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Unraveling the dynamics of mesozooplankton of the southwestern Indian Ocean
No full textThe Seychelles–Chagos Thermocline Ridge (SCTR) is formed by strong air–ocean interactions that induce open-ocean upwelling in the western Indian Ocean (wIO). This process enhances nutrient concentrations in the upper ocean, supporting phytoplankton growth, high mesozooplankton abundance, and productive nursery habitats for fish. To evaluate the ecological significance of upwelling in the SCTR, mesozooplankton communities and associated environmental parameters were examined along the 67°E transect (5°N–16°S) during the boreal summer monsoon, and along 60°E and 67°E transect (3–12°S) during the spring inter-monsoon. Mesozooplankton were sampled using a Multiple Opening/Closing Net and Environmental Sensing System. The abundance of mesozooplankton was highest in the surface mixed layer (SML; mean: 1,275 inds. m⁻³), where Noctiluca scintillans was ubiquitous and significantly differentiated in the cold-core eddy region (p < 0.05). In the middle layer (ML), SCTR-II region exhibited significant peaks in mesozooplankton abundance (962 inds. m⁻³, p < 0.05) with lower temperatures (mean: 17.7 °C), dominated by N. scintillans and Oncaea copepodites. In contrast, non-SCTR ML sites had lower abundance and were dominated by Scolecithricella and Scolecithrix copepodites. In the bottom layer (BL), abundance was more variable (mean: 57 inds. m⁻³) and driven by ostracods or Scolecithricella copepodites. Principal component analysis showed that dominant mesozooplankton were influenced by high temperatures (25.3–29.8 °C, p < 0.05) in the SML and high salinity in the ML, while no clear environmental drivers were found in the BL. These results suggest the ML of the SCTR functions as a hotspot for opportunistic Oncaea spp., linked to open-ocean upwelling. In addition, mesozooplankton dynamics during this weakened SCTR period were influenced by enhanced cold-core eddy activity and surface–subsurface current interactions. Hydrographic data revealed clockwise circulation between the westward South Equatorial Current and the eastward South Equatorial Countercurrent. An eastward subsurface undercurrent was also observed at 3°S along 60°E down to 400 m depth. Mesozooplankton abundance was higher at 60°E (mean: 297 inds. m⁻³) than at 67°E (mean: 218 inds. m⁻³), with strong aggregation in the SML and thermocline layer. Copepodites dominated (52.7%), and clustering analysis revealed the highest abundances in group G (898 ± 261 inds. m⁻³). Temperature, chl-a concentrations, and dissolved oxygen significantly correlated with Oncaea media and N. scintillans, reinforcing the influence of physical drivers on mesozooplankton in the wIO. These findings highlight the role of the SCTR’s ML as a persistent mesozooplankton hotspot, particularly under weakened upwelling conditions. The dominance of opportunistic taxa such as Oncaea spp. and N. scintillans reflects rapid ecological responses to variations in thermohaline structure and mesoscale circulation.1
Extended predictability of metabolic constraints on fish habitat
No full textPredicting the migration of marine life due to climate change is important not only ecologically but also for the management of valuable living marine resources. Anticipating how the habitable area of species will change on decision-relevant time scales, however, remains a challenge. Here we assess the predictability of a normalized metabolic index that expresses habitat-relevant anomalies in metabolic constraints using a coupled physical-biogeochemical prediction system based on an Earth system model. The normalized metabolic index was generally more predictable than temperature, especially in the subsurface tropics where persistent lateral oxygen advection anomalies at the boundary of oxygen minimum zones extended the predictability horizons. Further investigations suggest that interannual catch variations of bigeye tuna in the tropical exclusive economic zones can be anticipated from the predicted metabolic constraints a year in advance, supporting the potential utility of Earth system model-based physiological prediction for the proactive climate-informed management of living marine resources.11Ysciescopu
Climate-induced variability ofsedimentary mercury depositionin thesouthern Scotia Sea, Southern Ocean,over the last 35 kyr
No full textHigh-resolution sedimentary records of mercury (Hg) in the southern Scotia Sea, Southern Ocean, reveal the close link between climate change and Hg deposition on orbital timescales. Hg levels and fluxes in core sediments were higher during the glacial period than during the interglacial period, despite the latter having higher biological productivity. This suggests that increased productivity does not necessarily enhance Hg sequestration, challenging previous assumptions of a positive association. This orbital-scale variation in Hg appears to be driven by the availability of dissolved Hg for scavenging by organic matter in the water column. During the sea ice-free interglacial period, enhanced microbial and photochemical Hg reduction likely enhanced oceanic Hg evasion, thereby lowering dissolved Hg concentrations and reducing Hg scavenging into sediments. Thus, in polar sedimentary archives, negative excursions in Hg records likely indicate warm periods with high productivity and ice-free conditions. Isotopic evidence, marked by a shift in Δ199Hg signals from highly positive values in interglacial sediments to near-zero values in glacial sediments, suggests that interglacial Hg primarily originates from the atmosphere, while glacial Hg is derived from the bedrock erosion in the surrounding area. Our findings indicate the variations in Hg deposition in Antarctica are closely linked to biogeochemical processes (e.g., oceanic emissions) driven by sea-ice dynamics and biological productivity. This study contributes to the debate concerning positive linkages among climate warming, productivity, and Hg sequestration, particularly in productive ocean regions like the Southern Ocean.1
Effects of hull cleaning wastewater on coastal plankton community: A mesocosm experiment
No full textIn-water hull cleaning, widely used to manage biofouling on ship hulls, releases wastewater (HCW) that contains high levels of heavy metals and suspended solids. These contaminants can directly alter water chemistry and disrupt planktonic community dynamics, yet their ecological effects in coastal environments remain poorly understood. In this study, a mesocosm experiment was conducted to evaluate the effects of increasing HCW concentrations (1 %, 5 %, and 10 %) on coastal marine planktonic ecosystems, including phytoplankton, zooplankton, and periphyton. Exposure to ≥ 5 % HCW resulted in sharp declines in phytoplankton abundance (e.g., from 144 × 104 cells L⁻1 to 2 × 104 cells L⁻¹), coinciding with elevated dissolved copper (Cu) and zinc (Zn) levels, while zooplankton abundance declined rapidly even at 1 % exposure. In contrast, periphytic diatoms (e.g., Cylindrotheca closterium, Navicula spp.) exhibited relative resilience, with abundances increasing up to 101 × 103 cells cm⁻2 during the later stages, particularly under nutrient-enriched conditions. Community composition analyses revealed a shift toward metal-tolerant, attached microalgal taxa at higher HCW concentrations. Trait-based functional diversity analyses indicated reduced trait dispersion and redundancy under high HCW exposure, while ordination analysis indicated that changes in trait composition were linked to environmental gradients. These findings demonstrate that HCW acts as a complex ecological stressor that alters plankton community structure and reduces functional capacity, and emphasize the importance of integrating ecological response indicators into future management strategies for robotic hull cleaning discharges.11Nsciescopu
Improvement of Small Fishing Vessel Detection Performance Using Polarimetric Combination from Dual-Polarization Sentinel-1 SAR data
No full textMaritime Domain Awareness (MDA) is important to ensure maritime security because of the threat of illegal fishing activity [1]. Synthetic Aperture Radar (SAR) has been widely employed to improve MDA, providing weather-independent capabilities with extensive coverage. From SAR, the backscattering intensity of vessels is expected to be significantly more substantial than the surrounding sea surface, facilitating the detection of vessels using various approaches. [1][2]. Thus, a number of ship detection approaches have been proposed. The Constant False Alarm Rate (CFAR) technique is widely used for ship detection [3]. Researchers have effectively adapted deep learning models based on Convolutional Neural Networks (CNNs), such as Single Shot MultiBox Detector (SSDD) and You Only Look Once (YOLO), for experimental ship detection in satellite imagery [4][5]. [6] used dual-polarized Sentinel-1 GRD data and proposed a method to suppress Radio Frequency Interference (RFI) and azimuth smearing by combining co-polarized and cross-polarized images. Different targets interact with plane electromagnetic waves of varying polarization in distinct ways, providing characteristic information through polarimetric SAR (PolSAR). Several detectors have been developed for ship detection [7][8]. However, Sentinel-1 SAR, which operates with dual polarization, has not been thoroughly validated for PolSAR applications. Furthermore, most previous studies have focused on merchant vessels equipped with Automatic Identification System (AIS), with relatively few qualitative studies examining small ship detection. Therefore, this study proposed a polarimetric combination method using Sentinel-1 Single Look Complex (SLC) data to improve small fishing vessels detection performance. The proposed method consists of two steps: polarimetric combination and ship detection. The amplitude of a SAR image is a complex number, and the use of dual-polarimetry allow to extract 〈||2〉 and 〈| |2〉, representing the intensity of each polarization channel. 〈 ∗ 〉 (sym) denotes the cross- correlation of the two polarization channels [9]. First, to reduce smearing and ambiguities, a combination method is applied that considers the following: a) Primarily, VH intensity is used; or b) if the difference between VV and VH polarization channels is less than 6.53 (dB), the value obtained by subtracting 6.53 (dB) from the VV intensity is used. We refer to this observable as fusVH [6]. Secondly, small fishing vessels are selected using a polarimetric combination of sym and fusVH. Specifically, fusVH is used under the following conditions: a) if the difference between sym and fusVH is less than 7.2 (dB), and b) if sym is higher than -18.03 (dB). Additionally, if sym is greater than fusVH, then sym is used. This combination is referred to as the fusSym image. The thresholds were established by analyzing a dataset of small fishing vessels from V-Pass (small fishing vessel tracking system). For ship detection, the Radar Cross Sections (RCS) are categorized based on the VH polarimetric channel, distinguishing between merchant ships and small fishing vessels. Appropriate thresholds are then applied for each image. Final small fishing vessels are confirmed by filtering out the merchant ships. The results were evaluated using 14 scenes from 2021 to 2023 year, and the average matching results were calculated to be 0.85 for the matching rate and 0.24 for the false alarm rate.1
RGO/epoxy composite coatings as a dual barrier: Microstructural insights into superior wear and corrosion resistance
No full textThis study investigates the enhancement of wear resistance, corrosion protection, and long-term stability of epoxy resin coatings on steel through the incorporation of reduced graphene oxide (RGO) nanosheets. RGO/epoxy composite coatings with varying RGO contents (0, 0.05, 0.1, 0.5, and 1.0 wt%) were fabricated and systematically evaluated. Among them, the coating containing 0.1 wt% RGO exhibited the best wear resistance, achieving the lowest wear rate (3.17 × 10−8 mm3 N−1 s−1), attributed to the synergistic effects of lubrication and enhanced crosslinking. In addition, the 0.1 wt% RGO coating demonstrated superior corrosion resistance, with a significantly improved corrosion potential (Ecorr = −0.285 V). This improvement was ascribed to the uniform dispersion of RGO within the epoxy matrix and the “maze effect,” which enhanced both barrier performance and interfacial adhesion. Long-term immersion tests in saline and simulated marine environments confirmed that the 0.1 wt% RGO coating maintained excellent protective performance and structural integrity over 10 weeks, significantly outperforming the pure epoxy coating. However, higher RGO contents (≥ 0.5 wt%) led to nanosheet aggregation, resulting in microcrack formation and performance degradation, highlighting the critical importance of optimizing both RGO content and dispersion. These findings provide valuable insights into the application of two-dimensional nanomaterials in protective composite coatings and offer practical guidance for the development of high-performance, corrosion-resistant, and wear-resistant coating systems.11Nsciescopu
Mapping the Landscape of Marine Giant Virus Research: A Scientometric Perspective (1996–2024)
No full textAlthough giant viruses have introduced new perspectives on the definition and evolution of viruses and are increasingly recognized for their significant biological roles within marine ecosystems, systematic evaluations of development trends and scientific contributions in this research field remain limited. This study conducted a bibliometric analysis of the global academic literature on marine giant viruses (MGVs), focusing on nucleocytoplasmic large DNA viruses (NCLDVs), from 1996 to 2024. Using the Web of Science Core Collection, 1544 publications related to giant viruses were identified. After filtering using marine-related keywords and manual review, 300 studies specifically addressing marine giant viruses were selected for the final analysis. This study comprehensively examined the structural characteristics and evolutionary trends in this field by analyzing annual publication productivity, citation patterns, contributions by countries and institutions, author collaboration networks, and keyword co-occurrence patterns. The results show that research on MGVs has steadily increased since the mid-2000s, with a notable surge after 2018 driven by advancements in metagenomics, next-generation sequencing technologies, and global ocean exploration initiatives. The United States and France have taken leading positions in terms of research productivity and impact, with key institutions such as the CNRS (Centre National de la Recherche Scientifique) and Aix-Marseille Université playing central roles. A multipolar network of international collaborations between countries and institutions has been formed. Research topics have evolved from an early focus on virus classification and genome analysis to more diverse themes, including interactions with marine microbiota, viral ecological functions, infection dynamics, virophage research, and metagenome-based ecosystem-level studies. This study provides an overview of the chronological and structural evolution of the marine giant virus research field by systematically presenting key research themes and collaborative networks. The results provide a valuable foundation for determining future academic directions and planning strategic research initiatives. Furthermore, it is expected to facilitate interdisciplinary research in marine biology, environmental science, systems biology, and artificial intelligence-based functional predictions.11Ysciescopu
Ecological and Anthropogenic Drivers of Hairtail Catch Distribution: A Spatial Analysis of the Southern Coastal Waters of South Korea
No full textHairtail (Trichiurus lepturus) is a commercially important fish species in South Korea, serving as both a vital food source and a major contributor to the local fishing industry. However, catch rates vary spatially and temporally in response to oceanographic conditions, including water temperature, dissolved oxygen levels, salinity, and food availability. In this study, we investigated the spatial and seasonal distribution of hairtail catches across the southern coastal waters of South Korea. We applied a spatial analytical approach that accounts for both site-specific conditions and the interactions among neighboring areas. Our results indicated that hairtail abundance was positively associated with areas of higher salinity and lower oxygen concentrations. Furthermore, regions with elevated phytoplankton biomass, an essential food source for smaller marine organisms, were found to enhance hairtail presence in adjacent waters. These findings advance our understanding of the species’ habitat preferences and environmental responses, providing insights that can inform more effective and sustainable fisheries management strategies. By integrating spatial mapping and environmental data, this research offers critical information for shaping future fishing policies and conserving key fishery resources such as hairtail.11Ysciescopu
A Legal Analysis of the Structural Consistency of Environmental Standards under the UNCLOS and Its Implementing Agreements Regime: Focusing on Pollution, Harmful Effects, and Serious Harm Standards
No full text본 논문은 UN해양법협약(UNCLOS)과 그 이행협정 체제(심해저이행협정, 공해어업협정, BBNJ협정)에 내재된 환경기준들을 포괄적으로 구조화하고, 수직적･수평적 정합성의 법적 쟁점을 심층 분석하는 데 목적을 두었다. 이를 위하여 본 논문은 우선 UNCLOS, 심해저이행협정, 공해어업협정, BBNJ협정에 각기 등장한 ‘오염’, ‘해로운 영향’, ‘심대한 해’, ‘상당하고 해로운 변화’, ‘사소하거나 일시적인 효과’ 등 환경기준을 구조적으로 분석했다. UNCLOS는 오염과 심대한 오염, 실질적 오염을 계층화하지만 등위성에 대하여 명확한 구별기준을 제시하지 않으며, 해로운 영향 및 심대한 해는 각 조항과 부속서, 심해저 규정에서 서로 다른 적용범위와 예시적 요소로 나타난다. 공해어업협정은 사전주의 접근과 별도의 기준점(제한･목표 기준)이 환경관리 원칙으로 도입되어 있다. 특히, BBNJ협정은 사소하거나 일시적인 효과, 상당하고 해로운 변화, 심대한 또는 회복 불가능한 해 등의 기준을 환경영향평가의 구체적 판단 요소 및 비상조치 발동 요건으로 새롭게 채택하였다.
먼저 수직적 정합성 분석에서는, UN해양법협약이 최상위 일반문서로서 이행협정들에 규범적 틀을 제공하는 구조임을 확인하였다. 법문서간의 수직적 정합성은 이행협정과 심해저 탐사 및 개발규정에서 일부 확보되고 있는 것으로 평가되었다. 그러나 오염기준내에서 상당한 오염, 해로운 영향, 심대한 해 등 주요 환경기준 간 위계는 명확하지 않아 수직적 정합성은 아직 미비한 것으로 평가된다. 수평적 정합성 측면에서는, 심해저이행협정과 BBNJ협정은 모두 환경영향평가 체제를 운영하지만, 면제 기준 등에서 정합성 확보를 위한 추후 작업이 필요하다. 수평적 정합성이 확보되지 않으면 국제해저기구와 BBNJ 당사국 총회 간의 간섭 문제가 발생할 수 있다.
이상의 분석을 바탕으로, 본 논문은 UN해양법협약 환경기준의 구조적 정합성을 향상시키기 위해 절차적, 실체적 방안을 제언한다. 첫째, 절차적 제언으로 UN해양법협약 이행 체제내 권한 조항들인 UN해양법협약 제145조, 제162조 제2항 (o)와 심해저이행협정은 제1부속서 15, BBNJ 협정 제38조와 제48조 제6항을 활용할 것으로 제안하다. 둘째, 실체적 제언으로 수직적 수평적 정합성 확보를 제언한다. 수직적 정합성 확보의 목표는 UN해양법협약상 내부 환경기준들간의 수직적 정합성, 이행 협정내 환경기준의 수직적 정합성, UN해양법협약상과 이행협정 환경기준들이 명확한 수직 구조를 가지도록 하는 것이다. 그리하여 환경기준과 각 이행협정의 환경기준간 수직적 관계를 명확히 하여 이행 주체들이 환경 기준과 그 기준에 따라 부여되는 의무를 명확히 이해할 수 있도록 해야할 것이다. 수평적 정합성 확보는 심해저이행협정, 공해어업협정, BBNJ협정 및 향후 심해저개발규정과 같은 각종 이행문서들이 특정 환경 기준에 대하여 같은 등위를 부여하여, 하나의 환경 기준이 UN해양법협약과 이행협정체제 내에서 다르게 해석되지 않도록 해야 할 것이다. 이는 동일 환경 의무에 대하여 이행협정들이 다른 환경 기준을 적용하여 같은 등위의 환경 기준을 부여하여 이행 주체의 혼란을 막고, 낮은 환경기준을 가진 법문서 체제를 이용하려는 시도를 방지해 줄 것이다.22Nkc
