We investigate the spatial distributions of transparent exopolymer particles (TEP) in the Pearl River Estuary in summer by analyzing the TEP concentration and size-fractions of Chl a. TEP concentration (calculated by the amount of xan-than; the same below) ranged from 85.0μg•L?1 to 1234.9μg•L?1, with an average of 690.9μg•L?1. The averaged TEP concentra-tions in the surface layer and bottom layer were 562.3μg•L?1 and 778.2μg•L?1, respectively, and for most stations lower con-centration of TEP was found in the surface layer as compared to the bottom layer. In the surface layer, TEP increased from the up stream to down stream, and decreased gradually towards the open sea and towards the east and west in the estuary. In the bottom layer, the maximum TEP was observed in the S3 near Humen. The correlation between TEP and Chl a suggests that the excretion of naon-phytoplankton (3-20µm) may contribute more to TEP than other size phytoplankton. The ratio of TEP/(Chl a) shows positive correlation with salinity but negative correlation with nutrition (NO3—N, NH4—N, SiO3—Si and total phos-phorus).

Mangroves are salt-tolerant plants of tropical and subtropical intertidal regions distributed mainly between latitudes 25°S and 25°N globally. They have high productivity, high return rate, high decomposition rate, and high resistance, which cover roughly 60%-75% of the world’s tropical coastlines. Mangroves are distributed over more than 118 countries with a total area near 17 million hectares in the world, and their net primary productivity is up to 2000 gC·m^-2·a^-1. They form a widespread ecosystem and also play an important role in the process of global change. Global climate change has aroused great concerns in the last three decades. Mangroves are a vulnerable and eco-sensitive ecosystem along tropical and subtropical intertidal shores that are regulated by both lands and oceans. They are one of the typical marine ecosystems that can be affected by global climate change. As an important ecological barrier along the coast, global climate change will also affect the survival and distribution of mangroves in the world. The present paper briefly reviews the impacts of global climate change on mangroves in terms of global warming, sea-level rise, atmospheric CO₂ concentration increase, and extreme weather. The ongoing global climate change will bring great challenges and opportunities to research, maintenance, and development of mangroves in the future.

The development of marine sciences depends on observations. Satellite is one of the most important observation platforms for marine research. Satellite data are of great significance in marine research. Since the beginning of this century, China has successfully launched several satellites dedicated to ocean observations, and preliminarily established a global ocean satellite observation system. According to the basic situation of marine satellite resources at home and abroad, we study and analyze the current situation of the application and development of marine satellite data in China, especially in terms of receiving, processing, management and application of marine satellite data, put forward the scientific research demand for satellite data in China's marine research, and probe into the existing problems and development strategies of the scientific application of marine satellite data in China.

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.

Because of their unique habitat and metabolic pathways, marine microorganisms can produce a variety of bioactive substances with novel structures and functions, which make natural products from these marine microorganisms become a research hotspot of new marine drugs. Combining the methods and perspectives of bibliometrics, we review in this paper the research status of natural products from marine fungi and marine bacteria, the artificial synthesis of natural products of marine microorganisms, the biological activity and druggability evaluation of natural products from marine microorganisms, to clarify the current status and development trend of natural products from marine microorganisms.

In recent years, marine natural products of fungal origin have gained considerable recognition, as many of them possess novel structures and interesting biological and pharmacological properties. This review includes 134 indole alkaloids of marine-derived fungi with their structures and activities published during 1991-2010. Of the indole alkaloids, there were 19 fumitremorgins, 22 notoamides, 18 cytochalasans, 9 fumiquinazolines, 11 indole terpenes, 21 peptides and other single indole alkaloids, and 34 bisindole alkaloids. These indole alkaloids showed not only unique structures but also a variety of important biological activities and had potential values in application.

Microbe-mediated nitrification is an essential part of global nitrogen cycle; and nitrite-oxidizing bacteria (NOB), which catalyze the second step of nitrification, have received more and more attention recently. Up to date, those isolated NOB have been identified as four phyla, belonging to seven genera. Among them, Nitrospira bacteria become a hotspot for research due to the high diversity and wide ecological distribution. In this paper, we reviewed the composition, phylogenetic relationship, nitrite oxidizing and carbon fixation pathways of NOB. We also emphasized the functional importance on global nitrogen and carbon of NOB, and highlighted research prospect for NOB.

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

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.

With the increase of marine plastic waste, marine microplastics have attracted more and more attention as a new type of marine pollution. At present, studies of the source, distribution and analytical approach of microplastics are well recognized. Most research focuses on plastic ingestion by marine organisms, and on the effects of microplastics adsorbing and releasing toxic chemicals. However, the role of microplastics as a vector for pelagic microorganism, phytoplankton and micozooplankton is poorly understood. In this review, we address three functions of microplastics as a biological vector. 1) Aggregation, it is easy for biofilms to form a microbial community on the surface of microplastics, which provide the means for horizontal transfer of organisms and genes, and may lead to the transformation or transduction of pathogenic gene, antibiotic resistance gene (ARGs), called genetic exchange. 2) Dispersal, the spread of harmful algal species, pathogenic bacteria and drug-resistant bacteria as well as other microorganisms may happen when the microplastics are freshly from the waste water flow, which potentially poses a risk of invasion when arriving in a new habitat with favorable condition. 3) A feeding enhancement concept, we propose this concept because a piece of microplastics is full of the attached biofilms, nutrients and organisms, which may attract large grazers or predators and can also improve their predation efficiency. As a result, these grazers/predators may seek pieces of microplastic as foods, which may cause more serious toxicological effects. The review focuses on the ecological effects of “microplastic + biology”.

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.

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.

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 investigated the abundance and species composition of phytoplankton community in the northern South China Sea (110°－120°E, 18°－23°N) from 10th to 29th August 2007, using 208 samples taken from 41 sampling stations. A total of 216 species belonging to 80 genera of 5 classes were identified. Diatoms contributed to 64.81% of the total phytoplankton species number and 89.11% of the total phytoplankton cell abundance; followed by dinoflagellates, which accounted for 30.56% of total phytoplankton species number and 10.62% of the total phytoplankton cell abundance. The dominant species were Thalassiosira sp., Thalassionema nitzschioides, Skeletonema costatum, Prorocentrum minimum and Gymnodinium sp.. Trichodesmium erythraeum that belonged to Cyanophyta was also commonly found at many survey stations. High phyto-plankton cell abundance was located in the Pearl River Estuary and in Taiwan Shoal. The horizontal distribution pattern of phytoplankton abundance was different in the surface and sub-surface waters. In the surface water, the average abundance of phytoplankton was 25.21×103cells•L?1 with a high value near the Pear River Estuary; while in the sub-surface water, the aver-age abundance was 9×103cells•L?1 with a high value in the Taiwan Shoal. On the whole, phytoplankton abundance was lower at deep-water stations (>200m) than at shallow-water stations (<200m). In general, the vertical profiles showed that total phytoplankton abundance presented a peak at 10m and then decreased with increasing water depth. The vertical distribution patterns of phytoplankton abundance also appeared to be different between deep-water and shallow-water stations. Diatoms abundance decreased with increasing water depth at the shallow-water stations, but formed a maximum peak at sub-surface (75m) of the deep-water stations; dinoflagellates abundance significantly decreased with increasing water depth, but evenly distributed in the water above 75m at the deep-water stations. The ratios of diatom to dinoflagellates showed a decline ten-dency approaching to the pelagic region. Higher productivity and phytoplankton abundance regions corresponded with a larger ratio of diatom to dinoflagellates. At the survey stations, the average Shannon-Wiener diversity index of phytoplankton com-munity was 2.8 in the surface water and 3.0 in the sub-surface water. High phytoplankton biodiversity located in the Pearl River Estuary and the coasts of Guangdong and Hainan provinces. The diversity of phytoplankton at the shallow stations was far enriched than that at the deep-water stations.

Using satellite measurements and high-resolution ROMS simulations, we analyze submesoscale characteristics of a typical anticyclonic mesoscale eddy in the Kuroshio Extension. Both satellite observations and high-resolution simulations show obvious submesoscale phenomena in the vortex region in the Kuroshio Extension. Our analysis results show that the strength of submesoscale kinetic energy is in close connection with kinetic energy of geostrophic velocity, which means that the frontogenesis may be an important way to enhance the submesoscale kinetic energy in the eddy periphery. Our analysis of the eddy’s vertical constructure shows submesoscale process can induce strong vertical velocity, which can be up to 100 m·day^-1. The strong vertical velocity can reach a depth of hundreds of meters, indicating that submesoscale process can provide an efficient way for sea surface-internal material exchanging and air-sea interactions.

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.

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

The densities of symbiotic zooxanthellae from 170 coral samples (with twenty-three species, thirteen genus, and eight families) collected during different seasons in Daya Bay, northern South China Sea, were analyzed in order to investigate seasonal variation of zooxanthellae density and its relationship to coral bleaching. The results showed that the density of zooxanthellae in all coral species had significant seasonal characters, with lower density in summer and proximately 2-fold higher density in winter. Coral symbiotic zooxanthellae density was mainly affected by seasonal fluctuation of sea surface temperature (SST) and solar radiation. It was speculated that coral bleaching (hot bleaching in summer) be the cause of the appearance features of coral when zooxanthellae density was reduced to a certain lower threshold, whereas coral cold bleach-ing happened in winter was associated with mortality that corals were directly killed by extremely low SST. High levels of zooxanthellae density in winter probably play an important role in protecting coral from low SST stress.

In recent years, the demand for marine sand and gravel increased sharply. Accordingly, its exploration and exploitation developed rapidly. To avoid naming confusion in the field of marine sand and gravel investigation and research, we analyzed the characteristics of the existing grading scales and sediment classification schemes based on years of marine sand and gravel investigation experience and previous research results, and put forward a set of grading scale and sediment naming method suitable for marine sand and gravel. Based on the Udden-Wentworth geometric series grading scale (phi scale), we proposed a particle size grading scale for marine sand- and gravel-related sediments, which divides the particle size grades into three categories of gravel (>2 mm), sand (2~0.063 mm) and mud (<0.063 mm), and nine subcategories. Based on preponderant grain-size composition, we proposed a “gravel-sand-mud triangular diagram + detailed naming of sandy and gravelly sediment” classification scheme, which embodies the idea of “detailed naming of sandy and gravelly sediments while simplifying naming of muddy sediments.” This can directly reflect the grain-size composition and content of marine sand and gravel.

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.

Coral reef ecosystem is one of the ecosystems with the highest primary productivity in the world. It plays an important role in maintaining marine biodiversity, preventing waves and consolidating beaches, and it is great resources for mankind. At the same time, the remote sensing geomorphological classification system of coral reefs is the necessary basis for the protection, management and sustainable development of coral reefs. However, there is no corresponding classification system taking coral coverage into account. Based on WorldView-2 high-resolution remote sensing image, we selected the reef of Zhaoshu Dao and Xisha Zhou in the north of Qilianyu Island, Xisha Islands, South China Sea as our study area. In this paper, coral coverage, regional geomorphic composition and hydrodynamic conditions are used to establish a coral reef geomorphic unit classification system suitable for remote sensing monitoring and are related to the survival of coral reefs. The method of object-oriented support vector machine (SVM) and random forest (RF) were used to extract the coral reef geomorphic units, and the accuracy of the extraction results was evaluated. The results showed that both SVM and RF classification methods can extract reef geomorphic units, and the classification accuracy was 87.59% and 79.81%, respectively. Aiming at the problem of misclassification and omission in the process of classification, we modified the classification results according to the causes and distributions of coral reefs. And the accuracy of modified classification was 91.3%, and the kappa coefficient was 0.9041. They showed that the coral reef geomorphic unit classification system constructed in this paper can meet the need of information extraction of coral reefs to some extent.

Chlorophyll a (Chla) concentration is an important indicator of phytoplankton biomass for estimating primary production, which exhibits inhomogeneous vertical distribution. In this study, optical measurements with high vertical resolution were used for studying the spatio-temporal variability of Chla profiles and its influencing mechanism, providing us much insights for understanding marine environmental dynamics in the South China Sea. In this study, an optical inversion method was proposed to retrieve Chla profiles from in situ measurements with high-spectral absorption/attenuation spectrophotometer in the northeastern South China Sea. Based on the in situ data of the Kuroshio Cruise in summer 2015, an empirical relationship between the absorption line height at 676 nm and Chla was developed for inverting Chla with a high accuracy (Chla=49.96×(a_LH(676) (676))^0.9339, the coefficient of determination R²=0.87, the root mean square error RMSE=0.16 mg·m^-3). Moreover, the response characteristics of Chla profiles to different hydrodynamic processes were studied. Results showed that large spatial differences existed in the vertical distribution of Chla. In the nearshore area, surface Chla varied from 0.42 to 1.57 mg·m^-3, which generally followed a decreasing trend with depth. Uniform vertical distribution of Chla in upper ocean was observed in the coastal upwelling region. The Subsurface Chlorophyll Maximum (SCM) layer is nearly ubiquitous in stratified waters of the open ocean, with its vertical structure being influenced by mesoscale processes. The depth of SCM ranged between 34 and 100 m, which showed consistent variability with the isopycnal depth of 1023 kg·m^-3. The SCM layer was uplifted to about 34 m due to the mixing effect in the upper ocean caused by Kuroshio intrusion in the western area of Luzon Island. The uplifting and widening of the SCM layer were also observed in the area affected by a cold eddy, with obviously different features in the eddy center from that on the eddy edge.

Human activities around the islands are having growing impacts on aquatic ecosystems in the region, with increasing eutrophication and algal bloom events, despite the fact that the development of island tourism has brought considerable economic benefits to the locals. In this paper, we discuss the potential impacts of the Pearl River discharges and human activities on the aquatic ecological status around the natural estuarine islands, based on comparative study of environmental characteristics and phytoplankton distribution in the adjacent waters of representative islands (Miaowan Island, MI; and Wailingding Island, WI) in the Pear River Estuary during the wet season and dry season. In the dry season, 76 and 74 phytoplankton species were found in the waters around WI and MI, with average abundance values of 2.62 × 10 ⁴ and 2.08 × 10 ⁴ cells·L^-1, respectively. In the wet season, the numbers of species were 38 and 47, and the average abundance values were 52.91 × 10 ⁴ and 170.57 × 10 ⁴ cells·L^-1, respectively. In the wet season, Skeletonema coatatum was the predominated species around both islands, while in the dry season, the dominant species were Chaetoceros affinis in WI and Cylindrotheca closterium in MI. The phytoplankton species diversity indexes of both islands in the dry season were higher than those in the dry season. Nano-phytoplankton was always the most predominated group among three size-fractionated phytoplankton groups, although in the wet season, the contribution of micro-phytoplankton increased from 16.32 % to 26.75 % and from 12.12 % to 24.78 % in MI and WI, respectively. Among the pico-phytoplankton groups, Synechococcus (Syn, ~10⁷ cells·L^-1) and eukaryotic pico-phytoplankton (Euk, ~10⁸ cells·L^-1) were detected during our investigation. The comparative analysis results with environmental variables showed that the spatial distribution patterns and seasonal variation of phytoplankton were affected by several factors. The seasonal variation was regulated by the intensity and affecting area of Pearl River discharge, the relative salinity and nutrient input. In the wet season, the island shielding effect (ISE) showed significant influences on spatial distribution of phytoplankton abundance around each island, with higher biomass often found in the area facing the Pearl River flow direction; however, the phytoplankton community structure was not significantly affected by the ISE. In the dry season, the horizontal and vertical distributions of phytoplankton showed much smaller variation, and were probably impacted by human activities and intensified vertical mixing.

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.

Exotic species are only used in some places in China for mangrove restoration, as they often perform better than native species on these desired restoration sites often with highly stressful habitats. Here, we conducted a mesocosm experiment to detect the differences of survivability between exotic and native mangrove seedlings under accretion/erosion disturbances on tidal flats, using exotic species Laguncularia racemosa and native pioneer species Avicennia marina as examples. Our results demonstrated that for both species the erosion resistance of seedlings correlated positively with root-to-shoot length ratio. Sediment accretion disturbance inhibited the root development of seedlings so that the root-to-shoot length ratio increased, while sediment erosion promoted root elongation with the root-to-shoot length ratio decreased. Compared with the native species A. marina, exotic species L. racemosa seedlings have greater root-to-shoot ratio, and are thus more resistant to erosion with better adaptability to sediment dynamics via root elongation. Our study indicates that the exotic species L. racemosa are more adaptable to erosion disturbances on tidal flats than the native species A. marina. These findings shed light on the selection of tree species and suitable planting sites for mangrove restoration, and might provide helpful insights into assessing the risk of species invasion in mangrove ecosystems.

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.

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

In situ hydrographic data of sea surface salinity (SSS) revealed a freshening trend in the northern South China Sea (SCS) during 2004—2012, which was the freshest in 2012. Such freshening was also found in the UK Met Office EN4 objective analysis product and the ocean general circulation model for the Earth Simulator (OFES) output during 1993-2014, particularly west of Luzon Island and in the southeastern SCS. The salinity budget analysis in the upper layer indicated that the fresh water forcing and horizontal salinity advection contributed to the trends of SSS west of Luzon Island and in the western SCS, respectively. The excessive precipitation in summer accounted for the decrease of SSS to a great extent west of Luzon Island, which was associated with the strengthening trend of the Walker Circulation.

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.

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