Quantifying eddy mixing in the ocean is a hot and tough problem in the area of physical oceanography. Based on the theory of effective diffusivity, the present study investigated the stirring effects of geostrophic turbulence that led to stretching, distorting, deforming, and folding of tracer contours. These changes are then related to the efficiency of turbulent mixing. Results show that under the stirring effect of geostrophic turbulence, the length of tracer contour can be quickly elongated and fine-scale tracer filaments and fronts are also generated. This fractal elongation of tracer contour, about 10~20 times longer than the original length, is the dominant contributor to the mixing efficiency, whereas the gradient enhancement associated with filament and front generations only plays a secondary role. On the other hand, fine-scale features are smoothed out by small-scale diffusivity which eventually suppresses the increase of contour length and the generation of tracer filaments. This imposes an upper bound of the mixing efficiency when the stirring and smoothing effects are in a dynamical balance. Through a ‘box-counting’ method, the fractal dimension of tracer contour is also found between 1.4~1.6, indicating a geometric dimension lies somewhere between 1D and 2D. Due to the limitation of data resolution, contour length and thus mixing efficiency may be underestimated. Finally, the present study made an empirical relation between the fractal dimension and mixing efficiency, providing an opportunity for estimating mixing efficiency through a well-developed pattern recognition technique in remote sensing, and a new way of diagnosing ocean mixing and its parameterization.

Based on 26 years of data on sea level anomalies, sea surface wind speed anomalies, and sea surface temperature anomalies, using the spatiotemporal series prediction model PredRNN++, this paper predicts the trajectory of mesoscale eddies in the South China Sea and dipole activity in the western South China Sea over a period of 1 to 28 days. The results indicate that the PredRNN++model can comprehensively consider the spatiotemporal evolution characteristics of the entire South China Sea region and the role of environmental wind and temperature fields, and has good performance in short-term (1~2weeks) and medium-term (3~4weeks) forecasting. This model has the ability to predict the generation and disappearance of eddies to a certain extent, and can control the 4-cycle prediction error of eddy trajectories to 42.1 km. For eddies with a lifespan of less than 100 days, the mid-term position and amplitude prediction error are small. In addition, the model can better track the evolution and intensity change of dipole structure at any time point under the monthly average, 4-day average and any forecast time effect in August-November. The prediction error of dipole eddy related attributes is the smallest and there are interannual and type differences. In 2017, the amplitude position, prediction and radius error of eddy 1-4 cycles are the smallest, which are 40~60 km, 3~5 cm and 20~40 km respectively, and the prediction effect of cyclone position is better than that of anticyclone.

A three-dimensional numerical simulation using MIKE 3 was carried out to explain the tidal distribution characteristics of the Luoyuan Bay in terms of flow field and cross-sectional vertical velocity, calculate the tidal residual flow field in the Luoyuan Bay, simulate the transport of material with particle characteristics in the bay using Lagrangian particle tracking method, and analyze the movement pattern of particles. The results show that the residual circulation structure is formed in the north-western part of the Luoyuan Bay, the northeastern recess and the inner bay mouth, and the material distribution in different areas of the bay is significantly correlated with the tidal residual current structure. This study provides a scientific basis for further investigation of the distribution mechanism of pollutants in the Luoyuan Bay, and provides technical support for pollution control and environmental protection in the Luoyuan Bay.

Concerning the low sea surface temperature (SST) prediction accuracy of numerical modeling and empirical methods in near-shore stations, we consider sea surface temperature prediction as forecasting of multivariate time series data, construct the sea surface temperature time series model of near-shore stations by convolutional neural network (CNN) to predict the maximum, minimum and mean sea surface temperature for the next day, and compare CNN model with empirical forecast method and long short-term memory (LSTM) model through experiment. The experimental results show that compared with empirical forecast method, the mean absolute error (MSE) of CNN model on daily maximum SST forecast drops 0.14℃ to 0.36℃, root mean squared error (RMSE) drops 0.21℃ to 0.49℃, the MSE of CNN model on daily minimum SST forecast drops 0.17℃ to 0.36℃, RMSE drops 0.24℃ to 0.63℃, the MSE of CNN model on daily mean SST forecast is 0.30℃, RMSE is 0.47℃, its forecast performance is as good as LSTM model in the testing set. It shows that the application of CNN to SST modeling is feasible, improve the accuracy of sea surface temperature prediction which can compare favorably with LSTM model.

Based on the sea surface temperature and wind data from 1968 to 2021, this paper analyzes the interannual variation of upwelling intensity in Zhoushan in summer, and the impact of El Niño-Southern Oscillation (ENSO) on upwelling. The temperature and wind upwelling indices both show that the upwelling in Zhoushan sea decreased in summer during 1982—2021, with the decreasing rates of 0.062℃·10a^-1and 0.35 m³·s^-1·(100m·a)^-1, respectively. Recently, the weakened coastal wind stress causes the temperature upwelling index to decrease. According to the results, the wind upwelling index during La Niña events is larger than that during El Niño events and climatology. Further analysis of the relationship between ENSO and the wind upwelling index shows that ENSO affects the intensity of upwelling mainly by influencing the wind. In El Niño events, the southeast wind dominated Zhoushan sea weakens, leading to a decreasing upwelling intensity. While in La Niña events, the enhanced south wind benefits the development of upwelling.

In this paper, a new hybrid data assimilation method is designed based on particle filter and 3Dvar. The new method generates an ensemble deviation with background error information through an optimal estimation of particle filter, thus providing flow-dependent background error covariance for 3Dvar. Particle degeneracy has always been the main obstacle of particle filtering in data assimilation field. In order to make the hybrid method work better, an improved residual resampling method is proposed to solve the problem of particle degeneracy. By sampling particles in the normal distribution, the lack of particle diversity caused by degeneracy is solved. Data assimilation experiments were tested on the ideal lorenz-63 model. The results show that the new method is better than the ETKF-3Dvar method when the model error is large, and as the model error increases, the new method is also better than the traditional data assimilation method. In the comparison experiment with hierarchical resampling and general residual resampling, the improved residual resampling method can ensure the stability of the assimilation results within a given time window, while the other two methods have a large deviation in the assimilation results.

Using the track data of landed tropical cyclones (TCs) during 1949—2021 from Shanghai Typhoon Institute of China Meteorological Administration, this study analyzes the variation and mechanism of TCs landed in autumn in Guangdong area, and compares with the results in summer. The results show that a total of 76 TCs landed in Guangdong in autumn during the past 73 years, accounting for 28.5% of the landed TCs in whole year. The landed TCs in autumn (ALTCs) are mostly in categories of strong typhoon and super typhoon, and the mean peak intensities are stronger than those in summer. 72.4% of the ALTCs generated in the Western North Pacific, a higher portion than summer landed TCs and the average latitude and longitude of TCs generation move southward and eastward. The yearly power dissipation index (PDI) of autumn TCs reaches 0.4×10⁷m³·s⁻², comparable to that of summer TCs; during landfall to dissipation, the average duration time of autumn TCs is less, the translation speed is slower and PDI is less than those of summer TCs. In long-term variations, the declining trend and decrease rate of the number of ALTCs is similar to that in summer, while the landing intensity of ALTCs increases with a rate 1.8 times higher than that in summer. The translation speed of ALTCs slows down but with a rate 2.5 times lower than summer TCs, the PDI of ALTCs shows a weaker decreasing trend than summer TCs. Unlike more TCs landed in summer in La Niña year, more ALTCs appeared in El Niño years. The number of ALTCs is related to the ENSO (El Niño-Southern Oscillation) index in previous winter and spring with correlation coefficient of about 0.3. It can be used as an indicator for next-year ENSO prediction. In decadal variability, the correlation coefficients between the number of ALTCs and the PDO (Pacific Decadal Oscillation) index, were -0.51 and 0.68 in the warm phase (1977—1996) and cold phase (1997—2016), respectively. The composite analysis shows that ALTCs can occur with a warm sea surface temperature anomaly in the northern South China Sea, which induced cyclonic atmospheric circulation in the South China and favors TCs landed in Guangdong.

A severe sea fog occurred in the West Side of the Taiwan Strait from 8PM April 19, 2019 to 7AM April 26, 2019. Based on the coastline automatic weather station, the generation and dissipation law of sea fog was studied. Sea fog occurred from 2AM to 8AM, and the closer the generation time is to the early morning, the shorter the duration. Sea fog is mostly generated locally, some stations are formed for the purpose of propagation, and there is little correlation between north and south sea fog. The visibility decreased rapidly before the sea fog occurred and increased rapidly after the fog dissipated. When sea fog formatted LST-T (LST, land surface temperature; T, temperature) between −1.7~2℃, LST-Td (dewpoint temperature, Td) between 1~2.7℃, T-Td between 0.2~1℃. During the sea fog maintenance period, RH (relative humility) ≥ 96%. Under the background of abundant water vapor, the formation and development of sea fog are closely related to wind speed and weakly related to wind direction. Combined with Himawari-8 satellite image and ERA5 reanalysis data, the characteristics of this sea fog process was analyzed. Satellite images show the extent of the process and the characteristics of occurrence and dissipation. Circulation analysis indicated that this sea fog event occurred under the control of weak southwest flow at 500 hPa, while at 850 hPa and 925 hPa Fujian was affected by southwest airflow, bringing abundant water vapor. According to the analysis of the sea and air conditions, the type of sea fog was advection fog.

Anti-Mullerian hormone receptor Ⅱ (Amhr2) is the specific receptor of Anti-Mullerian hormone (Amh) in the TGF-β pathway. It is critical for gonadal differentiation and development in fish and determination of the sex in some fish species. However, the expression and function of amhr2 in fish has been poorly studied. To clarify the expression characteristics and function of amhr2, a 1536 bp CDS encoding 511 amino acids, was obtained from Paralichthys olivaceus, an important commercially cultured marine fish in China. The flounder Amhr2 protein was clustered with those from other teleosts, with the highly conservative motifs occurring in the C-terminal region. Gene collinearity analysis revealed that the amhr2 collaborates with specificity protein 1 (sp1) upstream, and proline-rich protein 13 (prr13) and poly (rC) binding protein 2 (PCBP2) downstream of the teleost genome. The predicted flounder Amhr2 protein was composed of a signal peptide, two transmembrane domains, and a conservative tyrosine protein kinase domain. Real-time quantitative PCR (qPCR) results showed that amhr2 was mainly expressed in the adult gonads, with significantly higher expression in the testes than in the ovaries (P<0.01). At stages I-V of the testis, the expression of amhr2 remained at a high level, whereas the expression level in the ovaries was significantly higher at stage I than at stages Ⅱ-V (P< 0.05). During the flounder gonadal differentiation period, gynogenesis (control, 20 ± 0.5℃, 100% female) and gynogenesis at high temperature (HT, 28 ± 0.5℃, 100% male) were used to detect the expression of amhr2. The results showed that the expression of amhr2 in the control group was highest at 2 cm total length (TL) and then decreased continuously, while the expression in the HT group first increased and then decreased. The inflection point of amhr2 expression in the HT group was at 6 cm TL, with the highest level. To investigate the effect of Amh on amhr2, we examined the co-localization of Amhr2 and Amh with Hela cells. Examination of subcellular localization showed that both Amhr2 and Amh were mainly located in the cytoplasm. Subsequently, the recombinant protein Amh of the flounder was obtained by prokaryotic expression. After in vitro incubation with the recombinant Amh, the expression of amhr2 in the testes showed no significant difference, whereas the transcription level in the ovaries increased significantly at 12 and 48 h (P<0.05). In addition, a dual luciferase reporter assay in HEK293T cells showed that co-transfection of Amh and Amhr2 could inhibit the promoter activity of the cytochrome P450 aromatase gene (cyp19a) (P<0.01), the key gene for estrogen synthesis. These findings suggest that amhr2 is mainly expressed in the testis, but its expression varies at different stages of the gonadal development. And amhr2 may affect the transcription of cyp19a together with Amh, which plays a role in the onset of the male phenotype formation and gonadal development in the flounder.

In order to understand the characteristics of macrobenthic communities in the intertidal zone for mangroves, two sections of bare flat, two sections with a small number of Spartina alterniflora distribution and two sections covered by Spartina alterniflora were selected in Beihai for ecological investigation, and the community structure of macrobenthic animals and its relationship with environmental factors were analyzed. There were 29 macrobenthic species in the survey area, and there were significant differences in mollusc biomass, arthropod habitat density and crab burrow number in different habitats (P< 0.05), and the species composition of macrobenthic animals was positively correlated with sediment skewness (P< 0.05). The HJ community structure was stable in the bare flat, but the community structure of macrobenthic animals in the other plots was unstable. The growth of Spartina alterniflora affects the structure of macrobenthic communities.

The copulation behavior, embryonic and post-embryonic development of Sphaeramia nematoptera were investigated in this study. The results showed that the mating behavior was dominated by females, mating between 1:00 and 3:00 am, and the reproductive cycle was 11~18 d without seasonal fluctuations. The release of eggs by female were 3126~4882 at a time, which were incubated by the male’s mouth. The fertilized eggs were suborbicular, (720±10) μm in diameter, with several oil globules inside. It took 187 h for a fertilized egg to be hatched under (27.0±0.5) ℃. The embryo development process included Cleavage, Blastocyst, Gastrulation, Neurula and Organ formation stages. The post-embryonic development could be divided into juvenile stage, larval stage, juvenile stage and adult stage. The whole length of the first hatchling was (2.8±0.1) mm, the height of the mouth cleft was (0.202±18) mm, and the juvenile opened its mouth to feed at the second day after hatching. Fins began to form and two black bands appeared on the body when ending the floating stage and entering the larval stage 24d after hatching. Scales were fully formed 50d after hatching and the body color and markings as well as other appearance characteristics were similar to the adult fish, which indicated that the fish entered the juvenile stage. Maturation of gonad was achieved 360d after hatching.

Based on the triangle model of urban safety resilience, this paper constructs a comprehensive risk assessment framework for storm surge disasters from the perspective of resilient cities. By using the data of 33 coastal districts in Fujian Province from 2011 to 2020, and through the urban resilience evaluation index system, this paper scientifically evaluates the spatial-temporal differentiation characteristics of urban resilience level in Fujian Province. With the help of geographic information analysis tools to evaluate hazard, vulnerability of storm surge disasters and urban resilience, the comprehensive risk assessment of storm surge disasters at the regional scale for Fujian Province is realized. The results show that: (1) the resilience level of coastal cities in Fujian Province in 2020 is at a descending order: Fuzhou, Xiamen, Zhangzhou, Quanzhou, Ningde, Putian; (2) with the improvement of urban resilience level, the storm surge disaster index of Fujian Province is showing a downward trend; (3) the comprehensive storm surge risk level I zone is mainly distributed along the Xinghua Bay and Meizhou Bay in Putian City; (4) we should pay attention to estuaries, trumpet shaped bays and other areas, focus on preventing typhoon storm surges along the northern and central routes, and formulate marine disaster prevention countermeasures and resilient city construction plans according to local conditions.

Mangrove wetlands provide important ecological support for ecological security, social and economic growth. In this paper, we discuss the temporal and spatial changes of mangrove wetlands in the Leizhou Peninsula during 1995—2020 by decision tree classification combined with the tidal pattern in different regions, based on Landsat Thematic Mapper (TM) and Operational Land Imager (OLI) sensing images. Improving the precision of mangrove information extraction is combined with artificial correction. Using high-resolution Google Earth remote sensing data, the classification accuracies in 1995, 2005, 2015, and 2020 were 99.79%, 98.95%, 99.45%, and 99.15%, and the corresponding Kappa coefficient of those years were 0.9913, 0.9642, 0.9624, and 0.9766. Over the past 25 years, mangrove wetland areas show a trend of early decrease followed by subsequent increase. The results were summarized as follows: (1) the Leizhou Peninsula’s mangrove wetlands are concentrated in wave sheltering bay or estuary, such as the Yingluo Port, Anpu Port, Qishui Port, Haikang Port, Wushi Port, Liusha Port, Wailuo Port, Leizhou Bay, Tongming Sea and Zhanjiang Bay, where silt deposits and tidal flats distribute widely. Lack of the above conditions, there is none of mangrove distribution in the seaboard of the Hai’an town of Xuwen county to the Jinhe town and east of the Wuyang town of Wuchuan county; (2) mangrove uniformly distributes all cities and counties of the Leizhou Peninsula. In early years, the Mazhang town has the largest mangrove, followed by Leizhou and Lianjiang, and Chikan has the least mangrove. Currently, Lianjiang has the largest proportion of mangrove forests; (3) the decreasing mangrove area is more than the increasing mangrove area, and half of area is lost in the Mazhang town; (4) the conversion of mangrove forest and non-mangrove mutual landscape occurrs to water, beach and mariculture. The monitoring analysis of regional mangrove forest provides a basis for the protection of mangrove wetland and the sustainable development of ecological resources.

The chemical constituents and their bioactivities of Aspergillus fumigatus DL-p0m-g2 from the Beibu Gulf were studied in order to obtain bioactive compounds. The compounds were isolated and purified by reversed-phase ODS column chromatography, semi-preparative liquid chromatography and other chromatographic methods. Their structures were identified by physicochemical properties, mass spectrometry and nuclear magnetic resonance spectroscopy. The cytotoxic, antibacterial and cholesterol transporter NPC1L1 protein binding activities of the isolated compounds were evaluated. As a result, a total of 21 alkaloids and one steroid were isolated and identified as 6-methoxyspirotryprostatin B (1), spirotryprostatin A (2), fumitremorgin C (3), cyclotryprostatin A (4), fumitremorgin B (5), pseurotin A (6), azaspirofuran A (7), azaspirofuran B (8), cephalimysin C (9), cephalimysin B (10), fumiquinazoline C (11), fumiquinazoline B (12), fumiquinazoline A (13), fumiquinazoline D (14), fumiquinazoline F (15), tryprostatin B (16), verruculogen (17), chaetominine (18), bisdethiobis(methylthio)glitoxin (19), helvolic acid (20), 7-deacetylpyripyropene A (21), terezine D (22). Compound 6 showed moderate cytotoxic activity against human hepatoma cells (HepG2), human lung cancer cells (A549) and human rectal cancer cells (HCT116). Compounds 1, 3 and 20 showed antibacterial activity against Staphylococcus aureus. Compound 14 showed a good binding with NPC1L1 protein, indicating its potential in the development of lipid-lowering drugs.

The volume scattering function (VSF, \beta \left(\theta ,\lambda \right)), the absorption coefficient a\left(\lambda \right), and attenuation coefficient c\left(\lambda \right) are the basic parameters of the inherent optical properties of seawater, based on the above parameters, all the inherent and apparent characteristic parameters of the seawater can be further deduced, and the important information data for the basic and front-end research on the primary productivity of the ocean and the global carbon cycle, as well as the military-civilian integration fields application such as the development of the water color remote sensing, the water environment monitoring and disaster early warning, the underwater light field distribution, target tracking, and the photovoltaic power generation will be supported. Limited by the strong directionality of VSF, its measurement technology is difficult and immature. In this paper, with the goal of high-frequency profile measurement of high-angle resolution multi-angle VSF and attenuation coefficient of seawater, a multiangle volume scattering function and attenuation coefficient meter (VSAM) that can simultaneously measure 17 angular VSFs, the attenuation coefficient, the profile depth and temperature information has been described, the measurement angle range of VSF is 10° ~ 170° with the interval of 10°, while the theoretical measurement frequency and deepest profile depth are 20 Hz and 200 m, respectively. With VSAM, the distribution of optical parameters of Sanya Bay and Yazhou Bay has been investigated and studied, and on the whole, the VSFs and attenuation coefficient of Yazhou Bay and Sanya Bay have large changes in horizontal, vertical and angle (for VSFs). The minimum and maximum of VSFs in 120° and 10°, respectively, and the maximum is two or more orders of magnitude larger than the minimum. The attenuation and VSFs show a decreasing trend from west (the Yazhou Bay) to east (the Sanya Bay) in the same water layer and an increasing trend from surface to underwater deeper in the profile at the same station. Combined with the results of water turbidity and chlorophyll concentration profile results measured during the same period, it is found that turbidity is the dominant contribution of the VSFs and attenuation coefficient of the Yazhou Bay, and it also has a good linear correlation with c_{\text{p}}\left(650\right) and {\beta }_{\text{p}}\left(90°,650\right) in these two bays. The attenuation coefficients and VSFs measured by VSAM are in good agreement with the attenuation coefficient measured by Viper (www.trios.de) and the VSFs by ECO-VSF3 (www.seabird.com) in the same stations and water layer during the same period.

The thermocline depth in the southwest tropical Indian Ocean (TIO) is shallow, and thermocline variations are closely related to the sea surface temperature, making southwest TIO feature a unique ocean-atmosphere interaction. Based on the observation and model data, this study analyzed the climatic effects of the southwest TIO SST warming on the tropical Indo-Western Pacific from April to June. The results show that the local convective activities are enhanced by the warming of the southwest TIO from April to June, and the precipitation in the southwest TIO increases. In the lower troposphere of the tropical Indian Ocean, a “C-shaped” wind anomaly pattern appears with abnormal northeast winds north of the equator and abnormal northwest winds south of the equator. From May to June, abnormal north-easterly winds in the North Indian Ocean can weaken the Asian summer monsoon, reduce the latent heat release of the North Indian Ocean, and warm the North Indian Ocean. The climatic effect of the southwest TIO SST warming is not limited to the tropical Indian Ocean region. The warming can heat the tropospheric atmosphere and stimulate the eastward atmospheric Kelvin wave, and the easterly wind response in the lower troposphere of the tropical northwest Pacific Ocean can also trigger local positive ocean-atmosphere feedback under the background of trade winds. Both are conducive to the maintenance of anticyclonic wind anomaly at the lower troposphere of the tropical northwest Pacific. The anticyclonic wind anomaly can enhance the monsoon water vapor transport in May and June, which makes the rainfall increase significantly over the Yangtze River Valley in China. This study reveals that the heating anomaly in the southwest TIO could cause ocean-atmosphere interaction across the north Indian Ocean and tropical western North Pacific Ocean, which would provide a useful reference for the summer precipitation forecast in eastern China.

Using the 18S rDNA V4 region as the target gene, Illumina Miseq high-throughput sequencing technology was applied to study the phytoplankton community in the seawater of the Shenzhen Bay during the four seasons from the winter of 2019 to the spring of 2021, and to compare with the historical data of harmful algal blooms species in this area, in order to explore the community composition and succession pattern of toxic and harmful phytoplankton in the Shenzhen Bay. The high-throughput sequencing results showed that the eukaryotic phytoplankton in the sea waters of the Shenzhen Bay consisted of 7 groups, including Bacillariophyta, Dinoflagellata, Chlorophyta, Ochrophyta, Haptophyta, Cryptophyta, and Rhodophyta, with a total of 82 families and 269 species. Among them, microphytoplankton was the main group, Nannochloris sp. was the dominant species in spring and autumn, Isochrysis galbana was the dominant species in summer, and Thalassiosira minima was the dominant species in winter. The phytoplankton diversity index in winter was the highest in the four seasons. A total of 32 species of toxic and harmful phytoplankton were detected in this survey, including 15 dinoflagellata species, 13 bacillariophyta species, 3 ochrophyta species, and 1 of haptophyta species. Compared with the historical data, the toxic and harmful phytoplankton in the Shenzhen Bay showed a miniaturization trend and an increasing diversity. The monophasic harmful blooms dominated by dinoflagellates or diatoms have been succeeded to polyphasic blooms of dinoflagellates and diatoms.

According to the molecular and morphological analysis, the species of Gracilariaceae was studied using the samples collected from Zhanjiang, Guangdong province, China. Four Gracilariaceae species were identified, namely: Gracilaria tenuistipitata, G. firma, G. edulis and Gracilariopsis bailinae. Their taxonomic characters and phylogenetic relationships were discussed in detail. This is combined with data from the literature to clarify that G. tenuistipitata, G. tenuistipitata var. liui and G. longirostris are the same species, and G. firma and G. changii are the same species. This study revised the taxonomic information of Gracilariaceae species in the coastal waters of southern China, and also provided a taxonomic basis for the conservation and development of macroalgae resources in Zhanjiang sea area.

In this study, ovarian development, reproductive cycle, egg development and its ultrastructure of Paphia textile in Beibu Gulf of Guangxi were investigated using anatomical observation, ovarian tissue sectioning and transmission electron microscopy techniques. The results showed that P. textile has one reproductive cycle in one year, and the ovarian development of P. textile can be divided into five stages: proliferating stage (May to July), growing stage (July to September), maturing stage (September to November), spawning stage (November to January of the next year), and resting stage (January to April of the next year). According to the relevant characteristics of the egg development and vitellogenesis of P. textile, it can be divided into four main stages: the first stage is the oocytes stage, the second stage is the phase of previtellogenesis oocytes stage, the third stage is the phase of vitellogenesis oocytes stage, and the fourth stage is the phase of postvitellogenic oocytes stages. The phase of vitellogenesis is an important stage of vitellogenesis, during which mitochondria, endoplasmic reticulum, golgiosome, lysosomes and other organelles form yolk granule in different ways. The water temperature in the sea area was closely related to the ovarian development of P. textile and was an important factor affecting the ovarian development of P. textile. P. textile is hermaphroditic, and no hermaphroditism has been found. The results of the study provide providing basic data for reproductive biology, artificial breeding, breeding and germplasm resources protection of P. textile.

In this study, anatomical observation, spermary tissue section, scanning and transmission electron microscopy techniques were used to study the spermary development, spermatogenesis and ultrastructure of mature sperm of Paphia textile in Beibu Gulf of Guangxi. The results showed that no hermaphrodites were found in the collected samples, and all the observed individuals were dioecious. The spermary development of P. textile was divided into five main stages: proliferating stage, growing stage, maturing stage, spawning stage, and resting stage. The maturing stage and spawning stage of P. textile was from September to January of the following year. Sperm development is divided into five stages: spermatogonia stage, primary spermatocyte stage, secondary spermatocyte stage, spermatid stage and mature sperm stage. The mature sperm of P. textile consisting of the head, middle and tail, overall length approximately 46.04 μm. The sperm head is divided into the acrosome and the nucleus. The acrosome is conical in shape and the nucleus is long and cylindrical. The anterior end was 0.71 μm in diameter and the posterior end was about 1.34 μm in diameter. The middle part consisted of four mitochondria encircled in a circular shape and two mutually perpendicular proximal and distal centrioles. The tail flagellum was about 38.8 μm long and 0.21 μm in diameter, and the external plasma membrane was covered with a typical “9 + 2” duplex microtubule structure. The results of this study provide basic research information for the reproductive biology, artificial seed breeding and germplasm resource conservation of P. textile.

To explore the histological and ultrastructural changes of the annual development of the testis and spermatogenesis of Lutraria sieboldii in Beibu Gulf of Guangxi, the annual development of testis and ultrastructure of spermatozoa of L. sieboldii were studied through tissue section, scanning and transmission electron microscopy. Results showed that the testis completes a cycle in one year, which can be divided into proliferating stage, growing stage, maturing stage, spawning stage and resting stage. The spawning was from December to April of the following year, and the testis development of 5% ~ 10% individuals in each stage was slightly delayed. Spermatogenesis can be divided into proliferation period, growth period, mature period and metamorphosis period. The male reproductive cell can be divided into Spermatogonia stage, primary spermatocyte stage, secondary spermatocyte stage, spermatocyte stage and mature sperm stage. The sperm of L. sieboldii belongs to the flagella type, whose total length is (39.76 ± 0.50) μm. The sperm head was composed of a nearly subelliptic spermatic acrosome and nucleus, the bottom of the acrosome and the spermatozoa connected with the spermatozoa were depressed to form a subacrosomal cavity. The electron density in the nucleus was uniform, and there was a gap in the middle of the nucleus. There are four mitochondria around the centriole complex to form the middle part of sperm, and the mitochondria are nearly round with apparent internal ridge. The plasma membrane wraps around the axial filaments to form sperm tail, and the “9 + 2” doublet microtubule structure can be clearly observed in the transverse section of the tail. In addition, there are two different types of spermatogonia: type A spermatogonia has no nucleolus in the nucleus while type B spermatogonia has nucleolus in the nucleus, and type B spermatogonia is distributed in the testis at different stages.

The island habitat and biological community composition are unique, but there are few reports on the island bdelloid rotifers. During 2021—2022, we investigated seven different habitats, i.e., moss, soil, leaf litters of bamboo, pine and other, petiolate plant petals and burned leaf stems, in the Weizhou island, Guangxi, to investigate species diversity and habitat preference of bdelloid rotifers. In the Weizhou island, a total of 53 species of bdelloid rotifers in three families, eight genera and 53 species were recorded, of which three species were newly found in China. The results showed that the species diversity of bdelloid rotifers in the island was high (accounting for 10.6% of the global reported bdelloid rotifer species). There was significant difference in species richness among the first four habitats (p < 0.0001), and the difference of species composition between different habitats is significantly greater than that within the same habitat (p = 0.001). The habitat preference of bdelloid rotifer is obvious. In addition, IndVal index analysis showed that 10 rotifer species had significant preference for special habitats. In the future, we should strengthen the investigation of island habitats, especially rare habitats, for the purpose of finding more species of bdelloid rotifers and enriching their geographical distribution in China.

To evaluate the nutritional value, taste activity and health risk, the content of fatty acid, hydrolyzed amino acid, free amino acid and heavy metal in Phascolosama esulenta from Beihai of Guangxi, Zhanjiang of Guangdong, and Ningde of Fujian were analyzed. Twenty-two types of fatty acids were detected in these three regions. The hypercholesterolemia index HI was 13.11 in Beihai, 14.09 in Zhanjiang, 16.64 in Ningde, the atherogenic index AI was 0.49, 0.49, 0.56, and the thrombosis index TI was 0.62, 0.75, 0.81, respectively. There were 17 hydrolyzed amino acids in each of the three regions, with a total amino acids (TAA) of 159.70 mg·g^-1, 155.97 mg·g^-1, and 161.49 mg·g^-1, respectively, and there was no significant difference. According to the Food and Agriculture Organization of the United Nations / Word Health Organization (FAO/WHO), when using the amino acid score (AAS) and chemical score (CA) as standards, the first and second limiting amino acids of the three regions of the P. esulenta are Met + Cys, and Val, respectively. In addition, the essential amino acid indexes (EAAI) were 11.14, 10.62 and 11.37, respectively, indicating that the three regions of the P. esulenta can all serve as ideal protein sources. The results of free amino acids showed that the P. esulenta of Beihai contained 15 kinds of free amino acids, while Zhanjiang and Ningde both contained 16 free amino acids, with a significant difference in total free amino acid content (p < 0.05). It was found that the taste activity values (TAV) of Glu, Gly and Ala in the free amino acids of the three regions were all greater than 1, indicating that these three amino acids contribute the most to flavor formation. Additionally, the heavy metal content analysis indicated that the heavy metal level in Beihai and Zhanjiang was Zn > Pb > Cu > As > Cd > Hg, while the content of heavy metals in Ningde was Zn > Cu > Pb > As > Cd > Hg. The single pollution index showed that the three geographic groups were all heavily polluted by the heavy metal Pb, of which Ningde was the most serious. The comprehensive pollution index showed that the heavy metal pollution of P. esculeata in the Beihai reached the threshold for slight pollution (P = 0.96), Zhanjiang and Ningde were moderately polluted (1 < P < 2). The single target hazard quotient (THQ) and the compound target hazard quotient (TTHQ) were all less than 1, indicating that there was no potential health risk for adults and children for the consumption of this species. The results provide a theoretical basis for the utilization and subsequent industrial precision processing of P. esculeata.

Mangroves are located at the junction between marine and land, and their carbon storage capacity depends on a variety of factors. In this study, the plant growth, biomass, soil organic carbon content and soil bulk density as well as the carbon storage in both vegetation and soil were compared in the mangrove communities in the Gaoqiao District, Zhanjiang, Guangdong, to study the individual and coupled effects of tree species and intertidal elevation factors on carbon storage. The results showed that carbon storage of mangrove communities was 4.98×10¹⁰ g and carbon density was 107.76×10⁶ g·hm^-2, and the carbon storage was mainly concentrated in soil. The carbon density of mangrove in different intertidal elevations were significantly affected by tree species, and the carbon storages of mangrove at low intertidal elevation was higher than those at middle and high intertidal elevation. The carbon storage of Sonneratia apetala communities was significantly affected by intertidal elevation. The carbon storage of Rhizophora stylosa communities at middle intertidal elevation and S. apetala communities at low intertidal elevation was greatest in this mangrove area, regardless of the perspective of vegetation carbon pool or soil carbon pool. In all mangrove communities, the vertical distribution of soil organic carbon content was homogeneous with no significant difference among soil layers. The vertical distribution of soil organic carbon contents at the high and middle intertidal elevation was influenced by tree species. Among them, the soil organic carbon content in the majority of Aegiceras corniculatum communities was significantly higher than those at the same soil layer of Kandelia obovata, Avicennia marina and S. apetala communities. However, tree species had no significant effect on the soil organic carbon content at the low intertidal elevation. Although the relationship of soil bulk density and soil organic carbon content was influenced by both tree species and intertidal elevation, the linear fitting results were mainly negative correlations. This study can provide a scientific basis for the selection of tree species and intertidal elevation for carbon sequestration in mangrove afforestation project.

The secondary metabolites of marine fungus Phaeosporiopsis sp. ZYX-Z-811 were isolated and identified, and their biological activities were evaluated. The compounds were separated and purified by Silica gel, C18, Sephadex LH-20 column chromatography and high performance liquid chromatography (HPLC), ten compounds were separated, and their structures were identified by NMR, IR and UV spectroscopic methods. Ten compounds were identified as 4-epi-lignicol (1), lignicol (2), 6-demethylkigelin (3), 6, 8-dihydroxy-3, 4, 7-trimethylisocoumarin (4), 6, 7-dimethoxymellein (5), musaone A (6), 2-(4-hydroxyphenyl)ethylacetate (7), 3-indole formaldehyde (8), indole-3-acetic acid methyl ester (9), methyl p-hydroxybenzoate (10), among which compound 1 was not published in journal, and the absolute configuration was determined by ECD calculation. These compounds were evaluated for antioxidant activity and α-glucosidase in hibitoryactivity, respectively, compound 10 showed weak antioxidant activities.

The secondary metabolites of marine actinomycete Streptomyces sporoverrucosus 33510 were studied in order to obtain bioactive compounds. The compounds were separated and purified by column chromatography, semi-preparative liquid chromatography and other chromatographic methods. Ten compounds were identified as cyclo(D-Pro-D-Leu) (1), bisphenol A (2), methylp-hydroxyphenylacetate (3), N-phenethylacetamide (4), 3-indole-methylethanoate (5), dibutyl phthalate (6), cyclo(D-Pro-L-Leu) (7), cyclo(D-Pro-L-Ile) (8), cyclo(L-Pro-L-Phe) (9), and cyclo(L-Leu-L-Val) (10). Eight compounds were isolated from Streptomyces sporoverrucosus for the first time. Compound 2 showed inhibitory activity against Cryphonectria parasitica.

In order to investigate the secondary metabolites in hydranth of coral Goniopora columna, the ethanol extracted products were isolated and purified by silica gel column chromatography, Sephadex LH-20 gel column chromatography and semi-preparative high-performance liquid chromatography (HPLC). Their structures were identified by modern spectral technology. Meanwhile, the cytotoxicities of 1 ~ 8 were tested against anti-non-small cell lung cancer A549 cells (NSCLC) lines. As a result, a new alkaloid 1 and seven known compounds 2 ~ 8 were isolated and identified as alkalgoniopora A (1), theophylline (2), thymine deoxyribonucleoside (3), uracil (4), thymine (5), pregna-5, 20-dien-3β-ol (6), cinnamic acid (7) and protocatechuic acid (8). Among them, compounds 1, 2 and 6 had weak inhibitory activity on the proliferation of NSCLC, while other compounds had no obvious inhibitory activity on the proliferation of NSCLC. This investigation provides a reference basis for the study of metabolites and exploration of medicinal activity in hydranth of coral Goniopora columna.

Traditional bioreef genesis theory either lacks evidences for algae forming strong bioreef anti-wave frameworks or attributes them to an accessory reef biotic community. In this paper, microfocal X-ray (X-CT) scanning imaging technology is used to study the core of the Aethesolithon nanhaiensis reef framework rocks and Halimeda reef proglottid rocks of Miocene age in Wells Xike 1 and Xiyong 2. Through three-dimensional tomography visual perspective images, it was found that the wave resistance structure of algal reef created by calcareous algal organisms, including typical Aethesolithon nanhaiensis reef framework structure, baffle-structure rocks and Halimeda reef proglottid structure. It also verifies that algal reefs are important Miocene oil-gas reservoirs in the South China Sea depositional basins by quantifying the throat, areal porosity and porosity parameters using threshold approach. Besides, the genetic model of algal reef is put forward: the reef-building calcium algal algae adapted to the sea level rise and fall gradually succession-replacement, and after calcification, burial and fossilization, dolomitization, sedimentary algal reef dolomitization, resulting in the growth of the longitudinal sequence of the Xisha Reef in Miocene.

There are a lot of disputes over the initiation time of seafloor spreading in the Central Basin of South China Sea by comparison of magnetic lineations due to its multiplicity. It is necessary to re-define this important node of time because of data and new result accumulation in the SCS during the recent decades. It has been verified by this study that the Late Eocene and early Oligocene strata (T₇—Tog sequence) developed at southern and northern sides of initial spreading areas in the Central Basin, which indicates that the geological age of bottom stratum on oceanic basement was older than 32—33 Ma. At continental margins of the SCS, the structure movement of long lasting time, intensively activity and forming a structure system of E-W trend in the SCS took place approximately at 40 Ma, and it is more precise to take seismic reflector T₈ (37.2—40 Ma) as the break-up of the initial seafloor spreading of the Central Basin according to the comparison of unconformities. Therefore, the conclusion is the initial time of seafloor spreading of the Central basin was roughly 39—40 Ma.

A large number of core sampling data were obtained from marine geological survey. Different kinds of measurement data have different sampling depths, resulting in irregularly scattered distribution of 3D geological sampling. The irregularly scattered data on the three dimensional were not able being clustered using traditional clustering algorithm especially in the case of big data analysis. The present study designs a clustering algorithm for irregular geological sampling data based on spatial interpolation. In this way, the 3D geological scatter data can be effectively reduced to 2D data, and the computational complexity can be reduced. This algorithm can better solve the classification and analysis of inequality measurement data in geological bodies, and provides a basic technical method for marine geological big data analysis.

Based upon the deep seismic data and IODP drilling results, this study focuses on the mechanism of rifting and breakup processes of the northern South China Sea. During the implementation of the project (2018—2023), a 3D deep seismic survey was carried out during the Chinese National Natural Science Foundation Open Research Cruise (No. NORC2018-08). A total of 52 ocean bottom seismometers (OBSs) and 2 ocean bottom electro-magnetometers (OBEM) were deployed and a total of 8750 shots were fired. 49 OBSs and 1 OBEM have been recovered, and a large amount of data (294 GB) have been acquired. At the same time, a series of innovative results are obtained: 1) the 3D velocity structure of the COT in the northern margin of the SCS has been obtained for the first time, and the COT domain with width of 10 ~ 20 km is determined in 3D view; 2) the active magmatism was revealed in the northern margin of the SCS, and the styles of interaction between tectonism and magmatism were proposed in different geological stages; meanwhile, the magmatism propagated seaward and progressively increased during extension; 3) the geological model of rifting and breakup is established as the type of marginal seas, whose breakup occurred in a crocodile style dominated by basalt due to the strong magmatism during end-rifting, accompanied with significant along-strike variations in the tectonism and magmatism. This project builds up the opening mode of the SCS from the perspective of 3D deep seismic data, and promotes the Chinese basic research of the marginal sea, which has far-reaching scientific and strategic significances.

The key to unconventional oil and gas development, such as shale gas and tight oil and gas, is to improve quality and efficiency and reduce costs. This paper illustrates the adaptability of using local quartz sand instead of ceramsite as the mainstream proppant in the thin interbed tight sandstone of the L1 formation of the Fushan Oilfield, offshore Hainan, to optimize the fracture conductivity at low cost, and the laboratory test evaluation results of Hainan local 20/40 mesh quartz sand and 20/40 mesh ceramsite are provided. Under different stress and paving concentration, 20/40 mesh quartz sand and 20/40 mesh ceramsite have different conductivity; this further reveals the results of field tests conducted for two development wells with similar geological parameters on the basis of numerical simulation optimization tests. The fracture conductivity reaches 21 D·cm, which can meet the demand of tight sandstone reservoir in the L1 Formation. Under the stress condition of 35 Mpa, 10 kg·m^-2 laying concentration of 20/40 mesh quartz sand can obtain more than 21 D·cm conductivity. Field tests show that the quartz sand test well has the same effect as the ceramic test well in the early stage after fracturing. With longer production time, the cumulative oil production and stable production life of ceramsite well exceeded that of local quartz sand development well. Therefore, the economic benefits of ceramic-based proppant are higher and ceramic-based proppants are worth continuing to be used on a long-term and large-scale basis.

Coral reef ecosystems are important components of marine ecosystems and play a crucial role in maintaining marine ecological balance and biodiversity. This article summarizes the current international and domestic development status of coral reef ecology through literature review. The major international research focuses include global change and coral reef ecosystems, establishment and maintenance of coral symbiosis, development and evolution of coral reef biotic systems, coral reef biodiversity and species distribution patterns, as well as coral reef ecosystem conservation and management. The major domestic research focuses include global change and coral reef ecosystems, coral-algal symbiosis under global change, diversity of coral symbiotic relationships, human activities and the South China Sea coral reef ecosystem, and coral reef biodiversity and community patterns. The future development trends in coral reef ecology research will emphasize the coral and coral reef ecosystems under the context of global change, coral symbiotic mechanisms, marginal coral reefs, and coral reef conservation and restoration. Future research in coral reef ecology in China should enhance global perspectives, strengthen domestic and international collaborations, explore underlying mechanisms, improve systematic research, and enhance coral reef conservation and restoration studies.

Coral reef ecosystems play a crucial role in global carbon cycling and climate change. They serve as potential blue carbon sinks, with coral reefs in China covering approximately 11% of the global area. The annual carbon sequestration of these reefs is estimated to be 3.5×10⁶~4.5×10⁶ t. The total carbon storage capacity of coral reef ecosystems is immense, and they have significant potential value as carbon reservoirs in carbon trading. This article provides a review of carbon sequestration processes and storage mechanisms in coral reef ecosystems, including carbonate pumping, biological pumping, and microbially-mediated carbon pumping. The research progress on these three carbon pumps is discussed. Additionally, the article highlights the limitations and challenges in current research and proposes future research directions, aiming to provide scientific basis for the conservation and management of coral reef ecosystems in the South China Sea.

There is a taxonomic uncertainty on the species classification of Cladopsammia gracilis and Rhizopsammia wettsteini as well as the unresolved status of the closely related genera Cladopsammia and Rhizopsammia. In order to further analyze the phylogenetic relationship between C. gracilis and R. wettsteini, we examined the micromorphological and microstructural features and systematically compared the gene structure, genetic distance and codon preference of two mitochondrial genomes. The results show that there are three distinct characteristics: reptoid budding, costae and septa. The genome composition of the two species is very similar, containing 13 protein-coding genes, 2 rRNA genes and 2 tRNA genes. Unlike most scleractinians, there were no overlaps between genes. In addition, phylogenetic analysis based on CO1 genes show that C. gracilis and R. wettsteini are closely related but distantly related to other species of the genera Cladopsammia. The present study highlights the need for an integrative approach to conduct a deeper species delimitation of genera Cladopsammia and Rhizopsammia.

Light is one of the most important factors influencing the growth and distribution of reef corals, but the physiological response and adaptability of reef corals to low light is not well understood. In this study, we used an in-situ shading experiment with three typical coral species (Pocillopora verrucosa, Porites lutea and Dipsastraea matthaii) to test how physiological response of corals under light limitation. The experiment site is located at the depth of 10 meters of the Yongle atoll, in which the irradiance in the shaded area was reduced by 80%~90%, and the photosynthetically active radiation (PAR) ranges from 20.2 μmol photons·m^-2·s^-1 to 41.5 μmol photons·m^-2·s^-1. The results showed that the physiological parameters of three corals changed significantly under light limitation. During 7-day experiments, the effective photosynthetic efficiency (Φ _PSII) of the three corals increased, while the maximum electron transport rate (r-ETR_max) and the minimum saturating irradiance (E_k) decreased significantly. Meanwhile, the zooxanthellae density (except Dipsastraea matthaii), chlorophyll a content, tissue thickness and tissue biomass of the three corals decreased in diverse degrees, with the most severe reduction found in Porites lutea that the zooxanthellae density and tissue biomass decreased by 14.2%and 32.9%, respectively. These results suggest that the reef corals adapt to shading by improving their effective photosynthetic efficiency in short-term light limitation, but the energy transformed by photosynthesis could not meet the metabolic needs of coral growth, thus coral tissue biomass and tissue thickness decrease.

We studied the responses of coral Acropora hyacinthus to the increase of CO₂, with a simulated experiment in which corals were cultured in natural seawater as the control group with pCO₂ of 565 μatm and in high CO₂ treatment with pCO₂ of 1135 μatm. The effects of seawater acidification on the calcification and gene expression were investigated. The results showed that under acidification stress, the calcification rate of A. hyacinthus significantly decreased, and the gene expression was greatly affected. As the pathways of organic matter transport, anion transport, chemical stress were up-regulated, and animal organ development, lipid transport, cell biosynthesis, cell surface receptor signal and other pathways were down-regulated. Among the calcification related genes, carbonic anhydrase was down-regulated, and Ca²⁺-ATPase and calcium ion transport related genes were up-regulated. This experiment showed that high CO₂ significantly affected the calcification and gene expression of A. hyacinthus, in which the decrease of calcification was mainly due to the down-regulation of carbonic anhydrase resulting in the decrease of $\mathrm{HCO}_{3}^{-}$.

To explore the effects of ocean warming and acidification on coral growth and calcification rate, two widespread coral species, Pocillopora damicornis and Galaxea fascicularis, in the Luhuitou area of the Sanya Bay, were selected for a 28-days controlled incubation experiment. With the interactive treatments of temperatures and pCO₂, our results indicated that corals were significantly affected by seawater acidification. Moreover, acidification affected strongly the growth rate of G. fascicularis and the calcification rate of P. damicornis. The chlorophyll fluorescence index (F_v/F_m) of the symbiotic zooxanthellae in P. damicornis was significantly higher than G. fascicularis. Interestingly, the quantitative study showed that there was an antagonistic effect between temperature and pH at some levels, which could effectively alleviate coral bleaching. Thus, we concluded that the growth and calcification rate exhibited interspecific specificity in response to seawater warming and acidification.

Coral communities in the northern South China Sea (SCS), which have the potential to act as regions of refugia for many coral species in the face of global warming. However, the temporal and spatial diversities of coral communities in the northern SCS and the effects of coral bleaching caused by marine heat waves are still unclear. In this study, the status of coral communities across the northern SCS, including the Daya Bay, the Weizhou Island, the Xuwen and Luhuitou fringing reefs, and the space differences are studied on the basis of ecological materials in the field investigations during August 2020, and its response to marine heatwaves. Our results indicate that coral communities across the northern SCS show remarkable regional characteristics. The dominant species composition, species number and α diversity index of coral communities are subject to significant regional differences, and the live coral cover is higher in the Luhuitou and Daya Bay (37.78% and 17.97%, respectively). Thus, the coral communities in Xuwen and Weizhou were subject to mass coral bleaching events during the field investigation, and the coral bleaching rate and mortality rate was 84.78% and 10.68%, 65.52% and 0.70% in Xuwen and the Weizhou Island, respectively, while no coral bleaching occurred in the Daya Bay and Luhuitou. Based on historical data analysis, although the live coral cover of coral communities in the northern SCS has dropped significantly since 1980s, there has been a recovery trend in recent years; the proportion of heat bleaching tolerant genera and heat bleaching resistant genera increased in the coral communities of the Weizhou Island, Xuwen and Luhuitou. In general, the coral community in the northern SCS has a strong resistance to heat bleaching. Strengthening the conservation and management of coral reef areas is crucial for the restoration and refuge of coral communities in the northern SCS under global warming.