To elucidate the species composition of fishes in the Langhua Reef of Xisha Islands, reveal their evolutionary traits, and ensure the protection and sustainable use of coral reef fishes in this region, a comprehensive survey was conducted in 2023. Employing techniques such as dive-fishing, hand-fishing, underwater videography, and environmental DNA (eDNA) analysis, this study integrated historical data from 1979, 1998—1999, and 2003 to analyze the species composition and temporal fluctuations in the fish population of the Langhua Reef. To date, a total of 259 fish species have been identified in the reef, classified into 12 orders, 47 families, and 115 genera. Among these, the most populous are the perch-like species, accounting for 200 varieties. The results indicate an exponential relationship between the number of fish species in the reef and their corresponding maximum overall length, with a significant decline in species count as the maximum length increases. Predominantly, the reef is inhabited by small-sized and carnivorous fish, constituting 49.03% and 59.07% of the total species, respectively. The 2023 survey highlighted that 77 fish species, previously recorded in historical data, have not been observed in recent years, predominantly among carnivorous types. Notably, almost all large fish in the reef are carnivorous. Seven species, listed on the IUCN Red List and categorized as large fish, were absent from the current study, with the exception of the brown-spotted grouper (Epinephelus fuscoguttatus).The species composition, dietary patterns, and historical similarity indices of the Langhua Reef fish varied significantly, especially among large and carnivorous species, which demonstrated the lowest similarity indices. Furthermore, the study revealed a downward trend in both the mean taxonomic distinctness index (Δ⁺) and the variance in taxonomic distinctness index (Λ⁺), falling significantly below the 95% confidence intervals. These findings suggest that environmental disturbances, climate change, and human activities have led to a notable turnover in the fish composition of the reef, with large carnivorous species being the most severely affected. This research provides a theoretical reference for a deeper understanding, effective management, and conservation of the Langhua Reef coral reef ecosystem. It also offers foundational data and scientific insights crucial for the restoration of the coral reef ecosystem.

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.

The degradation of coral reef ecosystem can alter the topographic complexity and biotic composition, thereby affecting the coral reef fish community significantly. Coral reefs in the South China Sea have undergone rapid degradation in recent decades, but the ecological consequences for coral reef fish community remain unclear. The coral reefs of the Xisha Islands have experienced ecological degradation in recent years due to the impacts of high temperature and the outbreak of crown-of-thorns starfish (CoTs). We conducted an ecological investigation on the Yinyu Island of the Xisha Islands, through underwater video transect survey, difference tests and liner regression analysis to assess the ecological degradation of the coral reef and its effect on the coral reef fish community. The results show that: from 2020 to 2021, the live coral cover on the Yinyu Island declined from 33.27%to 9.07%, while the turf algae cover increased from 8.38%to 36.50%. The coral recruitment, species richness and Shannon-Weaner index also decreased from 21.42 ind·m^-2 to 3.64 ind·m^-2, 40.00 to 16.83 and 3.26 to 2.14, respectively. The fish density, species richness, Shannon-Weaner index, declined from 1.77 ind.·m^-2 to 1.05 ind.·m^-2, 30.56 to 17.17 and 2.24 to 1.63, respectively. The biomass of corallivore, carnivore, omnivore and total biomass also declined from 2.45 g·m^-2 to 0.43 g·m^-2, 7.35 g·m^-2 to 1.70 g·m^-2, 7.04 g·m^-2 to 0.95 g·m^-2, and 32.99 g·m^-2 to 11.66 g·m^-2, respectively. Within two years, turf algae and macroalgae have dominated the Yinyu Island, but the fish community has not demonstrated top-down control of algae. Among the four functional groups in the whole fish community, the herbivore functional group is the least affected by ecological degradation. The coral species richness constrains the fish species richness and diversity. Based on the results above, we speculate that the rapid degradation of the Yinyu Island is the main reason for the decreased in species diversity, density and the change in the structure of coral reef fish communities. We hope to further increase the frequency and scope of investigations in the future, in order to reveal more deep dynamic relationship between fish communities and coral reef ecological changes.

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.

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.

With the growing global demand for clean energy, hydrogen energy, as an important renewable energy reserve, has garnered widespread attention for its storage technology. Onshore hydrogen storage systems pose risks such as hydrogen leakage, drinking water contamination, and catastrophic injuries. In contrast, offshore geological environments are relatively stable and well-sealed, leading to widespread attention to and rapid development of offshore hydrogen storage technology. Currently, the main underground gas storage technologies include salt caverns, aquifers, and depleted oil and gas reservoirs. Salt cavern gas storage has been operating for many years in Europe and the USA and has a relatively mature technical foundation. However, there are no suitable locations for constructing salt caverns along China’s coast, which limits the build-up of salt cavern hydrogen storage to inland regions. However, China’s coastal areas have abundant underground aquifers and oil and gas reservoirs, necessitating timely related geological research to promote the development and application of relevant technologies in different marine areas and the comprehensive development of the hydrogen energy industry. Developing offshore hydrogen storage technology requires not only integrating the unique geological conditions of the margin with the special physical and chemical properties of hydrogen, but also considering geological, hydrological, biochemical, and mineralogical factors to ensure a rational planning and safe operation, in addition to using the latest geophysical methods in site selection. Looking ahead, offshore hydrogen storage technology will not only provide theoretical support for the development of renewable energy technologies in China but also play a significant role in promoting a low-carbon, green, and sustainable development.

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.

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.

Mangroves are located at the junction between marine and land, and their carbon storage capacity depends on a variety of factors. In this study, the plant growth, biomass, soil organic carbon content and soil bulk density as well as the carbon storage in both vegetation and soil were compared in the mangrove communities in the Gaoqiao District, Zhanjiang, Guangdong, to study the individual and coupled effects of tree species and intertidal elevation factors on carbon storage. The results showed that carbon storage of mangrove communities was 4.98×10¹⁰ g and carbon density was 107.76×10⁶ g·hm^-2, and the carbon storage was mainly concentrated in soil. The carbon density of mangrove in different intertidal elevations were significantly affected by tree species, and the carbon storages of mangrove at low intertidal elevation was higher than those at middle and high intertidal elevation. The carbon storage of Sonneratia apetala communities was significantly affected by intertidal elevation. The carbon storage of Rhizophora stylosa communities at middle intertidal elevation and S. apetala communities at low intertidal elevation was greatest in this mangrove area, regardless of the perspective of vegetation carbon pool or soil carbon pool. In all mangrove communities, the vertical distribution of soil organic carbon content was homogeneous with no significant difference among soil layers. The vertical distribution of soil organic carbon contents at the high and middle intertidal elevation was influenced by tree species. Among them, the soil organic carbon content in the majority of Aegiceras corniculatum communities was significantly higher than those at the same soil layer of Kandelia obovata, Avicennia marina and S. apetala communities. However, tree species had no significant effect on the soil organic carbon content at the low intertidal elevation. Although the relationship of soil bulk density and soil organic carbon content was influenced by both tree species and intertidal elevation, the linear fitting results were mainly negative correlations. This study can provide a scientific basis for the selection of tree species and intertidal elevation for carbon sequestration in mangrove afforestation project.

The microbial carbohydrate active enzymes (CAZymes) are important in the process of carbohydrate mineralization in marine sediment. In this study, metagenomic analysis is used to identify microbial CAZymes genes and predict glycan utilization in the surface sediments from the Daya Bay in spring. The microbial communities showed specific utilization for the different structure glycans. Delta-proteobacteria were dominant for encoding CAZymes genes for the degradation of peptidoglycan and chitin. Gammaproteobacteria, Bacteroides and Planctomycetes were the dominant groups encoding CAZymes genes for the degradation of complex polysaccharides (fucoidan, laminarin, cellulose and hemicellulose), which was associated with their highest Shannon diversity of CAZymes families. Acidobacter was the primary contributors of CAZymes genes for cleaving oligo-galacturonic acid. The contributions of Archaea to most CAZymes genes were less than 1%, while their contributions of genes encoding carbohydrate esterase, binding module relating cellulose and hemicellulose degradation ranged from 2.18 %to11.1%. According to the functional of glycoside hydrolases, the substrate of CAZymes were mostly derived from autochthonous debris, i.e., bacterial sugars (peptidoglycans and α- glucan), algal cell wall (fucoidan and laminarin) and chitin. The relative abundances of CAZymes genes in the mouth for the algal derived organic debris with complex chemical structure were higher than those in the east-northern of the bay. The relative abundances of Auxiliary Activity families (AAs) genes related to lignin degradation were the highest in the east-northern of the bay, and their dominant AAs may help to increase lignocellulose solubility and subsequently enhance the bioavailability of GHs to lignocellulose. The compositions of CAZymes genes were mainly related to the particulate organic matter deposition from water columns and the depth of water body.

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.

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.

The global carbon and nitrogen cycles depend heavily on deep-sea microorganisms, and the majority of current, refined research on these organisms is based on high-pressure simulation culture and detection in laboratories. However, when deep-sea samples are brought in for culture and detection, the environmental parameters, such as temperature, pressure, etc, change at various degrees, which has an impact on the results of subsequent experiments and detection. For this reason, a device (ocean automatic series incubation system, OASIS) was developed for in situ automatic series incubation of deep-sea microorganisms. This research emphasizes the accuracy of deep-sea liquid transfer and focuses on the OASIS operating concept, system design, and experimental validation. The device can function normally under 30 MPa high pressure, and it can automatically finish the culture of microorganisms and the fixation of life information in accordance with the chronological order. These test results demonstrate that OASIS has passed the pressure, sea, pool, and other tests. They also accurately provide an understanding of the ecological benefits of deep-sea ecosystems. It offers strong equipment assistance for precisely identifying the ecological advantages of deep-sea environments.

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.

Using in-situ data collected by summer cruises during 2021−2023, summer hydrological variations and their influencing factors were studied. The results show that the summer temperature and salinity were charactered by northeast-southwest distribution pattern, while variations in values were significant during the investigation. Mean sea surface temperature (SST) was lowest in 2021 but highest in 2022. Bottom temperature was highest in 2021, but moderate in 2022 and lowest in 2023. Strong runoff caused a significant outward expansion of diluted waters, sea surface salinity (SSS) was strikingly lower in 2022 than those in 2021 and 2023. Bottom salinity was highest in 2023, moderate in 2021 and lower in 2022. Temperature and salinity variations in the middle and low layers were related to the passage of typhoons and invasion of shelf cold and saline water. Those vertical temperature and salinity observed after Typhoon Lupit passed in 2021 mixed homogeneously, weakening stratification. Bottom shelf water intruded into the Lingding Bay, forming a low-temperature zone and apparent salinity front. Middle and bottom temperature (salinity) decreased (increased) owing to the enhanced bottom shelf water intrusion in sequence in 2022 and 2023. In 2023, strong upwelling inhibited the expansion of diluted water seaward to increase SSS over the shelf higher than those in 2021 and 2022. Bottom temperature and salinity varied with the tide, in which the shoreward movement of cold and saline water tended to decrease temperature and increase salinity during flood tide, while the opposite occurred during ebb tide. The positive correlation between SST and air temperature suggested that SST varied with air temperature.

The structure of phytoplankton community was investigated based on morphological identification and high-throughput sequencing in the Nan’ao waters in May 2022. The spatial distribution of phytoplankton in relation to environmental factors was explored and results from two different methods were also compared and discussed. According to the cluster analysis of environmental factors, the survey area can be divided into nearshore area and offshore area. Totally, 105 species belong to 52 genera, 39 families, 27 orders, 8 orders, 5 phyla were morphological identified, while 543 species in 6 phyla, 32 orders, 97 families, 155 families, 272 genera through high-throughput sequencing were identified. Bacillariophyta and Dinophyta were the main groups, composing 74.54% and 24.78% through microscopic identification, and 17.52% and 67.84% through high-throughput sequencing, respectively. The abundance of phytoplankton identified by morphology ranged from 0.11×10⁵ to 6.85×10⁵ cells·L^-1, which was significantly correlated with the distribution of chlorophyll a concentration, and the phytoplankton diversity index was lower than that of the high-throughput sequencing method. 7 dominant species were obtained by both methods, of which the absolutely dominant specie in the morphological identification results was Chaetoceros compressus, and the absolute dominant specie in the high-throughput sequencing identification results was Heterocapsa rotundata. Correlation analysis showed that the main environmental factor affecting phytoplankton community structure in Nan’ao in spring was pH, salinity and DIP (dissolved inorganic phosphorus). Using the combination of morphological identification and high-throughput sequencing technology, the structure and diversity of the phytoplankton community can be described more comprehensively and accurately.

Based on mooring data deployed west of the Xisha Islands from October to November 2020, we investigated the characteristics of near-inertial waves (NIWs) triggered by three consecutive typhoons in detail, including the decay time scales and vertical structures of the NIWs, as well as the modulation of the background vorticity and current fields on the NIWs, etc. The vertical wavelengths of NIWs induced by Typhoon Saudel, Molave and Vamco are 109 m, 133 m and 117 m, respectively, and the vertical group speeds are 29 m·d^-1, 26 m·d^-1 and 18 m·d^-1, respectively. The decay time scales for these internal waves are 3 d, 7 d and 15 d, respectively. It reveals that ocean stratification significantly impacts the vertical group speed of NIWs. The longest decay time in the Vamco case is attributed to the second EOF (empirical orthogonal function) mode of NIW propagated from far field. The results of the dynamical mode decomposition (DMD) and EOF are consistent with each other. Both show that the first modes contribute the most to near-inertial kinetic energy (NIKE), and the distributions of NIKE in different modes obtained from DMD and EOF are comparable. For example, the NIKE is mainly distributed in the first, third and second DMD modes at depths of < 100 m, 100~150 m and 150~350 m. The observed frequencies of the NIWs are all blue-shifted, and the blueshifts in Typhoon Saudel and Molave are due to the combination of the background current and vorticity, while the positive background vorticity due to the cyclonic eddy during the Vamco is the main reason for the observed blueshift. Our results are useful for a deeper understanding of the characteristics, propagation, dissipation and energy distribution of strong wind-induced NIWs and their mechanisms, and they also provide a good reference for numerical simulations.

Using conventional observations and ERA5 reanalysis data, a diagnostic analysis of the thermal and dynamical characteristics of a heavy rainfall process in the eastern coastal area of Shandong on June 14, 2022, was conducted, and the results show that the heavy rainfall process occurred in the context of the cold trough at the bottom of the cold vortex in North China moving eastward to the coast of the Peninsula to induce a cold low vortex. Southeasterly cold and humid advective transport in the boundary layer from the Yellow Sea provides abundant water vapour for the heavy precipitation on the peninsula. The precipitation process was stage-specific. In the first stage of precipitation, the low level was continuously influenced by the western warm advection, and the atmosphere had convective instability, while in the second stage of precipitation, the atmosphere was gradually transformed from neutral laminar junctions to convective instability by the combined influence of the cold and warm advection, and was accompanied by obvious energy fronts. The early stage of both phases of precipitation is caused by the convergence of onshore wind speeds as well as topographic uplift. The cold pool caused by convection in the first stage has an important effect on the maintenance of precipitation in front of the Kunshan Mountains, while the maintenance of the strong precipitation in the second stage is closely related to the generation and maintenance of the mesoscale low eddy in the low altitude, and the obliquely pressurized frontal generation plays an important role in the generation of the mesoscale low eddy. The vorticity analysis shows that the boundary layer low-level convergence and absolute positive vorticity advection are the main vortex sources for the positive vorticity growth of the mesoscale low vortex, and with the emergence of the 500 hPa cutoff cold vortex, the negative effect of the vertical transport of vorticity is obviously strengthened, and the horizontal vorticity tilting effect above the boundary layer, which is related to the mesoscale convective activity, is weaker.

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.

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.

There are rich fishery resources and complicated hydrologic environment in the coastal waters of eastern Guangdong. In order to systematically improve the level of oceanic observation and the knowledge of ecological dynamic processes in the coastal waters of eastern Guangdong under the changing climate, a comprehensive investigation of ecological and environmental factors such as hydrodynamics, biology and chemistry during four seasons was carried out in May (spring), July (summer), October (autumn) 2022 and January 2023 (winter). Based on the taxonomic identification of zooplankton, the characteristics of community structure of zooplankton in the surveyed area were analyzed, and the effects of environmental factors on their spatial and temporal distribution were discussed. According to the environmental parameters, the survey area can be divided into the near-shore (mainly affected by human activities) and off-shore (mainly affected by ocean currents) areas, and the zooplankton were characterized by the seasonal and regional pattern. Seasonally, the species, biomass and abundance of zooplankton in spring and summer were higher than those in autumn and winter. Regionally, the species, biomass and abundance of zooplankton in the off-shore waters are generally higher than those in the near-shore waters. Moreover, there are differences in the contribution groups and dominant species to the total zooplankton abundance in different seasons in the off-shore waters. Although copepods and chaetognaths were the main groups of zooplankton, the abundance of planktonic larvae and fish eggs in spring was higher than in other seasons, and the peak value is concentrated in the southwestern Hanjiang Estuary, indicating that this surveyed area was still an important spawning ground in the coastal waters of eastern Guangdong. The increase in copepods species and abundance in summer is related to the high chlorophyll a concentration improved by coastal upwelling in eastern Guangdong. Warm-temperate species carried by Fujian and Zhejiang coastal currents in winter are the main contributors to zooplankton abundance. Although chlorophyll a concentrations are higher in the near-shore waters, zooplankton species, biomass and abundance are lower. Under the effect of anthropogenic activities and climate change, long-term systematic monitoring and analysis of the response of zooplankton to the dynamics of the marine environment are needed in the coastal waters of eastern Guangdong.

Coral communities in the northern South China Sea (SCS), which have the potential to act as regions of refugia for many coral species in the face of global warming. However, the temporal and spatial diversities of coral communities in the northern SCS and the effects of coral bleaching caused by marine heat waves are still unclear. In this study, the status of coral communities across the northern SCS, including the Daya Bay, the Weizhou Island, the Xuwen and Luhuitou fringing reefs, and the space differences are studied on the basis of ecological materials in the field investigations during August 2020, and its response to marine heatwaves. Our results indicate that coral communities across the northern SCS show remarkable regional characteristics. The dominant species composition, species number and α diversity index of coral communities are subject to significant regional differences, and the live coral cover is higher in the Luhuitou and Daya Bay (37.78% and 17.97%, respectively). Thus, the coral communities in Xuwen and Weizhou were subject to mass coral bleaching events during the field investigation, and the coral bleaching rate and mortality rate was 84.78% and 10.68%, 65.52% and 0.70% in Xuwen and the Weizhou Island, respectively, while no coral bleaching occurred in the Daya Bay and Luhuitou. Based on historical data analysis, although the live coral cover of coral communities in the northern SCS has dropped significantly since 1980s, there has been a recovery trend in recent years; the proportion of heat bleaching tolerant genera and heat bleaching resistant genera increased in the coral communities of the Weizhou Island, Xuwen and Luhuitou. In general, the coral community in the northern SCS has a strong resistance to heat bleaching. Strengthening the conservation and management of coral reef areas is crucial for the restoration and refuge of coral communities in the northern SCS under global warming.

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.

Pisodonophis cancrivorus is an important fish species in the southeast coast of China. In this study, the complete mitochondrial genome of P. cancrivorus was obtained by high-throughput sequencing technique, as well as the structural characteristics and phylogenetic relationships were also analyzed. The total length of the complete mitochondrial DNA is 17650bp, and the base compositions are A (31.72%), G (15.58%), T (26.26%) and C (26.44%), respectively, showing an obvious anti-G bias and A+T preference. Similar to the published mitogenomes of Ophichthidae species, some genes have undergone a tandem duplication-random loss (TDRL) event due to the natural selection, causing the ND6 gene and its conjoint tRNA-Glu(E) to be translocated between tRNA-Thr(T) and tRNA-Pro(P). Besides, another D-loop region with length of 966bp is located upstream of the ND6 gene, and these two D-loop regions show a trend of independent evolution. There are two start codons (ATG, GTG) and four stop codons (TAG, TAA, TA-, T--) among the 13 protein-coding genes (PCGs), and only COI gene is initiated with GTG. In the total of 3 824 encoded amino acids, the content of Leu is the highest, while the content of Cys is the lowest. There are 17 DNA mismatches in the secondary structures of 22 tRNAs. All tRNAs can form the clover-leaf structures, excepting tRNA-Ser^AGY(S) because of lacking the DHU arm. The origin of L-strand replication region (O_L) with the length of 21bp is situated in the “WANCY” region, and the conserved motif 3'-GGCGG-5' is detected in the 3' end of its hairpin secondary structure. The sequences of 12 PCGs (without ND6) are concatenated by removing stop codons, and the interspecific genetic distances of 17 Ophichthidae fishes are calculated to be 0.128-0.297 based on the Kimura two-parameter (K2P) model. The phylogenetic trees constructed by the maximum likelihood (ML) and Bayesian inference (BI) methods show a complex evolutionary relationship of Ophichthidae fishes. P. cancrivorus is located at the base of the phylogenetic tree and closely related to Ophichthus brevicaudatus and O. evermanni, suggesting that it may diverge later than other snake eels.

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.

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.

In this experiment, the conditions for amplifying polyp populations and strobilation of Phyllorhiza sp. were studied. The asexual reproductive process and the metamorphosis of ephyra into medusa were observed and described. Phyllorhiza sp. is characterized by two asexual reproduction modes: swimming buds and strobilation. Polyps can be permanently stored in laboratory. Both the producing swimming buds and strobilation can be observed at 20~25°C. It takes 10~12 days for metamorphosis to mature polyps after swimming buds attachment. It takes 2~3 days to produce swimming buds for polyp asexual reproduction. Monodisc is the strobilation mode of Phyllorhiza sp. and it takes 4~5 days before the ephyra gets rid of the residual polyp. The edge of the central disc of strobila keeps blue-purple from the formation of rhopalia to the disappearing of polyp tentacles. It takes 12 days for ephyra to develop into juvenile medusa under 25°C, 29‰~32‰ (salinity).

To evaluate the nutritional value, taste activity and health risk, the content of fatty acid, hydrolyzed amino acid, free amino acid and heavy metal in Phascolosama esulenta from Beihai of Guangxi, Zhanjiang of Guangdong, and Ningde of Fujian were analyzed. Twenty-two types of fatty acids were detected in these three regions. The hypercholesterolemia index HI was 13.11 in Beihai, 14.09 in Zhanjiang, 16.64 in Ningde, the atherogenic index AI was 0.49, 0.49, 0.56, and the thrombosis index TI was 0.62, 0.75, 0.81, respectively. There were 17 hydrolyzed amino acids in each of the three regions, with a total amino acids (TAA) of 159.70 mg·g^-1, 155.97 mg·g^-1, and 161.49 mg·g^-1, respectively, and there was no significant difference. According to the Food and Agriculture Organization of the United Nations / Word Health Organization (FAO/WHO), when using the amino acid score (AAS) and chemical score (CA) as standards, the first and second limiting amino acids of the three regions of the P. esulenta are Met + Cys, and Val, respectively. In addition, the essential amino acid indexes (EAAI) were 11.14, 10.62 and 11.37, respectively, indicating that the three regions of the P. esulenta can all serve as ideal protein sources. The results of free amino acids showed that the P. esulenta of Beihai contained 15 kinds of free amino acids, while Zhanjiang and Ningde both contained 16 free amino acids, with a significant difference in total free amino acid content (p < 0.05). It was found that the taste activity values (TAV) of Glu, Gly and Ala in the free amino acids of the three regions were all greater than 1, indicating that these three amino acids contribute the most to flavor formation. Additionally, the heavy metal content analysis indicated that the heavy metal level in Beihai and Zhanjiang was Zn > Pb > Cu > As > Cd > Hg, while the content of heavy metals in Ningde was Zn > Cu > Pb > As > Cd > Hg. The single pollution index showed that the three geographic groups were all heavily polluted by the heavy metal Pb, of which Ningde was the most serious. The comprehensive pollution index showed that the heavy metal pollution of P. esculeata in the Beihai reached the threshold for slight pollution (P = 0.96), Zhanjiang and Ningde were moderately polluted (1 < P < 2). The single target hazard quotient (THQ) and the compound target hazard quotient (TTHQ) were all less than 1, indicating that there was no potential health risk for adults and children for the consumption of this species. The results provide a theoretical basis for the utilization and subsequent industrial precision processing of P. esculeata.

The marine engineering survey focuses on the geological hazards that threaten the marine engineering. In the process of moving towards the deep water, it has also been found that several unique geological phenomena, distinct from shallow water areas, have a certain impact on the positioning of drilling platforms, the design of jacket platforms and floating platforms, and the optimization of submarine pipeline and cable routes. Based on the results of many deepwater well site surveys and deep-water oil and gas field development project surveys, this paper expounds the characteristics of deep-water geological hazards, the methods of research and evaluation and the impact on marine engineering through the results of engineering geophysical survey, engineering geological survey and marine environmental survey, and provides a better idea for the investigation and design of deep-water marine engineering. The researches show that the deep water is widely developed with sand waves, scarps, hard seabed, faults, submarine canyons, mass transport deposits and other geological disaster phenomena. When conducting engineering geophysical survey, the use of autonomous underwater vehicle (AUV) and other survey methods to obtain centimeter resolution survey results can effectively reduce the observation period of seabed sand wave movement rate, and obtain more accurate water depth topographic data to support the marine engineering design. Combined with the shallow soil sample results and shallow profile results of the engineering geological survey, the seabed strata can be effectively divided and the slope stability analysis can be carried out, providing the design basis for the offshore engineering construction.