed by distinct local hydrological conditions and human activities associated with land cover and land use, while the east-west spatial pattern revealed in TSS timeseries was associated with the gradient of tidal forcings and topographical changes keeping tidally induced resuspension low eastward.

To reveal the mechanism for the transport of water and suspended sediments by wind-induced estuarine residual circulations, in situ moorings of acoustic Doppler current profilers were conducted in microtidal Onsan Bay. Water circulation within the bay was characterized by freshwater discharge from the river and free exchange with the open sea, showing current seaward outflow and landward inflow in the western (M1) and eastern (M2) flanks of the navigation channel, respectively. This circulation was influenced by the intrusion of alongshore currents strengthened (weakened) by the northerly (southerly) winds. In M1, seaward outflow was dominant, except for surface disturbances caused by winds. Meanwhile, the classical estuarine circulation (72% of the entire period) in M2, which prevailed under the southerly winds, was switched into the reversed estuarine circulation when the stress of the northerly wind persistently exceeded 0.005 Pa (> 5 h). The water transport (Tr-w) in M1 did not significantly vary depending on the wind direction, but the Tr-w in M2 could be reduced by 53% within 10 m above the bed as the southerly winds were transited into northerly winds. Over the entire period, Tr-w tended to be mutually compensated for and balanced by the circulation system between M1 and M2. On average, however, the sediment transport (Tr-sed) in M2 was 37% higher than M1, indicating that the suspended sediments were preferentially deposited within the bay. Most of the suspended sediments causing the deposition within the bay were mainly transported by estuarine residual circulation rather than tidal pumping. In M2, the frequent resuspension events of the fine-grained sediments (d(50) = 6 mu m) due to the high variability of the along-channel current velocity could maintain a sediment concentration of 18 mg l(-1) in the bottom layer. These suspended sediments responded mainly to landward current in bottom layer (classical estuarine circulation) rather than seaward current (reversed estuarine circulation), contributing to increase in Tr-sed. Considering that the prevailing winds from 2013 to 2020 in Onsan Bay mainly create a favorable condition for the development of the classical estuarine circulation, the sedimentation is expected to persist.

Prokaryotes play an important role in marine nitrogen and methane cycles. However, their community changes and metabolic modifications to the concurrent impact of ocean warming (OW), acidification (OA), deoxygenation (OD), and anthropogenic-nitrogen-deposition (AND) from the surface to the deep ocean remains unknown. We examined here the amplicon sequencing approach across the surface (0-200 m; SL), intermediate (200-1000 m; IL), and deep layers (1000-2200 m; DL), and characterized the simultaneous impacts of OW, OA, OD, and AND on the Western North Pacific Ocean prokaryotic changes and their functional pattern in nitrogen and methane cycles. Results showed that SL possesses higher ammonium oxidation community/metabolic composition assumably the reason for excess nitrogen input from AND and modification of their kinetic properties to OW adaptation. Expanding OD at IL showed hypoxic conditions in the oxygen minimum layer, inducing higher microbial respiration that elevates the dimerization of nitrification genes for higher nitrous oxide production. The aerobic methane-oxidation composition was dominant in SL presumably the reason for adjustment in prokaryotic optimal temperature to OW, while anaerobic oxidation composition was dominant at IL due to the evolutionary changes coupling with higher nitrification. Our findings refocus on climate-change impacts on the open ocean ecosystem from the surface to the deep-environment integrating climate-drivers as key factors for higher nitrous-oxide and methane emissions.

The East/Japan Sea (hereafter, East Sea (ES)) is a semi-enclosed marginal sea and considered as a miniature ocean with oceanic features (e.g., currents, eddies, fronts, upwelling) and dynamic marine environments. The ES is significantly influenced by the global ocean warming with fast increases in sea surface temperature during the last several decades. The climate-induced environmental changes can affect marine ecosystem and food webs in the ES. Therefore, more accurate estimates in phytoplankton biomass in the ES with high spatial and temporal resolutions are necessary to investigate phytoplankton production, fisheries, and carbon budget as well as biological responses to the environmental and climate changes. The NASA ocean chlorophyll-type (OCx) chlorophyll-a (Chl-a) algorithms based on blue to green band ratio for the satellite ocean color data in the global ocean have been evaluated using the in situ radiometric and Chl-a measurements in the ES. The model-derived Chl-a data using the OC Chl-a algorithms present systematic overestimation in the lower Chl-a concentrations between about 0.1 and 1.0 mg/m3 in the ES (with ∼40% uncertainties). New Chl-a algorithms for the ES has been derived from the 3rd polynomial regression fits of in situ Chl-a and maximum band ratios of remote sensing reflectance (Rrs). The revised Chl-a algorithms considerably improve the Chl-a data in the ES from the satellite ocean color data in the lower Chl-a concentrations. Thus, the new Chl-a algorithms can provide more accurate assessments in biological and biogeochemical processes such as primary productivity, phytoplankton phenology, phytoplankton dynamics, and carbon cycles.

Historical trends of polycyclic aromatic hydrocarbons (PAHs) contamination were reconstructed from eleven sediment cores located in intertidal zones of the Yellow and Bohai seas for a period encompassing the last 80 years. The analysis encompassed 15 traditional PAHs (t-PAHs), 9 emerging PAHs (e-PAHs), and 30 halogenated PAHs (Hl-PAHs), including 10 chlorinated PAHs (Cl-PAHs) and 20 brominated PAHs (Br-PAHs). Concentrations of target PAHs were highest in industrial and municipal areas situated along the coast of the Bohai Sea, including Huludao, Yingkou, Tianjin, and Dandong, constituting a substantial mass inventory. All target PAHs showed increasing trends since the 1950s, reflecting the development history of South Korea and China. High molecular weight PAHs accumulated in sampling sites more than low molecular weight PAHs. A positive matrix factorization model showed that the PAH sources were coal and gasoline combustion (35%), diesel combustion (33%), and biomass combustion (32%). Over the last 80 years, the contribution of coal and gasoline combustion increased in all regions, while diesel combustion and biomass combustion varied across regions and over time. Toxicity equivalence values were highest for t-PAHs (>99% contribution), followed by Cl-PAHs, Br-PAHs, and ePAHs. Concentrations of t-PAHs in Eastern Asia seas have increased since the 1900s, particularly in intertidal areas compared to subtidal areas. The intertidal zone removed 83% of the total flux of PAHs originating from land and thus appears to serve as a buffer zone against marine pollution. Overall, this study provides novel knowledge on the historical trends and sources of PAHs on a large scale, along with insights for future coastal management.

Light is one of the primary resources in regulating phytoplankton growth and productivity. Recent satellite observations have started to report optimal light intensities for phytoplankton blooming in various physiological and ecological environments. To investigate the optimal light intensities required for phytoplankton spring bloom development in the East Sea (ES), we constructed a 10-year climatology of the mean photosynthetically available radiation (PAR) in the mixed layer at the onset times of spring blooms using satellite data and in situ temperature- depth profiles. The PAR estimates in the southern ES (<40 degrees N) are nearly uniform, with an optimal value of 4.5 +/- 2.1 E m(-2) day(-1); this value is comparable to the PAR in the western North Pacific and the North Atlantic, where bloom initiation has been explained by a shallowing of the mixed layer depth and an increase in the light availability. The PAR estimates for the northern ES are also nearly uniform, with an optimal value of 16.0 +/- 7.3 E m(-2) day(-1). However, the PAR is about three times larger in the northern ES than in the southern ES. The value of the northern ES is comparable to the PAR estimate in the Southern Ocean, which is known as a high-nutrient and low-chlorophyll region, owing to iron limitation and zooplankton grazing pressures. These distinct regional differences in the PAR estimates indicate that a variety of physiological and ecological conditions can control the onset of spring blooms.

Axial survey and in situ mooring in microtidal Masan Bay were conducted to reveal the mechanism for movement of secondary turbidity maximum (STM) and sediment resuspension. The Bay is characterized by sluggish water circulation with a vertically well-mixed water column. The strength of the residual estuarine current (& UDelta;u) was enhanced by the combined effects of decreased tidal currents, increased precipitation, and down-estuary (northerly) winds, whereas & UDelta;u was weakened by increased tidal currents and up-estuary (southerly) winds. The variability of current asymmetry originated from & UDelta;u contributed to the entrapment of suspended sediments, creating a mobile sediment pool in central regions of the Bay. The sediments resuspended from the mobile sediment pool were more influenced by residual currents than the tidal currents, and they remained in suspension near bed. When the down-estuary winds were applied to the mobile sediment pool, the near-bed sediments were readily resuspended to form an STM > 40 mg l(-1). The STM moved up-estuary by persistent high & UDelta;u and down-estuary by an intermittent low & UDelta;u. Over the entire measurement periods, the STM moved by at least 450 m toward the up-estuary. As the consolidated sediment layer was exposed by the movement of the STM, near-bed currents were ineffective in resuspending sediments from the consolidated layer even though the winds provided sufficient current strength. Due to the depletion of available sediments for resuspension, the STM was not fully generated. This study highlights that the STM in a microtidal estuary can be determined by the combined function of various forcings such as tide, wind, and precipitation.

Archaea live in diverse habitats including extreme environments. Although they are sometimes the dominant heterotrophic organisms in microbial communities, relatively little is known about their ecological roles in microbial food webs. To explore predator-prey relationships between archaea and heterotrophic protists, we determined feeding occurrence by the heterotrophic nanoflagellates Bodo sp., Goniomonas sp., and Pedospumella sp. the common heterotrophic dinoflagellates Cryptoperidiniopsis brodyi, Gyrodinium dominans, Oblea rotunda, Oxyrrhis marina, and Polykrikos kofoidii on ammonia-oxidizing archaea (AOA) by examining the food vacuoles of these heterotrophic flagellates under an epifluorescence microscope using fluorescently labeled AOA. In addition, we measured the ingestion rates of Goniomonas sp., C. brodyi, G.dominans, and O. marina on AOA as a function of prey concentration. Cells of Bodo sp., Goniomonas sp., Pedospumella sp., C. brodyi, G.dominans, and O. marina were able to feed on AOA, whereas O. rotunda and P. kofoidii were not. With increasing initial prey concentration up to 1.7 x 10(6) - 9.3 x 10(6) cells mL(-1), the ingestion rates of Goniomonas sp., C. brodyi, G.dominans, and O. marina on AOA increased rapidly but increased slowly or became saturated at higher concentrations. Although the maximum ingestion rates of the smaller flagellate Goniomonas sp. (23.1 cells predator(-1) h(-1)) on AOA was much lower than that of the larger flagellate O. marina (296.4 cells predator(-1) h(-1)), AOA supported the positive growth of only Goniomonas sp. The results of the present study suggest that these small heterotrophic flagellates could be effective heterotrophic protist grazers of AOA in marine ecosystems. (C) 2022 Elsevier B.V. All rights reserved.

Blue carbon science requires the estimates of organic carbon stock and sequestration rate; however, holistic data analysis remains limited in South Korea. The present study reports current organic carbon stocks and sequestration rates in the coastal areas of West Sea, South Sea, and East Sea of South Korea, encompassing entire intertidal areas using long-term field survey combined with remote sensing technology. Twenty-one intertidal flats were targeted across seven provinces (Gyeonggi, Chungnam, Jeonbuk, Jeonnam, Gyeongnam, Gyeongbuk, Gangwon). Out of the evaluated environmental parameters, mud content represented a significant factor controlling sedimentary organic carbon stocks across target areas, and was significantly positively correlated to the total organic carbon (p < 0.05). Organic carbon stocks measured in salt marshes (i.e., upper intertidal zone) reflected the high carbon fixation capacity of halophytes through primary production. Sediment textural type was classified using analysis of remotely sensed imagery, and was closely correlated to field-based classification data (p < 0.05). Using field and remote sensing results, we estimated total organic carbon stocks (13,142,149 Mg C) and sequestration rates (71,383 Mg C yr−1) in the tidal flats of South Korea. This study presents the first report on blue carbon potential in the Korean tidal flats, providing baseline information on the carbon dynamics of intertidal sediments in this region and, potentially, elsewhere.

The morphodynamics of tidal flats responds mainly to the nonlinear interaction between tides and seasonal wave activity. Man-made activities such as reclamation further complicate the morphodynamics by disturbing physical processes acting on the tidal flats. Decoupling the anthropogenic influence from the natural forcing on the tidal-flat morphodynamics is crucial in assessing the adverse effects of man-made activities. Still, it remains a challenge due to inherent difficulties in characterizing spatiotemporal variability of the tidal-flat morphology. A three-year-long field survey using unmanned aviation vehicle (UAV)-assisted photogrammetry, sedimentological and benthic fauna data was conducted on the Shinsi tidal flats near the Saemangeum dike, west coast of Korea, to evaluate the relative significance between natural and anthropogenic influence on the morphologic changes of the tidal flats and benthic community structures. The Shinsi tidal flats exhibited non-seasonal sedimentation patterns and experienced overall erosion despite their sheltered location from the offshore waves. The Saemangeum dike contributed to the sustained erosion by reflecting offshore waves toward the tidal flats during winter to spring. Heavy rainfalls also promoted erosion of the tidal flats in summer. The small-scale embankments complicated the spatial sedimentation trend by protecting tidal flats from offshore waves or promoting erosion with shoaling waves. Notable mud deposition occurred during winter, incompatible with the general hydrodynamic condition, resulting from intensive dredging activity inside and outside the Saemanguem dike. The proliferation of the opportunistic species followed the mud deposition for several months until the enhanced wave activity removed the muddy sediments from the flats. Overall erosion dominance and the temporary occurrence of opportunistic species imply that the Shinsi tidal flats are subject to non-seasonal changes in sedimentology and morphology due to artificial structures and man-made activity, leading to the instability of the benthic communities in the tidal flats.

A tidal saltmarsh supporting marine ecosystem services becomes more recognized, but an understanding of its trophic dynamics is far limited. We investigated the benthic food-web dynamics in Ganghwa tidal flat, a representative tidal saltmarsh of South Korea. The stable carbon and nitrogen isotope ratio values were analyzed for the sixteen species of macrobenthos and their potential food sources such as microphytobenthos (MPB) and various organic matters. A year-round survey was conducted in the three sites at Ganghwa showing the different types of sediment bottom (sandy mud or mud) and/or vegetation (Phragmites or Suaeda). In general, the isotopic signature fairly well demonstrated that trophic structure is primarily influenced by sediment mud content and/or dominated vegetation. Among the four feeding types of consumers (filter feeder; deposit feeder; omnivore; carnivore), the deposit feeders such as mollusk, arthropod, and annelid showed increased dietary dependency on MPB at bare sites. Whilst they actively utilized 13C-depleted organic matters at vegetated sites. Meantime, significantly enriched stable nitrogen isotopic ratio of macrobenthos was evidenced in fall, which reflected the seasonal variation of food sources and physiological processes in survival strategy. Overall, the stable isotopic approach was useful to address the key factors (in)directly influencing the benthic food web structure and its functioning in a typical tidal saltmarsh of the Yellow Sea.