Search Results (10)

Marine archaea play crucial roles in global biogeochemical cycles and climate regulation, yet their ecological functions in many coastal environments remain poorly understood. Jinhae Bay (JB), a eutrophic and environmentally stressed coastal system in Korea, has attracted growing attention; however, its archaeal community composition has not been characterized. In this preliminary study, we investigated the summer archaeal community structure in JB water columns based on a survey conducted in July 2018. We identified 5 archaeal phyla—primarily Euryarchaeota and Thaumarchaeota—along with 11 classes and 18 orders, with Nitrosopumilales and Methanobacteriales as dominant orders. Several ammonia-oxidizing archaea (AOA), including Candidatus Nitrosopumilus adriaticus, Candidatus Nitrosopumilus salaria, Candidatus Nitrosopumilus sediminis, and unclassified Nitrosopumilus spp., were detected. Additionally, the presence of methane-oxidizing archaea (MOA) such as Candidatus Methanoperedens nitroreducens, although at low relative abundance, suggests potential roles in nitrogen and methane cycling. These findings provide initial insights into the archaeal contributions to biogeochemical processes in JB, highlighting the need for further seasonal and functional investigations. Full article

Rainfall-induced freshwater influx is a major nutrient source in estuarine and coastal waters, often driving changes in phytoplankton community structure and blooms. In Jinhae Bay of Korea, a critical area for shellfish aquaculture, the interaction between the Nakdong River discharge and the Tsushima Warm Current creates a frontal zone conducive to phytoplankton proliferation. This study investigated the seasonal variation in phytoplankton communities, including harmful and toxin-producing species, in relation to environmental factors from February 2022 to November 2023 in Jinhae Bay. Except for the summer increase in certain dinoflagellates, diatoms, including Chaetoceros spp., Pseudo-nitzschia spp., and Skeletonema spp., dominated the phytoplankton community across seasons. In addition, nutrient influx from the Nakdong River, particularly nitrate + nitrite and silicate (p < 0.001), was a key driver of phytoplankton community structure. Spatially, phytoplankton communities differed between the inner (St. 1 and 4) and outer (St. 2 and 3) areas in the bay, likely due to the influences of seasonal river discharge, the Tsushima Warm Current, and tidal currents. Among harmful algal blooms causative species, dinoflagellate Margalefidnium polykrikoides was correlated with water temperature, exhibiting higher densities in summer. In contrast, Akashiwo sanguinea was mainly observed in winter. In addition, we found that toxin-producing dinoflagellates, such as Alexandrium catenella, Dinophysis acuminata, and Gonyaulax spinifera, were most prevalent in spring and summer, and their appearance was linked to complex interactions among freshwater influx, water temperature, and current dynamics. Our findings underscore the critical role of bay-specific oceanographic conditions, shaped by tidal and current patterns, in conjunction with riverine nutrient inputs, in driving seasonal phytoplankton blooms. This study provides valuable baseline data for understanding harmful/toxic microalgal dynamics in Jinhae Bay and offers key insights for effective coastal ecosystem management and conservation along the Korean Peninsula. Full article

This study investigates the impact of port construction on suspended solid concentrations and key water quality parameters in Jinhae Bay, using seventeen years of water quality data up to 2020. The study highlights the significant impact of suspended solids on marine water quality, particularly in areas affected by dredging operations at Busan New Port. Suspended solids concentrations peaked at 92 mg/L, exceeding 10 mg/L in both surface and bottom waters, with the highest levels near the port. These solids were identified as key predictors of coastal eutrophication in locations such as Jinhae Bay 01, 17, 19, where positive correlations with Chl-a suggest their role in promoting eutrophication. The highest average Chl-a levels were recorded at Jinhae Bay 01 (9.82 µg/L), while the lowest were at Jinhae Bay 14 (3.2 µg/L). The WQI, ranged from 1 to 3, with Jinhae Bay 19 showing the highest value and Jinhae Bay 14 the lowest due to low dissolved oxygen levels. Using ARIMA modeling, the study effectively analyzed the time-series dynamics of suspended solids, demonstrating their relationships with Chl-a and WQI components. These findings underscore the importance of monitoring and managing suspended solids to mitigate the risk of eutrophication and protect marine ecosystems in the context of port development. Full article

Despite efforts to use environmental DNA (eDNA), accurately quantifying fish populations remains a challenge. A recent eDNA approach provided reliable estimates of coastal fish population abundance, but it was not as effective for assessing spatial distribution due to a lack of eDNA samples relative to the study area. Therefore, we conducted a numerical case study to evaluate the ability of the eDNA approach to estimate fish (Jack mackerel) abundance and distribution based on the number of eDNA samples in a semi-enclosed bay (Jinhae Bay). Our study revealed that the eDNA approach can provide reliable estimates of fish abundance, even with knowledge of the eDNA concentration in just 1% of the study area. However, for estimating spatial distribution and fish school, significant estimates were obtained only when the eDNA concentration was identified in more than 70% of the study area. Our results confirm that the eDNA approach can reflect fish abundance but has limitations in estimating fish distribution. Full article

Jinhae Bay, a semi-enclosed bay on the southern coast of Korea, is a major aquaculture area that forms a spawning ground and nursery for commercially important fishes. Since the late 1960s, industrial and domestic waste from adjacent cities and industrial complexes has been released into the region, resulting in chronic hypoxia and red tides. As a central site of environmental monitoring efforts for aquaculture and fisheries in southeastern Korea, Jinhae Bay was surveyed every 2 months usually, and every 2–3 weeks during the hypoxia season, with the seawater properties observed at approximately 31–34 stations. The maximum area and duration of hypoxia in Jinhae Bay occurred in 2016 (316 km² and 26 weeks, respectively), with minima of area in 2013 (213 km²) and duration in 2011 (15 weeks). Correlation analyses of the seawater properties, weather parameters, and hypoxia indices showed that the hypoxic area was positively correlated with the surface-water temperature, air temperature, and rainfall; the minimum dissolved oxygen concentrations were negatively correlated with the air and water temperatures and bottom-water nutrient levels; and the water stability was negatively correlated with the surface-water salinity and positively correlated with both the surface- and bottom-water nitrate and silicate concentrations. These findings imply that the air temperature and precipitation may be important factors in the development and persistence of hypoxia in Jinhae Bay via the control of the stratification intensity and eutrophication of the water column. Therefore, we tested these parameters for their potential to predict hypoxia. Based on our results, we propose the following trends of hypoxia in Jinhae Bay: the initial hypoxia development generally depends on the criteria of an air temperature ≥ 19.5 °C for 1 week and total precipitation > 100 mm over 4 weeks, and it becomes more severe (≥50% coverage) under strong eutrophication, mainly due to organic matter discharge following heavy rainfall, based on the logarithmic correlation with the 4-week rainfall (R² = 0.6). Therefore, the hypoxic area index can be predicted using its linear regression relationships with the 1-week air temperature and 4-week precipitation (R² = 0.56). This study tested the prediction of the hypoxic area based on a simple calculation method and weather parameter criteria, and it demonstrated the potential of this method for precisely forecasting hypoxia in combination with biogeochemical models or other mathematical solutions to prevent massive fishery damage. Full article

Jinhae Bay in South Korea is a common typhoon shelter, but there are no established criteria for the area or vessel capacity. The aim of this study was to determine the optimal capacity and arrangement of typhoon shelters for vessels in the sea area surrounding Jinhae Bay. The study identified several areas that could serve as typhoon shelters and conducted a survey with experienced VTS operators and ship operators to identify the best typhoon avoidance areas. The study found that the Japanese and Spanish design criteria for anchoring in strong winds were useful in computing the optimal capacity of typhoon shelters. A nesting algorithm based on the genetic algorithm and the No-Fit-Polygon theory was used to optimize the arrangement of shelters. The study found that the Jinhae Bay typhoon shelter can be effectively managed by arranging shelter-seeking vessels based on the nesting algorithm. The study contributes to supporting quantitative methodology-based decision-making and has practical significance for managing typhoon shelters in the Jinhae Bay area. Further research is needed to evaluate the proposed arrangement plan for typhoon shelters and confirm the validity of the results through simulation and practical implementation. Additionally, the time complexity for vessels to approach the anchorage should be considered in future studies. Full article

Alexandrium pacificum, which produces the paralytic shellfish toxin (PST) saxitoxin (STX), is one of the causative species of paralytic shellfish poisoning outbreaks in coastal areas of Korea. In this study, we developed a chip-based digital PCR (dPCR) method for A. pacificum detection and tested it for monitoring in Jinhae-Masan Bay. Using the sequence of an A. pacificum strain isolated in 2017, species-specific primers targeting sxtA4 (a STX biosynthesis-related gene) were designed and used in a dPCR, detecting 2.0 ± 0.24 gene copies per cell of A. pacificum. Cell abundance in field samples, estimated by a chip-based dPCR, was compared with the PST content, and measured using a mouse bioassay. A comparison with shellfish PST concentrations indicated that cell concentrations above 500 cells L⁻¹, as measured using the dPCR assay, may cause shellfish PST concentrations to exceed the allowed limits for PSTs. Concordance rates between dPCR and PST results were 62.5% overall in 2018–2021, reaching a maximum of 91.7% in 2018–2019. The sensitivity of the dPCR assay was higher than that of microscopy and sxtA4-based qPCRs. Absolute quantification by chip-based dPCRs targeting sxtA4 in A. pacificum exhibits potential as a complementary approach to mouse bioassay PST monitoring for the prevention of toxic blooms. Full article

Paralytic shellfish toxins (PSTs) are produced mainly by Alexandrium catenella (formerly A. tamarense). Since 2000, the National Institute of Fisheries Science (NIFS) has been providing information on PST outbreaks in Korean coastal waters at one- or two-week intervals. However, a daily forecast is essential for immediate responses to PST outbreaks. This study aimed to predict the outbreak timing of PSTs in the mussel Mytilus galloprovincialis in Jinhae Bay and along the Geoje coast in the southern coast of the Korea Peninsula. We used a long-short-term memory (LSTM) neural network model for temporal prediction of PST outbreaks from environmental data, such as water temperature (WT), tidal height, and salinity, measured at the Geojedo, Gadeokdo, and Masan tidal stations from 2006 to 2020. We found that PST outbreaks is gradually accelerated during the three years from 2018 to 2020. Because the in-situ environmental measurements had many missing data throughout the time span, we applied LSTM for gap-filling of the environmental measurements. We trained and tested the LSTM models with different combinations of environmental factors and the ground truth timing data of PST outbreaks for 5479 days as input and output. The LSTM model trained from only WT had the highest accuracy (0.9) and lowest false-alarm rate. The LSTM-based temporal prediction model may be useful as a monitoring system of PSP outbreaks in the coastal waters of southern Korean. Full article

Marine bacteria are known to play significant roles in marine biogeochemical cycles regarding the decomposition of organic matter. Despite the increasing attention paid to the study of marine bacteria, research has been too limited to fully elucidate the complex interaction between marine bacterial communities and environmental variables. Jinhae Bay, the study area in this work, is the most anthropogenically eutrophied coastal bay in South Korea, and while its physical and biogeochemical characteristics are well described, less is known about the associated changes in microbial communities. In the present study, we reconstructed a metagenomics data based on the 16S rRNA gene to investigate temporal and vertical changes in microbial communities at three depths (surface, middle, and bottom) during a seven-month period from June to December 2016 at one sampling site (J1) in Jinhae Bay. Of all the bacterial data, Proteobacteria, Bacteroidetes, and Cyanobacteria were predominant from June to November, whereas Firmicutes were predominant in December, especially at the middle and bottom depths. These results show that the composition of the microbial community is strongly associated with temporal changes. Furthermore, the community compositions were markedly different between the surface, middle, and bottom depths in summer, when water column stratification and bottom water hypoxia (low dissolved oxygen level) were strongly developed. Metagenomics data contribute to improving our understanding of important relationships between environmental characteristics and microbial community change in eutrophication-induced and deoxygenated coastal areas. Full article

Acoustic surveys were used to locate coastal Pacific herring (Clupea pallasii) spawning grounds, and the spatial and temporal patterns of their spawning in Jinhae Bay, Korea were examined. We deployed mooring with a newly designed autonomous echosounder for ~70 days during the Pacific herring spawning season in Jinhae Bay, from January to April 2018. At the same time, ship-based acoustic surveys were conducted to identify the spatial distribution twice, at 38 and 120 kHz, onboard the fishing vessel in January and April 2018 in the bay. Fish school signals, including those from adult Pacific herring, are often detected through ship-based acoustic surveys in January, from outside the bay. In the spring, weak scattering signals from fish larvae and zooplankton were continuously detected inside the bay. Backscatter at the mooring in the center of Jinhae Bay was low from mid-January to early March, gradually increasing to higher levels until the end of March. The backscatter observed from the mooring correlated well with ship-based acoustic surveys in the center of the bay. This study proposes that the mooring type acoustic echosounder is a valuable tool for temporal abundance information and other aspects of fish behavior. Full article