South Sea Of Korea Research Articles

Influence of environmental parameters on marine plankton diversity in the southern coastal waters of Korea: Emphasis on thermal stratification

Plankton are fundamental to aquatic ecosystems, forming the base of the marine food web and playing a crucial role in the global carbon cycle. While the impact of environmental factors on marine plankton ecosystems has been widely studied, the seasonal variability in plankton diversity has received comparatively less attention. Here, we investigated the complexity and distribution of plankton species in Korean coastal waters in relation to seasonal environmental changes, particularly those linked to water mass characteristics and the presence of a thermocline, using alpha and beta diversity indices. A thermocline was observed at all stations in July, coinciding with the lowest diversity and richness, but was absent in September, when diversity indices peaked. In the upper layer above the thermocline, diatom species such as Pseudo-nitzschia delicatissima and Skeletonema costatum were dominant. Analysis of the Shannon index suggested that planktonic ecosystems in the South Sea of Korea from May to September 2021 were well-balanced. These findings enhance our understanding of the potential effects of environmental variability and thermal stratification on plankton biodiversity and community dynamics in Korean coastal waters.

Potential siderophore-dependent mutualism in the harmful dinoflagellate Alexandrium pacificum (Group IV) and bacterium Photobacterium sp. TY1-4 under iron-limited conditions

Specific bacterial species induce algal blooms by producing growth-promoting substances, such as siderophores, under iron-limited conditions. However, the molecular mechanisms underlying these effects remain poorly understood. This study investigates the interactions between the harmful dinoflagellate Alexandrium pacificum (Group IV) and siderophore-producing bacteria, with a focus on iron acquisition facilitated by bacterial siderophores. During algal bloom seasons in the South Sea of Korea, Photobacterium sp. TY1-4 was isolated, which enhances A. pacificum cell density under iron-deficient conditions, TY1-4 can use the sterile exudates from A. pacificum as the sole source of carbon, suggesting a mutualistic relationship. Transcriptomic and genomic analyses revealed siderophore-mediated redox-based signaling and non-reductive pathways enhancing iron bioavailability. Photobacterium sp. TY1-4 initiates siderophore production through quorum sensing, whereas A. pacificum utilizes specific receptors and transporters for hydroxamate-type siderophores (ApFHUA and ApFHUC) to uptake iron. Three redox key iron-uptake genes were also identified in A. pacificum: membrane-bound ferroxidase ApFET3, high-affinity iron permease ApFTR1, and ferric-chelate reductases/oxidoreductases ApFRE1, with transcription levels inversely related to bioavailable iron. Increased iron bioavailability mediated by siderophores alleviates iron stress in A. pacificum, supporting its growth in iron-scarce environments. Additionally, A. pacificum co-cultured with Photobacterium sp. TY1-4 synthesized high-toxicity STXs, including GTX4, GTX2, and STX. These findings highlight the critical role of bacterial siderophores in iron binding and their potential impact on harmful algal bloom dynamics.

Polaribacter ponticola sp. nov., isolated from seawater, reclassification of Polaribacter undariae as a later heterotypic synonym of Polaribacter sejongensis, and emended description of Polaribacter sejongensis Kim et al. 2013.

A Gram-stain-negative, yellow-pigmented, and strictly aerobic bacterium, designated as strain MSW5T, was isolated from seawater of the Yellow Sea in South Korea. The cells were non-motile rods exhibiting oxidase- and catalase-positive activities. Growth was observed at 15-25 °C (optimum, 25 °C) and pH 5.0-9.0 (optimum, pH 7.0-8.0) and in the presence of 1.0-5.0% (w/v) NaCl (optimum, 2.0%). Menaquinone-6 was the sole respiratory quinone, and iso-C15 : 0, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), iso-C15 : 0 3-OH, and C15 : 1 ω6c were the major cellular fatty acids. Major polar lipids included phosphatidylethanolamine, two unidentified aminolipids, and three unidentified lipids. Phylogenetic analyses based on 16S rRNA gene sequences and 92 concatenated core protein sequences revealed that strain MSW5T formed a distinct lineage within the genus Polaribacter. The genome of strain MSW5T was 3582 kb in size with a 29.1 mol% G+C content. Strain MSW5T exhibited the highest similarity to Polaribacter atrinae WP25T, with a 97.9% 16S rRNA gene sequence similarity. However, the average nucleotide identity and digital DNA-DNA hybridization values were 79.4 and 23.3%, respectively, indicating that strain MSW5T represents a novel species. Based on its phenotypic, chemotaxonomic, and phylogenetic characteristics, strain MSW5T is proposed to represent a novel species, with the name Polaribacter ponticola sp. nov. The type strain is MSW5T (=KACC 22340T=NBRC 116025T). In addition, whole genome sequence comparisons and phenotypic features suggested that Polaribacter sejongensis and Polaribacter undariae belong to the same species, with P. undariae proposed as a later heterotypic synonym of P. sejongensis. An emended description of Polaribacter sejongensis is also proposed.

Congregibacter variabilis sp. nov. and Congregibacter brevis sp. nov. Within the OM60/NOR5 Clade, Isolated from Seawater, and Emended Description of the Genus Congregibacter.

Two Gram-stain-negative, aerobic, motile by means of flagella, short rod-shaped bacterial strains, designated IMCC43200T and IMCC45268T, were isolated from coastal seawater samples collected from the South Sea of Korea. Strains IMCC43200T and IMCC45268T shared 98.6% 16S rRNA gene sequence similarity and were closely related to Congregibacter litoralis KT71T (98.8% and 98.7%, respectively). Complete whole-genome sequences of IMCC43200T and IMCC45268T were 3.93 and 3.86 Mb in size with DNA G + C contents of 54.8% and 54.2%, respectively. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the two strains were 74.5% and 23.4%, respectively, revealing that they are independent species. The two strains showed ANI values of ≤ 75.8% and dDDH values of ≤ 23.0% to the type and only species of the genus Congregibacter (C. litoralis), indicating that each strain represents a novel species. Both strains contained summed feature 3 (comprising C16:1 ω6c and/or C16:1 ω7c) and summed feature 8 (comprising C18:1 ω6c and/or C18:1 ω7c) as major fatty acid constituents. The predominant isoprenoid quinone detected in both strains was ubiquinone-8 (Q-8). The major polar lipids of the two strains were phosphatidylethanolamine, phosphatidylglycerol, phospholipids, and aminolipids. Based on the phylogenetic, genomic, and phenotypic characterization, strains IMCC43200T and IMCC45268T were considered to represent two novel species within the genus Congregibacter, for which the names Congregibacter variabilis sp. nov. and Congregibacter brevis sp. nov. are proposed with IMCC43200T (= KCTC 8133T = NBRC 116295T = CCTCC AB 2023139T) and IMCC45268T (= KCTC 92921T = NBRC 116135T) as the type strains, respectively.

Study on the Selection of Fishing Ground by Fishing Vessel Fishery in Gamak Bay, South Sea of Korea

Study on the Selection of Fishing Ground by Fishing Vessel Fishery in Gamak Bay, South Sea of Korea

Taxonomy and fatty acid profile of Picochlorum geojense sp. nov. (Chlorophyta, Trebouxiophyceae) from Korean coastal waters

ABSTRACT The microalgal genus known as Picochlorum, belonging to the green algae family Trebouxiophyceae, is recognized for its rapid growth and high lipid productivity. A Picochlorum strain (GJ210610) was recently established from the waters off Geoje, South Sea of Korea. Picochlorum sp. GJ210610 was a single, green ellipsoidal cell with an average size ranging from 1 to 2 µm. Its reproduction occurred through autosporulation. A phylogenetic tree based on nuclear small-subunit rDNA sequences revealed that this strain formed a unique branch, distinct from other Picochlorum species. Furthermore, the secondary structure of the ITS2 sequences was revealed for the first time within Picochlorum. The newly discovered Picochlorum sp. grew between 15°C and 25°C, with survival ceasing at 30°C. The maximum specific growth rate was measured at 0.91 d−1 at 25°C. The fatty acids of Picochlorum sp. GJ210610 were palmitic acid, oleic acid, linoleic acid, and alpha-linolenic acid. Based on morphological and phylogenetic analyses, we propose Picochlorum geojense sp. nov. (GJ210610) as a new species. The results of the present study may enhance our knowledge of the taxonomy and ecological characteristics of Picochlorum.

Trophic variability of inter- and intra-copepod species in the South Sea of Korea during summer

Spatial variation and interspecies differences in the trophic position (TP) of copepods were investigated using nitrogen isotope ratios of amino acids. In the summer of 2021, coastal waters and the Changjiang diluted water generated clear seawater temperature and salinity fronts in the South Sea of Korea. Paracalanus parvus s. l. was a dominant species in the copepod community, and the second dominant species differed among inshore, intermediate, and offshore sites. The TP of each copepod species was estimated in two ways, considering only metazoan diets (TPGlu, based on glutamic acid and phenylalanine nitrogen isotope ratios) and both metazoan and protistan diets (TPAla, based on alanine and phenylalanine nitrogen isotope ratios). Both TPGlu and TPAla indicated trophic variability among copepod species and the contribution of protistan diets as a food source in the study area. Calanus sinicus showed a similar herbivorous TP of 2.0 in both TPGlu and TPAla, suggesting little contribution from protistan diets. Two copepod species (P. parvus s. l. and Acartia omorii) exhibited TPGlu values of approximately 2.0 but their TPAla values increased from 0.1 to 0.5, indicating mixed diets of both primary producers and protists. The other three copepods (Pseudocalanus sp., Oithona similis, and O. atlantica) showed a wide range in TPGlu (2.4–3.1) and TPAla (2.7–3.4), suggesting that protistan trophic transfers enhance TPAla (by up to 0.5) in omnivorous copepods. We found a spatial variation in the TPs of copepods among water masses by various controlling factors including surface seawater temperature, salinity, and size-fractionated Chl-a. Our findings support that the TP values could be potential indicative of interspecies variability, providing useful information on the composition of the planktonic food web.

Distribution of Food Resources for Two Species of the Skate Family (Beringraja pulchra and Okamejei kenojei) in the South Sea of Korea

Distribution of Food Resources for Two Species of the Skate Family (Beringraja pulchra and Okamejei kenojei) in the South Sea of Korea

Characterizing anthropogenic litter pollutants in African freshwater ecosystems: A case study of Dunga Beach in Lake Victoria, Kenya

AbstractAnthropogenic litter (AL) in world's aquatic ecosystems presents critical ecological threats to environmental quality, aquatic biodiversity and human welfare. However, most studies on AL have been conducted in marine ecosystems with very little focus being given to freshwater systems like Lake Victoria. This study characterized AL pollutants in Dunga beach in Lake Victoria, Kenya, where sampling was done in the beach, riparian and benthic zones along a 100 m reach for 6 days. Across the sampled reaches, the AL associated with packaging, consumer products, building and construction, transport, electronic wastes, textile, fishery and medical materials were collected, counted, sun‐dried and weighed. AL were more abundant in the beach and riparian zone than in the benthic reaches with plastics being the dominant litter in all reaches. Based on Kruskal–Wallis rank sum test the density of AL associated with packaging and consumer products was significantly higher than other AL in all the reaches. Plastics, polystyrene and glass wastes dominated the beach zone at 31.19%, 12.14% and 11.14%, respectively. In the benthic area, the dominant wastes were plastics, fishery and polystyrene items at 22.14%, 16.34% and 12.14%, respectively. The top 10 AL pollutants in Dunga beach were as follows: bags/food wrappers, bottle caps, diapers, plastic and glass beverage bottles, plastic plates, forks, knives, spoons, straws and e‐wastes. Based on data from literature, several clear patterns emerged when comparing relative AL abundance across other aquatic habitats. In the Lake Michigan Beach, the AL were dominated by plastics (41.2%) followed by cigarettes at 29.3%. In contrast, Chicago River Beach contained more glass wastes (42.1%) while Chicago River Riparian had more plastics (57.8%). At the South Sea of Korea, fishing gear wastes were the majority AL (61.1%). AL consisting of fishing items was restricted to benthic and riparian settings, in which the benthic zone had the most items recorded. It is therefore evident that a large amount of AL waste accumulates at Dunga, Hippo point and other beaches in the world, thus justifying the need for beach cleaning and maintenance strategies. This study presents baseline data that is useful to environmental ecologists, aquatic scientists and management authorities to formulate policies, evaluate guidelines and recommend beach management strategies to conserve aquatic biodiversity, human health and aesthetic value of the freshwater habitats.

Impact of Phytoplankton Community Structure Changes in the South Sea of Korea on Marine Ecosystems Due to Climate Change

Herein, we conducted surveys during the 2018–2022 summers to investigate the impact of climate change-related changes in the phytoplankton community structure on the marine ecosystem in the South Sea of Korea. The average surface water temperature increased by ~1.07 °C at 0.0195 °C·yr−1 between 1968 and 2022. During the summers, the rate was 0.0211 °C·yr−1, with a total increase of ~1.16 °C, indicating a stronger increase in summer surface water temperature. Over the last 30 years, nutrient levels in the South Sea have decreased, particularly at the surface. Moreover, 29.3–90.0% of the phytoplankton community structure was dominated by nanoflagellates (≤20 μm). Based on the size of the phytoplankton chl-a, the average contribution rate of picophytoplankton was the highest (60.1%). Redundancy analysis revealed negative correlations between nutrients and water depth, excluding NH4. Increased stratification due to climate change is causing reduced nutrient availability at the surface mixed layer, and the size of the phytoplankton structure is progressively reducing. These changes are expected to manifest in a complex microbial food web centered on smaller phytoplankton with low primary productivity. This can reduce the efficiency of carbon transfer to higher consumer levels, suggesting a potential decrease in marine productivity.

Development and Application of an Integrated System for the Detection and Prediction of Harmful Algal Blooms in Korea

Harmful algal blooms (HABs) are types of phytoplankton overgrowth that adversely affect marine ecosystems and aquaculture resources. One such HAB species, Cochlodinium polykrikoides, occurs irregularly and causes significant damage to the aquaculture industry along the coastal regions of Korea. In this study, we developed and implemented an integrated system to detect and predict HAB occurrences in real time. This system comprises four main components: (1) a real-time detection system utilizing acoustic sensing, ocean weather, water temperature, salinity, and chlorophyll, satellite images, genetic analysis, and optics; (2) a prediction model system based on current and tidal, HAB occurrence, and HAB movement and diffusion models; (3) an additional data based on HAB information of sampling data and HAB information of GPS data, and (4) an integrated information system utilizing data storage servers and a visualization platform. We applied and assessed the efficiency of this integrated system in the South Sea of Korea from 2017 to 2019. Particularly, HABs occurred significantly in 2019, and the system demonstrated the feasibility of detection and prediction under field conditions. Implementing a more advanced integrated detection and prediction system in the field is anticipated to minimize the damage caused by irregular HAB occurrences every year.

Alishewanella maricola sp. nov., isolated from seawater of the Yellow Sea.

A Gram-stain-negative and facultative aerobic bacterium, strain 16-MAT, was isolated from seawater of Yellow Sea in South Korea. Cells were catalase- and oxidase-positive and non-motile rods. Growth occurred at 4-37 °C (optimum, 30 °C) and pH 6.0-11.0 (optimum, 8.0), and in the presence of 0-7.0% NaCl (optimum, 3 %). Strain 16-MAT contained ubiquinone-8 as the sole isoprenoid quinone, C16 : 0 and summed feature three as the major fatty acids (>10 %), and phosphatidylglycerol, phosphatidylethanolamine, an unidentified phospholipid, an unidentified aminophospholipid, and an unidentified polar lipid as the major polar lipids. The genome size and DNA G+C content of strain 16-MAT were 3.69 Mb and 46.0 mol%, respectively. Strain 16-MAT was most closely related to Alishewanella alkalitolerans LNK-7.1T with a 97.9 % 16S rRNA gene sequence similarity. A phylogenomic tree based on whole genome sequences showed that strain 16-MAT formed a phylogenetic lineage within the genus Alishewanella. Based on the phenotypic, chemotaxonomic, and molecular analyses, strain 16-MAT represents a novel species of the genus Alishewanella, for which the name Alishewanella maricola is proposed. The type strain is 16-MAT (=KACC 22238T =JCM 34596T).

A Comprehensive Investigation of Coastal and Shelf Sediment Sources in the South Sea of Korea: A Marginal Sea of the Northwestern Pacific

A Comprehensive Investigation of Coastal and Shelf Sediment Sources in the South Sea of Korea: A Marginal Sea of the Northwestern Pacific

Enhancing carotenoid production and exploring the potential use of microalga Desmodesmus cf. pleiomorphus DSHM22 as a biodiesel feedstock through photoheterotrophic cultivation

Improving biomass and value-added compound production is crucial for the industrial application of microalgae, achieved through the utilization of low-cost nutrients and various cultivation modes. This study aimed to enhance the biomass and biochemical production of the indigenous microalgae by comparing different cultivation modes. Among six algal strains obtained from the East Sea in South Korea, Desmodesmus cf. pleiomorphus DSHM22 exhibited the highest biomass productivity (0.0118 g L−1 d−1) and was selected for optimization. Algal growth responses were assessed under four commercially available soluble fertilizer media to identify a cost-effective nutrient substrate. The most effective fertilizer demonstrated 2.2-fold higher growth compared to the BG-11 algal medium after 14 days. Glucose was supplemented in the culture medium to evaluate organic carbon availability under light and dark conditions. While no growth responses were observed under glucose-supplemented dark condition, the highest biomass production (approximately 1.22 g L−1) was achieved under glucose-supplemented light condition. The algal strain showed growth under both photoautotrophic (PA) and photoheterotrophic (PH) conditions, excluding the heterotrophic mode. Biochemical accumulations were compared by analyzing photosynthetic pigments and fatty acids under both PA and PH modes. The algal strain effectively produced lutein, neoxanthin, and omega-3, 6, and 9 fatty acids. Although PH condition yielded significantly higher biochemicals and lipid production compared to PA condition, both culture conditions exhibited similar fatty acid compositions and biodiesel properties. This study suggests that PH cultivation is an effective approach for producing value-added biochemicals and biodiesel using microalga D. cf. pleiomorphus DSHM22.

First record of the genus Pseudaeginella Mayer, 1890 (Crustacea, Amphipoda, Caprellidae) with a new species from Korean waters.

A new species of the genus Pseudaeginella Mayer, 1890 belonging to the family Caprellidae Leach, 1814 was collected from the South Sea in Korea. Pseudaeginellacarinaspinosasp. nov. is morphologically similar to related congeners belonging to the genera Paradeutella Mayer, 1890 and Pseudaeginella, in having dorsal projections on pereonites, triarticulate mandibular palp, small or absent molar, and uniarticulate pereopods 3 and 4. However, this new species is distinguished from its congeners by the position and size of dorsal projection. This is the first record of Pseudaeginella from the Northwest Pacific region, including Korea, and a key to species of the genus Pseudaeginella is also provided.

Effects of intrusion and retreat of deep cold waters on the causative species of red tides offshore in the South Sea of Korea

To explore the effects of eutrophic deep waters offshore on red-tide outbreaks, waters were collected from 0, 20, and 40 m depths at an offshore station in the South Sea of Korea, and the growth rate of each major red-tide dinoflagellate Prorocentrum donghaiense, Tripos furca, Alexandrium fraterculus, and Margalefidinium polykrikoides in the waters was measured. No species grew at dissolved inorganic nitrogen concentrations (DIN) of < 7.0–8.4 µM, but the growth rates of all four species rapidly increased and became saturated at 12–15 µM DIN. On July 31, 2020, the DIN was 4.1–4.6 µM in 0–10 m depth waters but 8.9–18.4 µM in 20–50 m depth waters. Under these circumstances, considering that calculated reachable depths of P. donghaiense, T. furca, A. fraterculus, and M. polykrikoides were 10, 15, 24, and 52 m, respectively, A. fraterculus and M. polykrikoides can reach the deep waters and grow, but P. donghaiense and T. furca cannot. However, if the deep waters intrude and ascend by 10–20 m relative to that on July 31, four species can reach deep waters and grow, whereas if the deep waters retreat and descend by 10–20 m, only M. polykrikoides can reach the deep waters and grow. Red-tide outbreaks by M. polykrikoides in the South Sea in 2014 occurred after the deep water retreat. Thus, the position of the eutrophic deep waters, affected by their intrusion and retreat and solar insolation, can affect outbreaks of harmful M. polykrikoides red tides.

A new species of the genus Stylicletodes Lang, 1936 (Copepoda, Harpacticoida, Cletodidae) from South Korea.

Marine benthic harpacticoid copepods are poorly known in Korea due to the difficulty in obtaining specimens. Currently, the genus Stylicletodes Lang, 1936, which is known to occur in subtidal sediments, has not been reported in this area so far. During surveys on the subtidal meiofauna, we found a new species of Stylicletodes from several subtidal muddy sediments in the Yellow Sea and South Sea. In this study, we describe both sexes of a new species of Stylicletodes collected from the Yellow Sea and South Sea of Korea. Stylicletodestrifidus sp. nov. differs from its congeners in the following characteristics: the trifid rostrum, relative length ratio of the endopods to exopods on legs 1-4, reduced armature formulae on legs 3-4, constricted shape at mid-length of the anal somite, and structure of the sexually dimorphic male leg 3 with a two-segmented endopod. The new species underwent loss of the maxilliped, which is very rare in harpacticoids and is probably an important clue for the phylogeny of the species of Stylicletodes.

First report of abnormal body coloration in Sebastes koreanus (Actinopterygii: Perciformes: Sebastinae)

This study reports the first record of abnormal coloration in Sebastes koreanus Kim et Lee, 1994. The specimen (163.4 mm standard length and 197.3 mm total length) was collected from the Yellow Sea in South Korea in July 2021. The whole body of the specimens was red, and all fins also had red coloration while the slight dark red pattern under the eyes and dark spot on the opercula were similar to normal S. koreanus. It also showed a similar dotted pattern on the pectoral fins with a normal specimen.

Reproductive Characteristics of the Flat Oyster Ostrea denselamellosa (Bivalvia, Ostreidae) Found on the Southern Coast of South Korea

In this study, we investigated the reproductive pattern of the commercially and ecologically important species, Ostrea denelamellosa, to inform stock management strategies in South Korea. Prior to the reproduction experiment, the complete mitochondrial (mt) genome of the flat oyster, Ostrea denselamellosa, was analyzed using next-generation sequencing technology. Then, to determine the reproductive pattern of Ostrea denselamellosa, we investigated monthly changes in the gametogenesis, reproductive cycle, and sex ratio from January to October 2021 in females. The total length of the mt genome sequence of O. denselamellosa was 16,225 bp and contained 37 genes (13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes). Molecular phylogenetic comparison with 20 known species of Pteriomorphia showed that O. denselamellosa belongs to the family Ostreidae. In addition, O. denselamellosa clustered together with the O. denselamellosa Chinese strain, with a bootstrap value of 100%. Histological analysis indicated a discrepancy in gamete development of O. denselamellosa with synchronous maturation of oocytes and asynchronous development of spermatozoa in gonads. The spawning activity occurred between May and September with a temperature range gap of 6.5 °C. The spawning activity occurred from May when the temperature reached 16.7 °C until September when the temperature dropped below 23.2 °C. Furthermore, sex ratio bias was observed. This is the first study to report the complete mt genome sequence and examine the reproductive pattern in native O. denselamellosa in South Korea. Overall, these findings will help enhance the knowledge for the management and sustainable fishery of endangered oyster species including O. denselamellosa in the South Sea of Korea.

Seafloor litter generated by coastal and offshore fisheries operations in the South Sea of Korea

Seafloor litter sources, distribution and density were assessed in a bottom trawl survey of the South Sea around Jeju Island by the Ara-ho training ship of Jeju National University. Samples were taken from 14 transects at a depth range of 60–120 m in areas with sandy and muddy substratum. Generally, mean densities varied from 26.9 items/km2 to 62.4 items/km2 and 104.8 kg/km2 to 370.9 kg/km2. Mean densities of total litter sampled was 46.3 items/km2 and 228.6 kg/km2. Derelict gears were the most common litter items (92 % of total litter) with mean densities of 44.3 items/km2 and 228.1 kg/km2. Gillnets and traps were the most derelict with densities reaching 4.9 items/km2 and 99.2 kg/km2 and 25.0 items/km2 and 89.1 kg/km2 respectively. The results of this study indicate that significant level of pollution in the South Sea are generated from commercial fishing activities and gillnets and traps being high risk derelict gears.