Quantifying the impacts of human-induced (such as dredging for navigational channels) or natural (such as global sea level rise) interventions on estuarine environment is an important issue for estuary and coastal studies. For given simplified geometry and dynamics, analytical models are capable of rapidly identify the influence of human-induced or natural interventions on estuarine environment, which are invaluable tools for exploring response of tidal dynamics to external forcing. In this study, a one-dimensional hydrodynamic analytical model was used to explore the response of tidal dynamics in terms of different constituents to variation of tidally averaged water depth (mimicking the channel dredging and deposition) in the Guadiana estuary in Portugal, building on previous studies on nonlinear frictional interaction between different tidal constituents. The results show that the influence of variable depth on tidal dynamics in the seaward reach (x=0-60 km) is stronger compared to that in the landward reach (x=60-78 km). In particular, the influence of variable depth on the predominant semi-diurnal tides (M₂, S₂, N₂) is larger than that on diurnal tides (K₁, O₁). Analytical results also indicate that the basic tidal dynamic pattern along the estuary is more or less the same for a less intensive dredging of less than 2 m, while the pattern may substantially change for an intensive dredging activity. In addition, the channel bed deposition will weaken the tidal dynamics with a decrease of tidal amplitude, velocity amplitude, tidal wave celerity, and the phase lag between velocity and the elevation also decreases.

The real-time motion state of large-scale surface ocean can be obtained by remote sensing technology, while the motion state of the interior ocean can only be obtained by the fixed point observation, which cannot achieve the real-time monitoring of a large area. Based on the basic principles of ocean dynamics, we construct a relationship model between ocean surface and internal motion state in three-dimensional space under the barotropic shallow water continental shelf model. Based on the data of ocean surface velocity and direction detected by remote sensing, combining with the state parameters of wave height and speed, we use the finite difference method to obtain the information of speed and direction of the undercurrent. The inversion results conform to the law of ocean dynamics, reflect the overall distribution of the undercurrent and expand the application range of radar remote sensing.

The spring-neap tidal variation of the estuarine turbidity maximum (ETM) in the Pearl River Estuary (PRE) is studied, using the Regional Ocean Modeling System (ROMS). The longitudinal and lateral distribution of suspended sediment concentration (SSC) shows that the ETM is located between 22.3°-22.45°N and varies with flood and ebb tides. The main mechanism on the ETM formation is the bottom convergence generated by residual current. The location of the ETM is determined by horizontal advection. The sediment source is resuspended sediment on the shoal during spring tides. The fine sediment deposited on the shoal during neap tides is resuspended and transported downstream to the stagnation point during spring tides, and then trapped on the west shoal. The tidal pumping effect can transport suspended sediment seaward (landward) during spring (neap) tides, while the vertical shear always transports suspended sediment landward, both leading to the convergence of sediment in the ETM. The decomposition of residual current shows that the bottom landward residual flow is mainly induced by density difference, followed by asymmetric tidal-mixing. Moreover, there is little difference in residual currents between spring and neap tides.

Tidal wave propagation and tidal asymmetry in the Pearl River Estuary and Lingding Bay water areas affect estuarine dynamic environment and material transport in the areas. Based on tidal level statistics during June 2011 to July 2011 measured by stations set up in four east estuaries in the Pearl River and Lingding Bay, the theory of convergent estuarine tidal amplitude along the way is used for obtaining an analytic solution, and characteristics of tidal wave propagating from Guishan Island toward upstream is illustrated. Based on harmonic analysis, theory of skewness and method of constituent combination, tidal asymmetry distribution characteristics of east and west coasts in Lingding Bay, Hongqi outlet and Jiao outlet are explained; contrasts with analytical results, main control factors and response regulation of water area between Lingding Bay to Hu Estuary are noted. Our research shows that in Lingding Bay, which is approximately consistent with exponential convergent estuary, the tidal amplitude nearly accords with the change rule of the tidal amplitude analytical solution in exponential convergent estuary. The reason why tidal amplitude in the east coast being higher than in the west coast is that the water depth of the east coast is larger than that of the west coast; secondly, tidal amplitude is impacted by the Coriolis force. Although propagating wave is influenced by roughness consumes energy, and by energy transfer among constituents with different frequencies caused by nonliner effect, the convergence effect of convergent estuary can make sure that amplitudes of astronomical constituents keep steady even rise up in convergent segment, and the impact extent of convergence effect in semi-diurnal constituent is larger than that in diurnal constituent. Each nonliner term’s effect promotes the generation of shallow water constituent and increases energy continuously, making amplitude of shallow water constituent rising within a distance. Skewness of tidal asymmetry changes from ebb dominance in bay mouth to flood dominance in bay bottom, and transform to flood dominance at the line of Chiwan to Jinxing Port, which is located in the middle of Lingding Bay. It suggests that the decrease of ebb dominance asymmetry, which is caused by interaction of astronomical constituents K₁-O₁-M₂ with different frequency, and the increase of flood dominance asymmetry, which is caused by interaction of astronomical constituent M₂ with its shallow water overtide M_4, leads to the phenomenon. Water depth is the most important factor, which influences tidal asymmetry in properties of a convergent estuary.

In this paper, the circulations of Typhoon Nock-ten with abnormal northward turning and of Typhoon Omar with abnormal westward turning near Taiwan Island are analyzed and compared. The total flow is decomposed into climatic and anomalous flows, and the abnormal turning paths of Nock-ten and Omar are forecasted by using the beta-advection model. The results are as follows. 1) Analyses of total flow at 500 hPa reveal that the main influencing environmental systems include the western North Pacific subtropical high and the west trough during the period of unusual north-turning; the western North Pacific subtropical high and the Continental high merged and consolidated at the north and one typhoon in the southeast, which favored Orma’s unusual western turning. 2) Anomalous flows manifested that southwesterly wind gradually aggrandized on the south side of Nock-ten, the southeasterly wind gradually changed into southerly wind on the east side, forming a northwardly "belt" at the unusual north-turning time; there maintained an anticyclone during the unusual west-turning time on the north side of Orma. 3) The generalized beta-advection model is applied to identify the tracks of Nock-ten and Omar. Results show that the north-turning Nock-ten track is forecasted well by considering the climatic and anomalous flows, whereas the west-turning Orma is forecasted well with the consideration of anomalous flow.

Viruses are tiny intracellular parasites and rely on the cellular machinery for replication. Usually, internalized viruses hijack the microtubule for effectively moving from cell membrane to specific compartments for replication. However, the elaborate process of microtubule-dependent transport of viruses in live cells remains unclear. Singapore grouper iridovirus (SGIV) belongs to genus Ranavirus, family Iridoviridae, which is an important viral pathogens marine fish, and causes serious economic losses. In this study, different microtubule-dependent behaviors of SGIV were analyzed by the single-particle tracking technique. We found that some SGIV particles showed bi-directional and active motions from cell periphery to the microtubule organizing center (MTOC), with the highest speed reaching 0.2μm·s^-1. When reaching the microtubule intersection, SGIV particles slowed down. Then, some virus was confined near the intersection, with an average speed of 0.008 μm·s^-1. Other virus moved forward through the intersection, with a high speed of 0.2μm·s^-1 again. In addition, SGIV infection could affect the morphology. The microtubule gradually formed a circular structure around the nucleus and viral factory during SGIV infection. These preliminary results reveal the complex interaction between SGIV and microtubule, further our understanding of intracellular activity of iridoviruses, and contribute to our understanding of the pathogenesis of iridoviruses infection.

Seasonal investigation of intertidal zones of Naozhou Island was conducted from April 2011 to January 2012. The results show that there were 64 species of macroalgae in this Sargasso field, including 15 species of Phaeophyta, 28 species of Rhodophyta, 20 species of Chlorophyta and one species of Cyanophyta, accounting for 23.44%, 43.75%, 31.25% and 1.56% of the total species, respectively. Among the 64 species, 43 species were thriving in spring, 24 species were emerging in summer, 29 species were active in autumn and 31 in winter. Only nine species were thriving throughout the whole year, including six species of Rhodophyta, two species of Chlorophyta and one species Phaeophyta, while there were 14 species living through three seasons. There were about 12-26 common species that can be found between two seasons and the species turnover rate was from 0.42 to 0.78, associated with higher turnover rates in spring and summer and lower rates in autumn and winter. Moreover, there were 13 dominant species but only Pterocladiella capillacea was the all-year dominant species, while Sargassum hemiphyllum and Corallina pilulifera were the dominant species over three seasons. Average biomass vary greatly with season, with the order of spring (848.14 g·m^-2)＞ winter (378.57 g·m^-2)＞ autumn (297.99 g·m^-2)＞ summer (294.15 g·m^-2). There is clearly vertical variation in the species distribution as the species number increases significantly from high tidal zone to low tidal zone, while the biomass show similar changing trend, indicating both species and biomass increase with water depth in the tidal zone. The Shannon-Weinner index was from 0.03 to 2.33, with an annual average of 1.10, while the Pielou's index was from 0.01 to 0.70, with an annual average of 036; the Margalef index varied from 0.15 to 1.65, with an annual average of 0.72; and the Simpson’s dominance index varied from 0.01 to 0.78, with an annual average of 0.39. The total water content of seaweeds changes ranged from 51.42% to 97.52%, with an average moisture of 85.21%. The total organic carbon content of seaweeds varied from 4.34% to 42.06%, with an average of 27.99%, indicating a strong carbon storage capacity. We find a clear negative correlation between the biomass of large seaweeds and dissolved inorganic nitrogen (DIN), with a coefficient of 0.49 (P＜0.05). The lower DIN of seawater during spring and winter is coincided with microalgae thriving seasons.

The surface area of scleractinian corals is an important reference parameter required for various researchs of coral biology and coral reef ecology. However, due to its complex morphological structure, the accurate measurement of coral surface area remains difficult. The diversity of measurement methods leads to the unreachable direct comparison of important indicators between different coral species. Thus, it is necessary to make a systematic comparison of different surface area measurement methods in different coral species. Regarding coral surface area measured by 3D scanning technique as standard, this study investigated the accuracy of three traditional measurement methods (wax coating, aluminium foil and simple geometry), discussed the applicability of different methods for corals in different morphology, and calibrated the accuracy of traditional measurement methods by simple regression analysis of two scleractinian corals Porites pukoensis (massive) and Pocillopora damicornis (branching). Results showed that the accuracy of simple geometry method was the highest (72.71% and 94.52%), followed by that of wax coating method (68.86% and 83.08%), and the accuracy of aluminium foil method is the lowest (65.27% and 58.07%) for P. pukoensis and P. damicornis, respectively. A strong correlation between 3D scanning method and each of the three traditional measurement methods (r²>0.95) was revealed by simple regression analysis, except for the surface area of P. pukoensis measured by the aluminium foil method (r²=0.762). Overall, to improve the accuracy of traditional coral surface area measurement methods, regression equations constructed by simple regression analysis can be used for calibration.

Hydrates-filled discrete fractures have been observed within the gas chimney structure in marine gas hydrate stability zone worldwide. It indicates that naturally hydraulic fracturing process and stimulated fluid flow have occurred in the gas hydrate stability zone. Gas production can benefit from artificially hydraulic fracturing within the methane hydrate reservoir. There can be a change in fracture aperture during the gas production from the methane hydrate reservoir. In return, the evolution of the fracture network has effects on the gas production process. While quite a few researchers have developed codes for modelling the coupled process between hydrate dissociation and elastoplastic deformation, currently there is no numerical tool to investigate the coupled process between fracture network evolution and gas production. Here, we couple TOUGH+Hydrate codes with the already coupled IC-FERST and Solidity codes in order to simulate the hydraulic fracturing process within the gas hydrate stability zone. We run an example in which the pressure around a borehole will be increased to create hydraulic fracturing within the gas hydrate stability zone. The coupling method, with additional improvements in the future, can be used to simulate the coupled process between fracture network evolution and gas production.

Exploring the structure and tectonic characteristics of the low-velocity layer (LVL) in a transition zone of the Pearl River Estuary (PRE) area has significant geological and geophysical implications for understanding the mechanism of intraplate earthquakes, seismogenic structure and crustal structure in this area. In this study, we use the data from 19 seismic stations (include 14 onshore seismic stations and five ocean bottom seismometers) along the L2-ME profile of the 2015 onshore-offshore deep seismic experiment in the PRE area to image structure features of the LVL. On the basis of the conventional seismic phase, a large number of sliding wave seismic phases are added to calculate the structural model. With the increase of Ph seismic phases, the ray coverage density within the range of 10-20 km was significantly increased, and a more accurate P-wave velocity structure model of the LVL and its above crustal structure along the L2-ME profile were obtained. The result shows the LVL is clearly imaged in the crust within the depth range of 13-18 km under the profile. The velocity in the LVL is roughly stable in the range of 5.7-6.0 km·s^-1 and has an obvious low-velocity anomaly feature of 0.5 km·s^-1 difference compared with its top layer and of 0.4 km·s^-1 difference compared with its bottom layer. Its thickness decreases from 3.5 km on the land side to 1 km on the sea side, showing a trend of gradual thinning toward the sea side. The bottom boundary of the LVL has similar fluctuation characteristics to the Moho.

Fractures are favorable transport systems for forming of hydrocarbon reservoirs and gas hydrate deposits. However, it is difficult to identify micro-fractures by conventional means due to limited seismic resolution. For the development of practical fracture identification technique, we analyze seismic wave kinematic and dynamic characteristics of fractures, combine functions and principles of relevant techniques, and fuse 3-D visualization technique and coherent technique. Fissure channels were successfully characterized in diapiric structures of the Yinggehai Basin, and gas fields were discovered using this technique. Through practice and analysis, this technique can also be applied to the study of gas hydrate migration system of the Qiongdongnan Basin. It is an effective fracture identification technique.

The spatial-temporal variability of heaving mode in the ocean is critical to understanding climate variability on interannual and decadal time scales. Using reanalysis data and a reduced gravity model, we investigated the leading heaving modes in the Pacific Ocean. The heaving signals are dominated by two modes: the first mode in which thermocline depth anomalies in the eastern and western equatorial Pacific have opposite signs, and the second mode in which thermocline depth anomalies in the equatorial and subtropical Pacific Ocean have opposite signs. The time evolution of these two heaving modes and the physics leading to these two modes were explored. Results indicate that the first mode is directly linked to equatorial zonal wind anomalies, and the second mode is induced by the wind stress curl anomaly in the subtropics. Furthermore, these two leading heaving modes have profound impacts on basin-scale heat transport (with an amplitude of 5?10¹⁴W) and ocean heat content redistribution (with an amplitude of 1.5×10²⁰J) through ocean waves and Ekman transport, highlighting the importance of heaving modes in modifying the variabilities of the climate system and climate change.

Using the wind field from the Simple Ocean Data Assimilation (SODA) ocean reanalysis product and National Centers for Environmental Prediction (NCEP), we analyze the characteristics of eddy-mean flow interaction in the Bay of Bengal during summer and autumn (June-November) of 2000-2015 by means of energy analysis in different years of occurrence of Indian Ocean Dipole (IOD) anomalies. The results show that, in the context of southwest monsoon with stronger negative phase of the IOD, both eddy kinetic energy (EKE) and eddy potential energy have relatively large magnitude. In the process of ocean internal instability, more energy of the mean flow field has been transferred to the eddy field, while in the positive phase of the IOD the energy is transferred less than usual. In addition, we find that the EKE in the bay mouth area of the Bay of Bengal tends to develop a spatial distribution with significant anomalies of the climate state in negative IOD anomaly years, that is, the EKE maxima appears around (88°E, 5°N). A case study of 2010 when the EKE anomaly was most prominent reveals that a cyclonic circulation anomaly was developed in the surface of the Bay of Bengal, which significantly changed the upper-ocean circulation pattern and greatly affected the interaction between the mean flow field and the eddy field. After further diagnosis of each term that maintains the EKE balance, we find that the main influencing factor of interannual change of EKE in the bay mouth area was the pressure term inside the ocean, followed by the unstable barotropic process and the advection term; and the contribution of sea surface wind stress was minimal.

Natural gas-hydrate is a new clean energy resource. The geological conditions in Shenhu area in the northern South China Sea (SCS) are conducive to the formation and storage of gas-hydrate. It is difficult to obtain accurate velocity information from traditional multi-channel seismic (MCS) data, and we can only judge the vertical distribution of geological bodies from the time domain. Ocean bottom seismometer (OBS) is a widely used active-source seismic instrument, which can receive clearer air gun signals. Compared with MCS data, refraction seismic data of OBS profiles can reveal velocity information from deeper layers. In this paper, combining the advantages of MCS and OBS, we determine the reflection interfaces on MCS profile, and then obtain the initial model. The OBS and MCS stacking profiles are merged to determine the reflection interface in the OBS profile. The reflection and refraction phases of OBS stations were picked up, and the two-dimensional velocity model of hydrate region was obtained by forward modeling using RayInvr, which solved the difficult time-depth conversion problem in MCS. The final model shows the depth, thickness and velocity of hydrate and free gas regions; it also shows the depth and velocity characteristics of the deeper interface below BSR.

A Tropical Cyclone Wind Profile Model (TCWPM) and the NCEP/CFSR wind data are used to simulate Typhoon Conson, and a slab model is developed to simulate typhoon-induced oceanic near-inertial currents. The model results match well with both reanalysis data and in situ observations. Typhoon Conson presented a salient asymmetric wind field at the ocean surface, and the bias between the two sides of the wind field along the track reached up to 10 m·s^-1. Typhoon Conson generated strong oceanic near-inertial oscillations (NIOs) after the typhoon center, which lasted for more than four days, and a significant asymmetric distribution of near-inertial kinetic energy (NIKE) indicates the strong NIOs are mainly triggered on the right-hand side of Typhoon Conson under the resonance effect. We also show that the tropical storm yields a small fraction of NIKE, e.g., the mean NIKE does not exceed 35 J·m^-3, but the NIKE increases exponentially with the increasing radius of maximum wind speed (Rmax or R₀), and the influence area increases linearly with Rmax, e.g., when Rmax increases from R₀ to 1.5 R₀, the NIKE rises from 81 to 631 J·m ^-3, and the influence area increases from 600 to more than 900 km².

Coral reefs over the Nansha Islands have characteristic geomorphological patterns; they exist in the form of atolls. The Niu’e (also known as Mckennan) and Ximen (Whitsum) reefs of the Jiuzhang Giant Atoll are two secondary atolls with newly-formed debris deposits, which may represent an important stage of landform evolution from a submerged atoll towards a reef island. Grain-size analysis of the surficial sediment samples collected from the two reefs shows that gravel-sized coral debris is the main component of the deposit. Medium grain sizes of the samples (measured by the long axis) range from 14 to 45 mm. Sorting coefficients range from 4.5 (being poorly sorted) to 31 with a sphericity value of 0.52 to 0.68 (far from a sphere shape). Medium grain sizes show a trend of increasing away from the shoreline. Medium grain sizes of the sediment samples are positively correlated with sorting coefficients, whereas they are more or less negatively correlated with sphericity values. Based on an analysis of historical records and satellite images, these beach ridge- or sand bar-like deposits represent modern accumulation landforms; their formations are related to storm waves and to some extent to the winter monsoon waves. The sand bar on the Niu’e reef had been extending towards the southeast and at the same time moving towards the north. The sand bar on the Ximen reef had an overall migration towards the southeast, with recurved sand spits on both sides. The mechanisms for the formulation of these features, in terms of changes in coral material supply and storm wave pattern, need further investigations.

The feeding experiment lasted for 40 days to explore the effects of breeding density (30, 60 and 90 individuals·m^-3) on the growth, enzyme activity and mRNA expression of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) in liver and kidney of juvenile Pampus argenteus with an average body weight of (3.88±0.72) g. Results are as follows. The weight gain rate and specific growth rate of the 60 individuals·m ^-3 group were (235.19±10.23)% and (4.03±0.10)%, respectively, which were significantly higher than those in the 30 individuals·m^-3 group (p<0.05), but showed no significant differences with the 90 individuals·m^-3 group (p>0.05). The changes of enzyme activity of juvenile Pampus argenteus were the most significant in the 90 individuals·m^-3 group and were the least significant in the 30 individuals·m^-3group. The activities of LDH, ALT and AST in liver and kidney increased first and then decreased, and the values of the three enzyme activities reached the peak at 6 h, 10 d and 10 d, respectively, which were 2.0 times, 4.3 times and 2.0 times of the initial values. The peak values of the three enzyme activities appeared at 1 d, 3 d and 5 d in kidney, respectively, and the values were 2.1 times, 2.2 times and 3.1 times of the initial values. The changes of mRNA expression of AST, ALT and LDH genes and the changes of the three enzyme activities in liver and kidney showed significant correlations. In conclusion, the breeding density of 60 individuals·m^-3 could promote the growth of juvenile Pampus argenteus. However, the 90 individuals·m^-3 group might cause extra energy demand increases in Pampus argenteus juveniles. Increased expression of gluconeogenesis-related genes mRNA resulted in significant increases of AST, ALT and LDH activities in liver and kidney, and eventually slowed down the growth of juvenile Pampus argenteus.

Nan’ao Island in Shantou, Guangdong Province is one of the important marine aquaculture bases in eastern Guangdong. Zooplankton is of great significance for assessing the quality of the ecological environment. Based on the sampling of zooplankton in the eastern waters of Nan’ao Island in September 2014 (autumn), December (winter), April 2015 (spring), and July 2016 (summer), the community structure of zooplankton and the influence of environmental factors on their spatial and temporal distribution were analyzed. A total of 206 species of zooplankton (including planktonic larvae) were identified, of which the number of copepods was the highest, reaching 94 species. The number of zooplankton species in the inshore waters was higher than that in the offshore waters. Seasonal variations in zooplankton abundance and biomass were characterized by high values in summer and autumn and low values in winter and spring. The distributions of zooplankton abundance and biomass were consistent. In summer, the high value area of biomass and abundance occurred mainly in the inshore region, and in autumn biomass and abundance increased from inshore region to offshore region. The abundance of different groups and dominant species changed seasonally. Copepod was the group with higher abundance during the survey. The abundance of jellyfish and salps increased significantly in autumn. Euconchoecia maimai and Euconchoecia aculeata were dominant in summer, and Doliolum denticulatum was dominant in autumn. Temperature, salinity, and phytoplankton biomass were the main environmental factors driving the spatial and temporal changes of zooplankton in the eastern waters of Nan’ao Island, indicating that the zooplankton community was affected by physical processes and aquaculture activities.

Marine planktonic ostracods are small crustaceans with a wide distribution, playing an important role in ocean carbon cycle. The ostracods in smaller size are usually underestimated when marine zooplankton samples were collected with 505 μm mesh. Based on the zooplankton samples collected with 505 and 160 μm meshes in the northern South China Sea from July to August 2006 (summer) and from December 2006 to January 2007 (winter), the capture efficiency for the ostracods using two planktonic mesh sizes was compared, and the community structure and the influence of environmental factors on their distributions were analyzed. We found that the abundance of ostracods obtained by the 160 μm mesh net was six times that by the 505 μm net in summer. The community structure of planktonic ostracods collected by the 160 μm mesh was analyzed with the following findings. 1) The species richness of planktonic ostracods of a total of 32 species was identified to increase from nearshore to offshore, and the difference between the areas with water depth shallower and deeper than 100 m was extremely significant (p<0.01). 2) The abundance of planktonic ostracods was higher in summer, when the high abundance area appeared mainly in the coastal waters of the Leizhou Peninsula and northeast Hainan Island higher than that in offshore significantly (p<0.05), and lower in winter, when the distribution of ostracods abundance was homogeneous. 3) Euconchoecia aculeata, dominant species, contributed the most to high abundance in the nearshore. 4) The species richness of ostracods was positively correlated with temperature and water depth; and the abundance was negatively correlated with temperature and salinity, and positively correlated with chlorophyll α concentration. Qiongdong coastal upwelling and Yuexi Coastal Current boosted the abundance of planktonic ostracods up to 1252 ind·m ^-3 in the coastal waters of the Leizhou Peninsula and northeast Hainan Island. Results suggest that smaller mesh net should be used for the overall assessment of community characteristics of planktonic ostracods.

Superior to traditional monitoring methods, the marine monitoring buoys are able to obtain long-term and real-time continuous marine environmental data to reflect the dynamic changes in marine environmental conditions. In order to clarify the occurrence and development of the red tide of Karenia mikimotoi, and to carry out integrated monitoring and early warning of red tide disasters, we analyzed the evolution of Karenia mikimotoi bloom and environmental factors based on online monitoring buoy data obtained from the coastal area of Nanji Island of Zhejiang Province in June 2017. K. mikimotoi bloom occurs in the sea water with temperature and salinity ranging from 22.8℃ to 26.0℃ and from 28.8 to 31.8, and when the air temperature is between 20.4℃ and 27.3℃, which are suitable for the cell growth of K. mikimotoi. Higher light intensity can support higher K. mikimotoi cell density. Pearson correlation analysis shows that the cell density of K. mikimotoi is significantly positively correlated with chlorophyll a (chl-a). Dissolved oxygen (DO), dissolved oxygen saturation (DO%), pH, water temperature, and air temperature are all significantly positively correlated with chl-a. Salinity is significantly negatively correlated with chl-a. Wind blowing ocean current may facilitate the accumulation of algae to the shore, which creates suitable conditions for the outbreak of red tides. During the red tide, chl-a, DO% and pH have synergistic changes, which may carry out red tide early-warning signs based on the online monitoring buoy data.

Marine ecosystem dynamics model is an important means to study marine ecological environment. As the model complexity increases, the number and uncertainty of biological parameters increase, which has a great impact on model results; therefore, optimization of model parameters is particularly important. In this paper, a one-dimensional physical-biological model is applied to the northern South China Sea, and the key biological parameters obtained through sensitivity analysis are optimized by using genetic algorithm. The results show that the sensitive parameters in the model are related to phytoplankton growth, zooplankton growth, feeding and death, and detritus sinking. Based on the genetic algorithm optimization of the above-mentioned parameters, we find that the surface and vertical simulation errors of the model are reduced by 27.80% and 21.40%, respectively, by using only surface satellite data; the surface and vertical simulation errors are reduced by 14.90% and 32.70%, respectively, by adding observed profile data. The success of applying genetic algorithm in the one-dimensional model provides the basis for its further application in three-dimensional marine ecosystem models.

Mangroves are an important type of coastal wetlands with ecological, environmental, economic, and cultural values. Spartina alterniflora is an invasive alien plant, threatening mangroves in China. The competition between Spartina alterniflora and mangroves is an important ecological issue along the southeast coast of China. Accurate monitoring of Spartina alterniflora and mangroves with remote sensing is of great significance for scientific protection of mangrove ecosystems. We propose a new method to monitor Spartina alterniflora and mangroves, integrating Sentinel-1 SAR and Sentinel-2 optical imagery. The Yunxiao National Nature Reserve of Mangroves, located in Zhangjiang Estuary, Fujian, China, is chosen as the study area. We select one Sentinel-2A image at low tide in 2016, 2017 and 2018 to obtain the spectral and texture information of vegetation and other objects. The new method comprises of three steps: 1) use rules related to NDVI, EVI, LSWI, and DEM to get the potential masks of Spartina alterniflora and mangroves; 2) use random forest classification method to distinguish Spartina alterniflora and mangroves further; and 3) use all Sentinel-1 A/B images in that year to get the estuarine yearlong seawater body, and use the criterion interaction with sea water to refine the detected Spartina alterniflora and mangroves. The random forest classifier is found suitable for mapping wetlands with overall accuracy of 98.53%, 96.52% and 98.71%, and Kappa coefficients of 0.980, 0.952 and 0.978 in 2016, 2017 and 2018, respectively. The total areas of the detected Spartina alterniflora and mangroves in the study region are 109.23 and 56.85 hm ²in 2016, 124.00 and 59.88 hm² in 2017, and 142.39 and 58.61 hm² in 2018, respectively, consistent with previous research results in terms of spatial distribution and magnitude of the area.

Coral fish protection strategy based on ocean big data query technology is an important subject in marine science research. Among them, the competition of fish populations is of great significance to fish protection. In order to study the competition of fish populations, it is necessary to model the relationship between fish populations and coral reefs. As a simple and effective big data model, a graph model is a practical model to express this relationship. Therefore, we propose a competition graph model of coral fish populations and fish-dependent coral reef resources. Then, a big data graph query method based on Local Sensitive Hashing (LSH) is proposed to analyze the competitive pressure of fish populations and obtain real-time competitive pressure of fish populations. Third, according to the results of LSH query, the fish population that needs priority protection is analyzed. Finally, a resource allocation strategy based on constructing artificial reefs was designed for these fish populations to improve the overall competition of coral fishes in the region.

We investigate submesoscale characteristics of summer upwelling fronts in the western South China Sea (WSCS) and associated ageostrophic processes by using satellite measurements and high-resolution ROMS simulations. Active submesoscale filaments with a typical horizontal scale of O(1-10) km are detected to be characterized by O(1) Rossby number (Ro) from the fine-resolution satellite images and simulation results. The diagnostic analysis shows that down-front wind forcing drives a net cross-front Ekman transport and advects heavy water over light water. This process at submesoscale tends to reduce the stratification and potential vorticity (PV), exacerbates the frontal instabilities, and forms the cross-front secondary circulation. The high-resolution simulation results show that the maximum vertical velocity in the frontal zone can reach 100m?d ^-1, which significantly enhances vertical material exchange. In this context, active submesoscale processes may contribute to enhanced vertical exchanges of the upper ocean in the summer upwelling front of the western SCS.

Submesoscale eddies have smaller Richardson number and larger Rossby number, with horizontal scales between 0.1 and 10 km and time scale of ~0(1 day). They act to extract energy from the mesoscale circulation, drive forward energy cascade to the smaller scale turbulence and meanwhile contribute to the vertical flux of what in the upper ocean. In this study, anisotropy of submesoscale eddies in the Kuroshio Extension in a high-resolution simulation (?x≈500m) by the regional ocean modeling system (ROMS) is evaluated using the nummular variance ellipse method. A correlation between eddy anisotropy and submesoscale features is also analyzed. The results show that the submesoscale eddies, as well as the anisotropy, near the flow stream get intensified compared to those in the flanks. The isotropic ratio is well correlated with the strength of submesoscale processes, suggesting that the submesoscale processes tend to be isotropic. The nummular variance ellipse, known as the feedback of eddies to mean flow, may implies forward cascade of kinetic energy.

In this paper, we use reanalysis data and mixed layer temperature (MLT) budget analysis to study the differences of the North Atlantic sea surface temperature anomalies (SSTAs) between two Super El Ni?o (1997-1998 and 2015-2016) events and the causes for the differences. The results show that in the spring of 1998 the North Atlantic SSTA had clear positive, negative and positive distribution, while in spring 2016 it presented weakly negative, positive and negative distribution. The diagnostic results of factors influencing the SSTA in the tropical North Atlantic indicate that in the spring of 1998, in addition to the reduction of latent heat transferring from ocean surface to atmosphere and the increase in solar radiation absorption, the marine dynamic process, i.e., zonal Ekman drift, also played an important role. The thermal process was related to the negative phase of the North Atlantic Oscillation (NAO) that occurred after the peak of El Ni?o, which caused the Azores high pressure to weaken and generated southwesterly wind anomaly. The evaporation of the tropical North Atlantic was attenuated by the wind-evaporation-SST feedback mechanism. The eastward shift of the Walker circulation sinking branch also contributed to this warming. Different from the 1997-1998 El Ni?o event, the 2015-2016 El Ni?o event caused a weakly positive NAO phase instead of a negative one. The weak easterly anomaly in the tropical North Atlantic caused SST cooling; this may be the main reason for the significant difference between the North Atlantic SSTAs in the springs of 1998 and 2016.

Based on 12 cases of extreme landfalling typhoon disasters in South China from 2005 to 2016, extreme landfalling typhoon disaster risk assessment in South China was carried out by considering the vulnerability of disaster bearers and the ability of disaster prevention and mitigation. First, based on the grey relational degree of each index, the risk index, vulnerability index and disaster prevention and mitigation ability index of extreme typhoons in South China are constructed. Then, according to the mathematical expression of disaster risk, based on the system weight determined by analytic hierarchy process, an extreme typhoon disaster risk index in South China is constructed. Next, the original information matrix, fuzzy relation matrix and factor space theory are constructed by using two-dimensional normal diffusion technology. In this paper, the fuzzy approximate reasoning is carried out to obtain the risk estimate value of the direct economic loss index estimated by the risk index approximately. Finally, the super probability evaluation model is used to evaluate direct economic loss rate of each extreme typhoon. The results show that the constructed risk index is in good agreement with the actual situation, and the calculated risk estimate is consistent with the change trend of direct economic loss index, the mean square error is 0.20, and the correlation coefficient is 0.78 The results also show that the direct economic loss rate caused by extreme typhoons is 0.1%, which means it has become the normal risk, the transcendence probability and direct economy loss rate of extreme typhoon disaster in South China shows a good linear relationship.

Time service system is very important for inverting velocity structure of underground media via traveltime tomography. Due to the lack of GPS time access, the time errors (including time service error and time keeping errors) of the Ocean Bottom Seismometer (OBS) mainly come from the inaccuracy of internal quartz crystal oscillator, affected by external environment changes and switching and other factors. The long term practice finds that, some Chinese-made OBSs have large time deviation when recording air gun signals and natural seismic signals. In this study, 53 Chinese OBS records obtained from the crustal structure sea-land exploration experiments in Fujian and Taiwan straits in 2019 were used for time service system correction. To obtain OBS time service error, the consistency test of uninterrupted acquisition before going to the sea, as well as the sloshing caused by the transport ship during transportation, are used to correct the timing error by cross-correlation. For the time keeping error, the deviation between the calculated actual sampling frequency and the theoretical sampling frequency is corrected. The time service system is corrected comprehensively by using naturally occurred earthquakes. It has been demonstrated that the corrected OBS data can improve the accuracy of time record and reduce the error of seismic phase identification and traveltime picking. At the same time, the results of this paper provide important reference for the widespread use of domestic OBS and standardization of domestic OBS data acquisition process.

In view of the lack of marine seismic network at home and abroad, a mobile earthquake recording system in marine areas by independent divers (MERMAID) is introduced for global sea-area application. According to the research and development process of the mobile seismic recording system, the general design requirements and typical work cycle process of the buoy are established; the hydraulic buoyancy regulating system and mechanical structure are designed; comparison and analysis of different speeds and negative buoyancy diving process are carried out; and the laboratory pressure test and Qiandao Lake test are realized. The test results show that the MERMAID buoy can keep good sealing and stability under 15 MPa pressure, and the P wave of natural earthquake can be effectively collected by hydrophone, and the energy consumption of each module in a single period can be calculated to verify the design indicators.

Chaetognatha is often the most abundant carnivorous zooplankton, and a vital food source for pelagic fish in marine ecosystem. However, their survival strategy of maintaining population structure in tropical coastal waters remains unclear. In this study, molecular method was applied to compare the field diet of juveniles and adults of dominant chaetognath species Flaccisagitta enflata in Sanya Bay. We discuss the nutritional strategies of chaetognaths maintaining substantial population structure from the perspective of resource utilization. The results show that there were 21 and 19 species fed by juveniles and adults, respectively. Copepods, small jellyfish, diatoms, and polychaets were common food groups of both juveniles and adults. Food preferences differed significantly between the juveniles and adults. Small jellyfish made up 59% of the whole diet composition in adults, while copepods became the most abundant food items (60%) in juveniles. The trophic niche of juveniles (5.16) was higher than that of adults (2.89), and trophic overlap between them was low (0.21), suggesting that chaetognaths have obvious dietary shifts during different growth stages. These results reveal that even though adults and juveniles coexist in the same region with large numbers, they can reduce food competition by feeding differentiation. This feeding strategy is of great significance for maxillary species to ensure juvenile survival and maintain substantial population structure.

Aquaporin 4 (AQP4) is a major channel that passively transports water. In this study, based on a fragment of AQP4 of Pinctada fucata martensii obtained by transcriptome sequencing, the full cDNA was obtained using RACE technology, named PfAQP4, which includes 114 bp of 5'UTR, 839 bp of 3'UTR, and 858 bp of the Open Reading Frame (ORF) encoding a total of 285 amino acids. The PfAQP4 has six alpha-helix transmembrane regions, five loops, one major intrinsic protein (MIP) domain, and two NPAs (Asn-Pro-Ala) motif, indicating that it belongs to AQP1-like type. Real-time fluorescent quantitative PCR was used to analyze the mRNA expression pattern of PfAQP4 in different tissues, different developmental stages, and different salinity stress conditions. The results showed that: (1) PfAQP4 was expressed in all tested tissues, and its expression level was higher in adductor muscle, foot, and gill; (2) in different developmental stages, PfAQP4 was increased first and then decreased, highly expressed in the 2-4 cell stage and lowly expressed in eye-spot larva stage; (3) the expression of gill PfAQP4 mRNA in hypersaline group (36‰) increased significantly at 24h, 72h, and 120h, and returned to the control level at 168 h; in the hyposaline group (16‰), PfAQP4 was significantly up-regulated at 24 h, and the expression level returned to the control level at 72h. These results showed that the salinity can affect the expression of PfAQP4 in gill, and PfAQP4 had a very important effect on the osmoregulation of P. f. martensii.

In this study, the effects of growth and chlorophyll fluorescence characteristics in Coolia tropicalis under different concentrations of manganese (Mn, 0, 1, 5, 10, and 50μmol·L ^-1) were investigated by using chlorophyll fluorescence kinetics technique. The results are as follows. The relationships of specific growth rate (μ) and maximal relative electron transport rate (rETR_max) with the concentration of Mn were fitted by exponential functions; growth and electron transport had the same degree of response to manganese stress. The regular activity of photosynthesis can be maintained only when the concentration of manganese is at least 1μmol·L ^-1. when the Mn concentration was lower than that 1μmol·L ^-1, the photochemical efficiency (F_v/F_m) begins to decrease after 6 days, while the per reaction center of absorbed light energy (ABS/RC) and heat energy dissipation (DI₀/RC) increase, and no influence to electron transport (φ_E0) and the growth, which indicated Mn deficiency only decreased the number of active reaction center and increased the heat dissipation in this phase. While Mn deficiency extended to day 15, the rising of F₀ and the decreases of φ_E0 and growth indicated that Mn deficiency caused irreversible damage to the active reaction center and inhibited the electron transport in this phase. The repair rate to damage rate (r/k) under intense light was not affected by Mn deficiency, indicated Mn deficiency did not influence the photoprotection of C. tropicalis.

Coolia is a widespread and toxic genus of benthic marine dinoflagellate. In this study, four strains of Coolia species were examined as Coolia tropicalis, which were collected in the Xisha Islands of the South China Sea in recent years. Morphology was determined using light microscopy and scanning electron microscopy. Phylogenetic analyses were constructed based on the sequences of the large subunit rDNA and the internal transcribed spacer region. The bioassay toxicity test of brine shrimp (Artemia salina) demonstrated that the algal lysates extracted from different strains of C. tropicalis exhibited different toxic effects. At 48 h, the LC50 of XS554 strain was 1.42 mg·mL ^-1 (approximately 1.1×10 ⁵ cells·mL ^-1) and 5XS15 strain was 1.92 mg·mL ^-1 (approximately 1×10 ⁵ cells·mL ^-1).

The ultrastructural characteristics of spermatogenesis and spermatozoon of the barnacle Megabalanus volcano were observed by scanning and transmission electron microscopy. The results showed that its spermatogenesis included five developmental stages, i.e., spermatogonium, primary spermatocyte, secondary spermatocyte, spermatid, and mature spermatozoon. During spermatogenesis, a circular or oval nucleus extended along with an axial filament and bent in cytoplasm under the action of microtubules. The nucleus further elongated with longitudinal extension of a spermatid, and finally became filiform. Massive chromatin of nucleus underwent disintegration, fine granules, coarse granules, and eventually condensed into a high electron density homogenizer. The vesicles secreted by the Golgi complex coalesced to different sizes of precursors of accessory droplet, and finally fused into an accessory droplet of high electron density. Many small mitochondria fused to a slender one that was eventually positioned behind the nucleus. The spermatozoon (about 58.39 μm in length), which was divided into acrosome, neck, middle piece, and tail, was long filiform with an accessory droplet. The conical acrosome was located at the spermatozoon anterior, followed by a basal body. The neck was composed of a "9+2" type axial filament, and the filiform nucleus was parallel to the axial filament. The length of acrosome and neck was about 6.65 μm. The middle piece was about 42.95 μm in length. The spindle-shaped accessory droplet (about 9.33 μm long and 2.13 μm wide) was adjacent to the nucleus and axial filament, followed by a mass of glycogenosomes and a slender mitochondrion. The tail (about 8.79 μm in length) only had a typical "9+2" axial filament.

In this study, strains of Amphidinium from seaweeds and dead corals around Weizhou Island, Guangxi, China were isolated by single cell capillary pipette and cultured. The morphological features and phylogenetic analysis were determined based on light microscopy, scanning electron microscopy and molecular biology techiniques. Three Amphidinium species were identified, namely, Amphidinium operculatum, Amphidinium massertii and Amphidinium caeterae, among which A. operculatum and A. massertii were new records in China. The differences in morphology and phylogeny between different species were analyzed and compared. It was found that the morphological characteristics of the three Amphidinium species were significantly consistent with model species. This study adds information to the diversity and phylogenetic evolution of Amphidinium species in China, and extented the distribution of two new Amphidinium species to the coastal waters of southern China.

Previous studies on upwelling mainly focus on inter-annual or seasonal variation, but the high-frequency observations of upwelling gain more attention with the availability of high-temporal-resolution remote sensing products. In this paper, we propose an algorithm for detecting cold upwelling signal based on daily merged sea surface temperature (SST) data with a multi-scale segmentation method. The upwelling area and intensity variation reflect a complete process of upwelling off eastern Hainan Island. Analyses on SST images in recent decade demonstrate that the upwelling did not exist daily during summer; instead, it occurred with a mean time interval of 6 days. Colder signature of upwelling events appeared for approximately 98 days on average in every summer from June to September. The mean values of cold area and intensity are 7698 km² and 1.0℃, respectively, which are highly correlated. The frequency of upwelling occurrence is inversely proportional to the offshore distance, and the northeast is a high-frequent area. Offshore wind and wind stress curl make different contributions for different upwelling in the studied area. Offshore wind, wind stress curl and tropical cyclones are closely related to the short-term change of the upwelling.

A high-resolution hydrodynamic numerical model of the Malacca Strait and its adjacent sea was established using the unstructured Finite-Volume Community Ocean Model (FVCOM). The residual circulation structures and water transport caused by tides and winds were studied. The results show that the movements of tidal currents in the middle channel of the Malacca Strait are dominated by rectilinear currents with rotary currents at the edge, and that the velocities of ebb tides are slightly larger than those of flood tides in the main study domain. The southeast narrow channel is the region with the largest velocities of currents. The tidal currents show multiple convergence and divergence due to the great changes of topography, with three major residual circulations in the Malacca Strait. Forced by the idealized northeast monsoon used in the model, the currents in the Malacca Strait flow to the northwest, while the situation during the southwest monsoon is reversed. During the monsoon period, the residual circulation in the surface layer is destroyed, but still exists in the bottom layer; and as the wind becomes stronger, the number, size, shape, and position of the residual circulation in the bottom layer change. During the inter-monsoon period, the residual current structures change partly during spring tide, but significant change occurs during neap tide under the effect of winds.

Based on the wave height observation data of five buoys and parameters from the CMA Tropical Cyclone Database for the South China Sea from 2010 to 2017, fast calculation models of tropical cyclone-generated wave height are established by using Forward Feedback Back Propagation (FFBP) Artificial Neural Network (ANN). The results show that significant wave height calculated by the ANN model based on the tropical cyclone central location, minimum sea level pressure (MSLP), maximum sustained wind (MSW), the distance and azimuth between tropical cyclone center and buoy can well fit the observations. The root mean square errors between the calculation and observation of significant wave height are less than 0.3 m, the average relative errors are between 5.78% and 7.23%, and the correlation coefficients are greater than 0.9. Test results show that the model calculation of the maxima of significant wave height basically coincides with the observation, the relative errors being between -31.06% and 0.98%; however, when the calculated maxima of significant wave height appear is not in agreement with observation during tropical cyclone Mangkhut ( International number ID: 1822). The method introduced in this paper can be applied to calculating the maximum of significant wave height during tropical cyclone for ocean engineering and marine forecast.

The rainfall caused by typhoon is different from the other precipitation event due to its unique physical structure. The stable isotope composition of typhoon precipitation is also quite different from that of a general precipitation event. Based on meteorological data before and after the landing of Typhoon Mangkhut (2018) in Guangzhou and Dongguan and stable isotope data of precipitation at hourly resolution, we analyzed the characteristics of the stable isotope variation of the typhoon precipitation and its influencing factors. During the influence of Typhoon Mangkhut, the δ¹⁸O value of precipitation in Guangzhou ranged from -5.7‰~-19.2‰, with a variation of 13.5‰; and the average value was -15.5‰. The variation of δ¹⁸O value in Dongguan was -7.3‰~-20.0‰, with a variation of 12.7‰; and the average was -14.8‰. The variations of δ¹⁸O value of precipitation in the two places both showed the three-stage variation characteristics of inverted U-shape. Due to the influence of evaporation, the precipitation oxygen isotope values in the typhoon at the front and back were relatively positive in two places, of which Guangzhou was (-5.7‰~-9.3‰, and Dongguan was -7.3‰~-8.1‰. The stable isotope values of precipitation in the typhoon central area of the two places were extremely negative, ranging from -16.0‰ to -19.2‰ (Guangzhou) and from -13.0‰ to -20.0‰ (Dongguan), which were the most negative precipitation δ¹⁸O values reported in this region so far. According to the analysis, the generated distant typhoon intensity was enhanced during the El Ni?o. Thus, the stronger convection and water-vapor circulation in Typhoon Mangkhut (2018) led to extreme negative δ ¹⁸O value of its precipitation.

The Brushtooth lizardfish (Saurida undosquamis) is one of the economically important demersal fishes. The population genetic structure and genetic diversity of S. undosquamis from the coast of China were examined based on the complete control region (D-loop) sequences. A total of 129 individuals from six geographic populations were sequenced. Seventy-one polymorphic sites were detected, which defined 101 haplotypes. Results show S. undosquamis from the coast of China are characterized by quite high haplotype diversity (0.9873 ± 0.0048) and relative low nucleotide diversity (0.0132 ± 0.0067). Phylogenetic tree for haplotypes based on Neighbour-joining method shows shallow topology and reveals no significant divergent clades. Haplotypes from each geographic population were scattered throughout the NJ tree, showing no significant genetic differentiation between populations. Analyses of molecular variance suggest nearly all the genetic variation (99.87%) is attributed to variability within populations, while little variations (0.13%) are found between populations. Most of the pairwise F_ST values between different populations are quite low, which implies a high rate of gene flow and genetic homogeneity between populations. The results demonstrate high genetic diversity and little genetic differentiation for S. undosquamis from the coast of China. They belong to the same population (panmixia), and a single-stock management regime could be supported in fishery management.