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.

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.

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.

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.

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.

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.

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.

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.

By staining with Rose Bengal and using traditional morphological analysis, this study for the first time reveals the vertical changes of radiolarian community (Polycystinea, Acanthadaria, Taxopodia and Phaeodaria) from 0 to 2600m water depth in the central Bay of Bengal. Polycystinea may survive in full water depth, and the highest abundance is in the chlorophyll-a maximum layer, indicating that most Polycystinea prefers the well-lit and nutrient-rich environments. In the intermediate-deep water (200~1000 m) invaded by high saline water from the Arabian Sea, the change of abundances of living and dead Polycystinea are slight, indicating that they prefer high-salinity environment (>34.5‰). Considering that living Polycystinea did not change significantly from 1000m to 2000m, the abundance of the shells was obviously increased compared with that in the upper water, indicating that the central Bay of Bengal was affected by the lateral advection of ocean current in the 1000~2000m during the sampling period. The highest abundance of Acantharia appeared at 50~100m, then decreased sharply at 100~200m depth, and almost absent at 200~2600m. The number of shells from 0 to 200m was low, suggesting that Acantharia prefers the well-lit and nutrient-rich environments, and is speculated to be largely dissolved at ~100m depth. Different from other species in morphology, a new species Sticholonche indicum sp. nov. was described, which has the significantly longer oar-like axopodia. And its maximum abundance occurs between 200~300m, suggesting that they are new species, which prefer the moderate temperature and high salt environment, not limited by the oxygen minimum zone (OMZ). Phaeodaria mainly lives at a depth of 50m, with the highest abundance at 200~300m depth, the low abundance at 300~2600m depth, and the rare shells of thanatocoenoses at 0~2600m depth, suggesting that Phaeodaria is weakly affected by the OMZ, and some phaeodarian species can live in deep water without the limit of low temperature. Therefore, Polycystinea, Acantharia, Taxopodia and Phaeodaria have the significant differences in vertical distribution and environmental adaptation characteristics, and the above results would be helpful to understand the material cycle and environmental changes in marine ecosystems.

The change of river inflow sediment is an important content in the study of estuarine delta evolution. Against the backdrop of increased frequency and intensity of extreme weather caused by global warming, it is of great practical significance to study the variability of sediment fluxes in rivers entering the sea under the influence of extreme weather for understanding the environmental evolution of estuarine deltas. This paper takes the Nanliu River, a small and medium-sized river flowing into the sea, as an example. Based on the measured data of water, sediment and floods from 1966 to 2020, the variation coefficient of variation and mathematical statistics are used to analyze the variation law of water and sediment under the influence of extreme weather. The research results show that: 1) the multi-year average daily flow during the transit of tropical cyclones is 7.72×10² m³·s^-1, which is 4.73 times that of normal weather of 1.63×10² m³·s^-1. The multi-year average of the average daily sediment transport of tropical cyclones was 2.55×10⁴ t, which is 13.42 times that of 0.19×10⁴ t in normal weather. During the tropical cyclone, the amount of sediment entering the sea is large, and it has the characteristics of "rich water and sand"; 2) the multi-year average daily flow and sediment load during the flood period were 8.53×10² m³·s^-1 and 3.07×10⁴ t, respectively, which were the average daily flow (1.56×10² m³·s^-1) and sediment load (0.17×10⁴ t) 5.46 times and 18.18 times. During floods, the greater the amount of incoming sediment, the greater the flux of sediment into the sea, showing the typical feature of “more incoming and more transportation”; 3) extreme weather has an important contribution to the sediment flux of the Nanliu River into the sea. The multi-year average contribution rates of tropical cyclones to runoff and sediment transport were 6.78%and 19.31%, respectively, while the multi-year average contribution rates of floods to runoff and sediment transport were 14.33%and 36.21%, respectively.

The parent materials of acidic sulfate soils in coastal areas are rich in reduced sulfides (reduced inorganic sulfur, RIS) and reactive iron, which jointly control the environmental geochemical behaviors of iron, sulfur and heavy metal elements. For purpose of revealing the coupling mechanism and environmental significance of RIS and reactive iron in coastal acid sulfate soils wetland, this study collected a sediment core with a depth of about 40 cm at the Qinjiang river estuary. The contents and distribution of acid volatile sulfur (AVS), chromium reducible sulfur (CRS), elemental sulfur (ES) and reactive iron (Fe(Ⅱ) and Fe(Ⅲ)) were investigated. The results show that Fe(Ⅲ) is the main reactive iron in the acid sulfate soil of Qinjiang river estuary, and Fe (Ⅱ) and Fe (Ⅲ) in active iron are easily interconverted in the environment. The lower the REDOX potential (Eh) and the higher the content of Organic Matter (OM), the more beneficial the reduction of Fe (Ⅲ) to Fe (Ⅱ). The reducing inorganic sulfur is mainly CRS, followed by AVS and a small amount of ES. In the diagenetic process, the reducing inorganic sulfur will convert to each other, and the process is mainly controlled by active iron and OM, but the limiting factors of reducing inorganic sulfur formation are the content and activity of organic matter. Higher organic matter and Fe (Ⅱ) are more likely to lead to enrichment of AVS, and higher Fe (Ⅲ) and Eh values are more conducive to the formation of ES.CRS is not only controlled by organic matter and active iron, but also affected by AVS conversion rate. The CRS/AVS ratio of most samples in the study area was low, indicating that AVS could not be effectively converted into CRS, and the activity and bioavailability of sulfide were high. Therefore, the introduction of exogenous organic matter and human disturbance should be minimized to avoid the release of H⁺ from reductive inorganic sulfur oxidation to form acid damage, resulting in the leaching of heavy metals adsorbed or co-precipitation on inorganic sulfur.

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.

Although both the Red Sea and the Gulf of California are in the transitional stage from continental rifting to initial seafloor spreading, their tectonic backgrounds and evolutionary features are vastly different. To investigate their geothermal differences, curie-point depths in the Red Sea and the Gulf of California are estimated from magnetic anomalies using the centroid method based on both Fourier and wavelet transform. Our results reveal significant differences in the thermal states between the Red Sea and the Gulf of California. Curie depths in the Gulf of California are evidently deeper than those in the Red Sea. The spreading center of the Red Sea is relatively continuous and has active magmatic activity, whereas the spreading center of the Gulf of California is staggered by extensively developed transform faults and has strong localized hydrothermal activity that accelerates the thermal convection and loss of heat in this region. In addition, the spreading rate is highly coupled with the thermal state and hydrothermal activity in the spreading center. The spreading rate in the Gulf of California more than twice that of the Red Sea, further supporting stronger hydrothermal activity and deeper Curie depths in the Gulf of California than in the Red Sea.

Based on the triangle model of urban safety resilience, this paper constructs a comprehensive risk assessment framework for storm surge disasters from the perspective of resilient cities. By using the data of 33 coastal districts in Fujian Province from 2011 to 2020, and through the urban resilience evaluation index system, this paper scientifically evaluates the spatial-temporal differentiation characteristics of urban resilience level in Fujian Province. With the help of geographic information analysis tools to evaluate hazard, vulnerability of storm surge disasters and urban resilience, the comprehensive risk assessment of storm surge disasters at the regional scale for Fujian Province is realized. The results show that: (1) the resilience level of coastal cities in Fujian Province in 2020 is at a descending order: Fuzhou, Xiamen, Zhangzhou, Quanzhou, Ningde, Putian; (2) with the improvement of urban resilience level, the storm surge disaster index of Fujian Province is showing a downward trend; (3) the comprehensive storm surge risk level I zone is mainly distributed along the Xinghua Bay and Meizhou Bay in Putian City; (4) we should pay attention to estuaries, trumpet shaped bays and other areas, focus on preventing typhoon storm surges along the northern and central routes, and formulate marine disaster prevention countermeasures and resilient city construction plans according to local conditions.

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.

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.

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.

Redox-sensitive elements (Mo, U, V, Re, Ni, Co, Cr) have been widely used as geochemical indicators to infer the redox states of marine sediments at deposition, as well as oxygen concentrations in overlying water and atmosphere. However, the sulfidation environment in pore water formed by cold seepage due to microbial activity can result in alterations and ambiguities of redox signals indicated by these elements, which may challenge the effectiveness of the reconstructed redox state. In this paper, the contents of redox-sensitive elements of three push core sediments at the active seep site F of the South China Sea were studied. Compared with the oxic sediments, the seep sediments generally show higher Mo content, indicating the fixed Mo by hydrogen sulfide from the anaerobic oxidation of methane. U/Th, V/Cr, and Ni/Co indicate that the seep sediments are formed in the bottom water with high oxygen concentration, which is consistent with the measured results. However, V/(V+Ni) > 0.7 indicates anoxic conditions, which may be related to the lower Ni content in terrestrial debris. The Re/Mo ratio is similar to the modern seawater value, indicating a euxinic environment. The above analysis shows that Re and Mo in cold seep sediments are easily affected by methane seepage and possibly not used as geochemical indices for redox conditions in a methane-rich environment.

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.

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.

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.

El Niño and South Oscillation (ENSO) asymmetry between El Niño and La Niña events in the positive and negative Pacific Decadal Oscillation (PDO) phases is examined using HadISST and ORAS3 ocean reanalysis products. It is found that ENSO asymmetry in the equatorial eastern Pacific is significantly weaker in the negative PDO phase than that in the positive PDO phase. It is found that the eastern Pacific's subsurface nonlinear dynamical heating (NDH) is likewise greatly affected by the various PDO phases, and it is much stronger during the PDO positive phase than that during the PDO negative phase through heat budget analysis of the ocean subsurface layer. The subsurface NDH is largely contributed by NDHx. A larger gap between the El Niño event and the La Niña event Subsurface Temperature Anomaly (SubTA) during the positive phase of the PDO is caused by the stronger subsurface NDHx in the East Pacific, which causes the asymmetry of the SSTA, and results in a stronger ENSO asymmetry in the East Pacific during the positive phase of the PDO than that during the negative phase of the PDO.

In some harsh ocean environments, there are complex interactions between extreme waves and onshore winds that seriously threaten the safety of coastal facilities. Based on two-dimensional incompressible two-phase flow numerical model, this paper systematically studied the influences of onshore wind on overtopping characteristics of coastal seawall under focused wave, and focused on the mechanism of influences of onshore wind speed, significant wave height, and crest freeboards on overtopping hydrodynamic process of coastal seawall under focused wave. The research results show that, with the increase of onshore wind speeds, significant wave heights, and the decrease of crest freeboards, the maximum overtopping volume, maximum runup height, maximum hydrodynamic forces exerted at the coastal seawall, and spatial distributions of the maximum water elevation gradually increase. Onshore winds can affect the propagation and evolution of focused waves, increase the wave steepness and the propagation speed of focused waves, and cause the moment and position of wave breaking to advance. The high-speed flow area of focused waves also significantly increases. Compared with the no-wind condition, the maximum wave overtopping volume, maximum runup height, maximum hydrodynamic forces and spatial distributions of the maximum water elevation are increased under onshore winds. The research results of this paper can provide corresponding reference for the prevention and reduction of extreme waves and the design of coastal protection engineering.

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.

Ocean acidification (OA) poses strong threat to marine organisms, and studying the impact of OA on their associated microbial communities is important for understanding the adaptive mechanisms of host and microbial response to environmental stresses. Moon jellyfish (Aurelia coerulea) is the dominant species of disaster jellyfish in China and plays an important role in marine ecosystem. In this study, we investigated the effects of future OA (pH 7.8 and 7.6) on the structure and function of the A. coerulea polyp-associated microbial communities using Biolog-ECO and metagenomic approaches. The results showed that the structures and functions of the microbial community associated with A. coerulea polyps were conserved in different degrees of seawater acidification. Biolog-ECO results showed that seawater acidification had little effect on the microbial metabolic activity, diversity index and carbon source utilization of the associated microbial community of A. coerulea polyps. The metagenomic results showed that seawater acidification did not affect the dominant species and community structure of the microorganisms. Tenericute, Proteobacteria, Firmicutes and Bacteroidetes were the dominant groups of the community. Moreover, there was no significant difference in the function of associated microorganisms exposed to different acidification conditions. Therefore, we speculate that future OA will not affect the polyps by altering the community structures of their associated microorganisms.

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.

In order to simulate the growth environment of microorganisms to change or increase the production of secondary metabolites in the presence of other microorganisms and protect the ecological environment of marine herbs, soft coral-associated two fungi Aspergillus sp. EGF7-0-1 and EGF15-0-3 were cocultured on rice medium. Firstly, GNPS (Global Natural Products Social Molecular Networking) method was used to analyze secondary metabolites. Then, the secondary metabolites were separated and purified by silica gel, ODS (Octadecylsilyl), Sephadex LH-20 and HPLC (Preparative High Performance Liquid Chromatography). Their structures were identified by HR-ESI-MS (High Resolution Electrospray Ionization Mass Spectroscopy), NMR (Nuclear Magnetic Resonance), ORD (Optical Rotatory Dispersion) and the relative physical constants were compared with the literature. Ten steroids were obtained and identified as Chaxine C (1), Herbarulide (2), dankasterones A (3), 25-hydroxyergosta-4,6,8(14),22-tetraen3-one (4), Ganodermasides D (5), Ergosta-4,6,8(14),22-tetraen-3-one (6), Ergosta-4,7,22-trien-3-one (7), Isocyathisterol (8), Stigmasta-4,22-dien-3-one (9) and β-sitostenone (10). Compounds 1~3 were steroids with oxidative rearrangement and 4, 5, 7 and 9 were firstly acquired from Aspergillus sp. compared with the single culture of EGF7-0-1 and EGF15-0-3. Based on the coculture strategy, the content types of steroids were more abundant.

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.

The expression of fatty acid metabolism-related genes of Thalassiosira pseudonana under different salinities and different growth stages was analyzed by transcriptomic sequencing in this study. A total of 40 coding genes that are related to the fatty acid metabolisms were retrieved from this study with distinct expression levels at different salinity concentrations. The results showed that the expression levels of genes related to fatty acid biosynthesis and elongation (such as ACC1, armB) in T. pseudonana cells were significantly higher at the second and fourth days compared to those at the first day across the salinity gradients, while the expression levels of genes related to fatty acid degradation (such as ACADM, ECI1) did not change significantly. The expression of genes related to fatty acid biosynthesis and elongation in the experimental group were differentially expressed compared to the control group (for example, the expression levels of KASⅠ, ACAA2 and other genes, which play an important role, increased significantly, but a few of them decreased or changed slightly), although the fatty acid degradation related genes were significantly increased in the experimental group. This study improves our understanding of the survival and adaptation strategies of diatoms in the offshore euryhaline environments, and supports the exploration of outbreak and vanishment of harmful algal blooms.

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.