This study aimed to investigate the allelopathic effects of Sesuvium portulacastrum (Aizoaceae) on typical red tide algae and identify the sources of the active compounds. Three red tide algae species, Prorocentrum micans, Karenia mikimotoi, and Alexandrium catenella, were selected as test subjects. The planting water of the coastal salt-tolerant plant Sesuvium portulacastrum served as the research material. Root exudates from the plant were adsorbed using a C₁₈ solid-phase extraction column and then extracted with methanol, ethyl acetate, dichloromethane, and n-hexane. The four extracts exhibited varying degrees of inhibition on the growth of the algae, with the dichloromethane extract showing the most significant inhibitory effect. At a concentration of 10 g/L, the inhibition rates for the three algae species were 50.83%, 97.30%, and 81.41%, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis identified 19 fatty acids and their derivatives. Among these, stearic acid, oleamide, and docosanol exhibited algicidal activity, with docosanol showing the strongest effect. At a concentration of 2 mg/L, the inhibition rates for the three algae species were 90%, 100%, and 81.04%, respectively. These results indicate that Sesuvium portulacastrum can release fatty acids and their derivatives to inhibit the growth of red tide algae, demonstrating its potential as a plant-based tool for red tide control and environmental remediation.

Phytoplankton blooms in polar regions with seasonal sea ice cover show a unimodal seasonality. However, the bloom processes are controlled by multiple physical and biogeochemical factors, including sea ice, light availability, mixed layer depth, and nutrients; those may result in great uncertainties in simulating phytoplankton bloom by the Earth System Models (ESMs). In this study, the results of 11 Coupled Model Intercomparison Phase-6 (CMIP6) ESMs were analyzed and evaluated with various types of observational products in order to determine whether those ESMs can correctly model the phytoplankton blooms in three Arctic shelf seas, Barents Sea, Chukchi Sea, and Bering Sea. By calculating multiple indices that represent light and nutrient limitations, the error sources of simulated surface chlorophyll a concentrations were comprehensively analyzed. Our results show that the 11 ESMs can be divided into three groups based on ice-adjusted photoperiod, rate of change of mixed layer depth, and surface nitrate concentration. Some groups are characterized by the smallest bias between modeled indices and observation-based reference, and those ESMs perform best in simulating phytoplankton bloom characteristics. The other groups of ESMs differ significantly from the reference values in terms of surface nitrate and/or rate of change of mixed layer depth, resulting in delayed occurrences of annual chlorophyll a peak concentration and greater differences in corresponding peak values. In general, in addition to the two primary constraints of light and nutrients, the ESMs should also well represent the upper mixed layer controlled by temperature and salinity distributions, so as to accurately simulate the seasonal variation of surface chlorophyll a concentration. The above analyses indicate ESMs can be used in assessing polar planktonic ecosystems, and there is room for improving ecosystem-related parametrization in future ESM development.

In order to identify the functional diversity of the adjacent waters of the Changshan Islands in the ecotone between the Yellow Sea and the Bohai Sea, based on the quarterly survey of fish biological resources and environment factors from October 2016 to August 2017, combined with 13 functional traits such as feeding habit, trophic level, migration type, thermophily, resilience and fish eggs type, the spatio-temporal pattern of functional diversity and its relationship with environmental factors were studied by using community weighted mean index (CWM), functional diversity index and Spearman rank correlation analysis. The results showed that the dominant species of fish community in spring and winter were depressiform, warm temperate and demersal species with the characteristics of anterior or upper mouth, low growth coefficient, high vulnerability, low resilience and non-migration or short distance migration. The dominant species in summer and autumn showed more functional traits, such as long distance migration, pelagic, fusiform and compressiform. FRic in summer and autumn was significantly higher than that in spring and winter, FEve was the highest in spring, and FDiv was the lowest in autumn and was significantly lower than other seasons. FEve in spring and season and FDiv in spring and autumn showed a trend of high in the west and low in the east, while FRic in summer and winter and FEve in autumn showed a trend of high in the east and low in the west. There was a certain correlation between environmental factors and functional diversity index. As an ecotone between the Yellow Sea and the Bohai Sea, the functional traits of the dominant species and functional diversity show seasonal variations made by the fish migration, and the spatial pattern of functional diversity shows complexity and heterogeneity made by environment changing in the adjacent waters of the Changshan Islands.

Due to the limitations of the Rayleigh criterion, classical harmonic analysis (CHA) model requires half a year of data records to analyze the eight main tidal constituents, namely, M₂, S₂, N₂, K₂, K₁, O₁, P₁, Q₁. For short-term tidal records, the unresolved constituents typically rely on the ratio differences from nearby long-term tidal stations for estimation. However, there is a scarcity of publicly available long-term tidal data in the coastal areas of Zhejiang, which currently prevents the accurate extraction of the main constituents from short-term records. This paper introduces a modified harmonic analysis model, referred to as the Modified Harmonic Analysis model based on the Credo of Smoothness (MHACS). Based on the smooth functions established by the intrinsic connections between major constituents, it breaks through the Rayleigh criterion, significantly reducing the length of tidal records required, especially suitable for coastal areas with abundant short-term data. This algorithm was applied to the multi-island area of Zhejiang offshore, using tidal records shorter than 15 days. The results show that the harmonic constants of the eight main constituents at the Shipu station are very close to the results obtained by the CHA method, and the required data length is reduced from 8760 hours to 336 hours, which can be used to calculate characteristic parameters such as the theoretical depth datum. For analyzing the eight main constituents along the Zhejiang coast using MHACS, a minimum data length of 5 days is recommended.

The Zhujiang River Estuary is located in the northern South China Sea. It has a wide intertidal zone and a high diversity of intertidal macrobenthos. However, most of the previous intertidal-related studies and intertidal species records were carried out on the east coast of the Zhujiang River Estuary, while studies on the west coast of the Zhujiang River Estuary were relatively scarce. From 2021 to 2023, a comprehensive survey focus on Brachyura (crabs), one of the main groups of intertidal macrobenthos, was conducted in the intertidal zone of Qi’ao Island, Zhuhai City, western Zhujiang River Estuary. Combined with the collection and revision of species recorded in previous studies, an updated checklist of intertidal crabs in Qi’ao Island was created, and the ecological and geographical distribution of these crab species were described. A total of 90 specimens were colleted and 31 species from 10 families and 21 genera were identified. Seventeen species (e.g. Orisarma patshuni and Anomalifrons lightana) were new to the Qi’ao Island, and one species (Hemigrapsus takanoi) were new to the Zhujiang River Estuary. The updated checklist includes 48 intertidal crab species belonging to 13 families and 29 genera, among which Sesarmidae (10 species), Varunidae (10) and Ocypodidae (8) are the three most species-rich families. The crab fauna composition of the island is mainly composed of East Asian endemic taxa and Indo-West Pacific/West Pacific widespread taxa, showing overwhelming East Asian warm water characteristics. Mudflats and mangroves are the most abundant habitat types for crab species on the island. Our results has increased the number of intertidal crab species on the west coast of the Zhujiang River Estuary from 31 to 55 species, which is the same as the number of species recorded in Shenzhen Bay on the east coast of the Zhujiang River Estuary. The total number of intertidal crab species recorded in the Zhujiang River Estuary has reached 77 species in 14 families and 38 genera, of which 33 species (42.9%) has been reported on both the east and west coasts.

In order to study the carbon burial rates and sources of early to middle Holocene sediments in the Changjiang River palaeo-valley area, the determination of total organic carbon (TOC), total nitrogen (TN) and δ¹³C of sediments from ZK1 hole was carried out, and the spatial and temporal distribution characteristics and TOC sources of carbon burial in the Changjiang River palaeo-valley were analyzed by combining AMS¹⁴C (plant debris, shells) dating, foraminiferal and grain size data. Using a combination of historical geography and sedimentary geology combined with AMS¹⁴C data, the chronostratigraphic classification was carried out from bottom to top as tidal channel (U1), estuarine bay (U2), tidal sand ridge (U3), and pre-delta (U4). Sediments were influenced by the effects or factors of water depth, runoff, estuarine after-circulation, tidal currents, waves, storms and remineralization, and the mean value of TOC was 0.41%, which was lower than the surface layer of the Changjiang River Estuary. The ZK1 hole carbon burial flux (TOC_BF) ranged from 7.4 g/(m²·a) to 110.5 g/(m²·a), with large variations. The TOC_BF values were mainly controlled by the sedimentation rate. The results of δ¹³C and TOC/TN (C/N) projection points indicate that there are TOC sources with multi-source characteristics, and the overall performance is partial to terrestrial sources. The linear fit correlation between C/N and δ¹³C was high, which allowed the quantitative analysis of organic matter sources using C/N and δ¹³C. The organic carbon source analysis was carried out based on C/N and δ¹³C using a three-terminal source model. The U2 and U3 depositional periods were in the Holocene Great Warm Period, and the sea-derived and land-derived carbon was higher than that of the U1 and U2 depositional units, which was mainly related to the increase of marine and terrestrial primary productivity. The mean contribution of marine phytoplankton to total organic carbon was 31% in ZK1 hole. The mean contribution of estuarine phytoplankton to total organic carbon was 31%; the mean contribution of terrestrial organic carbon to total organic carbon was 38%. Overall, the contribution of terrestrial organic carbon was greater than that of estuarine phytoplankton and marine phytoplankton, which was basically consistent with the analysis results of the graphical method.

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.

Mangroves represent the most productive ecosystem along the coastline. The mangrove forest is a source of diverse organic carbon, which contributes to the complexity of the trophic structure of the benthic food web. This study employed the benthic animals in the mangroves along Yanpu Bay as the research object, analysing the community trophic structure and determining the potential food sources through the utilisation of the stable isotope technique in conjunction with the Stable Isotope Bayesian Ellipses (SIBER) model and the Stable Isotope Mixing Models (Simmr). The study demonstrated that the carbon stable isotope (δ¹³C) values of benthic animals ranged from −22.04‰ to −11.27‰, while the nitrogen stable isotope (δ¹⁵N) values ranged the trophic levels ranged from 1.33 (Cerithidea rhizophorarum) to 3.95 (Periophthalmus cantonensis), with carbon stable isotope (δ¹³C) values from 5.86‰ to 16.21‰. The trophic level of fish is relatively high, ranging from 2.38 to 3.95, while that of crustaceans is 2.61 to 3.52. In contrast, the trophic level of mollusc is relatively low, ranging from 1.33 to 3.15. These differences are related to the feeding preferences of the different groups. The analysis of the nutritional structure indicates that the length of the food chain and the nutritional diversity of fish are greater than those of crustaceans and mollusc. The diversity of food sources and nutritional uniformity of crustaceans are the highest, while the nutritional diversity and similarity of mollusc are the highest. Overall, there is a varying degree of overlap between the core nutritional niches of fish, crustaceans and mollusc. An analysis of the potential food sources of benthic animals based on a Simmr mixed model revealed that SOM was the primary carbon source, accounting for 78.2% of the total, followed by phytoplankton, which constituted 21.6% of the total, while litter and POM represented the lowest proportions, at 3.7% and 3.3%, respectively. The findings of this study enhance our comprehension of the trophic relationships of benthic animals in mangrove ecosystems along the northern coast of China. They will facilitate more effective conservation and restoration of mangrove biodiversity from a trophic regulation perspective.

Typhoons, as one of the common natural disasters in coastal zones, have severe impacts on tidal flats. However, there is a significant lack of field data on typhoons, and studies on how salt marsh vegetation protects tidal flats during typhoon events are still very limited. This study selected Chongming Dongtan in the Changjiang River Estuary as the research site. During the passage of Typhoon In-Fa in July 2021, hydrodynamic instruments and UAV photogrammetry (elevation measurements) were used to monitor hydrodynamics and sediment in both salt marsh and the marsh front areas, as well as to monitor the salt marsh ecosystem before and after the typhoon. The findings are as follows: (1) During the typhoon, wind speed, water depth, and wave height were 1.1−2.8 times those before and after the typhoon, and the hydrodynamic forces in the marsh front area were higher than those in the salt marsh area, with water depth, wave height, and flow velocity being 1.3 times, 1.2 times, and 1.9 times those of the salt marsh area, respectively. (2) Under the influence of Typhoon In-Fa, vegetation patches at the marsh front, directly exposed to strong winds and waves, experienced hydrodynamic forces such as water depth and wave height that were 1.1−1.9 times those of the salt marsh area, resulting in erosion at the marsh front being 1.2−1.8 times that of the inland vegetation patches under the same vegetation coverage conditions. (3) In the marsh-front area, densely vegetated patches demonstrated stronger sediment accretion capacity compared to sparsely vegetated patches, with the maximum accretion thickness in densely vegetated areas reaching 45 cm, whereas sparse patches were mainly subject to erosion, with a maximum erosion depth of 17 cm. This indicates that the density of vegetation patches directly affects the sedimentation and erosion dynamics of the tidal flat. This study reveals that the arrangement and location of vegetation patches are crucial to the sedimentation and erosion of tidal flats under extreme weather events, which has significant implications for tidal flat management and ecological protection. It also provides theoretical support for establishing a robust natural barrier in response to extreme weather conditions.

The PHC, ECCO2, SODA, GECCO3 and CMIP6 data were used to analyze the horizontal distribution characteristics, seasonal variation and long-term trend of the Arctic Ocean heat content, and analyze the simulation ability of the CMIP6 models in this paper. The results show that the heat content of the Arctic Ocean shows obvious seasonal change, with the lowest in April and the highest in September. Under historical circumstances (1850−2014), compared with the observation and reanalysis data, the heat content of the upper 500 m of the CMIP6 models ensemble average (MME) is warmer in the Greenland Sea, colder in the Norwegian sea, Barents Sea and Eurasian Basin, while the whole water column heat content of MME is warmer in almost all regions of the Arctic Ocean, with the largest deviation in the Greenland Sea. CMIP6 models have a large deviation in the simulation of Arctic Ocean temperature profile, and the average temperature of MME is higher than the observation and reanalysis data at the depth of more than 1 000 m. In the future case (2015−2100), the simulation of ocean heat content of MME shows obvious Arctic Ocean warming, but most of the Chinese models show no obvious warming situation. BCC-CSM2-MR and BCC-ESM1 are poor in simulating the annual mean heat content of the Arctic Ocean, CIESM is poor in simulating the seasonal and interdecadal variations of ocean heat content, while FIO-ESM-2-0 is good in simulating the annual heat content of the upper 500 m, the seasonal and interdecadal variations of heat content of the Arctic Ocean.