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.

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.

Study on the coral reef canopy hydrodynamics not only provides guidance for the health of coral reef ecosystem and the ecological restoration project, but also supports the decision-making process for the reef coast hazard prevention and mitigation under extreme wave events such as the typhoons. Meanwhile, it also has significant value for predicting the sediment transport over the reef and the reef coast evolution. This paper reviews the state-of-the-art research on reef canopy hydrodynamics, and systematically summarize the research progress from three aspects: the flows inside and outside of reef canopy, the characteristics of canopy resistance as well as the simulation of canopy resistance. This paper finally proposes the further research directions as follows: future study can focus on the hydrodynamics under more severe wave condition or under combined action of wave and current. It should also fully consider the anisotropy of canopy skeleton. Moreover, it can solve the Navier-Stokes equations directly to reproduce the finer flow field at the canopy scale.

Beach is a common and vulnerable coastal ecosystem with huge ecological service functions. Due to the multiple impacts of climate change and human activities, beach ecosystem has been seriously damaged. Beach nourishment is an effective approach to prevent coastal erosion and improve the beach environment by using sand replenishment to restore beach morphology. Previous nourishments have often neglected the impacts on beach ecosystem. Many studies show that beach nourishment have multifaceted, multi-scale and complex impacts on beach ecosystem. Based on reviewing previous researches, the compositions, characteristics and functions of beach ecosystem are summarized. The basic characteristics of beach ecological damage, the impact process and mechanism of beach nourishment on beach ecosystem at various scales are analyzed. Then, some adaptive measures for beach nourishment are suggested from the perspective of reducing negative ecological impacts, which would support coastal management and sustainable utilization of beach.

Based on the high-resolution oceanic numerical model product of MITgcm with a resolution of (1/48)°, the geostrophic balanced motion and unbalanced wave motion are decomposed via the frequency-wavenumber spectrum analysis method to analyze the distribution of submesoscale characteristics and diagnose the main factors affecting their seasonal variations in the Agulhas current system. The results show that the submesoscale processes in the Agulhas current system have a significant seasonal distribution with strong features in winter but weak features in summer. The mixed layer baroclinic instability is the main reason affecting the submesoscale seasonal differences in the area. In addition, the geostrophic balanced motions are predominant in the submesoscale process in the regions with stronger eddy kinetic energy (EKE) and have no obvious seasonality. For the regions with weaker EKE, the balanced and unbalanced geostrophic motions show significant seasonality, where the local mixing layer shallowness is responsible for the increase of the unbalanced kinetic energy in summer. Our analysis helps to further clarify the characteristics of submesoscale seasonal variation and its primary factors in the Agulhas current system. The effective separation of geostrophic balanced and unbalanced motion enhances our understanding of energy transformation between multiscale processes in the ocean.

The Sardinops melanostictus and the Scomber japonicus are important economic species in the northwestn Pacific Ocean, and exploring the correlation between their habitat changes is conducive to the rational development and management of fishery resources. This study utilizes fishery data of Sardinops melanostictus and Scomber japonicus in the northwestern Pacific Ocean from June to November between 2017 and 2021. By incorporating three key environmental variables, namely sea surface temperature, sea surface height, and chlorophyll a mass concentration, habitat models with different weights are constructed. The models are then validated using fishery data from 2021. The optimal models are selected to predict the most suitable habitat distribution of Sardinops melanostictus and Scomber japonicus under different El Niño-Southern Oscillation (ENSO) events. The study analyzes the differences and synchronicity in the spatial and temporal distribution of the most suitable habitat between the two species under different ENSO events. The results indicate that the suitable habitat area of Sardinops melanostictus (above 15%) was higher than that of Scomber japonicus (less than 6%) under different ENSO events; however, the growth rate of the most suitable habitat area for Sardinops melanostictus under La Niña events is higher than that of El Niño events. The former has a growth rate of 0.197 and the latter has a growth rate of 0.123, on the contrary, the growth rate of Scomber japonicus under the La Niña event is lower than that of El Niño event, the former has a growth rate of 1.114 and the latter has a growth rate of 2.082; additionally, when the distribution locations of Sardinops melanostictus and Scomber japonicus are close to each other, it promotes favorable conditions for their habitats. On the other hand, when the distribution locations are far apart, it somewhat inhibits the increase in the suitable habitat area for Scomber japonicus. The co-variation of suitable habitat areas for Sardinops melanostictus and Scomber japonicus under different ENSO events may be related to their interspecies relationship (competition/predation-prey) and the distribution of ocean currents in the northwestern Pacific Ocean.

Based on the data from 56 acoustic survey sections in the southwestern Indian Ocean from 2011 to 2020, a total of 201 diel vertical migration were observed. The characteristics of diel vertical migration of the deep scattering layer and its spatiotemporal differences were analyzed. The research results show that the deep scattering layer in the southwestern India Ocean exhibits a stratification phenomenon, with the first scattering layer located in the shallow water layer below 200 m. The average depth of its nautical area scattering coefficient (NASC) peak is (58.66 ± 24.63) m, and there is a significant difference between summer and winter (p < 0.001); the second scattering layer is located in the water layer between 400 m and 700 m, with an average depth of (589.02 ± 66.33) m for its NASC peak. There is no significant difference between summer and winter (p = 0.51). The average time for the scattering layer to migrate upwards is 16:20, the average time for the end of migration is 18:31, and the average migration rate is (5.28 ± 1.53) cm/s; the average time for the scattering layer to start migrating downwards is 4:38, and the average time for the end of migration is 6:52. The average migration rate is (5.56 ± 2.13) cm/s. As latitude increases, the start time of downward migration become later and the migration rate slows down; as the longitude increases, the migration rate of the scattering layer also slows down, and there is a significant difference between different longitude sea areas (p < 0.001). Analysis suggests that studying the seasonal changes in the physical and chemical environment of the sea area, as well as the different life cycle stages of organisms in the scattering layer, are the main reasons for the spatiotemporal differences in the vertical structure and diurnal vertical migration characteristics of the scattering layer. They are of great significance in explaining the diurnal vertical migration behavior of tuna and indicating the distribution of tuna fishing grounds.

The concept of ecosystem-based fisheries management has been widely recognized, but it’s application in the construction of marine ranch is still very rare. In this study, based on the data from a bottom trawl survey of fishery resources conducted in the waters of Wuzhizhou Island from 2020 to 2021, a marine ranch fish community size-spectrum model (SSM) was built, which reflects the complex structure of food webs and interspecies interactions in marine ranch, to assess the impacts of fishing on the fish community in marine ranch. The study analyzed the effects of changes in species-specific fishing death coefficient on fish community by simulating two management strategies (single-species management and multispecies management) and monitored the state of fish community characteristics using five community ecological indicators: the total biomass of the community, the slope of size spectrum, the mean maximum weight, the mean weight, and the large fish index. The results of the single-species management strategy showed that the marine ranch ecosystem of Wuzhizhou Island showed top-down control, and there was a strong regulatory effect of carnivorous fish on plankton-feeding fish. Complex interactions such as competitive predation among different species produce trophic cascade effects after changes in fishing death coefficient. The results of the multispecies management strategy showed that fishing death coefficient of Muraenesox cinereus had the greatest effect on the slope of size spectrum, and that fishing death coefficient of Trachiocephalus myops and Muraenesox cinereus had the greatest effect on fish community biomass and community structure and function. The results of this study have important implications for the conservation and stabilization of fish community, and can help managers to better understand the potential impacts of changes in fishing death coefficient rates on fish communities, so that viable and effective conservation and management strategies can be developed based on the importance of the species to the fishery.

The semienclosed pyloric caecum of Larimichthys crocea is an ideal organ to perform the host source tracking, as it containes several local bacteria colonized during early development. The alpha diversity, relative abundance of core bacteria and network relationship of the pyloric caecum microbiota in L. crocea from Sansha Bay were analyzed using the Illumina high-throughput sequencing. Furthermore, the random forest model was used to predict the population source (the wild population or the farmed population). The results showed that the farmed fish had more unique OUT and higher alpha diversity than the wild one. The wild and farmed fish significantly differed in the relative abundance of dominant bacteria (Proteobacteria, Firmicutes, Bacteroidota, Actinobacteria and Acidobacteria) (p < 0.05). The result of network analysis showed that the wild fish had higher ratio of negative to positive edges and modularity, but fewer nodes and edges than the farmed fish. Furthermore, a random forest classification prediction model with the accuracy of 92.31%, the Kappa coefficient of 0.8452, and an area under the ROC curve of 0.952 4 was constructed. Using this prediction model, the accuracy of source identification for the wild and farmed fish was 91.67% and 92.86%, respectively. Overall, the structure of microbial communities in the pyloric caecum of L. crocea was different between the wild and farmed populations, making it a potential marker for host source tracking. Our findings provide new insights into distinguishing wild and farmed L. crocea.