Based on eddy dataset, this paper analyzed the spatial distribution and temporal variation characteristics of the generation location, quantity, size, lifetime and moving trajectory of mesoscale eddies in the South China Sea. In terms of the generation location, the eddies were mainly generated in the sea areas to the southwest of Taiwan island and to the west of Luzon island, and the cyclonic and anticyclonic eddies had their own main generation locations in different seasons. In terms of the number of eddies generated, the number of cyclonic eddies was greater than that of anticyclonic eddies. The total number of eddies was relatively the largest in winter, and the prevailing was cyclonic eddies. The total number of eddies was the least in summer, and anticyclonic eddies were prevalent. In terms of eddy size, the average radius of anticyclonic eddies was slightly larger than that of cyclonic eddies. The average radius was the largest in fall and the smallest in spring. Except in fall, the average radius of anticyclonic eddies was greater than that of cyclonic eddies. In terms of eddy life, the average life of anticyclonic eddies was slightly longer than that of cyclonic eddies. The average life was the longest in winter and the shortest in fall. The average life of cyclonic eddies was longer in winter and fall, but opposite in summer and spring. From the perspective of eddy trajectory, most of the eddies to the southwest of Taiwan island moved southwestward along the edge of the continental shelf after generation. Most of the eddies to the northwest of Luzon Island moved locally after generation, and most of the eddies to the southwest of Luzon island moved westward after generation. In addition, the main parameter characteristics of eddies in the South China Sea were also related to the El Niño phenomenon.

Under the changing environment, the stationary of tide level observation data was destroyed, and the traditional hydrological frequency analysis method was not applicable. In this paper, the measured tidal level data of Shek Pik station in Hong Kong from 1998 to 2020 were selected, and the GAMLSS model of distribution parameters time-varying was used to analyze the non-stationary of tidal level series. Then, based on the optimal GAMLSS model, the corresponding design value of tidal level was deduced by using the expected number of exceedances, design life level, equal reliability and average design life level methods. The results showed that the design value of tide level based on non-stationary conditions could provide reference for the design and construction of coastal and marine engineering under the changing environment.

Water exchange capacity is an important indicator of evaluating the environmental capacity and environmental quality of the bay. The strength of the capacity will directly affect the water quality of the bay. The water exchange capacity is closely related to the size of the water flux. In this study, a numerical model of the hydrodynamics of the Bohai Strait was constructed using the Deleft3d model based on a rectangular grid, driven by the eight subtidal reconciliation constants of M₂, S₂, N₂, K₂, K₁, O₁, P₁ and Q₁. By comparing with the measured data, the model can simulate the hydrodynamic conditions of the Bohai Strait waters very well. On this basis, the hydrodynamic conditions of each waterway cross-section in the Bohai Strait were simulated, and the water fluxes each waterway in this sea area during large, small and medium tides as well as the whole semimonthly tides were further estimated to evaluate the water exchange capacity each waterway. The results showed that Old Tieshan waterway has a large water flux, and the high and low tides can basically reach more than 0.5 Sv, which is the area with the strongest water exchange capacity in the Bohai Strait sea area and also the main water exchange channel in the sea area. In addition, the water flux of other waterways is relatively small compared with the old Tieshan waterway, and the water exchange capacity is weak. However, these waterways are also important channels of circulating seawater and maintaining water quality in the sea.

Seawater conductivity is one of the important physical parameters of seawater. Intense seawater movement caused by typhoon can lead to changes in the temperature, salinity structure of seawater and the seawater conductivity. In order to study the influence of typhoon on the conductivity distribution of seawater, the HYCOM temperature, salinity and pressure data during Typhoon Nakri in 2019 were used to calculate the conductivity, and the spatial and temporal distribution characteristics of seawater conductivity under typhoon were analyzed. It was found that the influence of the typhoon on seawater conductivity existed lag and persistence in time. During the strengthening process of the typhoon, the conductivity of the sea surface significantly decreased from 5.5 S/m to 4.9 S/m with a low value center appearing. The maximum diameter of the conductivity range affected by typhoon could reach 550 km. In addition, the vertical distribution of seawater conductivity also significantly changed during the typhoon and the depth of seawater conductivity affected by the typhoon was about 200m. The thickness of the mixing layer increased about 20 m under the influence of typhoon and the mixing layer bottom conductivity decreased about 0.4 S/m.

The local scour around offshore wind turbine foundations has become an increasingly prominent issue, posing a serious threat to the overall structural stability and presenting significant challenges for operation and maintenance. Suction anchor foundations have garnered widespread attention due to their numerous advantages and inherent scour resistance performance. This study developed a coupled numerical model of the umbrella suction anchor foundation, seabed, and tidal currents, systematically investigating the effects of current-induced loads on the scour range, morphology, and depth around the foundation. The study compared the scour morphology and maximum scour depth under different flow conditions. The unidirectional flow condition was taken as a baseline, and the contribution mechanisms of two different hydrodynamic environments to the scour around the foundation were analyzed in detail. The results indicated that, compared to unidirectional flow, the scour depth and flow velocity profile under tidal currents exhibited significant differences. The reciprocating feature of the flow field induced by tidal currents played an important role in the scour evolution process around the foundation and the tidal scour depth reduction coefficient. This study provided new insights into the scour mechanism of seabed soil under the influence of tidal currents and offers theoretical guidance for the optimal design of offshore wind turbine foundations.

The scattered offshore wind turbine and clustered aquaculture cages ascertain the potential for their integration. The development model of offshore wind turbine-fish farm integration is of great significance for the promotion of marine economic development and the construction of marine ecological civilisation. In order to effectively use the space of wind farm, this study proposed a wind-aquaculture integration scheme that combined wind turbine monopile foundation and elevatable cage. Based on the lumped-mass method, a mathematical model of wind-aquaculture integration structure was developed, and the effects of different wave-current conditions and different diving depths on the dynamic characteristics of the outline rope were analysed. The results showed that the maximum tension of the upper rope was significantly greater than that of the lower rope, the tension of the leeward side rope was greater than that of the windward side rope, and the increase of the diving depth could reduce the extreme value of the tension. The results of this study could provide a reference basis for the design and safety analysis of the wind-aquaculture integration structure.

When an offshore decommissioned oil and gas platform is dismantled, releasing its structural components as artificial reefs and building reefs on the platform is an economical, green, low-carbon and ecological effective treatment method. However, the studies on the hydrodynamic performance of decommissioned platform structure to reef have not been widely carried out. In this study, the artificial reef-based flare boom was taken as the main researching object. Through CFD numerical simulation, the changing characteristics of the flow field effect of the artificial reef under different flow velocity, flow angle and the combination arrangement with jacket structure were studied. The results showed that the volume and height of the flow site can be maintained at a higher level when the flow is placed at less than 30° from 0° to 90°. When the artificial reef and jacket structure were placed together, the flow fields around the adjacent reefs influence each other, and some upwelling areas are connected with each other. Compared with the separate placement of artificial reef and jacket in different places, the combination placement can make the overall flow field of reef group produce positive expansion effect, and the formation of artificial reef group in situ is an ideal way to carry out platform reef building engineering.

Oscillating buoy wave energy generation device captures energy through oscillation. Its surface must subjected to the continuous action of complex loads. It is important to improve the stability of the buoy operation to explore the load characteristics of the float subjected to the action of complex marine environment. Based on the continuity equation and the recombination model RNG k-ε of Reynolds-Averaged Navier-Stokes equations (RANS), the coupling process of wave-flow interaction with the buoy was simulated, the three-dimensional numerical wave-flow model was built and the accuracy of the model was verified. Through the numerical model, the distribution characteristics of the impact pressure under wave-current action on the buoy and the variation pattern of wave-current load were investigated. The results showed that the impact pressure of the buoy has obvious cyclical under wave-current action. The pressure at the rear of the buoy is greater than that at the front and the pressure range is more concentrated. Wave steepness parameter and Froude number are the main factors affecting the maximum horizontal wave-current force. The scattering parameters have little effect on the maximum horizontal wave-current force and the maximum vertical wave-current force.

This paper studied the statistical characteristics of observed wave height and wave period distributions in the shallow area of the subaqueous Yellow River delta, and the relationship between relative wave height, spectrum width and wave breaking was further analyzed. The reasons for the deviation of statistical wave height/period distribution from theoretical distribution were also discussed. Conclusions were drawn as follows: (1) When the relative wave height was less than 0.18, the wave height conformed to Weibull distribution, the wave period to Longuet-Higgins distribution, and the joint wave height-period to Sunfu distribution. (2) When the relative wave height was higher than 0.18, the probability of wave breaking in the study area was greater than 4% and the spectral width was greater than 0.5, and the measured wave elements did not conform to the theoretical distributions. (3) There was a linear relationship between spectral width and breakage probability with the correlation coefficient of 0.62.

The South China Sea is one of the most active areas of internal wave activity in the world. In this paper, a total of 1001 GF-1 satellite remote sensing images of the northern South China Sea from 2019 to 2021 were used to extract the wave direction and wave train information of 881 internal waves. The frequency of internal waves in the northern South China Sea was obtained, and the corresponding spatial internal wave distribution map was drawn. From the position distribution of the multi-year wave crest line, it could be found that the deep-sea basin in the northeastern South China Sea, the vicinity of the Dongsha islands and the eastern part of Hainan island were the three main sea areas where the internal waves were concentrated in the northern South China Sea. The single internal solitary waves in the deep-sea basin originate from the Luzon strait and the number of observable waves were small. The number of internal waves near the Dongsha islands was the largest, and the abrupt terrain was the main reason for the generation of complex wave group systems. The frequency statistics of internal waves showed that the internal waves in the northern South China Sea showed obvious seasonal periodic changes due to the influence of solar radiation and ocean stratification. The peak period of internal wave activity in the South China Sea was from May to September every year. The frequency of internal waves in May and June was the highest in the whole year. The frequency of internal waves continued to increase during the transition from spring to summer, and the frequency continued to decrease during the transition from autumn to winter. The frequency of internal waves in winter was the lowest in the whole year. The statistical results obtained from the remote sensing observations of GF-1 matched the measured results of on-site anchor system.

A Sequencing Batch Biofilm Reactor (SBBR) was used to establish an aerobic denitrification process (AD-SBBR) based on mixed-culture systems. The effect of DO (dissolved oxygen) on the nitrogen removal efficiency and microbial community of AD-SBBR treating marine recirculating aquaculture wastewater was investigated. Different from the pure strain Halomonas sp.HRL-11 which had the highest NO^-₃-N removal rate of 91.5% when the optimal DO is 7.48 mg/L, the AD-SBBR had excellent aerobic denitrification performance under aerobic conditions (DO varying between 2 and 6 mg/L), above 96% nitrogen removal efficiency of NO^-₃-N and TN, and no NO^-₂-N accumulation. At the DO concentration of 6 mg/L, AD-SBBR exhibited the maximal NO^-₃-N removal efficiency of 99.2% and the maximum SNRR of 7.34 mgN/(g VSS(h). When DO was 6 mg/L, the periplasmic nitrate reductase (Nap) activity related to aerobic denitrification in AD-SBBR sludge was up to 6.31 U/mg protein, which was 38.7% higher than that when DO was 2 mg/L, which was 38.7% higher than that at DO concentration of 2 mg/L. The genes, napA/B, encoding Nap enzyme in AD-SBBR sludge, accounted for up to 33.7% among the entire genes encoding nitrate reductase. The species richness in AD-SBBR sludge increased with the increase of DO concentration and reached the maximum at DO concentration of 6 mg/L. The dominant species of aerobic denitrifying bacteria among AD-SBBR sludge at different DO concentrations was Pseudomonas-stutzeri.

Xiaoqing River is a typical small river in North China, which is low in runoff but high in pollutant concentration. In order to address the migration and transformation of nitrogen and phosphorus and evaluate the aquatic quality precisely, the different forms of nitrogen and phosphorus were monitored from lower reach to the mouth of Xiaoqing River Estuary in May, August, October and December, 2018 and May, 2019. The results showed that, the contents and compositions of total nitrogen and phosphorus obviously varied temporally and spatially, with the general tendency of decreasing from high in freshwater to low in seawater. Dissolved inorganic and organic nitrogen dominated comparably while particulate nitrogen was averaged at 3.9%. Phosphate and particulate phosphorus primarily contributed to the total phosphorus by >60% in river water and >50% in sea water correspondingly while dissolved organic phosphorus contributed less. The compositions and distributions of nitrogen and phosphorus were primarily regulated by physical and chemical factors and the phosphorus composition related to biological factors as well. Nitrogen and phosphorus were significantly removed from the aquatic system generally; however, dissolved organic nitrogen and particulate phosphorus were imported in certain month. The results provided a solid evidence for the exact monitoring on nitrogen and phosphorus, and assessment and management of the aquatic quality of small estuaries in North China.

In order to understand the pollution characteristics of heavy metals in surface sediments of Laizhou Bay, the concentrations of heavy metals including Hg, Cu, Pb, Cd, Cr, Zn, As in 7 samples were measured by atomic absorption spectrophotometry and atomic fluorescence spectrometric. The index of geoaccumulation and the potential ecological risk index were then employed to evaluate the pollution degree and potential ecological risk of seven heavy metal elements in the sediments. The results indicated that the average contents of seven heavy metal elements in surface sediments of Laizhou bay were Hg(0.05 mg/kg)、Cu(13.63 mg/kg)、Pb(25.36 mg/kg)、Cd(0.15 mg/kg)、Cr(30.26 mg/kg)、Zn(63.43 mg/kg)、As(7.86 mg/kg), respectively. The pollution level of heavy metals in sediment by geoaccumulation index (I_geo) followed the order: Hg>Pb>Cd/Zn>Cu>Cr>As, and the pollution level of Hg and Pb were particularly severe. According to the potential ecological risk factors (Eⁱ_r), the level of potential ecological risk of Hg and Pb were particularly high, the potential ecological risk of other elements followed the order: As>Pb>Cu>Cr>Zn. The ecological risks near stations 3, 5 and 6 in the study area were more severely, and other areas were in the low level.

To assess the combined impact of high temperature and petroleum hydrocarbon stresses on the growth and photosynthesis of Zostera marina seedlings, we established three Water Accommodated Fraction (WAF) concentration groups, 0 mg·L^-1, 10 mg·L^-1 and 20 mg·L^-1. Each treatment was subjected to two cultivation temperatures, 15°C and 20°C, for a period of >6 days. We observed the changes in leaf morphology, leaf length, wet weight, maximum photochemical quantum yield (denoted as F_v/F_m), fluorescence quenching parameters including qL and Non-Photochemical Quenching, NPQ, and the photosynthetic electron transfer rate (ETR) of Z. marina seedlings. The findings suggested that the combined stresses of high temperatures and petroleum hydrocarbons can detrimentally affect the leaf morphology and the growth and development of Z. marina seedlings. Chlorophyll fluorescence parameter analysis indicated that the combined stresses significantly curtailed the photosynthetic capabilities of the seedlings. Moreover, our findings revealed that high temperature acts as the primary inhibitory factor within the combined stresses. Interestingly, low concentrations of petroleum hydrocarbons appeared to mitigate the suppressive effect of high temperatures on Z. marina seedlings. However, with the increase of petroleum hydrocarbon concentration, the inhibitory impact on the growth of the seedlings, their development and photosynthesis intensified.

Due to global climate change, environmental pollution and human activities, the degradation trend of coral reefs in the South China Sea is serious. Genetic diversity of reef-building corals is very important for the restoration and protection of coral reef ecosystems. In order to obtain molecular markers suitable for the analysis of genetic diversity, simplified genome sequencing of Platygyra daedalea was performed using RAD-Seq, and MISA software was used to identify the microsatellite loci on RAD-tags. The characterizations of microsatellite loci were analyzed by bioinformatics methods, and the polymorphisms of microsatellite loci were test using Wenchang population. The results showed that a total of 6,862 microsatellite loci were detected, of them tetranucleotide microsatellite motif was the highest, 2,294 in total, accounting for 33.43% of the total. The second richest was trinucleotide microsatellite motif, 2,223 in total, accounting for 32.40% of the total. One hundred and twenty-four pairs of primers were designed randomly and tested among 33 individuals of P. daedalea. A total of 20 primer pairs showed polymorphism. The allele range of 20 microsatellite loci was from 4 to 13. The ranges of observed heterozygosity, expected heterozygosity and polymorphism information content were from 0.143 to 0.875, from 0.256 to 0.867, from 0.248 to 0.853, respectively. The microsatellite markers developed by RAD-seq in this study can be used in the characterization and conservation analysis of P. daedalea.

Based on the two-dimensional nonlinear sea surface model and the framework of the two-scale scattering method, the Doppler shift of Ku-band radar echoes return from sea surface had been investigated. In order to weight the Doppler shift, the scattering coefficient (NRCS) evaluated by the Ku-band dual-polarized (HH/VV) empirical geophysical model function (Ku-MOD) was employed to replace the traditional Bragg NRCS results. Furthermore, the influences of tilt modulation and hydrodynamic modulation of large scale waves on Doppler shift were also analyzed in detail. The results indicated that, since the tilt modulation was more significant in the HH polarization case than in the VV polarization, the tilt modulation had a larger effect on the Doppler shift of HH signal from sea surface. Besides, there was no significant difference in the effect of hydrodynamics modulation on the Doppler shift of the HH polarized and VV polarized radar echoes. The Doppler shift caused by different factors was sensitive to the change of azimuth angle, and its absolute value increased with the increase of wind speed. Finally, a semi-empirical model for Ku-band sea surface echoes Doppler shift was developed based on the simulated results and polynomial fitting method.

As a new method used in shallow water survey, continuous resistivity profiling has shown great potential in water engineering survey, environmental assessment and disaster investigation in recent years. However, the key factor restricting development of continuous resistivity profiling is the low resistance shielding effect of water. This study took the domestic first set of independent research and development on air type E60sea resistivity detection system as an example. The arrangement was made for the device and power strength through the electrostatic field theory and frechet derivative calculation. The electric field sensitivity distribution and theoretical measured potential difference of the device under the background of different dielectric resistivity were obtained, and the theoretical potential difference was detected in situ for validation. The results showed that the sensitivity of electric field was only related to the arrangement of devices. The maximum detection depth was about half of the total length of arrangement of devices. The measured potential difference was affected by the device offset, power supply electrode distance, power supply current, dielectric resistivity and other factors. The in-situ detection result was close to the theoretical calculation, indicating that the theoretical calculation value had high reliability.

The reliability of SMAP satellite remote sensing sea surface salinity data for salinity observation in the Yangtze River Estuary and its adjacent waters was verified using in situ data in spring, summer and autumn seasons from 2019-2021, and the deviation of SMAP satellite data was reduced from 0.62 to 0.26 after fitting correction, and its reliability was improved. The SMAP satellite data was firstly used to analyze the monthly average distribution of the salinity of the Yangtze River diluted water, and then the seasonal variation of the sea surface salinity of the Yangtze River Estuary and its adjacent waters was analyzed by the EOF method, and finally the SCHISM model was applied to reproduce the detachment process of the Yangtze River diluted water. The remote sensing of sea surface salinity had enriched the study of sea surface salinity in the Yangtze River Estuary and its adjacent waters, and was useful for the study of the detachment of the Yangtze River diluted water and low-salinity water masses.

The Yellow River delta was once the fastest land-building delta in the world. However, in recent decades, it is facing an erosion crisis due to a sharp decline in water and sediment load to the sea caused by climate change and strong increased human activities. Therefore, the evolution of the Yellow River delta is of great concern to scientist and society worldwide. In this paper, based on multi-period bathymetric data, the spatial and temporal characteristics of accumulation-erosion of typical isobaths were analyzed by calculating the enveloping area of the isobaths. Meanwhile, the water and sediment discharges at Lijin station from 1976 to 2018 and the marine dynamics data were used to reveal the main control mechanism of the evolution of different sedimentary units. The results showed that: (1) The Qingshuigou mouth changed from deposition to erosion because of the diversion to Qing 8 in 1996, and the south lobe within 5 m water depth slowly accreted due to the influence of gradual weakening of marine dynamics and sediment dispersal pathway. In the Gudong nearshore area, as part of the Qingshuigou mouth at the beginning of the 1976 diversion, all the isobaths accreted seaward from 1976 to 1980. With the sharp decrease in the water and sediment load and the southward migration of the Qingshuigou mouth, the subaqueous delta of the Gudong was subjected to erosion by the action of marine dynamics. The shallow-water area was continuously eroded during 1988-2015 due to dike construction, wind, waves and tidal shear fronts, while the deep-water area was slowly deposited under the influence of northward accretion of the current river mouth. In the current river mouth of Qing 8, all the isobaths accreted seaward during 1996-1998, the deep-water area turned into erosion due to the sharp decline of the water and sediment load during 1998-2002, while the shallow water continued to silt up. The sediment discharge had increased after the conduction of the water-sediment regulation scheme in 2002, substantially increasing sediment particle size. The changes in sediment dispersal patterns and the blocking effect of the tidal shear caused the current river mouth accreted seaward with the rates in shallow waters higher than that in deep waters.

Reclamation is an important way to exploit marine space in coastal areas. However, large-scale and unreasonable reclamation activities may damage the ecological environment of near-shore marine areas, therefore, timely monitoring of the evolution of reclamation has become an important research task. Based on Landsat TM/ETM+/OLI image data for the years 2000, 2005, 2010, 2015 and 2020, the present study extracted and analyzed the dynamic evolution characteristics of reclamation along Dalian urban coast in the past 20 years. Results showed that: 1) The overall area along Dalian urban coast continued to grow during the 20 years, reaching 237.38 km² by 2020. The main types of reclamation had shifted from fisheries to industrial and not yet utilized types. 2) Reclamation was mainly distributed in important ports and bays along the coast, as well as in economic zones and industrial zones adjacent to ports or airports. 3) The changes in the scale and distribution of various reclamation types presented multi-stage characteristics. Before 2010, the increase of reclamation mainly came from new additions. While after 2010, dynamic transfers between types were frequent. Some of the abandoned breeding space and industrial salt pans were eventually shifted into urban construction, industry and transportation reclamation to meet urbanization development needs. 4) The landscape pattern of the reclamation was strongly influenced by coastal human activities. The morphological complexity of the various types of patches had increased, and landscape diversity was increasing year by year. The overall development of reclamation tended to be homogenization and intensive utilization. In general, combining the results on the evolutionary characteristics of reclamation with relevant policies could more effectively guide the scientific planning and governance of marine resources in the study area.

The rapid development of coastal mariculture industry in China has caused severe environmental problems, thus the evaluation of suitability for marine aquaculture has become an important tool for scientific management and rational development and utilization of mariculture space resources. In this study, we built an evaluation model which considered the habitats, cultivation environment and infrastructure conditions of three representative species of Sanmen Bay in Zhejiang Province. ArcGIS was used to analyze the spatial data and visualization of results. The most suitable cultivation areas for laver, oyster and large croaker were 184.49km², 115.27km² and 87.57km², respectively, accounting for 20.37%, 12.79% and 9.70% of the total of Sanmen Bay, respectively. From the comprehensive analysis of evaluation results, Shepan waterway, Baijiao waterway, Gaotang village sea area and offshore area of Shipu Port have the potential of developing integrated multi-trophic aquaculture, which form an integrated ecosystem. The cultivation scale of laver could be appropriately increased in the coastal waters to alleviate the eutrophication problem in the bay, and the mixed cultivation mode of shellfish and algae could be gradually established. The results of the empirical study could provide a technical support and a reference for mariculture development in Sanmen Bay and regional suitability evaluation of mariculture in China.

In this study, the phytoplankton and environmental factors of Zhangzidao aquaculture waters were investigated from September 2020 to August 2021. The temporal and spatial distribution characteristics of phytoplankton community structure were studied, and the relationship between phytoplankton and environmental factors was explored. A total of 115 species belonging to 60 genera and 5 phyla of phytoplankton were identified, including 80 species of diatoms, 32 species of dinoflagellates, 1 species of chrysophyta, 1 species of cyanobacteria and 1 species of chlorophyta. The range of phytoplankton abundance varied between 8.1×10³ and 486.3×10³ cells/L. Seasonal variations of phytoplankton abundance were observed, with the highest values in summer followed by those in autumn. There is no obvious regularity in spatial distribution. There were 30 dominant species of phytoplankton, 17 species of diatoms and 13 species of dinoflagellates, of them, 6 species belonged to poisonous algae. The non-parametric test (Kruskal-Wallis test) showed that the diversity index H ′ and evenness index J of phytoplankton had significant seasonal differences (P<0.05), and the diversity index H ′ and evenness index J of phytoplankton in autumn were significantly higher than those in summer. There was no significant difference in environmental factors among different stations in the same season (P>0.05). By comparison, temperature, salinity, inorganic nitrogen, ammonia nitrogen, nitrate and nitrite had extremely significant difference among seasons (P<0.01). The results of RDA analysis showed that diatoms were significantly affected by phosphate while dinoflagellates were significantly affected by nitrate and nitrite.

Mangrove wetlands are blue carbon ecosystems that have an important impact on the global carbon cycle. Their carbon storage function has a positive effect on mitigating climate change caused by greenhouse gases. In this study, Gaoqiao core area and its surrounding area of Zhanjiang Mangrove Nature Reserve in Guangdong Province were selected as the studying area based on six Landsat remote sensing images. The change of coastal wetlands dynamically in Gaoqiao study area from 1977 to 2017 was analyzed by comparing normalized vegetation index (NDVI) and land type change matrix. It was found that the change of mangrove wetland in Gaoqiao studying area is mainly caused by the change of land use type formed by human activities. The mangrove wetland experienced the degradation process before 1986 and gradually recovered since the establishment of the provincial nature reserve in 1990. However, problems such as pollution discharge, urban construction and lack of management have been threatening the ecological environment. The change of mangrove wetland area plays a decisive role in the blue carbon sink by affecting aboveground biomass accumulation, sediment carbon storage, lateral transport among others. The carbon storage in the Gaoqiao studying area also changes with the wetland area, showing a trend of first decreasing and then increasing.

In this study, the grain size analysis, AMS¹⁴C dating, and common and trace elements and rare earth elements analyses of ZJK31 columnar sediment samples from the Pearl River Mouth Basin were used to illustrate the geochemical characteristics and the material source in the studying area. The results showed that there are two layers of the ZJK31 columnar sediment samples from 80 to 100 cm depth, and may have rapid changes from 8 ka BP to 4.5 ka BP. Besides, the R-mode factor analysis pointed out that the sedimentation of the Pearl River Mouth was mainly influenced by terrigenous clastic, marine biological and marine chemical sedimentations. Moreover, the rare earth elements and the ratio stated that the provenance areas of ZJK31 columnar sample include the Pearl River, Taiwan River and Hainan Island. Through the calculation of end element mixed model, it is found that the contribution of rivers in Hainan Island to the study area has decreased significantly since 4.5 ka BP. It is speculated that the summer monsoon weakened since 4.5 ka BP, and the ability of summer surface flow to continue to carry River materials from Hainan Island to the studying area decreased.

In order to explore the current situation of heavy metals in sediments of marine pasture and its adjacent waters in Haizhou bay, the contents and distribution characteristics of eight heavy metals (Zn, Cu, As, Cr, Cd, Pb, Ni and Hg) in this area were analyzed, and their sources were analyzed by correlation, principal component analysis and positive definite matrix factor model. The ecological risk of heavy metals in surface sediments was evaluated by geo-accumulation index and potential ecological risk index. The results showed that As, Cr, Cd, Cu, Ni and Zn showed a decreasing trend from the inshore aquaculture area to the offshore natural sea area. Pb decreased first and then increased; Hg was gradually increasing. Source analysis showed that As, Cu, Zn, Cd, Cr and Ni mainly came from pollutants discharged into the sea by Linhong river, Pb mainly came from marine transportation, and Hg mainly came from natural sources such as sedimentary parent materials. The results of risk assessment showed that Cd in sediments was slightly to moderately polluted, while other heavy metals were basically pollution-free, and the overall level of potential ecological risk was low. The quality of sediments in the study area was generally good, so it is necessary to focus on the discharge of heavy metal pollutants near the shore.

The Jiaozhou Bay wetland is characterized by diverse biological species and abundant water nutrients, holding an important developmental status in the Jiaodong Peninsula region. Based on remote sensing data of the Jiaozhou Bay wetland from 2003 to 2021, combined with methods such as the ecological service value evaluation model, we investigated its ecological evolution and dynamic changes in ecological service value. The results showed that (1) from 2003 to 2015, the wetland area decreased from 3.96×10⁴ hm² to 3.49×10⁴ hm², with a gradually slowing reduction trend, and recovered to 3.56×10⁴ hm² by 2021; (2) the ecological service value provided by the Jiaozhou Bay wetland has continuously declined in the past two decades, from 1 381.53×10⁷ yuan in 2005 to 1 124.71×10⁷ yuan in 2020, and the downward trend has slowed over time; (3) among the ecological service values supplied by the Jiaozhou Bay wetland, aquatic product supply, water quality regulation and climate regulation account for more than 90%, demonstrating the crucial role of Jiaozhou Bay wetland in regional ecological and economic development.

In order to identify the characteristics of marine economic vulnerability in coastal areas more accurately, in this study, we introduced the Catastrophe Progression Model (CPM) that does not need to be substituted into the index weight calculation, and adopted the Criteria Importance Through Intercriteria Correlation (CRITIC) method to improve the index importance ranking problem in the Catastrophe Progression Model, and creatively proposed the CRITIC-CPM model. Based on the connotation of marine economic vulnerability and the composition of the marine economic system, an indicator framework of economy-resources-environment-society is proposed. We selected 36 evaluation indicators, and used the constructed CRITIC-CPM model to evaluate the marine economic vulnerability in coastal areas of China. Based on vulnerability analysis and by mapping with GIS technology, the temporal and spatial distribution characteristics and abrupt changes of marine economic vulnerability in coastal areas of China from 2006 to 2018 were discussed at provincial and regional spatial scales, and the obstacle degree model was introduced to measure the main influence factors. The results showed that (1) the coastal areas of China economic vulnerability as a whole are at moderate vulnerability levels; (2) in terms of time, such vulnerability shows the characteristics of overall decline, local abrupt changes and obvious stages. Tianjin, Hebei and Jiangsu are becoming more vulnerable while Zhejiang, Fujian, Guangdong and Hainan are becoming less vulnerable and Liaoning, Shanghai, Shandong and Guangxi are fluctuating in change; (3) the spatial distribution pattern is high in the south and low in the north, and the vulnerability of the three marine economic circles decreases from south to north; and (4) the main obstacle factors are different among coastal areas, but the area of marine protected area per capita, the supply of marine products per capita and the total number of invention patents are the three obstacle factors with the highest frequency. Finally, we put forward specific suggestions for the future development direction each region.

Marine carrying capacity is an important indicator of the carrying capacity of resources and environment and achievement of sustainable development. In this study, an evaluation index system of marine carrying capacity is constructed, which consists of three aspects, the pressure of marine economic and social development, the supporting capacity of marine resources and environment and the regulatory capacity of marine development and protection. The marine carrying capacity of Jiangsu Province from 2010 to 2019 was evaluated using the comprehensive evaluation method. Based on Weber Fechner′s law, the threshold interval of the state of marine carrying capacity was determined. Finally, the obstacle factors restricting the enhancement of marine carrying capacity were identified with the obstacle degree model. From 2010 to 2019, the marine carrying capacity index of Jiangsu Province increased from 0.5184 to 0.5849, showing an “N-shaped” fluctuation-rising trend, rising first, then falling and then rising again. The marine carrying capacity was at a critical overload state from 2010 to 2012 and from 2016 to 2018, and at a loadable state from 2013 to 2015 and 2019 with a stable and good trend. From the perspective of barriers to marine carrying capacity, the contribution of barriers to the marine carrying capacity of Jiangsu will expand from the centralized to the decentralized from 2010 to 2019. The main factors restricting further improvement of the marine carrying capacity of Jiangsu are insufficient resource development, space resource supply, environmental pollution, resource regulation and scientific and technological investment.

The development strategy proposal of marine disaster prevention and mitigation in Shandong Province were given basing on analyses of strengths, weaknesses, opportunities and threats (SWOT analysis) under the current situation. The advantages of marine disaster prevention and mitigation in Shandong Province mainly include knowledge of significant disaster characteristics, completeness of scientific and technological talents and coping system construction. The disadvantages contain few practitioners and lack of innovation platform. The opportunities include clear policy guidance and rapid technological development. The threats mainly contain the permanence of disaster and increasing refinement of demand services. In order to improve the comprehensive ability of marine disaster prevention in Shandong Province, the following four countermeasures are proposed, promotion of disaster risk management, compaction management of responsibility, improvement of the level of intelligence and enhance awareness of disaster prevention and mitigation.

Marine spatial resources are an important guarantee for economic growth in coastal areas. In the context of territorial spatial planning, it is significant to measure the comprehensive using efficiency of marine development space, which promotes the rational allocation of marine resources and the sustainable development of the marine economy. Existing research has achieved certain results in the using efficiency of sea areas and intensive sea area usage. The efficiency measurement method for marine development space needs to be further explored. Based on the super SBM-Malmquist model, the comprehensive using efficiencies of Zhoushan, Ningbo, Taizhou, and Wenzhou, from 2011 to 2021, were analyzed. The results showed that from 2011 to 2021, Zhoushan’s comprehensive using efficiencies of marine development space were at a higher level among the four research objects. The improvement of the scientific and technological of the marine industry drove the improvement of Zhoushan’s comprehensive using efficiency.

In order to conduct an in-depth analysis of the evolution process and innovative logic of the marine fishery resource protection system of China, In this study, we used the Citespace visual literature analysis tool to visually analyze a total of 463 relevant literature retrieved from the Chinese core journals of the CNKI General Library from 1992 to 2022, including keywords such as fishery resource protection, fishery system and fishery policy. The cited frequency is greater than 1. The number of publications in the early stage of the study was relatively small, and in the middle stage, it showed a tortuous growth state. Currently, the overall number of publications is in a stable state. The active publishing institutions are mainly marine universities. Lack of cooperation among high-yield researchers. The research on the protection system of marine fishery resources in China can be divided into the initial stage (1992—2000), the rising stage (2001—2011) and the development stage (2012—2022). The innovative evolution logic of the fishery system of China has the following three aspects (1) the decisive driving force of the decline of marine fishery resources; (2) the internal drive under the influence of national ocean and fishery management policies; and (3) the external drive formed under the inspiration of advanced fisheries management systems in developed countries abroad.

Regional Fisheries Management Organizations (RFMO) serve as the primary mechanism underlining governing global high seas fisheries today. For China, participating in RFMO is integral to the development of its distant-water fishing industry and engagement in international fisheries governance. While China has accrued considerable experience through its participation in RFMO, the domestic theoretical foundation for RFMO remains relatively underdeveloped, exhibiting some limitations in both breadth and depth. There are foundational studies on establishment and operation of RFMO, but they often lean toward descriptive accounts and tend to be fragmented without a focus. Most of these studies pertain to conservation and management measures of RFMO, but there is relatively less studies on specialized topics. While there are also scattered studies focusing on individual RFMO, they haven’t formed a comprehensive and systematic analysis including each RFMO in a global context. Researches specific for the involvement of China in RFMO, particularly regarding the discursive power of China within these organizations are limited in quantity. Consequently, domestic studies on RFMO are inadequate for supporting the substantive participation of China in RFMO, necessitating strengthening in terms of systematicity, pertinence, continuity, comparability, practicality and prospective. In the future, a concerted effort should be made to consolidate theoretical researches on mechanisms, organizational characteristics and developmental changes of RFMO. Additionally, the proactive exploration of applied researches to enhance the discursive power of China through substantive RFMO engagement should be prioritized.