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.

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.

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.

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.

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.

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.

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.

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.

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.

To understand the vertical distributions of zooplankton in regions of the “Haima” cold seep and the possible effects of seep activities, zooplankton samples were collected from 0 to 1250 m at five stations in September 2020. These zooplankton samples were analyzed using ZooScan image analysis system. The abundance, biovolume and size spectra of zooplankton in different water layers were obtained in this study. The results showed that zooplankton abundance and biovolume were mainly occurred in the 0 ~ 100 m water layer. Below 100 m, zooplankton abundance and biovolume decreased rapidly with increased depth. The average abundance and biovolume of zooplankton were only 8.33 ind·m^-3 and 12.10 mm³·m^-3 at the layer of 1000 ~ 1250 m. In general, copepods were the dominant zooplankton in each water layer, and the proportion of gelatinous zooplankton increased in deep layer. The slope of normalized biovolume size spectra (NBSS) in the regions of the “Haima” cold seep ranged from -0.94 to -0.57, and the intercept ranged from -2.10 to 5.94. From surface to bottom, the slope of NBSS increased while the intercept decreased gradually. This indicated that the productivity of planktonic ecosystem declined gradually from surface to bottom, but the energy transfer efficiency of pelagic food web increased gradually. The layer of 1000 ~ 1250 m at ROV1 station showed abnormal size spectrum characteristics, and the slope “a” is significantly lower than that of other stations in the same water layer. It suggested that the zooplankton community might be affected by cold seep activities.

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.

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.

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.

The change characteristics of physio-biochemical indexes of four mangrove plants Rhizophora stylosa, Kandelia obovata, Bruguiera gymnorhiza and Ceriops tagal seedlings after 28 days of heavy metal aqueous solution stress at different concentrations were studied, including soluble protein content, superoxide dismutase (SOD), and peroxidase (POD) activity and oxidative damage marker malondialdehyde (MDA) content. The study results showed that the SOD and POD activities in the leaves of the four plants all increased first and then decreased. When the Rhizophora stylosa were treated with 10 times the heavy metal aqueous solution, the Kandelia obovata and Bruguiera gymnorhiza were treated with 5 times the heavy metal aqueous solution, the Ceriops tagal were treated with 1 time the heavy metal aqueous solution, it has good antioxidant enzyme activity during heavy metal aqueous solution treatment, which can effectively remove active oxygen and reduce oxidative damage. Under the same concentration of heavy metal aqueous solution treatment, the results of MDA content showed that the damage of the Rhizophora stylosa was the least, the Kandelia obovata and the Bruguiera gymnorhiza were equally damaged, and the Ceriops tagal were the heaviest. The ability of Rhizophora stylosa to resist heavy metal stress is stronger than Kandelia obovate and Bruguiera gymnorhiza, while the ability of Ceriops tagal to resist heavy metal is the weakest. These results show that mangrove plants have strong ability for anti-pollution, which has important guiding significance for mangrove ecological restoration and protection in China.

Surface sediments were collected on the Dongshan Bay of Fujian Province China in November 2016. Dinoflagellate cysts were analyzed in the sediments with a particular focus on the distribution of toxic and harmful dinoflagellate cysts. The contents of biogenic elements were examined to reveal the relationships between cysts and biogenic elements. A total of 22 cyst taxa were identified, including 14 autotrophic and 8 heterotrophic taxa. Cysts of Protoperidinium dominated in the sediments. Shannon-Wiener diversity index (H') ranged from 1.70 to 2.38, and Pielou’s evenness index (J) ranged between 0.64 and 0.84. Cyst concentrations ranged from 70.6 to 136.4 cysts·g^-1, with an average of 107.2 cysts·g^-1. Cyst concentrations were lower in the Zhangjiang estuary and Bachimen area. The high percentages of cysts of heterotrophic dinoflagellates (averagely 75.5%) suggested the high primary productivity and eutrophication level on the Dongshan Bay. Notably, cysts of seven toxic and/or harmful algal bloom (HAB) species were identified in this study, including cysts of the paralytic shellfish toxin (PSP) producers Alexandrium ostenfeldii and A. catenella/tamarense, the yessotoxin (YTX) producers Gonyaulax spinifera, the potential azaspiracid (AZP) producer Azadinium sp., the ichthyotoxic species Polykrikos hartmannii, and the bloom species Barrufeta bravensis and Scrippsiella acuminata. Cysts of the HAB species generally occurred in small numbers, however, high numbers of cysts of G. spinifera in some stations need to be concerned.

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.

Transcriptome differential analysis revealed that the DEAD-box RNA helicase family plays an important role in the response of Lumnitzera littorea to low temperature stress. In this study, we analyzed the bioinformatic properties, tissue-specific expression and differential expression of four genes, LlDEAD12, LlDEAD32, LlDEAD43 and LlDEAD65, in L. littorea seedlings under low temperature treatments. The results showed that LlDEAD12, LlDEAD32, LlDEAD43, and LlDEAD65 are hydrophobic proteins with secondary structures consisting of α-helix, β-turn, extended chain and irregular coiling, with many glycosylation sites and phosphorylation sites, and do not contain transmembrane structural domains or signal peptides. Subcellular localization analysis showed that LlDEAD12 and LlDEAD32 are localized in the cytoplasm and nucleus, respectively, while LlDEAD43 and LlDEAD65 are localized in the mitochondria. Comparative analysis of protein amino acid sequences indicated that LlDEAD12, LlDEAD32 and LlDEAD43 had similar affinities to DEAD-box RNA helicase enzymes of Pinus massoniana, Eucalyptus grandis and Punica granatum, respectively. Analysis of the tissue expression specificity of the four genes by fluorescence quantitative PCR revealed that LlDEAD12 and LlDEAD32 highly expressed in leaves, while LlDEAD43 and LlDEAD65 highly expressed in stems and flowers, and none of the four genes expressed in roots, indicating that the regulation of growth and development of L. littorea by these four genes was mainly concentrated in leaf, stem and flower organs. The expression of these four genes was significantly suppressed in L. littorea seedlings under low temperature stress, indicating that these four genes are involved in the molecular response of L. littorea under cold temperature environment, among which LlDEAD12 and LlDEAD32 may be involved in chloroplast development, and LlDEAD43 and LlDEAD65 may be involved in maintaining the stability of mitochondrial function. Our results provide a scientific foundation for the breeding of cold-resistant seedlings of L. littorea.

In this experiment, 'Acanthopagrus latus', an important economic fish in the southeast coast of China, was used as the experimental material. The SNPs were discovered by DNA re-sequencing in fifty A. latus, and partial SNPs were genotyped using MassARRAY^® DNA mass spectrometry. The results are presented as followed: 1) the re-sequencing of 50 wild A. latus generated a total of about 233.48 GB raw data. After filtering adapters and low-quality data, 233.43 Gb clear data were obtained. The average data size of each sample was 4.67 GB, and the average GC content was 42.85%, Q20 is above 96.56%, Q30 is above 91.1%, and the comparison rate between the clear data and the reference genome is 98.06% ~ 99.47%; 2) a total of 13843766 SNPs were discovered from 50 individuals by GATK, and 6501 high-quality SNPs were obtained after filtering; 3) thirty SNPs from the high-quality SNP were selected randomly and genotyped using MassARRAY technology. The detection rate (loci that can be genotyped) was reached at 98%. The consistency between the genome re-sequencing and the MassARRAY results was 64.83%, which indicated that the two techniques were different in detecting SNPs. In summary, a method for mining, filtering and validating SNP markers of A. latus bream has been established in this study, and the developed SNP loci can be used in evaluation of proliferation and stocking effect and genome selection breeding of A. latus in the future.

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).

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.

Seagrass Halophila beccarii Asch has long been neglected due to its small size, and the coastal nitrogen loading accelerates its degradation. The physiological response of H. beccarii to ammonium toxicity is not clear. Based on the lab cultivation experiment, the effects of ammonium enrichment in four gradients (Control, 25 μmol·L^-1, 50 μmol·L^-1 and 100 μmol·L^-1) on the photosynthesis, chlorophyll, ammonium ion flux in mesophyll cell, glutamine synthetase activity and nutrients of H. beccarii are studied using chlorophyll fluorescence, non-invasive micro measurement technology and targeted metabolomics. The results showed that the maximum relative electron transport rate exhibits a trend of low ammonium enrichment>moderate ammonium enrichment>control>high ammonium enrichment. High ammonium enrichment significantly reduces the maximum relative electron transport rate and light utilization efficiency, while decreasing the carbon pool for ammonium assimilation. Meanwhile, ammonium enrichment significantly enhances the ammonium ion flux and glutamine synthetase activity, assimilating excess ammonium into amino acids. However, ammonium enrichment reduces the amino acid contents, which might be caused by that the amino acids are used to synthesize organic substances such as key secondary metabolites to further regulate and adapt to ammonium toxicity. Therefore, moderate ammonium enrichment is beneficial for the photosynthesis and growth of H. beccarii, while high ammonium enrichment has toxic effect on H. beccarii.

Exploring the cytotoxic compounds from marine natural products is one of the most important tasks for the discovery of anticancer agent in recent years. In this study, based on the marine natural product Piperafizine B, fourteen novel glycosyl-2, 5-diketopiperazine derivatives (1a-i, 2a-f) have been designed and synthesized by the glycosylation on the side phenol group at the 6-position of the 2, 5-diketopiperizine ring. The solubilities of the derivatives are obviously improved in both DMSO (dimethyl sulfoxide, 1.5~27.9mg·mL^-1) and phosphate buffer (0.1~0.9mg·mL^-1, pH=7.4). The cytotoxicity results show that some of the derivatives present good activities with the IC₅₀ values ranging from 1.0~9.1μmol·L^-1, and exhibit selective inhibitory activities on Huh-7 cell lines. Among the derivatives, compound 1c has the best inhibitory abilities on the cell lines K562, A549 and Huh-7 with an IC₅₀ values at 1.0, 3.6 and 3.3μmol·L^-1, respectively, while compounds 2a-f have no observable cytotoxicity.

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.

Zooxanthellae, bacteria, and reef—building corals have a close symbiotic relationship, but the phycosphere bacterial community of zooxanthellae is poorly studied. In this study, six strains of zooxanthellae from five genera were cultured in vitro, among which two were free-living zooxanthellae strains (type E) and four were anchorage-dependent living zooxanthellae strains (type A—D). Bacterial community analysis was performed by collecting three different particle size fractions (0.2-3μm, >3μm, and settling algae cells). Results showed that the phycosphere bacterial communities between the two lifestyle algal strains were significantly different. The bacterial species richness in anchorage-dependent living strains was significantly higher than that in free-living strains. Seven bacterial genera were observed to be present in all the algal strains, representing the core bacterial communities of zooxanthellae. Comparing the core bacterial communities in three particle size samples, we found that the core bacterial communities in >3μm samples and in 0.2-3μm samples are highly similar, but both were significantly different from the “Settling” samples.

Selecting 767 papers published in the Journal of Tropical Oceanography (JTO) from 2012 to 2021 as research objects, we carried out bibliometric metrology and visualization analysis with CiteSpace software to understand the development of this periodical journal during this decade, and provided advices for the construction and management of JTO in the future. The results showed that the impact factors and the number of articles published in JTO had a descend and ascend trend in the past ten years, ranking in the forefront among Q2 marine journals, and entering Q1 in 2018 and 2019, respectively. JTO has distinct characteristics on the research of tropical oceans, especially the South China Sea. The key research areas include mesoscale vortices, numerical simulation, upwelling, coral reefs, phytoplankton, etc. JTO has a group of high-level core authors, mainly from the University of Chinese Academy of Sciences and the South China Sea Institute of Oceanology, Chinese Academy of Sciences. Their research interests include marine geology, marine geophysics, ocean circulation, ocean remote sensing, marine biology and ecology, etc. Among the papers with high citation rate and high download rate, the review papers occupy a high proportion. In recent years, through the online launch, new media promotion and other means, the number of paper downloads has continuously increased and the influence of JTO has gradually enhanced.

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.

As the unique deep channel that connects the South China Sea (SCS) with the western Pacific Ocean, Luzon Strait is also the key oceanic passage that modulates the SCS circulation and its thermodynamic characteristics. Influenced by large-scale western boundary current, meso-scale eddies, tropical cyclones and other factors, Luzon Strait transport (LST) exhibits significant multi timescale variability. Tropical cyclones are strong and localized low-pressure weather systems that occur frequently in the area, therefore, understanding the dynamic connection between tropical cyclones and LST is one of the most essential topics in oceanography research. This study reviews the research progress in the characteristics of tropical cyclones near the Luzon Strait and its impact on the Kuroshio, ocean circulation and LST, and reveals their recent development. We further suggest that the future study should focus on the modulating mechanisms of the tropical cyclones on the LST and evaluate their contributions to the interannual variations of LST.

The global seagrass bed ecosystems are facing multiple threats. For instance, the seagrass Phyllospadix (Zosteraceae) is of great ecological importance and fishery value. And one of the seagrasses surfgrass, Phyllospadix, is relatively poorly studied. In particular, there are more study gaps in the description, micro-observation and germination process of the main breeding carrier, seeds of surfgrass, as well as in the identification of DNA molecules. In this study, Phyllospadix iwatensis was used as the study object to describe its growing environment, external characteristics of seeds, internal structure, germination process, etc. in both qualitative and quantitative ways, and the results show that fruits and seeds of surfgrass have the adaptability on external form and internal structure in the marine environment, and have the advantage of becoming tool species for vegetation restoration in coastal zone. External morphological features include unique fruit inflorescence and fruit shape, as well as wing-like structure and medial mane, of which the fruit inflorescence is curved shrimp-shaped with an average length of 3.4 cm and the fruit is horseshoe-shaped with a diameter of 3-4 mm. The internal structural features include a large proportion of endosperm and complex anatomy of the peel and seed coat. This study complements the lack of in-depth study on the seeds of marine submerged plants, such as surfgrass, and provides valuable suggestions and reference contents for the protection of surfgrass and other types of seagrass seed banks, as well as the restoration of seagrass beds, and also yields a basis for the practical application of surfgrass in seedling restoration.