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.

Mono-, bi-, and tri-algal cultures were applied to Aureococcus anophagefferens, Skeletonema costatum, and Chattonella marina under two temperatures of 20℃ and 25℃, to investigate species-specific interaction and competition in different temperatures. Single cultures showed the environmental carry capacity (K) for A. anophagefferens and S. costatum were significantly reduced by increased temperature, indicating they are sensitive to rising temperature. In contrast, the inherent growth rate (r) for C. marina significantly increased at 25℃ whereas K remained the same as that at 20℃. In contrast to the death under A. anophagefferens addition at 20℃, K of C. marina increased 120% at 25℃. Although r of S. costatum was promoted by C. marina addition at both temperatures, its K showed from 43% increase to 48% decrease from 20℃ to 25℃. The change of temperature did not influence the results of co-culture of S. costatum and A. anophagefferens with 40% increases and 60%-70% decreases of K at both temperatures. The results of bi-cultures indicated that interspecies competition is not only influenced by fixed interaction relationship of co-cultured species, but also by difference of algal temperature adaptability. In tri-algal cultures at 20℃, the inhibition rate of A. anophagefferens and the stimulation rate of S. costatum both reached the highest of 79% and 108%, respectively, which probably illuminated a synergistic effect within three algal interaction.

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.

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.

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.

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.

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.

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.

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.

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.

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.

A bloom caused by giant colonies of Phaeocystis globosa was observed in Mirs Bay in late January 2021. To better understand the bloom dynamics and their controlling factors, in situ investigations on phytoplankton succession, colony numbers and size, inorganic nutrient concentrations, and other environmental factors were conducted from Jan. 20 to Feb. 1, 2021. The phytoplankton bloom, initiated by an early Skeletonema costatum bloom, was followed by a large bloom of P. globosa. Phytoplankton community was dominated by the population of Akashiwo sanguinea after the decline of P. globosa bloom. The maximum colony density observed during the P. globosa bloom was up to 69 colonies ·L^-1, while colony diameters were up to 1.2 cm. Analytic results showed that ammonium and nitrate were the key environmental factors that initiated the P. globosa bloom. In addition, turbulence and competitive advantage over S. costatum under phosphate limitation might also play important roles in the occurrence of the bloom. The bloom of A. sanguine could be the major cause for the decline of P. globosa bloom. Overall, the P. globosa bloom was a combined result of various physical and chemical factors and biotical factors.

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.

Food resources are crucial for the survival and reproduction of marine animals. The trophic niche of marine organisms refers to the ecological roles and functions in marine ecosystem. It plays an important role in studying interspecific relationship, resource partitioning, community structure and function. In this study, by collecting the relevant research on trophic niche of marine animals, we review current research methods (stomach content analysis, bulk tissue stable isotope analysis, fatty acid profiles and compound-specific isotopic analysis) and their applications by focusing on their corresponding ecological models on quantitively evaluating the breadth and overlap of the trophic niche. Moreover, potential development and directions for further studies are presented, with the aim of providing supports for future research on feeding ecology of marine animals.

Macroalgae, together with corals, provide faunal foods and habitats in clear tropical waters, maintaining the rich biological diversity in coral reefs. In this paper, we compared biochemical compositions and photosynthetic features, as well as photophysiological responses to temperature rise of two red algae (i.e., Grateloupia ellipitica and Liagora samaensis) and two green algae (i.e., Udotea flabellum and Halimeda discoidea), the dominating macroalgae species in the Zhongsha Atoll of the South China Sea. Results showed that the red algae contain less chlorophyll a and carotenoids than the green ones, but contain the unique phycoerythrin and phycocyanin. Both the light compensation point (E_C) and dark respiration (R_d) of the red algae are lower than the green algae. The temperature rise enhances E_C, R_d and light utilization efficiency (α), as well as the daily carbon fixation of both red and green algae; and it lowers the saturation irradiance (E_K) of the former algae species but enhances the maximum photosynthetic oxygen evolution rate (P_max) of the later species. Moreover, the temperature rise enhances the photosynthetic rate of the red algae under lower light, but reduces it under higher light, while such temperature-induced enhancement on the photosynthetic rate of the green algae occurs throughout the measured light range. Considering the inter-specific photophysiological characteristics of the four macroalgae as well as the effects of temperature, the temperature rise would benefit the photosynthesis of macroalgae in the Zhongsha Atoll and benefit the red algae better than the green algae.

Artificial proliferation and release is the most effective and rapid method to restore Limulus resources. Understanding and grasping the influence of environmental factors on the growth of juvenile Chinese horseshoe crab (Tachypleus tridentatus), and then choosing a suitable time and sea area for release are the key steps to ensure the success of manual release. Under laboratory conditions, we studied the effects of different salinity (5‰, 10‰, 15‰, 20‰, 25‰, 30‰, 35‰, and 40‰) on the survival rate, molting rate, molting weight gain rate, Na⁺-K⁺-ATPase activity, immune enzyme activity, and antioxidant enzyme activity of juvenile Chinese horseshoe crab. The changes of growth, molting, osmotic adjustment, immunity, and antioxidation of the juvenile horseshoe crab at different salinity levels were recorded. The culture experiment lasted for 56 days. The results showed that different salinity levels significantly affected the survival rate, molting rate, average weight of the 2nd instar horseshoe crabs, and molting weight gain rate of the juvenile horseshoe crab (P< 0.05), which increased at first and then decreased with increasing salinity. Regression analysis of molting rate, molting weight gain rate and salinity showed that the optimum salinity for molting and growth of young horseshoe crab were 24.10‰ and 24.94‰, respectively. The Na⁺-K⁺-ATPase activities of the 1st and 2nd instar horseshoe crabs increased at first and then decreased significantly with the increase of salinity (P< 0.05). The acid phosphatase (ACP) activities of the 1st instar larvae in the 35‰ and 40‰ test groups were significantly higher than those in the other test groups, while the alkaline phosphatase (AKP) activities of the 5‰ test group were significantly lower than those in the 25‰ test group (P< 0.05). The activities of ACP, AKP and lysozyme (LZM) of the 2nd instar larvae did not change significantly under different salinity conditions (P> 0.05). The catalase (CAT) activities of the 1st instar larvae in 35‰ and 40‰ test groups were significantly higher than those of low-salinity test groups (P< 0.05). And the glutathione peroxidase (GSH-Px) activities of the 2nd WHAT tended to increase with the increase of salinity, and those in 10‰ test group were significantly lower than those in 35‰ and 40‰ test groups (P< 0.05). We show that salinity had a significant effect on growth, molting, Na⁺-K⁺-ATPase activity, immune index, and antioxidation of the juvenile horseshoe crab. The optimum salinity for molting was between 24‰ and 25‰. Too high or too low salinity will cause the growth rate, survival rate of juvenile silver carp, the osmotic adjustment ability, immunity, and antioxidation of the juvenile horseshoe crab to decrease significantly.

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.

Driven by the southwest monsoon, an offshore jet is usually formed in the western South China Sea (SCS) and sandwiched by a cyclonic eddy in the north and an anticyclonic eddy in the south, which affects the ecosystem of the region. Using in-situ and satellite data in September 2014, we analyzed the impact of this jet with two eddies on phytoplankton size structure in this region. The data showed that picophytoplankton (0.2~2 µm) dominated the surface, averaged at 76.7% of the total chlorophyll. The contributions of nanophytoplankton (2~20 µm) and microphytoplankton(20~200 µm)in the jet area were respectively higher, and had a positive relationship with the total chlorophyll. Comparatively higher percentage of microphytoplankton appeared in the anticyclonic eddy at surface (average 10.3%) than in the cyclonic eddy (average 3.6%). The results suggested that physical processes significantly influenced summertime surface phytoplankton size structure in the western South China Sea. Both the jet and eddies can affect phytoplankton size structure by increasing the contribution of microphytoplankton. Surface horizontal advection of phytoplankton by the northeastward jet formed the coastal upwelling area and was the main source of microphytoplankton in the open sea. The interactions of convergence and divergence in the eddies with the jet formed a chlorophyll front and increased the microphytoplankton component. Upwelling in the center of the cyclonic eddy brought up nutrients, which increased the percentage of the microphytoplankton component.

Variability of light backscattering coefficient in the ocean can be used to quantify the biomass of phytoplankton, which can be applied in remote sensing and optical profile observation platforms to obtain the characteristics of phytoplankton biomass spanning various spatio-temporal scales and vertical profiles in the ocean. Significant variabilities of the bio-optical properties exist off the eastern Hainan coast, being influenced by upwelling. Based on the in-situ data collected off this area in 2013, we established a regional algorithm between the backscattering coefficient of particle [b_bp] and chlorophyll a concentration [Chl a]. The algorithm is based on the assumption that the particle backscattering coefficient is determined by the constant background backscattering value independent of Chl a and two components by pico (< 2 μm) and large(>2 μm)phytoplankton. Results show that the modelled b_bp values agree well with measurements, especially for low Chl a concentration. The relationships between b_bp and Chl a vary in different water layers. For example, the constant background backscattering values at the bottom layer are significantly higher than those in the upper layer, indicating that driven by upwelling, the increasing concentration of submicron particles not covariant with Chl a might produce an increasing backscattering coefficient. At the chlorophyll maximum layer, the background backscattering values are significantly lower than those in the upper water, and the contribution percentage of background backscattering value is about 21%~35%. With the increase of Chl a concentration, the contribution of large phytoplankton to b_bp increases significantly, accounting for 50% or higher, while the contribution of pico phytoplankton remains stable around 40%. Understanding the regional relationship of b_bp and Chl a off the eastern Hainan coast can improve our understanding of marine biogeochemical processes in the region.

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.

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.

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.

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.

Based on the daily-averaged data derived from the NCEP/NCAR reanalysis dataset and using the single-layer (500hPa, and 850hPa) and the whole-layer (four layers) EOF methods, the leading modes of the subtropical high with vertical structure are extracted. It is found that the modes obtained by different ways are the same, which implies that there truly exist the same spatial distribution and temporal-change features from high to low of the subtropical high. Further, by applying the wavelet energy spectrum, it is found that there exist marked low-frequency oscillations of 20−30 days and 30−60 days. Considering the weather in 1995, the possible mechanism that the low-frequency potential wave at different latitude restricted the subtropical high in 1995 is diagnosed, i.e., the low-frequency potential wave of sub-tropical areas restricted the medium-term movement with a period of 20 days of the main body of the subtropical high, while the short-term process with a period of 5−10 days of the western subtropical high was related to the accumulated disturbance energy of the low-frequency potential wave coming from high latitude and tropical areas in the western Pacific region.

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.

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.

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.