Using the AVISO (archiving validation and interpretation of satellite oceanographic) eddy trajectories atlas product from 1993 to 2020, this study comparatively analyzes the characteristics and evolution patterns of mesoscale eddies during eddy life span in the South China Sea (SCS), a marginal sea of the Pacific Ocean, and the Kuroshio Extension (KE), an open ocean. The results show that there is significant seasonal variation in the eddy characteristics in the SCS, with opposite polarity probability distribution of cyclonic eddies (CEs) and anticyclonic eddies (AEs) in winter and summer, while the distribution in KE has no seasonal variation. The AEs are stronger than CEs in summer in the SCS, while CEs are stronger than AE in the KE both in winter and summer. During the eddy life span, the eddy kinetic energy (EKE) exhibits asymmetrical growth, stable and decay stages both in the SCS and KE. The eddy growth stage in the SCS is shorter than the decay stage, while the decay stage is shorter in the KE. The change rate of EKE during life span has larger values in summer than that in winter in the SCS, but has 1.5 times larger in winter in the KE. The mean propagation velocity curves shown that the AEs move northwestward and then southwestward in the SCS with average zonal speed of 3.3 cm·s^-1, while in the KE, CEs move southwestward and AEs move northwestward in the whole life span, with average zonal speed of 1.3 cm·s^-1, which is slower than that in the SCS. There is a significant negative correlation between the eddy propagation velocity and the EKE in the eddy life cycle in both regions.

The dissolved heavy metals (As, Cd, Cr, Cu, Hg, Pb and Zn) were investigated based on the geochemical analysis of 106 surface seawater samples in the Northern Bay of Hainan Island. Correlation and factor analysis were used to study the sources and main controlling factors of distribution of heavy metals. The pollution levels of heavy metals were evaluated by the factor index and the Nemero index with weight modified. The results indicate that, the average contents of As, Cd, Cu, Hg, Pb and Zn are 0.58, 0.14, 8.68, 0.057, 2.07 and 26.24 μg·L^-1, respectively. Additionally, the content of Cr is less than the minimum detection limit. The surface seawater, in the Dongzhai Harbor, east and north coast of the Puqian Bay, estuary of both the Maiya River and the Daomeng River, is with high content of dissolved heavy metals. The estuary of Nandu River, surrounding waters of the Ruyi Island and offshore waters of Haikou Bay are highly clean and non-pollution. The periphery of the Haikou Port, the estuary of the Maya River and the Daomeng River, the top and east coast of the Puqian Bay, and the west side of the Mulan Bay, where the pollution levels are low to medium. The pollution of the Dongzhai Port is moderate to serious. Furthermore, the pollution of the estuary of the Yanfeng River is the most serious. The pollution level of 6 heavy metals were sequenced in the decreased order of Pb> Cu> Zn> Hg> Cd> As. Therefore, Pb, Cu and Zn should be regarded as the key environmental monitoring and marine ecological research objects in the future. The heavy metals in the coastal seawater mainly came from terrestrial and ship pollution, meanwhile, the sources of heavy metals also included atmospheric input, agriculture and aquaculture. Higher salinity and lower pH can promote the desorption and release of heavy metals from suspended particles in seawater. In addition, hydrodynamic condition was also one of the main factors that controlled the heavy metals content in seawater.

Microbial nitrogen fixation is a crucial part of nitrogen cycling in mangrove ecosystems, it plays an essential role in the nitrogen nutrient supply and primary productivity improvement of ecosystem. This paper reviewed the diazotrophic community structure, nitrogen fixation rate, and the main measurement methods of nitrogen fixation in mangrove ecosystems. We also explored the application of nitrogen-fixing microorganisms in mangrove restoration and the ecological indicators of nitrogen-fixing microorganisms for mangrove habitats, emphasized the vital roles of diazotrophs in coupling carbon, nitrogen, and sulfur cycles in mangrove wetlands, and highlighted new perspectives for nitrogen-fixing microorganisms in the mangrove ecosystem.

Mangrove endophytic fungi has evolved a unique metabolic pathway due to its high salt, high temperature, strong light and anoxic living environment, and then produced a large number of secondary metabolites with rich species, novel structure and significant activity, making the secondary metabolites of mangrove endophytic fungi a research hotspot in recent years. In the field of mangrove endophytic fungi, Aspergillus and Trichoderma are two genera that have been studied frequently. This paper reviews the recent advance on the chemical structure and biological activity of new secondary metabolites of the endophytic fungi of genus Aspergillus from mangrove from January 2018 to October 2022 and the endophytic fungi of genus Trichoderma from mangrove from January 2015 to October 2022, summarizes them by polyketones, alkaloids, terpenoids and other compounds, and highlights the challenges in the current research. It can provide reference and guidance for the future study of mangrove endophytic fungi.

Long-term monitoring site was deployed in the southern Sanya Bay of the South China Sea, and continuous wave observations covering four seasons were carried out in April ~ October 2020 and December 2021 ~ February 2022. Based on the observational data, the basic statistical features of the wave in the sea area and their response characteristics to typhoon processes are systematically analyzed. The results show that the waves at the site are affected by local factors, such as wind field, bottom topography, shoreline, and current dynamics, thus showing characteristics of nearshore waves. Due to the weakening effect of shallow water topography and the control of shoreline boundary, the waves maintain long-term shoreward (i.e., northward) propagation with relatively small wave heights and periods, in which the significant wave heights and mean periods are less than 1 m and 4 s, respectively, for most of the time. Due to the influence of dynamic factors such as tidal current and sea-land breeze, the wave heights show a strong diurnal variation, and both wave heights and steepness increase (decrease) significantly when the flow direction is opposite to (the same with) the wave direction; driven by the strong wind speed in the same direction, the wave height and steepness also increased significantly. Waves respond significantly to the typhoon process, and the wave height increases significantly under the synergy of current. When the typhoon process is close to the site, the wave energy extends to both low and high frequencies, with the direction distribution changing significantly. If the path is far from the site, the wave energy mainly propagates to the site by the swell, and the energy distribution expands to low frequency while the direction distribution remains unchanged.

Coral reef ecosystems are important components of marine ecosystems and play a crucial role in maintaining marine ecological balance and biodiversity. This article summarizes the current international and domestic development status of coral reef ecology through literature review. The major international research focuses include global change and coral reef ecosystems, establishment and maintenance of coral symbiosis, development and evolution of coral reef biotic systems, coral reef biodiversity and species distribution patterns, as well as coral reef ecosystem conservation and management. The major domestic research focuses include global change and coral reef ecosystems, coral-algal symbiosis under global change, diversity of coral symbiotic relationships, human activities and the South China Sea coral reef ecosystem, and coral reef biodiversity and community patterns. The future development trends in coral reef ecology research will emphasize the coral and coral reef ecosystems under the context of global change, coral symbiotic mechanisms, marginal coral reefs, and coral reef conservation and restoration. Future research in coral reef ecology in China should enhance global perspectives, strengthen domestic and international collaborations, explore underlying mechanisms, improve systematic research, and enhance coral reef conservation and restoration studies.

Observations from three moorings deployed in the continental slope area west of the Dongsha Plateau on the northern South China Sea (NSCS) from September to October 2021 are collected for the characteristic analysis of internal waves and internal solitary waves in the Liuhua oilfield area. Harmonic analysis shows the barotropic currents are obviously less than the baroclinic currents on the surface and bottom water layer. By comparison with the barotropic tidal currents obtained from TOPEX/Poseidon Global Inver Solution (TPXO7.2), it is found that the model results of semidiurnal tides are significantly better than that of diurnal tides, and the simulated results underestimate the current amplitude of O₁ tidal constituent, but overestimate that of K₁ tidal constituent. The internal tides show surface-bottom intensified baroclinic mode-1 structure, and the major axis of tidal ellipse of O₁ tidal constituent is larger than that of K₁. During the whole observation period, there are four internal solitary waves (ISWs) clusters passed by the Liuhua oilfield area in total, and the appearance time lags 3~4 days behind the astronomical spring tide of Luzon Strait. There are a total of 88 ISWs recorded at mooring of LH2, including 31 solitons and 57 ISW packets, and the averaged amplitude is 31 m. The daily appearance time for the ISWs concentrates between 4~6 am, 11 am-1 pm and 6~8 pm, and more than 45% of solitons appears between 4~6 am. By tracking the propagation process passed by LH1, LH2 and LH3 of 5 ISWs appeared between 8~12 September, the calculated phase speed for the ISWs is 1.23 m·s^-1 between LH1 and LH2 and 1.77 m·s^-1 between LH2 and LH3, and the theoretical propagation speed is 1.55 m·s^-1 based on the linear wave equation and Kdv equation. The statistical results in this paper further strengthen the understanding of the internal waves in the Liuhua oilfield area on the NSCS under the typical autumn environment.

To explore the effects of ocean warming and acidification on coral growth and calcification rate, two widespread coral species, Pocillopora damicornis and Galaxea fascicularis, in the Luhuitou area of the Sanya Bay, were selected for a 28-days controlled incubation experiment. With the interactive treatments of temperatures and pCO₂, our results indicated that corals were significantly affected by seawater acidification. Moreover, acidification affected strongly the growth rate of G. fascicularis and the calcification rate of P. damicornis. The chlorophyll fluorescence index (F_v/F_m) of the symbiotic zooxanthellae in P. damicornis was significantly higher than G. fascicularis. Interestingly, the quantitative study showed that there was an antagonistic effect between temperature and pH at some levels, which could effectively alleviate coral bleaching. Thus, we concluded that the growth and calcification rate exhibited interspecific specificity in response to seawater warming and acidification.

To investigate the trophic structure characteristics of the main fish species in the coral reefs of the Nansha Islands, twenty three fish species were collected from waters of the Yongshu Reef and Meiji Reef during the spring of 2023, and the stable isotopes of carbon and nitrogen of fish were measured and used to analyze their trophic structure, and a trophic level spectrum was constructed for the fish. The δ¹³C and δ¹⁵N values of fish from the Yongshu Reef ranged from -18.74‰ to -14.33‰ and 5.96‰ to 9.37‰, with an average value of (-16.33±1.28)‰ and (8.46±0.48)‰, respectively. The δ¹³C and δ¹⁵N values of fish from the Meiji Reef ranged from -18.01‰ to -12.70‰ and 7.31‰ to 8.82‰, with an average value of (-15.02±1.53)‰ and (8.21±0.93)‰, respectively. The δ¹³C values of fish from the Yongshu Reef and Meiji Reef showed significant differences, indicating a wider food source for fish in the Meiji Reef. However, there was no significant difference in the δ¹⁵N values of fish between the two the reefs, indicating no difference in trophic structure composition between them. Cluster analysis based on the values of carbon and nitrogen stable isotope of fish divided the fishes from the two reefs into the benthic fish group and the mixed group of benthic and pelagic fishes. The trophic groups in the Meiji Reef were more vaguely defined, with evident feeding competition among carnivorous fishes. The trophic levels of fish from the Meiji Reef and the Yongshu Reef were (2.79-3.23) and (2.39-3.39), respectively. Both coral reefs were dominated by carnivorous fish at medium and low trophic levels. Most carnivorous fish were in relatively narrow ecological niches. These results suggest that the fish from the coral reefs of the Nansha Islands had a more complex trophic structure composition, wider food sources and lower community redundancy, compared with the fish from coastal tropical and subtropical bays. This study provides basic data and scientific basis for the protection and sustainable management of fishery resources in the coral reef waters of the Nansha Islands.

The copulation behavior, embryonic and post-embryonic development of Sphaeramia nematoptera were investigated in this study. The results showed that the mating behavior was dominated by females, mating between 1:00 and 3:00 am, and the reproductive cycle was 11~18 d without seasonal fluctuations. The release of eggs by female were 3126~4882 at a time, which were incubated by the male’s mouth. The fertilized eggs were suborbicular, (720±10) μm in diameter, with several oil globules inside. It took 187 h for a fertilized egg to be hatched under (27.0±0.5) ℃. The embryo development process included Cleavage, Blastocyst, Gastrulation, Neurula and Organ formation stages. The post-embryonic development could be divided into juvenile stage, larval stage, juvenile stage and adult stage. The whole length of the first hatchling was (2.8±0.1) mm, the height of the mouth cleft was (0.202±18) mm, and the juvenile opened its mouth to feed at the second day after hatching. Fins began to form and two black bands appeared on the body when ending the floating stage and entering the larval stage 24d after hatching. Scales were fully formed 50d after hatching and the body color and markings as well as other appearance characteristics were similar to the adult fish, which indicated that the fish entered the juvenile stage. Maturation of gonad was achieved 360d after hatching.

To explore the histological and ultrastructural changes of the annual development of the testis and spermatogenesis of Lutraria sieboldii in Beibu Gulf of Guangxi, the annual development of testis and ultrastructure of spermatozoa of L. sieboldii were studied through tissue section, scanning and transmission electron microscopy. Results showed that the testis completes a cycle in one year, which can be divided into proliferating stage, growing stage, maturing stage, spawning stage and resting stage. The spawning was from December to April of the following year, and the testis development of 5% ~ 10% individuals in each stage was slightly delayed. Spermatogenesis can be divided into proliferation period, growth period, mature period and metamorphosis period. The male reproductive cell can be divided into Spermatogonia stage, primary spermatocyte stage, secondary spermatocyte stage, spermatocyte stage and mature sperm stage. The sperm of L. sieboldii belongs to the flagella type, whose total length is (39.76 ± 0.50) μm. The sperm head was composed of a nearly subelliptic spermatic acrosome and nucleus, the bottom of the acrosome and the spermatozoa connected with the spermatozoa were depressed to form a subacrosomal cavity. The electron density in the nucleus was uniform, and there was a gap in the middle of the nucleus. There are four mitochondria around the centriole complex to form the middle part of sperm, and the mitochondria are nearly round with apparent internal ridge. The plasma membrane wraps around the axial filaments to form sperm tail, and the “9 + 2” doublet microtubule structure can be clearly observed in the transverse section of the tail. In addition, there are two different types of spermatogonia: type A spermatogonia has no nucleolus in the nucleus while type B spermatogonia has nucleolus in the nucleus, and type B spermatogonia is distributed in the testis at different stages.

Storm surges caused by typhoon seriously affect life and business in coastal areas, which is one of the most serious marine disasters that cause economic losses. Shenzhen is located on the edge of the northern South China Sea, which is vulnerable to typhoon induced storm surges. The study of Shenzhen offshore storm surges can not only promote understanding of the physical mechanisms of storm surges, but also has an important significance for the effective disaster prevention and reduction warning of coastal cities. In the process of storm surge modelling studies, a typhoon meteorological field is the key factor for the accuracy of storm surge model simulations. Based on the FVCOM (finite volume community ocean model) current model and SWAN (simulation wave nearshore) wave model, a regional storm surge and wave coupling model is established for the offshore area of Shenzhen. We use reanalysis of meteorological data (European center for medium weather forecasting, ECMWF), ideal typhoon model (Holland) and atmospheric model (weather research and forecast, WRF) as driving field conditions to simulate the storm surge process during Typhoon Mangkhut. The main conclusions are as follows: the low resolution ECMWF reanalysis meteorological data is difficult to accurately reflect the horizontal structures of typhoon, which leads to simulation errors. Overall, Holland meteorological field can accurately simulate Typhoon Mankhut, but it cannot reproduce the structural deformation of typhoon in the coastal region, which results in high simulated storm surge water levels in and around Shekou (Shenzhen Bay, inside the Pearl River Estuary). WRF has a good simulation effect on wind speeds, air pressure fields, water levels and waves as a whole. WRF is a good solution to the problem of high storm surge levels in Holland near the typhoon landfall. The quantitative improvement of WRF in the Pearl River Estuary and Shenzhen Bay area can reach about 20%~30%. In the future storm surge study, if the Holland meteorological field is used, care should be taken into simulation results of the above areas. In addition, both Holland and WRF have good wave simulation results.

To address the complexity and uncertainty of tropical cyclone disaster, this study proposes a new tropical cyclone disaster risk assessment model based on the Bayesian network and geographic information system (GIS). The model can automatically explore the causal relationships among disaster influencing factors from objective historical data, and express them in the form of probabilities to assess and predict uncertain disaster risks. Based on the historical data of tropical cyclone disaster in three southeastern coastal provinces (Guangdong, Fujian, and Zhejiang) of China from 1980 to 2016 for risk assessment experiments, a total of 12 assessment indicators in three aspects, i.e., hazard of disaster-causing factors, sensitivity of disaster-inducing environment, and vulnerability of disaster-bearing bodies, were selected as model inputs, and direct economic losses were quantified as disaster risk levels as model outputs to construct a Bayesian network-based risk assessment model. The model was then tested against cyclone disaster data from 2017 to 2021, and the accuracy of the assessment prediction was 80.75%. The relative errors of very low, low, medium, high and very high risks predicted by the model were 27.72%, 8.45%, 18.58%, 16.52%and 19.12%, respectively, and the zonal results of risk prediction values were highly consistent with the actual disaster loss distribution in terms of spatial patterns. In addition, the assessment construction method was applied to the risk assessment of individual cases of Typhoon “Meranti”. The results showed that the high and very high risk areas assessed by the model were basically consistent with the actual disaster reports. Thus, the tropical cyclone disaster risk assessment model established in this study has high accuracy and credibility, and provides a new methodological approach and technical support for tropical cyclone disaster risk assessment.

Tide level correction is an important step in coastline extraction. Regarding to the current problems of remote sensing based coastline extraction, such as the predominance of instantaneous water boundary line, the diversity of tidal level correction methods, and low accuracy, this paper introduces a new high-resolution remote sensing coastline tidal level correction method based on the improved Bodge balanced profile tidal level correction, and makes a comparative analysis of common tidal level correction methods. The research selects typical sandy beaches, Haimen Bay and Pinghai Bay in Guangdong Province, and coordinates with normalized difference water index, Otsu algorithm, mathematical morphology and edge detection operator to realize fast and automatic extraction of instantaneous water boundary line, then, different tidal level correction methods are used to obtain real coastline data. Finally, combined with real-time kinematic (RTK) measured point data, the results of tidal level correction based on the balanced profile model, fitting linear tidal level correction, and traditional tidal level correction methods are compared and analyzed. The results show that: (1) The accuracy of the tidal level correction method based on the balanced profile model is superior to the fitting linear tidal level correction method and the traditional tidal level correction method. (2) Among the tidal level correction methods that are both based on the balanced profile model, the tidal level correction method based on the improved Bodge balanced profile model has higher accuracy than the tidal level correction method based on the Bruun-Dean balanced profile model; based on the reference coastline data, the accuracy of the extracted shoreline is verified to be 2 meters using the cross-sectional method. The research results can provide cases and decision-making basis for accurate coastline extraction and coastal planning.

Based on the daily river discharge time series of Wuzhou station from 2015 to 2017, the spatial and temporal variations of tide levels along the tidal reach of the West River (Makou — Modaomen) were simulated by applying a one-two dimensional coupled numerical model, and considering the flood and dry season variation of Manning's coefficient. During the propagation of tidal waves from the estuary to the upstream of the river, the deformation characteristics of tidal waves, the spatial and temporal distribution of tidal extreme levels and the tide range attenuation characteristics of river were studied. The results show that the water level of the river is influenced by river discharge with obvious characteristics of flood and dry seasons; the daily average water level shows semimonthly cycle variation during spring and neap tide, and the semimonthly variation gradually increases along the upstream of the river, indicating that the ocean tidal waves propagate upstream of the river in the form of a semimonthly low-frequency tidal constituent; the tidal asymmetry is more and more obvious upstream due to the influence of river discharge, and the difference between the flood tide calendar time and ebb tide calendar time increases upstream. The extreme tide level at each hydrographic station tends to increase upstream due to the influence of river discharge, and occurs mostly during spring tide due to the action of the ocean tide. The tide range in the river channel tends to decrease from downstream to upstream, and the seasonal difference is significant, and the downstream stations of Denglongshan and Sanzao have obvious characteristics of semi-annual cycle.

Mangrove wetlands provide important ecological support for ecological security, social and economic growth. In this paper, we discuss the temporal and spatial changes of mangrove wetlands in the Leizhou Peninsula during 1995—2020 by decision tree classification combined with the tidal pattern in different regions, based on Landsat Thematic Mapper (TM) and Operational Land Imager (OLI) sensing images. Improving the precision of mangrove information extraction is combined with artificial correction. Using high-resolution Google Earth remote sensing data, the classification accuracies in 1995, 2005, 2015, and 2020 were 99.79%, 98.95%, 99.45%, and 99.15%, and the corresponding Kappa coefficient of those years were 0.9913, 0.9642, 0.9624, and 0.9766. Over the past 25 years, mangrove wetland areas show a trend of early decrease followed by subsequent increase. The results were summarized as follows: (1) the Leizhou Peninsula’s mangrove wetlands are concentrated in wave sheltering bay or estuary, such as the Yingluo Port, Anpu Port, Qishui Port, Haikang Port, Wushi Port, Liusha Port, Wailuo Port, Leizhou Bay, Tongming Sea and Zhanjiang Bay, where silt deposits and tidal flats distribute widely. Lack of the above conditions, there is none of mangrove distribution in the seaboard of the Hai’an town of Xuwen county to the Jinhe town and east of the Wuyang town of Wuchuan county; (2) mangrove uniformly distributes all cities and counties of the Leizhou Peninsula. In early years, the Mazhang town has the largest mangrove, followed by Leizhou and Lianjiang, and Chikan has the least mangrove. Currently, Lianjiang has the largest proportion of mangrove forests; (3) the decreasing mangrove area is more than the increasing mangrove area, and half of area is lost in the Mazhang town; (4) the conversion of mangrove forest and non-mangrove mutual landscape occurrs to water, beach and mariculture. The monitoring analysis of regional mangrove forest provides a basis for the protection of mangrove wetland and the sustainable development of ecological resources.

Coral reef ecosystems play a crucial role in global carbon cycling and climate change. They serve as potential blue carbon sinks, with coral reefs in China covering approximately 11% of the global area. The annual carbon sequestration of these reefs is estimated to be 3.5×10⁶~4.5×10⁶ t. The total carbon storage capacity of coral reef ecosystems is immense, and they have significant potential value as carbon reservoirs in carbon trading. This article provides a review of carbon sequestration processes and storage mechanisms in coral reef ecosystems, including carbonate pumping, biological pumping, and microbially-mediated carbon pumping. The research progress on these three carbon pumps is discussed. Additionally, the article highlights the limitations and challenges in current research and proposes future research directions, aiming to provide scientific basis for the conservation and management of coral reef ecosystems in the South China Sea.

Sea fog, as a hazard weather, affects maritime transportation and military activities. The coastal area of Fujian province is a national strategic area characterized by frequent sea fog. It is essential to monitor and study the sea fog in this area. cloud-aerosol lidar with orthogonal polarization (CALIOP) can detect the vertical structure characteristics of sea fog due to its vertical penetration through laser. Thus, it is very suitable for sea fog monitoring. In this paper, firstly, remote sensing monitoring of sea fog over the coastal area of Fujian was carried out through CALIOP L1 level 532 nm total attenuated backscattering and vertical feature mask (VFM) data. Based on the physical characteristics of sea fog, the detection range of sea fog was expanded. Secondly, the vertical characteristics of sea fog in this area were analyzed and it was found that subcloud fog occurred frequently. To explore the spectral characteristics of the subcloud fog and develop a high time coverage and large-scale synchronous sea fog monitoring algorithm. Besides, the spectral differences of cloud, pure fog, and subcloud fog were compared based on Himawari-8 data. According to the results, in the daytime, the spectral characteristics of pure fog and subcloud fog were not significantly different in each band, and the reflectance of bands 1~4 was much lower than that of cloud pixels; at night, the brightness temperature of pure fog at 3.9 μm band was generally lower than that of subcloud fog. It is expected to improve the monitoring accuracy of sea fog in Fujian Province by distinguishing cloud, pure fog, and subcloud fog based on the above spectral characteristics.

Coral reef, known as the tropical rainforest in the ocean, was an important spawning ground, nursery and feeding ground for marine fish. Yongle atoll and Dongdao Island were typical coral reef ecosystems of the Xisha Islands. In order to better manage and protect the fishery and germplasm resources of the Xisha Islands, this study collected fish eggs from the Yongle atoll and the Dongdao Island in April 2021. High-throughput sequencing technology is used to classify and identify them, and the differences in species composition and community structure between the two regions were analyzed. The results showed that only fish eggs were collected in both areas, and a total of 27 species were identified, belonging to 4 orders, 16 families and 25 genera. The perciformes was dominant, accounting for 95.45% in the Yongle atoll and 85.71% in the Dongdao Island. The similarity index of roe species composition between the Yongle atoll and the Dongdao Island was significantly different, among which the similarity of order, family, genus and species was 25.00%, 37.50%, 32.00% and 33.33%, respectively. The occurrence frequency of fish eggs was 100%. The average density of fish eggs was 0.984 ind·m^-3 in the Yongle atoll and 0.453 ind·m^-3 in the Dongdao Island. The dominant species (Y≥0.02) were Decapterus sp., Katsuwonus pelamis and Halichoeres trimaculatus in Yongle atoll and Scarus forsteni, Chlorurus sordidus and Parupeneus multifasciatus in the Dongdao Island, with significant differences in the dominant species. In addition, there was an undocumented species (Ambassis sp.) found in this investigation. The species richness index (D) showed that the Yongle atoll (2.46) was higher than the Dongdao Island (1.87), while Shannon-Wiener diversity index (H′) and evenness index (J′) showed that the Yongle atoll (1.08, 0.35) was lower than the Dongdao Island (1.32, 0.50). The composition of fish eggs in both regions was dominated by reef-associated fish, and the relative abundance of pelagic-oceanic fish in the Yongle atoll (88.02%) was higher than that in the Dongdao Island (0.44%). The research results showed that both the Yongle atoll and the Dongdao Island are spawning grounds for marine fish, and the Yongle atoll has an open lagoon, which is more suitable as spawning grounds for pelagic-oceanic fish (especially tuna) than the Dongdao Island. Moreover, high-throughput sequencing technology can fill the gap of traditional morphological methods in the identification of fish eggs, and could be used as a supplementary means for the investigation of fishery resources. This study provides a scientific basis for the conservation and management of fishery and germplasm resources in the Yongle atoll and the Dongdao Island.

Based on the two-dimensional incompressible two-phase flow numerical model, the reliability of the two-phase flow surge computational model in simulating the interaction between the wave-like surge and the sea pond is verified by comparing the numerical computational results with the experimental data. Then, this paper systematically analyses the effects of wind speed, surge height, pre-tidal water depth and slope gradient on the wave-exceeding characteristics of the undulating surge on the seapond by setting up reasonable calculation conditions. Calculation results show that wind speed significantly affects the wave overtopping of the wave-like surge on the seapond, the higher the wind speed, the higher the wave overtopping of the surge, and the higher the load on the retaining wall; with the increase of surge height and pre-tidal depth, the wave overtopping of the surge and the load on the retaining wall increase; when the slope of the seapond is increased, the wave overtopping and the load on the retaining wall show the tendency to increase firstly and then decrease later. The research results of this paper have certain reference significance for the correct understanding of wave surge in the pond under the action of wind, and the change rule of the load law of wave retaining wall, which provides a scientific basis for the engineering design and safety assessment of water-related buildings in the river section of wave surge.

Typical tropical marine ecosystems are composed of unique habitats and organisms, such as coral reefs, mangroves and seagrass beds. These ecosystems are mainly distributed in tropical and subtropical marine areas worldwide. It is characterized by high material cycling efficiency, unique ecological functions, rich biodiversity and extremely high productivity, and thus a key object of marine scientific research and resource utilization. Under the multiple pressures of human activities and global changes, its degradation trend has become increasingly prominent. How to restore the function of these typical ecosystems and maintain their sustainable development for the benefit of mankind has attracted increasing amounts of attention from the academic community and the international society. In this paper, the distribution patterns, degradation trends and influencing factors of such typical marine ecosystems in the world are described, with an emphasis on the distribution patterns and biodiversity characteristics of coral reef, mangrove and seagrass bed ecosystems in China. Focusing on coral reef ecosystems, this paper discusses the causes of degradation in the ecosystems and relevant action measurements for restoration and protection in China. According to the global action plan for biodiversity conservation and the actual situation of China, countermeasures and suggestions for the restoration, reconstruction and protection of the typical marine ecosystems were proposed: 1) Establishment of a research center for typical ecosystems in the South China Sea, an intelligent monitoring system and database, and an expert think tank; 2) establishing a demonstration zone for the restoration and protection of the typical marine ecosystems, and inviting experts from multiple disciplines to work together on research-experimentation-demonstration-estimate--promotion-monitor; and 3) optimizing policies and regulations, strengthening law enforcement and management, increasing efforts in science popularization and education, raising public awareness of environmental protection, and promoting conscious social actions. This study aims to provide references for strengthening the conservation and management of typical marine ecosystems and biodiversity, maintaining their sustainable development and implementing the 30×30 goals of the Kunming-Montreal Global Biodiversity Framework.

Mucus-feeding pelagic tunicates are widely distributed in the open ocean and coastal waters, which have very high rates of reproduction, and the ability to form massive blooms. In this review, we provide a qualitative overview of the combination of high particle consumption and swarms of pelagic tunicates led to accumulate at the ocean floor as jelly-POM (particulate organic matter), substantial contributions to vertical export fluxes. As well as the swarms in relation to environmental drivers and unique life-history adaptation, its role in pelagic-benthic coupling, structure and energy flow of marine food web by selecting feeding are reviewed. Because pelagic tunicates have high filtering rates and efficiencies and can reach great abundances, they have the potential to remove a significant fraction of shelf water column primary production, are exported via mucous aggregates, fecal pellets, and jelly falls sinking to depth or restructure shelf pelagic food webs. The study of jelly-falls represents a major challenge in the understanding of the biological pump mainly due to technical/sampling hurdles, the ecological significance of pelagic tunicate blooms, for instance, the rate of this downward carbon flux may be further enhanced through in-situ observations on pelagic tunicates’ diel vertical migrations together with quantitative net catches. Future work should pay more attention to the coupling between fine scales of hydrodynamic grazing and breeding rates under in situ conditions, and link bloom impact on carbon cycling to more dimensions of the physical, chemical, and biological ocean environment, in order to more accurately assess the efficiency of the jelly carbon pump and its response to global change.

Based on 26 years of data on sea level anomalies, sea surface wind speed anomalies, and sea surface temperature anomalies, using the spatiotemporal series prediction model PredRNN++, this paper predicts the trajectory of mesoscale eddies in the South China Sea and dipole activity in the western South China Sea over a period of 1 to 28 days. The results indicate that the PredRNN++model can comprehensively consider the spatiotemporal evolution characteristics of the entire South China Sea region and the role of environmental wind and temperature fields, and has good performance in short-term (1~2weeks) and medium-term (3~4weeks) forecasting. This model has the ability to predict the generation and disappearance of eddies to a certain extent, and can control the 4-cycle prediction error of eddy trajectories to 42.1 km. For eddies with a lifespan of less than 100 days, the mid-term position and amplitude prediction error are small. In addition, the model can better track the evolution and intensity change of dipole structure at any time point under the monthly average, 4-day average and any forecast time effect in August-November. The prediction error of dipole eddy related attributes is the smallest and there are interannual and type differences. In 2017, the amplitude position, prediction and radius error of eddy 1-4 cycles are the smallest, which are 40~60 km, 3~5 cm and 20~40 km respectively, and the prediction effect of cyclone position is better than that of anticyclone.

Using the track data of landed tropical cyclones (TCs) during 1949—2021 from Shanghai Typhoon Institute of China Meteorological Administration, this study analyzes the variation and mechanism of TCs landed in autumn in Guangdong area, and compares with the results in summer. The results show that a total of 76 TCs landed in Guangdong in autumn during the past 73 years, accounting for 28.5% of the landed TCs in whole year. The landed TCs in autumn (ALTCs) are mostly in categories of strong typhoon and super typhoon, and the mean peak intensities are stronger than those in summer. 72.4% of the ALTCs generated in the Western North Pacific, a higher portion than summer landed TCs and the average latitude and longitude of TCs generation move southward and eastward. The yearly power dissipation index (PDI) of autumn TCs reaches 0.4×10⁷m³·s⁻², comparable to that of summer TCs; during landfall to dissipation, the average duration time of autumn TCs is less, the translation speed is slower and PDI is less than those of summer TCs. In long-term variations, the declining trend and decrease rate of the number of ALTCs is similar to that in summer, while the landing intensity of ALTCs increases with a rate 1.8 times higher than that in summer. The translation speed of ALTCs slows down but with a rate 2.5 times lower than summer TCs, the PDI of ALTCs shows a weaker decreasing trend than summer TCs. Unlike more TCs landed in summer in La Niña year, more ALTCs appeared in El Niño years. The number of ALTCs is related to the ENSO (El Niño-Southern Oscillation) index in previous winter and spring with correlation coefficient of about 0.3. It can be used as an indicator for next-year ENSO prediction. In decadal variability, the correlation coefficients between the number of ALTCs and the PDO (Pacific Decadal Oscillation) index, were -0.51 and 0.68 in the warm phase (1977—1996) and cold phase (1997—2016), respectively. The composite analysis shows that ALTCs can occur with a warm sea surface temperature anomaly in the northern South China Sea, which induced cyclonic atmospheric circulation in the South China and favors TCs landed in Guangdong.

Based on the sea surface temperature and wind data from 1968 to 2021, this paper analyzes the interannual variation of upwelling intensity in Zhoushan in summer, and the impact of El Niño-Southern Oscillation (ENSO) on upwelling. The temperature and wind upwelling indices both show that the upwelling in Zhoushan sea decreased in summer during 1982—2021, with the decreasing rates of 0.062℃·10a^-1and 0.35 m³·s^-1·(100m·a)^-1, respectively. Recently, the weakened coastal wind stress causes the temperature upwelling index to decrease. According to the results, the wind upwelling index during La Niña events is larger than that during El Niño events and climatology. Further analysis of the relationship between ENSO and the wind upwelling index shows that ENSO affects the intensity of upwelling mainly by influencing the wind. In El Niño events, the southeast wind dominated Zhoushan sea weakens, leading to a decreasing upwelling intensity. While in La Niña events, the enhanced south wind benefits the development of upwelling.

Quantifying eddy mixing in the ocean is a hot and tough problem in the area of physical oceanography. Based on the theory of effective diffusivity, the present study investigated the stirring effects of geostrophic turbulence that led to stretching, distorting, deforming, and folding of tracer contours. These changes are then related to the efficiency of turbulent mixing. Results show that under the stirring effect of geostrophic turbulence, the length of tracer contour can be quickly elongated and fine-scale tracer filaments and fronts are also generated. This fractal elongation of tracer contour, about 10~20 times longer than the original length, is the dominant contributor to the mixing efficiency, whereas the gradient enhancement associated with filament and front generations only plays a secondary role. On the other hand, fine-scale features are smoothed out by small-scale diffusivity which eventually suppresses the increase of contour length and the generation of tracer filaments. This imposes an upper bound of the mixing efficiency when the stirring and smoothing effects are in a dynamical balance. Through a ‘box-counting’ method, the fractal dimension of tracer contour is also found between 1.4~1.6, indicating a geometric dimension lies somewhere between 1D and 2D. Due to the limitation of data resolution, contour length and thus mixing efficiency may be underestimated. Finally, the present study made an empirical relation between the fractal dimension and mixing efficiency, providing an opportunity for estimating mixing efficiency through a well-developed pattern recognition technique in remote sensing, and a new way of diagnosing ocean mixing and its parameterization.

This study systematically investigates the evolution and energy characteristics of the climatic Sri Lanka Dome (SLD) using hybrid coordinate ocean model (HYCOM) and National Centers for Environmental Prediction (NCEP) reanalysis datasets. The results show that the SLD undergoes two peaks of intensity and eddy kinetic energy (EKE) during its lifecycle. During the first development stage (May 23 to June 10), SLD shifts from the southeast to the east of Sri Lanka, and its area gets wider while its intensity gets stronger. The strengthening of the SLD is attributed to a combination of wind stress work, eddy-mean flow interaction, and advection of the southwest monsoon current (SMC). During the mature stage (June 11 to 22), when the SLD is located to the east of Sri Lanka, the EKE and eddy available potential energy (EPE) in the SLD region reaches its first peak due to enhanced wind stress work and eddy-mean flow interaction. During the weakening stage (June 23 to July 20), the SLD moves northwestward and loses EKE and EPE due to the dissipation of the advection term, reduction of wind stress work and baroclinic instability. During the stable stage (July 21 to August 14), the SLD shifts to the northeast of Sri Lanka, with weaker wind stress work, pressure work, and eddy-mean flow interaction, which keeps the strength of the SLD at a weak level. During the second development stage (August 15 to 25), the SLD moves northward with increased intensity, mainly due to enhanced wind stress and pressure work. During the decay stage (August 26 to September 5), the process of ocean internal instability transforms EKE and EPE into mean flow energy, weakening the SLD. In summary, wind stress work, eddy-mean flow interaction, pressure work, and the advection of SMC are all essential factors in the evolution of SLD.

The health of aquaculture ecosystem and the ecological effects of aquaculture activities have been paid increasing attentions in recent years. As an important part of marine aquaculture ecosystem, ciliates play a key role in matter cycling and energy flow in aquaculture water. In this paper, the research progress about ciliates in mariculture water was reviewed. The biodiversity of ciliates, ciliates diseases, the impact of aquaculture activities on ciliates, and the indication of ciliates to aquaculture environment were introduced. In addition, the limitations of past studies are considered, and the potential research hotspots are prospected for ciliates in aquaculture. This review is aimed at providing some updated information on the ecological effects of mariculture and offering available reference for further understanding the ecological role of ciliates in mariculture.

Low solubility and limited source of iron in seawater are the main growth limiting factors for phytoplankton in 40%of the global ocean. Marine Synechococcus is a picocyanobacteria with global distribution and is one of the most important contributors to marine prime productivity. Affected by the source and concentration of iron in coastal and oceanic environments, marine Synechococcus has different adaptive mechanisms to iron limitation. In this study, we performed a comparative genomic analysis of 29 whole genome sequenced marine Synechococcus. The results showed that marine Synechococcus had high genetic diversity and belonged to four genera of Cyanobiaceae under the GTDB (Genome Taxonomy Database) taxonomy, and these four genera corresponded well to the subtype under NCBI (National Center for Biotechnology Information) taxonomy. The results of functional annotation showed that the number and types of unique genes differed between coastal and oceanic Synechococcus, and unique gene of coastal strains are more involved in inorganic ion transport and metabolism. Further analysis of iron limitation-related genes in marine Synechococcus revealed that the coastal strain had stronger abilities of iron uptake, homeostasis regulation and storage than the oceanic strains, and had a better ability to sense and respond to environmental changes. In this study, we reviewed the evolutionary relationships and taxonomic positions of marine Synechococcus using comparative genomics, and identified the differences in the genome and adaptive mechanisms of coastal and oceanic strains in response to iron limitation, to provide a basis for better understanding of the environmental adaptation of marine Synechococcus.

As one of the most important renewable energy sources, ocean wave energy is inexhaustible and has broad development potential. Herein, we propose a novel spring-assisted triboelectric nanogenerator (SS-TENG) for harvesting shore-based wave energy. SS-TENG realizes ocean wave energy conversion through the “wave-floating platform-spring” transmission structure, which avoids direct contact with seawater and minimizes the damage to the power generation module caused by a corrosive environment. The output performance of SS-TENG is significantly enhanced in two ways. First, by utilizing the elastic potential energy released by the spring, the instantaneous contact speed between the electrode and dielectric layer is boosted, and the peak current (I_P) output by a single triboelectric nanogenerator (TENG) unit increases from 7.36 to 12.12 μA. Second, benefiting from the synchronous movement of each TENG unit, the TENGs can be connected in parallel to achieve the linear increase of I_P from 12.12 μA for a single unit to 43.86 μA for four units. SS-TENG can provide sufficient energy to drive a digital calculator and up to 160 high luminosity LEDs, verifying its superior performance. The proposed design has the merits of modest structure, low production cost, excellent output performance, and long-term stability, and is expected to inspire the development of shore-based wave energy generators and self-sufficient ocean sensors.

Coral reefs stand as remarkably productive ecosystems within the vast ocean, wherein their carbon cycle is meticulously regulated through a complex interplay of three pivotal metabolic processes: photosynthesis, respiration, and calcification. These intricate mechanisms contribute to the intricate and sophisticated functioning of these ecosystems, rendering them worthy subjects of extensive scholarly inquiry and analysis. To explore the carbon sequestration potential of corals and shed light on the underlying mechanisms in both illuminated and dark conditions, this research was conducted using Acropora hyacinthus and Galaxea fascicularis specimens collected from the Wuzhizhou Island, Sanya. Employing the carbonate system, an analysis was carried out to assess the carbon sequestration capabilities of these two coral species. This involved measuring the changes in physicochemical factors in the surrounding water before and after the experiment, as well as determining the content of dissolved inorganic carbon (DIC) and partial pressure of carbon dioxide (pCO₂) using CO₂ system calculation software. By employing these methodologies, a comprehensive understanding of the carbon sequestration processes within these coral species was achieved. The findings of this study demonstrated distinct responses of the water parameters for A. hyacinthus and G. fascicularis under light and dark conditions. In the presence of light, the water bodies surrounding both corals exhibited a decrease in total alkalinity (TA) and pondus hydrogenii (pH), an increase in water temperature (WT) and dissolved oxygen (DO), as well as continuous consumption of DIC and CO₂, resulting in a pronounced carbon sink effect. Conversely, under dark conditions, TA, pH, and WT increased, DO decreased, and DIC and CO₂ were consistently released, indicating a carbon source effect. By comparing the outcomes of light and dark treatments, the carbon sequestration rate of A. hyacinthus was calculated to be 0.00576 mol·m^-2·h^-1, while that of G. fascicularis was determined to be 0.00022 mol·m^-2·h^-1. Notably, the carbon sequestration efficiency of A. hyacinthus surpassed that of G. fascicularis significantly (P<0.05). Both corals exhibited a net absorption of CO₂ through photosynthesis, surpassing the amount they produced, thereby acting as CO₂ sinks. In summary, these two coral species effectively reduced the total alkalinity, DIC, and pCO₂ within the water column, facilitating the transfer of atmospheric CO₂ to seawater and engendering alkalinity sink and carbon sink effects.

The intensification of extreme wave marine hazard induced by global ocean change is very likely to accelerate the geo-hazard risk of cliff erosion in Hainan Island. Shore platforms are expected to effectively attenuate wave energy approaching the shore and consequently reduce the erosive impact of extreme waves on cliff. Shore platforms are commonly observed in volcanic rocky coasts on NW Hainan Island, providing an ideal natural laboratory to evaluate the effect of shore platform morphology on cliff erosion. This study employs the Wucaiwan Bay rocky coastline in the E’man Town, Danzhou City, Hainan Island as the study area. Time-lapsed marine remote sensing images revealed the cliff erosion rate is about 0.26 m·a^-1 in the last decade in the area. Physical oceanography analysis suggested a maximum significant wave height of 7.8 m could be expected visiting the area in a 100-years return level. The geomorphological characteristics of the sloping shore platform and the rock strength of cliffs were further surveyed via coastal geomorphological approaches. Numerical computation outputs suggest the shore platforms is capable of reducing the wave erosional forces on cliff by over 80% under future extreme wave conditions. This study further discusses the natural coastal protection from sediment beaches, vegetations and in situ deposition of eroded boulders at rock cliff foot.

In summer, high phytoplankton biomass often occurs in the Vietnam Boundary upwelling System (VBUS) of the western South China Sea. Therein, the variation of surface chlorophyll concentration at the intra-seasonal scale (30~60 days) dominated by Madden-Julian Oscillation (MJO) can account for considerable variation, but the regulating effects and mechanism of the modulation to sea surface chlorophyll remain unclear. In this study, reconstructed remote sensing chlorophyll data and multi-source observation data were used to explore the characteristics and causes of the VBUS chlorophyll changes during MJO events. Composite analysis showed that in the late phases of MJO events, chlorophyll reached its intraseasonal maximum, while sea surface temperature (SST), zonal geostrophic current, Ekman pumping and wind speed were highly correlated in a decreasing order. Furthermore, the VBUS was divided into two sub-regions: nearshore and offshore regions. The analysis results of generalized additive model showed that the influencing factors and intensity of chlorophyll concentration in the coastal and offshore areas of VBUS were different. SST was the most important influencing factor in both regions. For the coastal region, zonal geostrophic current and Ekman pumping contributed secondly. For the offshore region, the second influence factor was zonal component of geostrophic current, and its influence was nearly equal to that of SST. We further investigated the MJO’s modulation in different El Niño years. When MJO is in the fourth to eighth phases, the El Niño’s negative effects on the chlorophyll can be compensated. In general, our study showed that the MJO’s phase determined the impact of MJO on chlorophyll in the VBUS. At the same time, the chlorophyll concentration in VBUS sea area under MJO events was controlled by SST, geostrophic zonal component and Ekman pump suction, and the impacts of different factors on VBUS were different. The study reveals the short-term variability of marine ecosystems and dynamics and can provide a new perspective for understanding the variation of chlorophyll in the South China Sea.

The separation of sea fog and low clouds is the current difficulty of sea fog monitoring, in order to improve the accuracy and real-time of daytime sea fog monitoring, a model of multi-satellite daytime sea fog detection based on cloud properties is established by analyzing the difference in the features of cloud properties, visible reflectance, brightness temperature, brightness temperature difference and texture features in the infrared bands between sea fog and cloud using the cloud and reflectivity products of MODIS (moderate resolution imaging spectroradiometer) on Terra/Aqua and VIIRS (visible infrared imaging radiometer suite) on S-NPP/NOAA-20 during eleven sea fog events from 2015 to 2020, which effectively separate low clouds from sea fog. Model precision was validated based on the true value of sea fog identified by CALIOP (cloud aerosol lidar with orthogonal polarization) backscattering and vertical feature mask products. The results showed that the highest probability of detection for MODIS(Terra), MODIS(Aqua), and VIIRS(S-NPP) sea fog identification were 0.97, 0.96, 0.89, respectively. There are more than 93.15% of the VIIRS(NOAA-20) sea fog detection images that show 80% consistency with VIIRS(S-NPP), indicating that the model can effectively monitor daytime sea fog. Meanwhile, based on the model presented in this paper, the consistency study of MODIS and VIIRS data is carried out, and the results show that the model has strong applicability and stability for different sensors and can realize the synergistic observation of the same sea fog process by multiple source satellites.

Hermit crab is a type of marine benthic animal. The complex structure of coral reefs makes it one of the areas with the highest diversity of hermit crabs. In response to changes in environmental conditions, such as increasing coverage of benthic algae, small benthic organisms such as hermit crabs can quickly adapt to changes in food resources and play a similar function to herbivorous fishes in maintaining the health of coral reef ecosystems. However, little is known about the differences in food composition on site and ecological functional positioning of different hermit crab species. In this study, three dominant hermit crab species were collected from the coral reef of the Nansha Islands in the spring of 2019: Dardanus lagopodes, Calcinus morgani, and Ciliopagurus strigatus, and their on-site food composition was analyzed using high-throughput sequencing technology. The results showed that there were nine phyla of food types for the three species of hermit crabs, including Rhodophyta, Pyrrophyta, Phaeophyta, Chlorophyta, Arthropoda and Bryozoa, etc. All three hermit crab species fed mainly on algae, including large amounts of Rhodophyta and Pyrrophyta algae (37.75% and 21.14%), and small amounts of Chlorophyta algae (3.13%). But the food composition of different hermit crab species was specific. Calcinus morgani fed mainly on algae turf and detritus and was a herbivorous hermit crab. Ciliopagurus strigatus took Ostracoid from epilithic algal matrix (EAM) as the main food source, accompanied by some branching coralline algae and filamentous Phaeophyta algae. Dardanus lagopodes fed on crustose coralline algae (CCA), macroalgae and epiphytic bryozoans. The results revealed obvious differences in the main foods of marine hermit crabs. Combined with the analysis of ecological niche overlap, it is found that the overlap of the three species of hermit crabs was low (0.059). The feeding areas of Dardanus lagopodes and the other two hermit crab species may not overlap in degraded coral reef areas dominated by CCA. Dardanus lagopodes plays an important role in clearing CCA and bryozoans, and maintaining the healthy development of coral reefs. Ciliopagurus strigatus and Calcinus morgani, as secondary consumers, transfer energy more efficiently to the upper level. These research results extend the previous understanding of the ecological status of hermit crabs.

Fungi are essential components of seagrass ecosystems, and they play important roles in maintaining seagrass health and nutrient cycling in the ecosystem. To elucidate the fungal community structure and their functions in seagrass sediment, we used Illumina MiSeq high-throughput sequencing technique to investigate the fungi in sediments of tropical seagrass Thalassia hemprichii in Hainan Island and Xisha Islands, respectively. FUNGuild database was introduced to predict fungi trophic types and annotate fungi guilds. Results showed that phylum Ascomycota (relative abundance 24.30% ~ 76.20%) and Basidiomycota (relative abundance 4.98% ~ 52.24%) were the dominant phyla in the two study areas, but the relative abundance of phylum Ascomycota was significantly different between the two study areas (p < 0.05). The percentage of OTUs numbers in seagrass sediment fungi shared in the two regions was 5.15%, and their relative abundance was 31.19%. In addition, there were significant differences between the Alpha diversity index (Shannon and Phylogenetic diversity) and Beta diversity of the fungal communities of seagrass sediments in the two study areas (p < 0.05). The FUNGuild functional prediction analysis revealed that the main fungal trophic types were undetermined (relative abundance 72.11% ~ 91.92%). The trophic types of the rest fungi were Symbiotroph, Saprotroph, and Pathotroph, and these three trophic types could be further divided into 41 functional guilds. Network analysis for fungal groups based on random matrix theory (RMT) showed that the fungi network structure of seagrass T. hemprichii sediment in Hainan Island was more complex, with higher average clustering coefficients, longer average path lengths, and higher densities. These fungal communities may be more sensitive to environmental change. While the fungal communities of seagrass T. hemprichii sediment in Xisha Islands were more modulized, the fungus belonging to Class Sordariomycetes was the key taxon in the molecular ecological network. This study provides essential primary data and theoretical support for further study on the structure and function of fungi in seagrass ecosystems, microbial resource mining, and ecological applications.

A three-dimensional numerical simulation using MIKE 3 was carried out to explain the tidal distribution characteristics of the Luoyuan Bay in terms of flow field and cross-sectional vertical velocity, calculate the tidal residual flow field in the Luoyuan Bay, simulate the transport of material with particle characteristics in the bay using Lagrangian particle tracking method, and analyze the movement pattern of particles. The results show that the residual circulation structure is formed in the north-western part of the Luoyuan Bay, the northeastern recess and the inner bay mouth, and the material distribution in different areas of the bay is significantly correlated with the tidal residual current structure. This study provides a scientific basis for further investigation of the distribution mechanism of pollutants in the Luoyuan Bay, and provides technical support for pollution control and environmental protection in the Luoyuan Bay.

In this paper, we compared the existing marine animal origin antibacterial peptides reported (Toxin except) with the holothurian proteome, combined with bioinformatics software to design, screen holothurian antibacterial peptides, and to investigate their physicochemical properties, antibacterial activity, mechanism, biocompatibility and cellular activity. It was found that through software simulation and antibacterial activity prediction, 7 holothurian bacteriostatic peptides (H1~H7) were finally screened and solid-phase synthesized. Among them, H4 (RVHRFLRR) could inhibit the growth of Staphylococcus aureus, Pseudomonas aeruginosa, Vibrio vulnificus through bacterial membrane potential depolarisation or membrane permeabilisation. At a lower concentration (31.25 µg·mL^-1), it reduced the total bacterial count of S. aureus to 84.93%±4.21%(p<0.01), P. aeruginosa to 95.92%±0.52%(p<0.01) and V. vulnificus to 77.14%±1.37%(p<0.01). It was also found that H4 was biocompatible and did not exhibit haemolytic or cytotoxic properties at < 1000 µg·mL^-1. In addition, H4 may interact with cell membrane receptors (EGFR, VEGFR2, FGFR1, etc.) to promote cell migration. H4 significantly promoted the migration of L929 cells at both 62.50 µg·mL^-1 and 250 µg·mL^-1 (p<0.05). The above experimental results indicate that holothurian antibacterial peptide H4 is biocompatible, has both antibacterial and pro-healing effects, and can be used as a potential functional active substance for the repair and regeneration of infected wounds.

Based upon the deep seismic data and IODP drilling results, this study focuses on the mechanism of rifting and breakup processes of the northern South China Sea. During the implementation of the project (2018—2023), a 3D deep seismic survey was carried out during the Chinese National Natural Science Foundation Open Research Cruise (No. NORC2018-08). A total of 52 ocean bottom seismometers (OBSs) and 2 ocean bottom electro-magnetometers (OBEM) were deployed and a total of 8750 shots were fired. 49 OBSs and 1 OBEM have been recovered, and a large amount of data (294 GB) have been acquired. At the same time, a series of innovative results are obtained: 1) the 3D velocity structure of the COT in the northern margin of the SCS has been obtained for the first time, and the COT domain with width of 10 ~ 20 km is determined in 3D view; 2) the active magmatism was revealed in the northern margin of the SCS, and the styles of interaction between tectonism and magmatism were proposed in different geological stages; meanwhile, the magmatism propagated seaward and progressively increased during extension; 3) the geological model of rifting and breakup is established as the type of marginal seas, whose breakup occurred in a crocodile style dominated by basalt due to the strong magmatism during end-rifting, accompanied with significant along-strike variations in the tectonism and magmatism. This project builds up the opening mode of the SCS from the perspective of 3D deep seismic data, and promotes the Chinese basic research of the marginal sea, which has far-reaching scientific and strategic significances.

To investigate the flow characteristics around the reef coast under the combined effects of waves and currents, a two-dimensional numerical wave tank is developed based on the Reynolds-Averaged Navier-Stokes equations (RANS), the SST turbulence model is solved for the turbulence and the volume of fluid (VOF) method is used to track the free surface. Different shoreward currents and seaward currents are tested and they are compared with the wave only. The effects of current on the cross-reef wave height and mean water level as well as the mean flow field, turbulent kinetic energy, and Reynolds shear stress around the surf zone are investigated. Compared to the measurements without the current, both wave height and wave setup on the reef flat are reduced by the shoreward current but they are increased by the seaward current. Furthermore, the ranges of their variations increase with the increasing flowrate. Around the surf zone, the flows along water depth are shoreward directed in the presence of shoreward current, but they are shoreward/seaward directed above/under the wave trough in the presence of seaward current. Moreover, the magnitudes of both currents below the wave trough increase with the increasing flowrate. Finally, both the turbulence kinetic energy and the Reynolds shear stress associated the breaking waves decrease as the shoreward flowrate increases, but their values increase as the seaward flowrate increases.