In order to explore the relationship between zooplankton community structure and environmental factors in the Oujiang River Estuary, four voyages were conducted in March (winter), May (spring), August (summer) and November (autumn) in 2021 to investigate the zooplankton and other environmental factors such as sea temperature, salinity and chlorophyll a concentration in the Oujiang River Estuary sea area. The results show that 78 species of zooplankton are identified, including 16 species of larva, it belongs to 8 classes and 14 categories , with the highest number of species in summer (47 species) and the lowest number in winter (23 species). The dominant species (Y ≥ 0.02) include Calanus sinicus, Sinocalanus sinensis, Acartia pacifica, and Centropages dorsispinatus, 17 species. The average annual abundance of zooplankton is (162.95 ± 310.96) ind./m³, and the average annual biomass is (118.85 ± 62.80) mg/m³. The abundance and biomass of zooplankton are the highest in spring and the lowest in autumn. The abundance in winter is higher than that in summer, and the biomass is lower than that in summer. The average annual Shannon-Wiener diversity index (H'), Pielou evenness index (J') and Margalef richness index (D) are 1.500 ± 0.702, 0.656 ± 0.270 and 2.301 ± 1.087, respectively. Spearman correlation analysis and canonical correspondence analysis show that sea temperature, salinity, Chl a concentration and phytoplankton abundance are important environmental factors affecting the dominant abundance of zooplankton in the Oujiang River Estuary. It provides scientific reference for the study on the influence of seasonal environmental changes on zooplankton in the Oujiang River Estuary, and provides basic data and theoretical basis for the sustainable development of biological resources in the Oujiang River Estuary.

Based on the survey data of fishery resources and environment of four voyages from April 2021 to January 2022, the spatial and temporal distribution of Portunus trituberculatus and its relationship with influencing factors in the Ruian sea area were studied, including its marine dominance, community structure and resource density distribution. At the same time, generalized additive model (GAM) is used to analyze the relationship between resource density and influencing factors. The results showed that: in the Ruian sea area, P. trituberculatus is an important species (100 ≤ IRI < 1 000) in spring and summer and a dominant species (IRI ≥ 1 000) in autumn and winter. The average carapace length and body weight of P. trituberculatus ranged from 33.9 mm to 60.4 mm, and 22.9 g to 126.1 g. The carapace length and body weight of P. trituberculatus were the highest in summer and the lowest in autumn. There were significant differences between different seasons. P. trituberculatus showed negative allometric growth in spring, summer and winter (b < 3), and positive allometric growth in autumn (b > 3). The average resource density of P. trituberculatus ranged from 16.57 kg/km² to 422.60 kg/km², with the highest in autumn and the lowest in spring, and the average resource density in autumn was 25.5 times of that in spring. GAM analysis showed that the interpretation rate of the model was 80.2%. Season, surface water temperature, bottom water temperature, bottom salinity and surface chlorophyll a concentration had significant effects on the resource density of P. trituberculatus (p < 0.05), among which season had the greatest effect. Through this study, it provides reference for grasping the dynamic change law of P. trituberculatus resources in Ruian sea area, and further provides theoretical support for the proliferation and release of P. trituberculatus.

To understand the characteristics and distribution of benthic shellfish communities in the vicinity of the Nanji Islands, we conducted bottom trawl surveys in the surrounding waters during October 2022 (autumn) and March 2023 (spring). The findings reveal that a total of 49 benthic shellfish species were captured, spanning 2 classes, 6 orders, and 17 families. During spring, the average abundance of benthic shellfish was (2 429 ± 2 038) ind./Agt, with an average biomass of (4 849.79 ± 2 513.84) g/Agt. In autumn, the average abundance was (1 149 ± 1 589) ind./Agt, with an average biomass of (4 985.30 ± 2 159.23) g/Agt. The primary dominant species comprised Turritella bacillum, Murex trapa, Tegillarca nodifera, Inquisitor jeffreysii, Bufonaria rana, Cancellaria sinensis and Trigonaphera bocageana. Notably, Turritella bacillum emerged as a dominant species in both spring and autumn, with dominance significantly surpassing that of other species. The dominance of benthic shellfish communities in this marine area appears relatively stable, with the community’s functionality and nature being primarily governed by a select few species. This study provides a reference basis for the dynamic changes in the marine ecosystem of the Nanji Islands and offers foundational data for the protection of marine ecological environments.

Wastewater is usually discharged into the sea in the form of jet, and its dilution process is the result of the interaction of jet, wave and tidal current. In this study, based on the reasonable assumptions, the governing equations are integrated to the form of ordinary differential equations. According to the hydrodynamic characteristics of the jet in the wavy current environment, the entrainment and drag force functions of the jet are introduced to close the governing equations, thus the integral model for the turbulent jet under the combined action of waves and currents is established. Through comparison and verification, it is confirmed that the integral model can accurately simulate the time average movement and dilution process of the near-field jet under the wavy current environment. It is found that compared with a pure current environment, the influence range of jet on the surrounding water is larger than that in a wavy current environment, and the dilution capacity of jet can be remarkably enhanced by the wave effect. Based on the momentum integral simulation results, the empirical fitting formulas for the position of the jet cross-sectional trajectory line and the minimum dilution in the wavy current environment are established. The developed model could be served as an efficient and accurate tool to assess the environmental impacts of submarine outfalls on the surrounding waters.

As a national key construction sea area, the trend of offshore wind power construction in the Jiangsu sea area towards the open sea is the main trend of future development. The open sea areas have more surge components, and the wave spectrum often appears in the form of bimodal spectrum. Therefore, the wave characteristics of bimodal spectrum waves need further in-depth research to provide reference basis for offshore construction. Based on the observation data of the buoy station throughout 2018, 1223 bimodal spectral data were obtained through outlier testing and bimodal spectral identification. The bimodal spectral characteristics of waves in the Jiangsu sea area were studied, and different typical bimodal spectral types were compared. The fitting of the measured bimodal spectra was carried out, and the corrected spectral width parameters were proposed. The dependency relationship between the correction coefficient, peak rise factor, and spectral width parameters was explored, and the bimodal spectral fitting expression was obtained. The results indicate that the Ochi–Hubble spectrum proposed based on the North Atlantic sea area and the Torsethaugen spectrum proposed based on the Norwegian sea area are not applicable to the bimodal spectrum type in the Jiangsu sea area. The bimodal JONSWAP fitting spectrum proposed in this paper has adaptability and can scientifically and reasonably describe the bimodal spectrum in the Jiangsu sea area, and is widely applied to different wind and terrain conditions in the sea area.

Based on the non-hydrostatic model SWASH, a numerical wave flume was established to systematically investigate the hydrodynamic characteristics of the interaction between waves, mangroves, and vertical sea dikes through a comparative experiment with and without mangroves. The study analyzed the influence of factors such as wave steepness, relative water depth, Ursell number, mangrove length, density, and characteristic diameter on the wave height in front of the sea dike and the maximum wave pressure on the windward side of the sea dike. The results indicate that in the absence of mangroves, the Goda formula cannot accurately estimate the impact load on the vertical sea dike. In a numerical experiment with a model scale of 1∶10, a 2 m-wide mangrove in front of the dike was observed to reduce wave height by 6% to 45% and wave pressure by 11% to 74%. However, in conditions with relatively large wave heights and smaller characteristic parameters of the mangrove, an increase in the wave height in front of the dike by approximately 4% to 26% was noted. In the hydraulic conditions considered in this study, the maximum wave pressure decreased by 58% to 93% with a decrease in wave steepness, by 42% to 72% with an increase in relative water depth, and by 87% to 96% with a decrease in the Ursell number. The attenuation rates of wave height and wave pressure in front of the dike non-linearly increased with the increase in the width, density, and characteristic diameter of the mangroves. These findings provide a scientific basis for a deeper understanding of the wave-damping effects of mangroves, as well as for the design and planning of coastal protection projects combining mangrove ecosystems with sea dikes.

Using multiple observational subsurface temperature and salinity datasets based on Argo, we analyze the trend of 0–1 500 m ocean heat content in the Pacific between 2004 and 2020. It was found that the long-term trend of the Pacific ocean heat content showed a shift in 2013. The ocean heat content in 2013–2020 increased rapidly compared with that in 2004–2012. The linear trend of the former reaches about 0.50 × 10²² J/a, which is significantly higher than that of the latter. The Pacific has recently experienced rapid warming. During 2013–2020, the largest linear trend of the ocean heat content in the Pacific appeared in the western North Pacific, followed by the Tropical Pacific and eastern North Pacific. While the ocean heat content in the entire South Pacific showed a slightly decreasing trend. In the western North Pacific, the rapid increase of ocean heat content was concentrated in the Kuroshio Extension areas, and this warming trend is likely to be caused by the northward shift of the Kuroshio Extension main axis. It is worth mentioning that there was a local decreasing trend of ocean heat content in the sea south of Japan, and this cooling trend is associated with the strengthening of the Kuroshio large meander. In the Tropical Pacific where the warming trend is the second largest, the rapid increase of ocean heat content is likely to be induced by the thermocline deepening. In addition, we point out that the rapid warming in the Pacific is reflected by the rapid rise of sea level. The linear trend of sea level per 1 cm/a corresponds to the linear trend of ocean heat content of 0.11 × 10⁹ J/(m²·a). This study elucidates the rapid warming of the Pacific since the end of the global warming hiatus, deepening our understanding of recent thermal conditions in the Pacific.

Quantitative studies on the spatial distribution of geometric parameters of complex submarine sand waves in the developmental area are rare, and the correlation between the complex geometric parameters of sand waves and environmental variables has not been clarified. Based on measured data of water depth, sediment grain size and flow velocity in the western area of Hainan Island, the environmental variables of the study area were quantified and extracted. The morphological parameters of complex submarine sand waves were calculated using an automated extraction and analysis method, and the correlation between sand wave geometric parameters and environmental variables was analyzed. The results show that the morphological characteristics of submarine sand waves in the study area are complex and variable, with an average wavelength ranging from 64 to 340 m and an average wave height ranging from 0.39 to 4.13 m. There is a strong positive correlation between wave height and steepness, as well as between wave height and the average angle of the lee side. There is also a strong positive correlation between wavelength and symmetry, and a strong positive correlation between median sediment grain size and the average angle of the lee side and wave height. The development of submarine sand waves in the study area is less influenced by water depth. Under the action of tidal currents, sediment transport is mainly by traction, and the erosion of submarine sand waves is relatively weak. The evolution of sand waves is mainly characterized by vertical growth and migration, with wave height growth prioritized over wavelength increase. Under stable tidal flow conditions, regional sediment supply and sediment grain size can both affect the scale of submarine sand waves.

Beach nourishment, as a widely-adopted soft solution to coastal erosion, can effectively alleviate the beach erosion induced by the construction of artificial islands. This paper takes the nourished beaches on both sides of the wave shadow zone of an artificial island in Haikou Bay as an example. Based on the bimonthly surveys of beach profiles and shorelines since nourishment, the characteristics of beach erosion and accretion and the associated driving factors were analyzed by using empirical orthogonal function (EOF) and digital shoreline analysis system methods. The EOF results showed that the first two eigenvalues accounted for more than 90% of the total variance, which could reflect the main spatio-temporal changes of the beaches. The area with conspicuous changes, corresponding to the first spatial mode, was located between the outer edge of the beach berm to the mean sea level, in which there were significant differences between the nourished beaches on both sides of the wave shadow zone and the natural beach in the wave shadow zone. The temporal mode showed that the most significant changes of the nourished beaches occurred in the initial four months after nourishment, followed by mild profile changes. The second spatial mode demonstrated the impact of typhoons on the beaches, resulting in the accumulation and leveling of some low-lying sites on the beach berms in the wave shadow zone. This study found that the evolution of nourished beaches under the influence of an artificial island in Haikou Bay could be divided into two stages. The first stage was the adaptation period, during which the artificially designed beach profile adjusted to the equilibrium state for adapting to the local hydrodynamics. The equilibrium time of nourished profiles was approximately 4 months, during which beach changes were dominated by cross-shore sediment transport. The second stage was dominated by the longshore sediment transport induced by the artificial island, resulting in sediment transport from the eastern and western sides of the artificial island to the wave shadow zone. At that time, the nourished beach shoreline in Haikou Bay had not reached the equilibrium state. The beaches on both sides of the wave shadow zone would continue to retreat in the future, while the shoreline in the wave shadow zone would advance into the sea for about 690 m until it reaches the equilibrium. This study would be helpful for the analysis of the beach evolution and beach restoration of similar cases.

Tidal flats maintain a complex ecosystem, while its formation is driven by multi-factor interaction, including hydrodynamics, sediment transport, and biological processes. In particular, investigating tidal flat biological processes and elucidating their biological-physical effects are current research hotspots and challenges in the field of marine science. This study focused on intertidal biofilms, constructed a two-dimensional biomorphodynamic model which coupled biofilms with hydrodynamics, sediment transport, and bed level change, to explore the role of biofilms in sediment transport and geomorphological evolution. The biomorphodynamic model was validated using literature data, indicating that the constructed model can simulate the growth pattern and interannual variation of biofilms well. Model results show that tidal creeks with biofilm attachment are more fully extended towards the landward side, showing a branching distribution when hydrodynamics are weak, and biofilms were distributed on both sides of the intertidal zone. Through quantitative analysis of tidal creek morphology, it is found that the presence of biofilms promoted an increase in the number of tidal creek and their development in the vertical direction, while limiting the increase in their width. Compared to tidal flats without the influence of biofilms, the average depth of tidal creeks increases, the total area decreases, the total length increases, the average width decreases, and the overall volume increases. The research outcome of this study deepens the understanding of the role of biofilms on tidal flat evolution and provides a scientific basis for coastal zone protection and ecological restoration projects.