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- Abstract：In late June, 2026, a massive harmful algal bloom (HAB) occurred along the western coast of Hainan Island, China, severely impacting mariculture operations in the Changjiang, Danzhou, Lingao, and Chengmai. The bloom resulted in widespread mortalities of economically important farmed fish, specifically cobia (Rachycentron canadum) and golden pomfret (Trachinotus ovatus). Morphological identification via light and scanning electron microscopy confirmed the causative agent as the ichthyotoxic dinoflagellate Margalefidinium polykrikoides. However, molecular characterization based on LSU rRNA gene sequences identified the causative species as a previously undocumented ribotype. Maximum-likelihood phylogenetic analysis revealed a strongly supported, monophyletic lineage, that is genetically distinct from the four established global ribotypes (East Asian, American/Malaysian, Philippines, and Mediterranean). Given its profound phylogenetic divergence and high toxicity-despite the lack of distinct diagnostic morphological markers, this strain is designated as a novel ribotype, South China Sea ribotype, or Group V. Our phylogenetic analyses also suggest that the subclade composed of four sequences from Republic of Korea, which is closely related to the Mediterranean ribotype, should be assigned as a new ribotype, Group VI. These findings reveal significant cryptic diversity within the M. polykrikoides complex and highlight an emerging threat to tropical mariculture, underscoring the necessity for enhanced surveillance and integrated monitoring strategies.Keywords：Margalefidinium polykrikoides;morphology;phylogeny;harmful algal bloom (HAB)0|0|0
Updated：2026-10-19 - Abstract：Mangrove plants, serving as critical blue carbon ecosystems and biodiversity hotspots, play critical roles in coastal protection, water purification, and climate change mitigation. In this paper, we present the first comprehensive analysis of chloroplast genomes from 15 mangrove species within the Rhizophoraceae family, with particular emphasis on their codon usage bias (CUB), phylogenetic connections, and evolutionary dynamics. The total GC contents of protein-coding genes (PCGs) span from 36.79% to 38.13%, with a distribution trend of 50%>1st-site GC (GC1)>2nd-site GC (GC2)>total GC (GCall)>3rd-site GC (GC3)>synonymous codon 3rd GC (GC3s). The average values of effective number of codons (ENC) range from 46.43 to 47.18, reflecting a relatively weak CUB across the genomes. This bias is shaped by both mutational pressure and natural selection, with mutation exerting a more significant influence. We identified 13–19 optimal codons across these species, with ACU, AUU, CAA, CGU, GGU, GUA, UGC, and UUA being the most common optimal codons. Among all the genes analyzed, the rps14 gene demonstrated the strongest CUB (ENC<35), primarily driven by natural selection that optimizes its expression to ensure the efficient and accurate synthesis of the ribosome, whereas rps18 gene exhibited clear signals of positive selection across all species against their terrestrial relative by the ratio of non-synonymous and synonymous substitution (Ka/Ks) analysis, suggesting it may be undergoing potential adaptive evolution within Rhizophoraceae mangrove species. Phylogenetic analysis based on common coding sequences (CDSs), concatenated sequences of rps14 and rps18, and relative synonymous codon usage (RSCU) values strongly supported monophyletic groups of four true mangrove genera. This study elucidated the synonymous codon usage patterns within the Rhizophoraceae family, offering valuable insights into their phylogenetic relationships, evolutionary processes, and potential applications in genetic engineering of Rhizophoraceae mangrove species.Keywords：Rhizophoraceae;chloroplast genome;codon usage bias;optimal codon;phylogenetic analysis1|0|0Updated：2026-10-19
- Abstract：Microbial mediated anaerobic ammonium oxidation coupled to ferric iron reduction (Feammox) represents a potentially crucial nitrogen removal pathway in eutrophic lakes. However, its response to cyanobacterial blooms in sediment environments remains unclear. In this study, the microcosms containing fresh cyanobacteria particles were cultured under natural conditions, and techniques of X-ray absorption fine structure spectrum (XAFS), high-throughput sequencing, and 15N isotope tracing were utilized to examine the impacts of outbreak and decline of cyanobacterial bloom on the iron forms, iron-reducing bacteria (FeRB) and Feammox potential rates in the surface sediment. The XAFS results revealed that cyanobacterial blooms promoted the formation of FeOOH, which theoretically favors Feammox. Surprisingly, the potential rate of Feammox was significantly suppressed during the active bloom phase compared to the control (P<0.05), likely due to the inhibition of FeRB growth under bloom-induced high dissolved oxygen and alkaline conditions, as evidenced by a lower relative abundance of FeRB. In contrast, after an 80-d cultivation under natural conditions, the degradation of cyanobacteria led to substantial accumulation of hydrochloric acid-extractable Fe(III), humic acid, along with a recovery in the relative abundance of FeRB, resulting in a significantly increase in the potential Feammox rate. These findings demonstrate that cyanobacterial blooms modulate sediment Feammox activity in opposite directions during distinct phases of outbreak and decline, by altering key substrates and microenvironments. This study highlights the complex role of cyanobacterial blooms in nitrogen cycling and advances our understanding of ecological nitrogen removal in eutrophic lakes.Keywords：cyanobacterial bloom;Feammox;iron-reducing bacteria (FeRB);sediment;Taihu Lake10|5|0Updated：2026-10-13
- Abstract：Chloride-type low-salt saline-alkali waters show promise for sustainable aquaculture of the mud crab (Scylla paramamosain Estampador, 1950), but low Cl- stress disrupts osmoregulation and homeostasis. We established Cl- gradients (0.5–5.0 g/L) to evaluate effects on survival, posterior gill histology, hemolymph osmolality, and ionic composition, and coupled these with transcriptomic profiling to resolve molecular responses to low-Cl- stress. At 0.5-g/L Cl-, survival decreased markedly; posterior gills exhibited edema and structural lesions; activities of key osmoregulatory enzymes (Na+/K+-ATPase, Na+-K+-2Cl- cotransporter, V-type H+-ATPase, carbonic anhydrase) were suppressed; and hemolymph osmolality and ion balance were disturbed. Conversely, when Cl-
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- Abstract：High-resolution Earth system models are essential for understanding and predicting extreme weather events. However, the performance of complex coupled models on ARM architectures and the intrinsic uncertainties introduced by the underlying computing infrastructure remain inadequately assessed in quantitative geophysical simulations. Using Typhoon Soulik (2013) as a case, this work ports the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model to a Huawei Kunpeng (ARM) server and systematically evaluates its performance and physical consistency against an Intel (x86) server, which was then validated with multi-source observational data. Results show that the ARM-based simulation reduced computational time by 15.44%. Both platforms achieved high consistency in simulating typhoon evolution and oceanic response (R2>0.99), confirming the reliability of ARM for scientific modeling. Quantitative analysis further revealed discernible architectural influences: dynamical errors exhibited spatiotemporal clustering, and the ARM platform showed slightly weaker air-sea coupling during landfall but better performance in simulating near-surface wind speed (0.23% reduction in RMSE). These findings highlight computing architecture as a source of uncertainty in high-resolution simulations and underscore the need for cross-platform validation in future research. This study verified the efficiency and stability of the ARM architecture for high-resolution coupled modeling and offered a reliable pathway for advancing ocean and extreme weather research through diversified high-performance computing infrastructure.Keywords：COAWST model;Kunpeng 920;Tropical Cyclone;high-performance computing;ARM architecture;model validation10|4|0Updated：2026-09-28
- Abstract：The giant freshwater prawn (Macrobrachium rosenbergii) is a globally important species in aquaculture, prized for its delicious, tender meat and favored by consumers. Research has revealed a distinct hierarchical differentiation phenomenon among male M. rosenbergii, classifying them into three morphotypes: blue claw (BC), orange claw (OC), and small male (SM). This differentiation has become a key factor constraining industry development. This study collected serum samples from male prawns during critical stages of this differentiation (at 100-, 110-, and 120-d-old). Utilizing liquid chromatography-tandem mass spectrometry (LC-MS/MS) combined with untargeted metabolomics analysis, differential metabolites were identified through principal component analysis and database comparison. Results show that differential metabolites such as caffeoylcholine, glucosamine, and phosphate were significantly enriched in amino acid metabolism, ABC transporter, and nucleotide metabolism pathways, indicating that these metabolites and pathways may be involved in regulating the hierarchical differentiation of male M. rosenbergii. Further integration of 16S rDNA sequencing, transcriptome sequencing, and phenotypic data enabled the construction of an “Intestinal Microbiota- Phenotypic Traits-Metabolites” correlation model. The study found significant associations between intestinal bacteria (Lactococcus spp., Achromobacter spp.), the host trypsin gene, and various differential metabolites. This suggests that these host genes and intestinal microbiota play important roles in the phenotypic differentiation and nutrient metabolism processes of M. rosenbergii. This research aims to elucidate the metabolic mechanisms underlying phenotypic differentiation in male M. rosenbergii through metabolomics approaches. By integrating 16S rDNA and transcriptome sequencing, it clarifies the regulatory roles of key metabolites, gut microbiota, and host genes in this process, providing an important theoretical basis for the selective breeding and efficient aquaculture of M. rosenbergii.Keywords：Macrobrachium rosenbergii;social hierarchy;metabolomics;gut microbe;multiomics10|3|0Updated：2026-09-28
- Abstract：Phytoplankton size and morphology are key traits influencing their ecological roles, buoyancy, and susceptibility to grazing. We investigated how water density, driven by salinity and temperature, affects phytoplankton size structure in two systems: (1) a observational study in a saline (~14) meromictic Lake Shira (Russia), characterized by seasonal water column stratification; and (2) the gradient experiment at the METU Mesocosm System II (Türkiye) with a large salinity gradient (0.5–50). In Lake Shira, while the overall phytoplankton community showed no consistent size variations across seasons or depth zones, colonies of the cyanobacterium Microcystis and filaments of cyanobacterium Planktolyngbya contorta exhibited larger area based diameters in denser, more saline deep waters compared to the less dense epilimnion in summer and fall and a positive response of the area-based diameter to the increase in water viscosity. In the system of 5 000-L mesocosms, phytoplankton average diameter increased with salinity, likely compensating for reduced sinking velocity in denser water. These findings suggest that water density influences phytoplankton size, particularly in species with colonial forms; however, ecological implications for food web dynamics remain uncertain. Our study highlights the complex interplay of physical and biological factors shaping phytoplankton size structure in saline ecosystems.Keywords：colonial phytoplankton;сyanobacteria;meromictic lake;mesocosm experiment;buoyancy13|3|0Updated：2026-09-24
- Abstract：The acoustic properties of fine-grained sediments have recently attracted increasing attention from the scientific community. Understanding the relationships between these properties and frequency is crucial for advancing the fundamental theory of sediment acoustics and its practical applications. An in-situ acoustic measurement system, namely, the geoacoustic probe, was developed for determining the broadband acoustic properties of seafloor sediment, and an experiment was conducted in the muddy area of the Zhujiang (Pearl) River estuary in Guangdong, South China. To calibrate the geoacoustic probe, measurements were made with a sound speed profiler in near-bottom seawater for comparison. In-situ measurements were subsequently performed at 28 frequencies ranging 5–200 kHz in clayey silt sediment. The speed of sound ratio and attenuation were calculated using interreceiver correlation and linear fitting methods. The calculated speeds of sound ratios were consistently lower than 1 and generally linearly increased with increasing frequency. In contrast, the attenuation in fine-grained sediment was less than that in sandy sediment, with an increase in f 1.36 dependence with increasing frequency. The measured acoustic properties approached those based on viscous grain shearing theory, revealing suitable agreement with the predicted values, except for a few attenuation measurements at the end of the frequency band.Keywords：speed of sound;attenuation;fine-grained sediment;in-situ measurement;modeling20|3|0Updated：2026-09-24
- Abstract：The Qihe River crucian carp (Carassius auratus) is an economically important freshwater germplasm resource endemic to Henan Province, China, where inland aquaculture is increasingly challenged by microplastic contamination. To assess the ecotoxicological risks of micro(nano)plastics in this regional species, a 28-d chronic exposure experiment was conducted to compare the biological effects of polystyrene microplastics (PS-MPs) and polystyrene nanoplastics (PS-NPs) at two concentration levels (50 and 500 μg/L), with a specific focus on growth performance, tissue histopathological characteristics, digestive and antioxidant enzyme activities, expression of immune-related genes, and intestinal microbiome composition. The results demonstrated that micro(nano)plastic exposure significantly reduced weight gain rate (WGR) and specific growth rate (SGR), induced intestinal villus shortening, splitting, and epithelial shedding, and caused hepatocyte vacuolization and hepatic sinusoid dilation. Intestinal α-amylase (AMS), trypsin, and lipase activities, as well as hepatic total superoxide dismutase (T-SOD), total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px), malondialdehyde (MDA), alkaline phosphatase (AKP), and lactate dehydrogenase (LDH) activities, were significantly altered in a concentration-dependent manner after exposure. Furthermore, in the liver, the expression of the immune-related genes such as tumor necrosis factor α (tnf-α), interferon γ (ifn-γ), interleukin 8 (il-8), and interleukin 6 (il-6) also responded in a size- and concentration-dependent manner. In the exploratory microbiota analysis, plastic exposure decreased community evenness and reshaped taxonomic composition, characterized by reduced potentially beneficial taxa and enriched stress-associated or opportunistic taxa. Overall, PS-NPs produced stronger adverse effects than PS-MPs under the same nominal exposure level. These results provide species-specific evidence that waterborne plastic particles can impair gut and liver health, antioxidant balance, and intestinal microbial homeostasis in Qihe River crucian carp, and support a size-dependent hazard assessment for micro- and nano-plastics in freshwater aquaculture.Keywords：microplastic;nanoplastic;Qihe River crucian carp;histopathology;digestive enzyme activity;intestinal microbiota10|7|0Updated：2026-09-24
- Abstract：Potentially toxic elements (PTEs) in agricultural soils and river sediments pose major ecological risks. However, their distribution, sources, and geochemical behavior in subtropical granite derived watersheds remain insufficiently constrained. In this study, 15 surface soil and 12 river sediment samples were collected from a granitic watershed in Zhejiang Province, China, to investigate the spatial distribution, provenance, and ecological risks of seven PTEs (arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn)). The resulted show that PTE concentrations vary widely, in the range of 1.4–38.4 mg/kg for As, 0.05–1.32 mg/kg for Cd, 4.0–94.0 mg/kg for Cr, 2.5–37.0 mg/kg for Cu, 2.0–27.5 mg/kg for Ni, 21.5–108 mg/kg for Pb, and 56–202 mg/kg for Zn. Cr, Cu, and Ni exhibit decreasing concentrations from upstream to downstream, reflecting dominant lithogenic control by granite weathering, whereas Cd, Pb, and Zn show enrichment in midstream and downstream areas due to anthropogenic inputs. On average, river sediment Cd concentrations are 2.5 times higher than those in soils. Risk assessment indicates that several PTEs exceed regional background values, but Cd exhibits the strongest enrichment, with enrichment factor (EF) values up to 12.1. Ecological risk assessment based on an adjusted potential ecological risk index (RI) indicates that the watershed is generally characterized by low to moderate ecological risk. However, Cd contributes disproportionately to total ecological risk, accounting for 42.2%–82.5% (mean 73.8%) of the RI values, and midstream sediments represent clear risk hotspots. Multivariate statistical analyses distinguish lithogenic PTEs (Cr, Cu, Ni, Ti) with low mobility and residual enrichment from anthropogenic PTEs (Cd, Pb, Zn) exhibiting strong particle-associated transport and cumulative downstream accumulation. These results demonstrate that soil-sediment transfer amplifies Cd-dominated ecological risks in granite-derived agricultural watersheds and highlight the need for targeted agricultural management strategies.Keywords：potentially toxic element;ecological risk;soil-sediment transport;granite weathering;anthropogenic pollution13|4|0Updated：2026-09-17
- Abstract：Environmental variability (e.g., temperature, salinity, pH) and seasonal fluctuations in pollutant concentrations often hinder the establishment of reliable reference sites in marine biomonitoring, challenging the accurate assessment of pollutant-induced biological effects. This study employed tiered biomonitoring and assessment approaches to evaluate endocrine disrupting compounds (EDCs) using embryos of Oryzias melastigma in the Jiulong River estuary (JRE) and nearby coastal seas of China, that are characterized by significant environmental variability and distinct seasonal fluctuations in pollutant concentrations. The findings demonstrated that the levels of alkylphenols and bisphenol A in the JRE and nearby coastal seas are relatively low to moderate in contrast to those found in other regions of the world. Consistent evidence from the chemical analyses, expression patterns of five EDC-inducible genes, and both integrated biomarker response (IBR) and integrated biomarker response version 2 (IBRv2) tiered-assessment systems identified sites S10 and S11 (Xiamen Western Harbor) as exhibiting the most severe EDC pollution. Correlation analysis confirmed the approximate functional equivalence between IBR and tiered-assessment approaches. It also demonstrated that IBR tiered-assessment approach provides a robust tool for biomonitoring in marine environments where establishing reference site is challenging.Keywords：biomonitoring;estrogenic endocrine disrupting compound;embryotoxicity;integrated biomarker response;tiered assessment14|3|0Updated：2026-09-17
- Abstract：Pseudoedtheriotia radiosa P. Yu, Q. M. You, J. P. Kociolek & Q. X. Wang, gen. et sp. nov., a new freshwater diatom is proposed from Qingjing River, Hubei Province, China, based on light and scanning electron microscopy observations, as well as molecular analysis. Diagnostic features of the new genus include: individual domed cribra on the valve face and individual areolae around the valve margin that are without occlusions; central area has valve face fultoportulae which have two arcuate opercles internally; lack of rimoportulae. Additionally, genetic distance and phylogenetic analyses of based on the chloroplast-encoded rbcL gene and nuclear small subunit (SSU) rDNA sequences suggested that the two strains of Pseudoedtheriotia radiosa investigated here could together be identified as a separate genus distinct from other similar genera (Discostella, Cyclotella, Edtheriotia, Stephanodiscus, Cyclostephanos, et al.) belonging to Stephanodiscales. These molecular data and morphological characters suggest an affinity of the new genus to the Stephanodiscaeae. In the set of diagnostic characters, especially the lack of rimoportulae, Pseudoedtheriotia is easily differentiated from these other genera. Furthermore, our phylogenetic analysis revealed complex relationships among several families, including Stephanodiscaceae, Thalassiosiraceae, and Skeletonemataceae, indicating that the current family-level classification within this group requires critical re-evaluation.Keywords：Pseudoedtheriotia;diatom;taxonomy;phylogeny;Stephanodiscales;China12|4|0Updated：2026-09-17
- Abstract：The Bohai Sea, China’s only seasonally ice-covered sea, exhibits complex backscattering signatures in C-band Synthetic Aperture Radar (SAR) observations, particularly in nearshore areas influenced by high concentrations of suspended sediments. Using Sentinel-1 C-band Vertical-Vertical (VV)-polarized data, this study investigates the regional-scale incidence-angle-dependent scattering behavior of seasonal sea ice in the nearshore Huanghe (Yellow) River estuary. A first-order Small Perturbation Method (SPM) is employed to construct an electromagnetic scattering model for finite thickness layered sea ice, representing the ice cover as a three-layer air-ice-seawater medium with two rough scattering interfaces. The model explicitly accounts for scattering contributions from the air-ice interface, the ice-seawater interface attenuated by propagation through the ice layer, and their coherent coupling effects, while the dielectric properties of sediment-laden sea ice are described using the De Loor model combined with effective medium theory. Incidence-angle-conditioned regional mean normalized radar cross section (NRCS) is derived through statistical averaging to characterize stable scattering behavior under realistic SAR observation conditions. Comparison between modeled and Sentinel-1 observed NRCS demonstrates that the proposed coherent layered scattering framework successfully reproduces the dominant incidence-angle-dependent behavior of VV-polarized C-band NRCS at the statistical level, with validation results mainly concentrated around a global correlation coefficient (R) of 0.71 and the root mean square error (RMSE) of approximately 0.9 dB. Tile-wise analysis reveals multiple angular-response types, including increasing, decreasing, convex, concave, and weakly varying responses, indicating that the observed NRCS cannot be reduced to a single monotonic angular trend. Model comparison further shows that explicitly separating the upper and lower interface contributions and including their coherent cross term improves the reproduction of the observed VV NRCS-incidence angle response. Forward sensitivity experiments show that sediment volume fraction mainly changes the NRCS amplitude while largely preserving the angular-response type. These results provide a physically consistent basis for interpreting regional-scale SAR backscattering behavior of sediment-influenced seasonal sea ice in complex nearshore environments.Keywords：synthetic aperture radar (SAR);Bohai Sea ice;normalized radar cross section (NRCS);two-interface scattering27|8|0Updated：2026-09-17
- Abstract：Flocculation is a common method for pollution treatment, and widely applied in various types of water pollution treatment due to its convenience and effectiveness. The dosage of flocculants is the key factor determining flocculation efficiency. There is a need to establish the relationship between the dosage of flocculant and the removal efficiency of pollutants (dosage-efficiency relationship), and the empirical method was deemed the most feasible way to address this problem. We successfully constructed the dosage-efficiency relationship among the dosage of modified clay, the cell density of red tide organisms, and algal removal efficiency, and assessed the empirical calculation equation of algal removal efficiency. The difference between the measured value and the theoretical value of the algal removal efficiency calculated by the equation was below 15%, the standard deviation was below 20%, and the empirical equation derivation method was proved suitable for various red tide organisms and various modified clays. By exploring the dosage-efficiency relationship between the dosage of aluminum sulfate-modified clay, the cell density of algae and algal removal efficiency, we provided data and theoretical support for the construction of a quantitative evaluation method for flocculation efficiency.Keywords：Flocculation;dosage-efficiency relationship;empirical model;modified clay;harmful algae bloom10|3|0Updated：2026-09-17
- Abstract：The Late Carboniferous–Early Permian was a period of profound paleoenvironmental transformation, yet the depositional response in the South Yellow Sea Basin (SYSB) on the eastern South China Block remains insufficiently understood. This study integrates petrographic, mineralogical (XRD), and geochemical (major and trace element) data from Well CSDP-2 to reconstruct, palaeoweathering, paleoclimate, redox conditions, salinity, terrigenous influx, and paleobathymetry across the Chuanshan, Huanglong, and Gaolishan formations. Geochemical proxies—including CIA, Sr/Cu, V/Cr, U/Th, and Sr/Ba—reveal a stratigraphic transition from a high weathering, warm-humid, brackish, high-energy shelf with predominantly oxic conditions (Gaolishan) to weak weathering, cold-arid, deeper marine carbonate platform characterized by more reducing, intermittently anoxic conditions (Chuanshan). Microfacies analysis identifies seven carbonate facies ranging from restricted platform interiors to high-energy shoals. Principal component and cluster analyses delineate mineralogical differentiation aligned with stratigraphic boundaries and depositional environments. These findings document a long-term transgressive trend accompanied by climatic deterioration and evolving redox conditions. This study provides the first integrated, high-resolution reconstruction of Late Paleozoic paleoenvironmental dynamics in the SYSB, offering critical insights into marginal basin evolution during a pivotal interval of global climate change and contributing to broader paleogeographic reconstructions of the South China Block.Keywords：South Yellow Sea;Late Carboniferous–Early Permian;paleoenvironmental reconstruction;geochemical-mineralogical analysis;microfacies7|3|0Updated：2026-09-17
- Abstract：To locate the tropical cyclone (TC) center is a critical task for reducing the impact of TC. However, traditional deep-learning methods struggle to extract high-dimensional features from the cloud structure of TC, leading to significant errors in the center location. We collected ~16 000 infrared images from the HURSAT-B1 Global Tropical Cyclone Satellite Dataset, covering TC samples from multiple satellite remote sensing platforms and ocean regions, and designed a TC center location model MSFF-CAA-ResNet that is built upon the classic residual structure by introducing the multi-scale feature fusion (MSFF) module and the center-aware attention (CAA) module, which works synergistically to enhance the model’s ability to locate the TC center position. Experimental results show that the MSFF-CAA-ResNet model could not only adapt to multi-source remote sensing platforms but also achieve high-precision TC center location worldwide. Ablation experiments indicate that both MSFF and CAA contribute to TC center location. The improved MSFF-CAA-ResNet-F model achieves an average location error of 23.9 km, representing a 12.7% reduction compared to the baseline model. Interpretability analysis shows that the MSFF-CAA-ResNet-F model focuses more on the central features of TCs compared to the baseline model. This indicates that the MSFF-CAA-ResNet-F model holds promising application prospects.Keywords：tropical cyclone (TC);deep learning;multisource data10|5|0Updated：2026-09-15
- Abstract：Macroalgae release large amounts of dissolved organic carbon (DOC) during growth, which greatly contributes to marine carbon sinks. However, the regulatory effects of environmental factors on DOC release remain unclear. We examined DOC release characteristics of golden tide-forming alga Sargassum horneri under three light intensities (30, 90, and 300 μmol photons/(m2·s)) at 15 and 20 °C. Results show that increased light and temperature significantly enhanced respiration, photosynthesis, and DOC release of S. horneri. Under the high light, the maximum photochemical quantum yields (Fv/Fm) at 15 °C (0.635±0.024) and 20 °C (0.705±0.031) were significantly lower than those under low and medium light, indicating that the alga experienced photodamage, but elevated temperature alleviated such inhibition. Pearson correlation analysis revealed a significant positive correlation between photosynthetic rate and DOC release rate. Although the photosynthetic rates of the alga exposed to medium and high light at 20 °C were 2.15 and 1.78 times of that at 15 °C, respectively, tissue carbon content remained significantly lower than at 15 °C due to more DOC release. Additionally, the DOC released at 20 °C had higher relative molecular weight compared with that at 15 °C, indicating that more polymerized metabolites were released at a higher temperature. These findings suggest that under certain temperature and light conditions, DOC release from S. horneri is regulated by the “overflow” mechanism, wherein excess carbon metabolites are released as DOC when photosynthetic carbon fixation exceeds growth demands. This study offered insight into the role of S. horneri golden tides in coastal ecosystem carbon cycling.Keywords：Sargassum horneri;dissolved organic carbon (DOC);overflow mechanism;carbon sink10|6|0Updated：2026-09-15
- Abstract：Based on continuous monitoring data from 16 standardized monitoring stations in the coastal waters of Laizhou Bay, Shandong Province, from 2020 to 2024, we investigated the spatiotemporal distribution characteristics of nitrogen and phosphorus nutrients and assessed the eutrophication status. Results indicate that the concentration of dissolved inorganic nitrogen (DIN) in the bay exhibited significant seasonal and spatial variations, and the overall trend was higher in the west and lower in the east, while the concentration of dissolved inorganic phosphorus (DIP) remained relatively stable. Specifically, the DIN concentration in spring was significantly higher than that in summer and autumn. The N/P ratio showed an initial increase followed by a decreasing trend during 2020–2024; however, the overall ratio remained substantially higher than the Redfield ratio, indicating a pronounced phosphorus-limited condition in the bay. Eutrophication assessment revealed that the eutrophication index (EI) in autumn was significantly higher than that in spring and summer. The western coastal area of the bay top was identified as a high-risk zone for eutrophication, while the outer bay maintained an oligotrophic state throughout the year. Complex coupling relationships were observed among pH, dissolved oxygen (DO), chemical oxygen demand (CODMn), and nutrients. Specifically, pH and DO exhibited weak correlations with nutrient levels, whereas CODMn showed a significant positive correlation with nutrients. The findings provide a theoretical reference for the construction of the Beautiful Bays Initiative in Shandong Province.Keywords：Laizhou Bay;nutrient;potential eutrophication;water quality;phosphorus limitation16|4|0Updated：2026-09-15
- Abstract：Recent studies have shown that east of Luzon both the Kuroshio in upper layer and the Luzon Undercurrent (LUC) in the intermediate and deep layers have significant intraseasonal variabilities associated with eddy activities. However, the integrated behavior of the western boundary currents in the full-depth ranges, the dominant variability mode of the western boundary currents east of Luzon and associated physical processes or underlying dynamics are still unknown. This study investigates the questions by using more than two-year mooring observations at 18°N/122.7°E. The results reveal that the dominant variability of the western boundary currents on intraseasonal to seasonal timescales is primarily barotropic in nature. The barotropic velocity component serves as an effective proxy for this variability and is closely linked to variations in the LUC as well as to temperature changes in the intermediate and deep ocean, typically below 1 000 m. During the observation period, the temporal evolution of the western boundary current is characterized by three abnormal events featuring an intensified LUC, which induce southward barotropic transport at 18°N. The third abnormal event with a temperature drop in observed depth range lasted about 6 months, mainly related to the wind stress curl on the basin scale, while the first two abnormal events have a much shorter duration and are likely related to local subsurface mesoscale or submesoscale eddy activity. Both large-scale wind fields and mesoscale processes may lead to a decrease in ocean temperature in the intermediate and deep layers, resulting in a strengthened LUC, dominating the variability of the western boundary current within the entire water column. This study highlights the important role of intermediate and deep ocean changes caused by large-scale wind fields or mesoscale processes in modulating barotropic velocity and the overall variability of western boundary currents.Keywords：deep ocean;mesoscale eddy;variability;Western Boundary Current;Luzon Island;barotropic11|2|0Updated：2026-09-15
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