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.

Artificial reefs are submerged structures artificially placed on the seabed to mimic some characteristics of natural reefs. They are able to exert the functions of enhancing the proliferation of fishery resources, promoting the restoration of marine habitats and supporting coastal recreation. Its origins date back to thousands of years, but systematic research and applications on artificial reefs only began in the last century. In recent years, with the increasing number of artificial reef studies, a large number of new materials, new structures, new methods and new applications have been proposed and practiced. By reviewing the research progress of artificial reefs in China and abroad, the current situation in this field is reviewed from three aspects: the design, research and application of artificial reefs. The research and application direction of artificial reefs in the future are prospected, aiming to guide the future relevant works on artificial reefs in China.

The material and energy exchange at the air-sea interface is an important cause of global climate and ecological environment change. As the largest shelf margin sea in China and the Northwest Pacific Ocean, atmospheric deposition plays an important role in the exogenous input of the South China Sea. With the continuous and rapid economic and social development of the surrounding countries in the South China Sea, the transport of anthropogenic pollutants to ocean through atmospheric deposition is increasingly enhanced, which is bound to have a non-negligible impact on the ecological environment of the South China Sea. Based on the research reports of atmospheric deposition of biogenic elements, micro-trace elements and new pollutants microplastics in the South China Sea in the past nearly 30 years, this paper systematically summarized the concentrations, fluxes and influencing factors of atmospheric dry and wet deposition in the South China Sea, and analyzed the eco-environmental effects of atmospheric deposition in the South China Sea. The results show that 1) The concentration of atmospheric particulates in the South China Sea is lower than that in the east coast of China, and there is almost no acid rain deposition. However, the atmospheric carbonaceous aerosol component concentration and deposition in the South China Sea are at a high level due to the influence of biomass burning in Southeast Asia and fossil fuel combustion emissions in China. 2) Nitrogen is the dominant nutrient in the atmospheric dry and wet deposition in the South China Sea, and the proportion of nitrogen species varies greatly in different sea areas, resulting in strong imbalance of nutrient structure in atmospheric deposition. 3) The solubility of anthropogenic metal elements in aerosols is high, and most of them in the form of wet deposition. Aerosol microplastics mostly exist in the form of fiber. Meteorological conditions (precipitation, wind speed, etc.) and source emission intensity are the main factors controlling atmospheric component concentration and deposition flux. 4) Atmospheric nitrogen deposition accounts for about 20% of the total nitrogen input in the sea surface of South China Sea. The addition of nitrogen will aggravate the hypoxia and acidification of the offshore, and nutrient deposition plays an important role in the explosive proliferation of phytoplankton. Atmospheric deposition will have multiple and complex impacts on South China Sea, an oligotrophic ecosystem, which is closely related to hydrologic conditions, initial nutrient status, phytoplankton groups, atmospheric composition and deposition characteristics. In the future, it is suggested that the researchers should pay more attentions to the depth and breadth of the research, focus on the precise and regular monitoring of the dry and wet deposition of various atmospheric components, especially organic nitrogen and phosphorus species and new pollutants, and fully explore the influence and feedback mechanism between the atmospheric deposition of biogenic elements and micro-trace elements and the South China Sea ecosystem from the perspective of interdisciplinarity. Atmospheric deposition is an important part of biogeochemical cycle in the South China Sea, and its impact on the ecological environment is a "double-edged sword". With the continuous enhancement of atmospheric deposition of terrigenous species in the South China Sea in the future, this effect will become more complex and far-reaching.

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.

Based on the mangrove plantation data and stand growth monitoring at different periods, we analyzed the spatial and temporal variation of mangrove forests and regional silvicultural growth differences in Zhejiang Province. The results show that: (1) The total area of mangrove forests in Zhejiang Province by 2020 is 386.77 hm², including 257.01 hm² in Wenzhou and 129.76 hm² in Taizhou; the main afforestation species are Kandelia obovata (368.48 hm²) and Myoporum bontioides (18.29 hm²); (2) The proportion of mangrove area at different periods was 0.11% (before 2000), 3.72% (2000-2010), 36.17% (2011-2015) and 59.99% (2016-2020), respectively; (3) The average heights of Kandelia obovata before 2000 and 2000-2010 were 205.5 cm and 246.13 cm, respectively; the cover was as high as 67.69% and 77.9%. And the average heights of Kandelia obovata in 2011-2015 and 2016-2020 was 106.63 cm and 50.17 cm, respectively; the cover was 68.66% and 24.56%; (4) There were significant differences in the alkali-hydrolyzed nitrogen, available potassium, organic matter and salt content in tidal flat sediments of mangrove plantations in different regions; (5) The height of 4-year-old Kandelia obovata in different regions was significantly higher (P<0.05) in the Xinmeizhou village, Longgang city than in the Shupaisha Island, while the diameter was significantly higher (P<0.05) in the Shupaisha Island than in the XimenIsland. The area of mangrove planting in Zhejiang Province has increased significantly in recent years; mangrove populations are growing vigorously, and the depression of early planted stands is high; the growth of Kandelia obovata varies significantly in different regions.

The Swan Lake in Rongcheng of Shandong province is a typical lagoon-barriers system. Since 1980s, under the influence of human activities, the environmental system of the Swan Lake has changed with strong erosion of the sand dam. Studying the erosion and deposition of underwater bank slopes is of great significance for understanding the evolution of lagoon-sand dam system and protecting the environment of Swan Lake. This paper focus on the underwater bank slope of the sand dam at the east side of the Swan Lake. Based on the combination of chart data from 1960 to 2014 and geographic information technology, we have obtained multi-year water depth of the coastal waters on the east side of the Swan Lake since 1960, and analyzed the contour changes, scouring and silting changes and topographic changes of the set profile in the sand dam area on the east side of Swan Lake. The results show that the overall depth contours moved towards the sea from 1960 to 1980, while the tendency of contours moving towards the sea from 1980 to 2014 slowed down, the 0 m depth contour at the entrance of the tidal channel retreated 126.70 m to the shore from 1960 to 2014. The underwater bank slope of the Swan Lake was at a state of siltation from 1960 to 1980, the annual siltation rate is 3.60 cm·a^-1. The erosion area increased significantly from 1980 to 2014, and the erosion and siltation phases were distributed, the annual siltation rate is 0.79 cm·a^-1. The underwater bank slope of the Swan Lake sand dam is steep and gentle, and the north side of the tidal channel entrance is more likely to be eroded than the south side. Human activities have changed the environmental state of the Swan Lake, leading to partial erosion and retreat of the underwater bank slope of the Swan Lake.

A total of 88 threatened fish species were selected for the study, and their spatial distribution was predicted using publicly available data and the MaxEnt model. The conservation gap analysis was performed based on the predicted distribution, and recommendations for the conservation of the East China Sea and adjacent sea areas were proposed. The results showed that the hotspot areas of threatened fish covered 1.58×10¹¹m², mainly located in the southern coastal area of the Yangtze estuary and the Taiwan Strait. Among them, the top 10%of the hotspot areas was about 5.68×10¹⁰m², mainly located in the coastal waters of Fujian and Guangdong provinces, and sea areas adjacent to Taiwan Island and Penghu Islands. Further investigation of the distribution patterns revealed that there were six different zones in the current distribution of threatened fish in the East China Sea. The existing marine protected areas are mainly concentrated in zones I and Ⅳ, while no protected area has been established in zones Ⅱ and Ⅲ, indicating that habitats of most threatened fish have not been effectively protected. These results provide a scientific basis for improving and optimizing the fish biodiversity conservation strategies in the East China Sea and adjacent sea areas.

Continuous measurement technology of suspended sediment concentration is the most fundamental requirement in the research fields of hydraulics, environmental science, estuarine and coastal science, as well as marine science. The current popular technical routes including optical backscattering and transmission, specular reflection, remote sensing, acoustic backscattering and transmission attenuation, tuning fork resonance, pressure difference and gamma-ray attenuation and other principles of technical methods were summarized in this paper. The main advantages and problems of each technical method are then discussed, and the future research focus and development direction are prospected as: (1) the principle of optical backscattering is the optimal technical route for low-cost, miniaturized, and high-time-frequency measurement of suspended sediment concentration, and is necessary to focus on range expansion and particle size sensitivity weakening study; (2) low uncertainty suspended sediment concentration profile measurement relies on the development of the acoustic backscattering technical route; (3) the tuning fork resonance technical route is particularly suitable for ultra-high range application scenarios under turbid current and fluid mud conditions; (4) integrate multi-technology sensors and use the artificial intelligence algorithms to replace traditional inverse theory model, etc.

Green sea dyke represents a new concept of coastal defense, which combines traditional engineering structure with coastal ecosystem, to cope with the future trend of sea level rise and storm intensification. Before its application, however, the feasibility of such a system must be tested for low-lying coastal areas, where the risk of storm surge, storm-induced waves and shoreline erosion is greatest. The major issue is associated with the process of wave attenuation by the ecosystem and the way of using the ecosystem within the sea dyke system. For many years, wave energy dissipation has been an important research field for tidal flats, a typical environment of low-lying coasts, as well as beaches and rocky coast environments. Theoretical analysis, field observation and physical-mathematical modelling show that the coastal ecosystem indeed plays a significant role in wave energy dissipation: (1) resuspension and fluid mud movement dominate over bed friction in the mud area, in terms of wave height reduction; (2) wave attenuation occurs due to bed friction and bedload transport on the silt-sand flat at the lower part of the tidal flat, while on the upper mudflat it is caused mainly by re-suspension and suspended, fine-grained sediment transport; (3) in the vegetated ecosystems such as salt marsh, mangrove and seagrass beds, the efficiency of plants in reducing flow velocity and dissipating wave energy is higher than that of bare flats, due to plant morphological resistance and stem movement; and (4) wave attenuation is high when passing through biological reefs (e.g., coral and oyster reefs), especially during storms, with bed surface friction and wave breaking being the major mechanisms. Although the wave attenuation theory has been established, the optimization of the way the ecosystem is used within the sea dyke system requires further investigations, especially the techniques of ecological niche reconstruction on eroding coasts and the design of the sea dyke to improve structure safety. The relevant scientific problems include: adaptive biology for salt marsh plants and oysters in conjunction with hard engineering; stability of ecosystem in response to future environmental change; spatial configuration of ecosystem in the green sea dyke and the match between the ecosystem life cycle and the temporal scales of storm events; and the optimization of the sea dyke configuration, on the basis of the equilibrium coastal profile theory.

In order to investigate the contents and sources of heavy metals in the Xisha waters in the South China Sea, 24 seawater samples at six sites were collected in December of 2021. Vertical profiles of temperature, salinity, turbidity, dissolved oxygen, colored soluble organic matter and chlorophyll were determined by Conductivity-Temperature-Depth instrument. Inductively coupled plasma mass spectrometry was used to measure the contents of heavy metals in seawater samples, and the average Cu, Pb, Zn, Cd, Ni, Cr, As, Fe and Mn contents were 0.22~20.79 µg·L^-1, n.d. (not detected) ~0.25 µg·L^-1, 1.90~15.90 µg·L^-1, 0.13~0.17 µg·L^-1, 0.54~1.31 µg·L^-1, 0.29~0.33 µg·L^-1, 2.93~3.17 µg·L^-1, 0.39~1.23 µg·L^-1 and 0.35~1.14 µg·L^-1, respectively; Hg was not detected. Only Cu or Zn contents in 5m-depth seawater at D2~D4 sites exceeded Class I requirement of National Seawater Quality Standard (GB 3097-1997), and the spatial distribution of heavy metals was influenced by terrestrial inputs, environmental factors and human activities. Principal component analysis indicated that the heavy metals in the Xisha waters are mainly from three sources: ship emission, terrestrial agricultural runoff, as well as terrestrial debris and industrial inputs. The measurements in this study are generally within the range of heavy metal contents previously reported in the South China Sea. However, compared with the background values of the South China Sea in 1998, the contents of Cu, Pb, Zn and Cd in surface seawater have increased by one order of magnitude, reflecting the impact of recent intense human activities in this region.

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.

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.

Eddy-induced transport in the Luzon Strait significantly affects the thermo-salt balance in the northern South China Sea. Using the AVISO satellite data from 1993 to 2018, this paper identifies and screens 76 Kuroshio shedding anticyclic eddies, 46 Kuroshio associated cyclonic eddies, 29 South China Sea (SCS) locally-formed anticyclic eddies and 40 SCS locally-formed cyclonic eddies in the northern SCS. The average nonlinear coefficients of the four types of eddies are all much larger than 1, which confirms that the screening eddies do have the capacity of transporting the saline Kuroshio water. The propagation paths of the eddy are affected by the topography of the northern SCS, and shift to the southwest during the westward propagation process. Compared with the cyclonic eddy, the anticyclonic eddy moved farther to the northern part of the SCS. The eddies are mostly formed in the middle of the Luzon Strait, and the probability of formation gradually decreases with the increase or decrease of latitude. The shedding (associated) eddies are mostly formed in autumn and winter and the least in summer and the average number of anticyclonic eddies is 2.5 more than cyclonic eddies per month. The annual average number of shedding (associated) eddies is about 4.6, and cyclonic eddies do not form every year. Overall, the El Niño event increases the number of Kuroshio shedding or associated eddies by affecting the Kuroshio path.

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.

The outbreak of crown-of-thorns seastar (CoTS, Acanthaster planci) is one of the main causes to coral reef degradation in the South China Sea and the Indo-Pacific region. The density of CoTS larvae is an important indicator to determine whether the outbreak of CoTS adult population occurs or not. However, as the larvae are not visible and thus difficult to be distinguished, conventional investigation and microscope observation cannot effectively detect the CoTS larvae in natural seawaters. Therefore, it is needed to develop a sensitive and specific method for detecting CoTS larvae. This study established specific polymerase chain reaction (PCR) method to detect the CoTS larvae based on CoTS mitochondrial cytochrome oxidase subunit I gene (ApmtCOI), and this method was applied to detect the CoTS larvae in the coral reef around Qilianyu Island, Xisha. The results showed that the designed and screened four pairs of specific primers could succeed in amplifying ApmtCOI gene, and had no cross-reaction with Linckia laevigata, Culcita novaeguineae, Choriaster granulatus and Echinaster luzonicus. Moreover, the primer 2aooniF/2anooiR had the best specificity and higher sensitivity when annealing temperature was 58.5°C, which could detect the CoTS genomic DNA in pictogram grade. Furthermore, this method had succeeded in detecting the CoTS larvae in the Qilianyu Island of Xisha at the end of October, and we found that the distribution of CoTS larvae was not uniform. Therefore, this detection technology can be used as an effective method for monitoring CoTS larvae population in the future.

Human-induced emissions of greenhouse gases such as carbon dioxide (CO₂) are the main drivers of global warming. Global warming poses a serious threat to the security of food, water resources, energy, economy, and other fields. Alleviating global warming is imperative. Not only does it require massive greenhouse gas emissions reduction, but also large-scale deployment of carbon dioxide removal (CDR) or negative emissions techniques to intentionally remove CO₂ from the air and sequestrate it for a long period so that to decrease global net CO₂ emissions to zero as soon as possible, and achieve "carbon neutrality". The ocean accounts for 70% of the earth's surface area and is the largest active carbon pool. It has a huge potential to absorb CO₂. Ocean-based CDR is necessary to achieve carbon neutrality. The research on the theory, method, and technology of ocean CDR has become a hot spot and frontier field. At present, the knowledge of ocean CDR is still relatively limited, and there is a large space for development. The urgent need to mitigate global warming is promoting the rapid development of the basic theory of marine carbon sinks and ocean CDR research, and original progress is emerging. This paper mainly summarizes the theoretical basis of the Iron-Aluminum Hypothesis and discusses the potential of ocean aluminum fertilization as a CDR strategy. The iron-aluminum hypothesis indicates that aluminum can enhance carbon fixation by phytoplankton in the upper ocean, reduce the decomposition rate of biogenic carbon, improve the efficiency of the biological pump, increase carbon export and sequestration to the deep sea, regulate marine carbon sinks, and affect the concentration of CO₂ in the atmosphere. Thereby, as well as iron, aluminum may be a key factor in influencing historical and modern climate changes. Aluminum improves the efficiency of iron use and carbon export to the deep ocean, which can make up for the shortage of artificial ocean iron fertilization, and endow ocean aluminum fertilization with the potential to become a new CDR method and technology based on natural carbon sinks. Despite its potential high efficiency, ocean aluminum fertilization as a CDR method is still nascent. We suggest further study on the mechanisms underlying the roles of aluminum in enhancing marine carbon sinks from the three aspects 1) carbon fixation by marine phytoplankton in the upper ocean, 2) biogenic carbon export to the deep ocean, and 3) long-term carbon sequestration, and thus to strengthen the theoretical basis of iron-aluminum hypothesis and ocean aluminum fertilization. We also propose to verify the CDR efficacy of ocean aluminum fertilization and its potential environmental impacts at different temporal and spatial scales. The above two works are expected to provide basic scientific knowledge for the development and application of ocean aluminum fertilization as a CDR strategy.

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.

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.

We analyzed the principal components of hydrology, water quality, and meteorological data in Pingtan, Fujian province from 2013 to 2019. We selected 5 meteorological factors and 4 water quality factors. Our study establishes four early-warning model, KNN (K-nearest neighbor), RF (random forest), GBRT (gradient-boosted regression trees), Bagging (bootstrap aggregating) with meteorological factors and water quality factors as input indicators, and algal cell density as output indicators. After normalizing the 802 sets of marine monitoring data from 2013 to 2019, 80% of the data were randomly selected as the model training samples, and the remaining 20% were used as data of model verification. When temperature, wind speed, sea level pressure, and chlorophyll a are used as input parameters, the calculation result of KNN regression model is more accurate (R²=0.624, RMSE=0.821 μg·L^-1, MAE=0.836 μg·L^-1). In the sea area without chlorophyll a monitoring index, a BP neural network early-warning model with chlorophyll a concentration as the output index and temperature, sunshine, wind speed and AOI as input parameters was established, which has better warning accuracy (R²=0.651, RMSE=0.062 μg·L^-1, MAE=0.033 μg·L^-1). Our results can provide a reference for the red tide early warning research in the Pingtan coastal area.

In order to clarify the influence of hydrological dynamics and environmental changes caused by human activities on the zooplankton community structure in the coastal waters of Guangdong-Hong Kong-Macao Bay Area, zooplankton samples were collected in 3 transections (in the Pearl River Estuary, Daya Bay and Huangmao Sea) in July 2019 (summer) and December 2020 (winter). The characteristics of meso- and micro-zooplankton community were analyzed, and the influencing factors of their seasonal and regional differences were discussed. A total of 211 zooplankton species (including larvae) were identified in the study area, among which copepods accounted for 42.18%. The diversity and abundance of zooplankton showed obvious seasonal and regional differences. The number of species and average abundance of zooplankton were higher in summer than that in winter, and the species diversity in offshore waters was higher than that in nearshore waters. The high values of zooplankton abundance were located in the interface of saline- and plume- waters of the Pearl River Estuary in both seasons. In summer, the average abundance in estuarine waters was obviously higher than that in the Daya Bay, while in winter there was no such difference in the nearshore waters. The results of cluster analysis showed that the zooplankton community could be divided into three groups, i.e. the estuarine group, the bay group and the far-shore group in summer. The estuarine waters was greatly affected by runoff, and the community structure was significantly different from that of the Daya Bay. However, there was no significant difference in community structure between the estuarine and the bay in winter. Parvocalanus crassirostris and Oithona brevicornis were dominant species in both seasons, Bestiolina amoyensis, Acartiella sinensis and Oithona simplex were also dominant in the wet season, while Paracalanus parvus was also dominant in the dry season. Pearson correlation analysis and RDA analysis results showed that there were interspecific and seasonal differences in the correlations between the abundance of different species and temperature, salinity, phytoplankton biomass and nutrients, suggesting that the complex water environment in the Greater Bay Area had a potential influence on the differentiation of meso- and micro-zooplankton community structure.

Diffuse attenuation coefficient of downwelling irradiance K_d(z, λ) is an important parameter for estimating the profile distribution of underwater light filed and water constituents, and studying the photosynthesis of the phytoplankton and warning method of harmful algae bloom. K_d(z, λ) is a “quasi-inherent” optical property as a function of wavelength \lambda and depth z. Not only is it sensitive to absorption and scattering/backscattering coefficient, but also sensitive to the angular distribution of the normalized volume scattering function (i.e., scattering phase function). In this study, based on the volume scattering function [VSF, β(ψ, z)] in seven directions determined with a custom in situ device called VSAM (volume scattering and attenuation meter), the absorption coefficient a(z) determined with the WET Labs ac9 and ac-s, and the downwelling irradiance E_d(z) determined with the Satlantic Profiler Ⅱ OCI/R-200 and HyperPro Ⅱ in the north South China Sea (SCS) with a broad range, using LightGBM, Random Forest (RF) and CatBoost, three machine learning models for estimating the profile distribution of K_d(z, 650) were developed at first, and they were then evaluated by the key indicators including R²、RMSE、MAPE, as well as the comparison between in situ measured K_d(650) and estimated K_d(650). The evaluation indicated that the CatBoost model performed the best with R² of 0.8534, RMSE of 0.0472 m^-1, MAPE of 11.0585%, and the estimated K_d(650) was also closest to the measured K_d(650). Using the established CatBoost model, input inherent optical properties (IOPs) were the absorption coefficient, the volume scattering function (VSF), and their profile depth, the K_d(650) profile distribution among 15 m in the north SCS was estimated. The result shows that K_d(650) varies from 0.275 to 0.7 m^-1 at 5, 10 and 15 m underwater. At 5 m, K_d(650) is relatively stable while it varies greatly at 10 and 15 m. The contribution of volume scattering function distribution to K_d(z, λ) is considered in this study, which provides a new idea and method for accurate estimation and acquisition of K_d(z, λ) based on inherent optical properties (IOPs).

In this paper, oyster hydrolysis products were prepared from Crassostrea hongkongensis as raw materials, and the basic nutrition and amino acid composition of oyster hydrolysis products were analyzed, and the improvement effect of oyster hydrolysis products on the lactation function of rats with postpartum lactation caused by Bromocriptine mesylate was explored. The results showed that protein content of oyster hydrolysis products was higher, which is followed by sugar, fat content was lower, and peptide content was 33.4%. The essential amino acids in oyster hydrolysis products accounted for 39.8% of the total amino acids and contained a high proportion of branched amino acids. The results of animal experiment showed that compared with model group, the lactation volume of rats in oyster hydrolysis products of high-dose group was significantly increased (p < 0.05), which was better than that in the positive control group. The index of mammary tissue and organ in each oyster hydrolysis products dose group was significantly increased (p < 0.01), which was close to the positive control group, but did not return to normal level. HE staining showed that there were more acinus in mammary gland tissues in all oyster hydrolysis products dose groups, which were round and full with more secretions, and the acinus had obvious enlargement and hyperplasia. Compared with the model group, the acinus had obvious recovery. Compared with model group, the contents of prolactin (PRL) and prolactin receptor (PRLR) in serum and mammary tissue of oyster hydrolysis products groups were largely increased (p < 0.05), indicating that oyster hydrolysis products could promote the secretion of prolactin in lactation-deficient rats, while the content of serum dopamine (DA) was greatly decreased (p < 0.01). These results showed that oyster hydrolysis products can reduce the high level of dopamine induced by bromocystine. In addition, oyster hydrolysis products strongly increased the contents of lactose (LC) and triglyceride (TG) in breast tissue (p < 0.05), and improved the nutritional composition of milk. The average hemoglobin (MCHC) and red blood cell (RBC) contents in all oyster hydrolysis products dose groups were also greatly increased (p < 0.05), which had a certain improvement effect on postpartum deficiency of qi and blood. Conclusion: Oyster hydrolysis products can improve the symptoms of lactation deficiency and increase milk yield after delivery, which has the potential to promote lactation.

Porites lutea, the representative species of reef building corals around the Hainan Island, is a spawning, massive coral with strong environmental adaptability. Exploring the genetic structure and connectivity of this species helps to reveal the genetic diversity pattern and larval migration path of coral metapopulation around the Hainan Island, thus clarifying the recovery potential of coral reefs. In this study, 11 P. lutea microsatellite markers were screened to analyze the genetic structure of 10 populations of the Hainan fringing reefs and 1 population (XsR) in the Xisha Islands. The results showed that, overall the genetic diversity of all populations was medium to low, with the average allelic richness Rs ranging from 2.8 ± 1.3 (Basuo population, Bs) to 3.7 ± 1.7 (Linchang Reef population, LcR), and the average observed and expected heterozygosity ranged from 0.31 (Tongguling population, Tgl) to 0.54 (Dachan Reef population, DcR) and 0.50 (Leigong Island population, LgI) to 0.64 (Haiwei population, Hw), respectively. Except for the Longwan Reef population (LwR) and the Dazhou Island population (DzI), which located in the east of the Hainan Island, and the Basuo population (Bs) and the Dachan Reef population DcR (in the west of Hainan Island), all other populations (7/11) showed evidence of heterozygote deficiency. According to genetic differentiation, the Hainan Island populations were divided into two groups: the north-south-east genetically connected zone and the west coast, and the differentiation between the two branches (AMOVA, 0.092) was significant. The former group included Bs, Luhuitou population (Lht), DzI, LgI and Mulantou population (Mlt), due to the significant gene flow created by exchange of ocean currents, there was no obvious genetic differentiation among these five coastal populations, whereas the gene flow of the offshore populations (LcR, DcR and Hw) of the west coast was blocked due to the discontinuity of coastal reefs and slow coastal currents. LwR in the east coast also converges to the west branch, which may be due to the isolation by environment and the convergent adaptation to offshore environment. Although the distance between Hw and Bs is less than 50 km, but they are obviously differentiated, possibly due to the isolation by salinity fluctuation and suspended sediments caused by the runoff of the Changhua River. Tgl showed strong inbreeding, low heterozygosity and non-random mating characteristics because it was located in the wave shadow area of the Tongguling headland, and the runoff of the Bamen River restricted its gene exchange with other coastal reef populations. Represented by P. lutea metapopulations, the fringing reefs of the Hainan Island has the natural resilience responding to environmental stress due to the strong gene flow and the genetic differentiation caused by ocean current, runoff and complex fringing reef structure, as well as the environmental differences between nearshore and offshore. The genetic differentiation between the Xisha Islands population and the coastal reef populations of the Hainan Island was large, showing significant geographical isolation. The Qilianyu Island may have lost the ability to replenish the Hainan Island with coral larvae because the coral reefs have declined there.

Based on the natural distribution of different mangrove populations, Avicennia marina, Aegiceras corniculatum and Bruguiera gymnorrhiza were chosen to be the experimental species that have different resistance of water-logging. The activities of peroxidase (POD), superoxide dismutase (SOD), ascorbate oxidase (APX) and catalase (CAT) in root tissues of three species of mangrove were tested after submerging for 0d, 1d, 3d, 5d, 7d and 14d. Under hypoxia environment, the balances of production and elimination of reactive oxygen species (ROS) would be destroyed and a large amount of ROS were accumulated. The results showed that POD increased with time during the period from 1d to 14d, which may be related to the involvement of scavenging of toxic substances in addition to the elimination of reactive oxygen. The CAT, SOD and APX increased when mangroves encounter the water-logging and then decreased. The enzymes play an important role in eliminating the large amount of ROS in the root tissues of mangrove plants during the early period of the waterlogging stress. There were some differences in the expression quantity of antioxidant enzyme system among the three mangrove plants but the fluctuations are similar. Hierarchical clustering analysis of various enzyme activity indexes indicated that the activity pattern of antioxidant enzyme system in A.marina was different from that in A. corniculatum and B. gymnorrhiza. There was no significant difference in the expression pattern between A. corniculatum and B. gymnorrhiza. The research aims to better understand the physiological mechanism of mangrove to resist waterlogging stress and to provide theoretical foundation for protecting mangrove ecosystem.

The Haitan Strait in Fujian province is an important channel for the southward transportation of material from the Minjiang River and the Zhejiang-Fujian Coastal Current to the Xinghua Bay and the south-central coast of Fujian. The topographic data of the Haitan Strait in the past 50 years was analyzed using GIS tools. The results indicate that strong siltation occurred in the Haitan Strait due to the influence of several catastrophic floods in the Minjiang River Basin during 1964~1975. The Haitan Strait experienced strong erosion during 1975~1990 which is caused by water and soil conservation and reservoir constructions in the Minjiang River Basin. After that, the erosion rate declined gradually and the strait maintained slight scouring. Large-scale artificial sand mining started since 2007 that caused severe erosion in the northern part of the Strait. Before 2007, sediment discharge from the Minjiang River was the main factor restricting the geomorphological evolution of the Haitan Strait. Flood, sand mining and reservoir construction had a direct impact on the geomorphologic evolution of the strait. However, after 2007, large-scale artificial sand mining activities and reclamation projects in the strait have gradually become the main factors to affect its geomorphologic evolution.

Storm surge disasters occur frequently along the Pearl River Estuary and are significantly affected by typhoon. This study analyzed the extreme surge at the Chiwan Station in the Pearl River Estuary during the past 30 years (1990-2019). The results show that the average annual storm surge in this region has not changed significantly recent years, but the extreme storm surge (99.9 quantile) has increased greatly (1.62 cm·a^-1), which means that the extreme storm surge disasters have continued to increase. In the past 30 years, the annual maximum storm surge in 20 years occurred during typhoons (accounting for 66.7%). In 2018, the maximum storm surge caused by super typhoon “mangkhut” reached 254 cm, which was the largest storm surge disaster in the past 30 years. The maximum response distance of storm surge to typhoon is about 500~800 km. Within the influence range of typhoon, the storm surge has an approximate linear relationship with typhoon intensity, and an exponential relationship with the distance from typhoon center. Different indexes of typhoon intensity (minimum pressure, maximum wind speed and maximum wind speed radius of typhoon center) were used to fit the storm surge with the distance from the observation station to the typhoon center, and it was found that the combination of wind speed and distance had the best description effect on storm surge (S_w=3.23e^-0.0036D×Γ_w-3.90)+4.48, R²=0.78, RMSE=9.69 cm). These results can improve the understanding of local storm surge disaster, provide validation data for typhoon storm surge simulation and reference for storm surge disaster risk assessment and response decision.

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.

A Reasonable interspecific composition structure of mangrove is the premise of effectively bringing into play the ecological value of mangrove wetland, and clear information of interspecific distribution of mangrove is an effective basis for mangrove ecosystem management and planning. For the mangrove wetland in the Hainan Bamen bay, based on GF-3 fully polarimetric Synthetic Aperture Radar (SAR) and GF-6 multi-spectral remote sensing data, 35 mangrove remote sensing features were extracted, and the importance ranking, feature screening and inter-species classification of mangrove were carried out using eXtreme Gradient Bo3osting (XGBoost) algorithm. The accuracy of XGBoost was compared with the traditional Support Vector Machine (SVM) and Random Forest (RF) machine learning algorithms, and the classification accuracy of three feature combination methods (preferred feature, multispectral feature and full polarization SAR feature) is compared based on the XGBoost algorithm.The purpose is to explore the applicability of XGBoost to mangrove interspecific classification and the ability of optical and fully polarized SAR data for mangrove interspecific classification. The results showed that: 1) The dominant features of mangrove species identification were multi-spectral spectral bands, polarization decomposition parameters, spectral vegetation index, and only the first eight (G, B, Y_s, NIR, EVI, RVI, NDVI, F_s) were used to achieve high classification accuracy. 2) XGBoost has the highest overall classification accuracy of 86.16%, and Kappa has 0.836. The classification accuracy of this algorithm is 3% ~ 8% higher than SVM and RF. The accuracy of mangrove interspecific classification using multispectral and fully polarimetric SAR was 10% ~ 12% higher than that used multispectral or fully polarimetric SAR alone. 3) The total area of mangroves in the Bamen bay was 797.58 hm², and there were 9 dominant true mangrove species, Avicennia marina, Bruguiera sexangular, Rhizophora stylosa, Sonneratia alba, Rhizophoraceae, Bruguiera gymnorrhiza, Lumnitzera racemosa Willd, Rhizophora apiculate, and Excoecaria agallocha Linn. The area of Sonneratia alba and Lumnitzera racemosa Willd were larger, accounting for 45.46% and 21.21% of the total mangrove area, respectively. In this paper, the interspecific classification of mangroves in the Bamen bay, Hainan province was studied based on high-resolution optics and fully-polarimetric SAR, which can provide data support and technical support for the protection and management of mangrove ecosystem.