Based on the fishery resources survey data in the outer waters of the Zhoushan Islands in April (spring) and October (autumn) 2018, the composition, quantity distribution and dominant species of fishes were analyzed, and the relationship between them and hydrological environment was analyzed by the CCA method. The results showed that there were 106 species of fish in the waters outside Zhoushan Islands, belonging to 12 orders, 47 families and 80 genera. The fish mass densities in spring and autumn are 210.50 kg/km² and 829.06 kg/km² respectively, and the abundance densities are 8.08×10³ ind/km² and 165.94×10³ ind/km² respectively. The density of fish resources in spring is higher in the northwest sea area and lower in the east sea area of the investigated sea area, while the density of fish resources in autumn is higher in the east sea area and lower in the northwest sea area. The dominant species of fish change substantially between the two seasons. The dominant species in spring and autumn were Lophius litulon、Lepidotrig lajaponica、Apogon lineatus and Apogon lineatus、Acropom japonicum. The number of fish species showed significant seasonal and spatial changes, and the number of fish species is higher in the west and northwest near the coastal islands, with most fishes inhabiting in waters with water depth of 50−80 m. The results showed that the spatial and temporal separations of fish communities were obtained from CCA analysis. Surface temperature, bottom temperature and surface salinity were the key environmental factors that affected the composition and quantity distribution of fish species in the sea area under investigation. The strong correlation between fish community and environmental factors reflected the climate change effect on the separation of fish species.

Jumbo squid Dosidicus gigas is the main fishing target by Chinese squid-jigging fisheries, which mainly distributes in the eastern Pacific Ocean. Its habitat can be greatly affected by climatic changes. In this study, we calculated the habitat suitability index (HSI) on the squid fishing ground in the Southeast Pacific Ocean off Peru based on data of sea surface temperature (SST), the anomalies of sea surface height (SSHA) and Niño3.4 index during 1950 to 2015. Spatio-temporal variations in the squid habitat were further examined under the El Niño, the normal and the La Niña conditions. The results showed that variations in SST anomalies (SSTA) and SSHA in the fishing ground were consistent with those of the Niño3.4 index. Cross correlation analysis indicated that both SSTA and SSHA were significantly positively correlated with the Niño3.4 index. However, the HSI values were significantly negatively correlated with the Niño3.4 index. We divided the years between 1950 and 2015 into three types, the El Niño years, the normal years and the La Niña years. During the El Niño years, water temperature became warm, and the SSH increased; these changes led to contracted areas of suitable SST and SSHA, therefore, the range of suitable habitats largely decreased. However, during the normal and the La Niña years, water temperature was cold, the SSH decreased, and ranges of suitable SST and SSHA enlarged; these changes resulted in the increases in suitable habitat for the squid. Furthermore, the latitudinal gravity centers of suitable HSI on the squid fishing ground were significantly positively correlated with the Niño3.4 index. The latitudinal gravity centers of suitable HSI shifted southward in the El Niño years. Our findings suggested that ENSO events significantly affected environmental conditions on the squid fishing ground, and thus affected ranges and latitudinal distribution of suitable habitat for the squid in the Southeast Pacific Ocean off Peru.

Global climate change has a profound impact on the world fisheries. Recently, the composition of catch in Northeast Atlantic Ocean has changed significantly. Based on the catch data in the Northeast Atlantic Ocean from 1982 to 2016 provided by the United Nations Food and Agricuture Organization, the diversity of catch, mean trophic level and the variation of principal component were analyzed in time series. Finally, combined with climate and environmental factors (sea surface temperature, SST; sea surface salinity, SSS; sea surface height, SSH; Sea Ice Concentration, SIC; North Atlantic Oscillation, NAO; Arctic Oscillation, AO; Atlantic Multidecadal Oscillation, AMO) in the Northeast Atlantic Ocean, the relationship between catches composition and climate change was explored by generalized additive model (GAM). The results showed that the diversity generally presented a declining trend, it was at a relatively low level during 2002 to 2010. The mean trophic level decreased slowly before 2002, then began to rise sharply. The correlation analysis showed that the changes of these two indicators were related to the environmental factors. The principal component analysis of catch composition showed that the variance of the first principal component was 35.3%, and it also has a close relationship with climatic and environmental factors, which could characterize the change of catch structure under the influence of climate. The results of GAM analysis showed that the orders of the contribution to structure change of catches were in sequence of SST, SSH, SSS, SIC and NAO.

Antarctic red algae play important roles in the coastal ecosystems and industrial applications. Meanwhile, their unique physiological acclimation mechanisms to the extreme environments endow them to be ideal organisms for discovering new genes and new metabolic pathways. In this study, we sequenced the transcriptomes of Antarctic red algae Iridaea cordata (Turner) Bory and Curdiea racovitzae Hariot, and compared with their moderate temperature close relatives. The transcriptome sequences of I. cordata and C. racovitzae were assembled into 14055 and 12006 Unigenes, with an average length of 1473 bp and 1448 bp, respectively. The Lhca2, Lhca6 and Lhcb genes homologous to the green algae genes were found in I. cordata transcriptome while not in other red algae. Lhcf gene encoding fucoxanthine and Chl a/c binding protein presenting in brown algae and diatoms were identified in both I. cordata and C. racovitzae. Photolyase repairs UV-induced DNA damages. 6-4 photolyase, CPD I and CPD II genes were identified in the transcriptome of I. cordata, while only CPD II gene was found in the transcriptome of C. racovitzae. Although the functions of those specific genes in Antarctic red algae are expected further investigation, our study provides a foundation for the following researches on the acclimation mechanisms of seaweeds to the extreme light environments in Antarctica.

Photochemical properties and photochemical degradation of chromophoric dissolved organic matter (CDOM) were investigated in the upper water of the western Pacific Ocean during the autumn in 2018. The results showed that the absorption coefficient a(320) of CDOM ranged from 0.025 m⁻¹ to 0.64 m⁻¹, with an average of (0.20 ± 0.08) m⁻¹. The a(320) showed relatively lower values in the surface water, which was mainly related to the photobleaching removal of the surface CDOM. The higher values of a(320) were observed in the 100−200 m water layers, which was mainly related to the biological production in the subsurface layer. The tyrosine-like component C1 and the marine humic-like component C2 were identified by FDOM excitation/emission matrix spectroscopy and a parallel factor analysis. The production of C1 was mainly originated from the production of phytoplankton and the degradation of microorganisms, while C2 was mainly originated from the input of the marine humic brought by Kuroshio. Moreover, the absorption loss spectra of CDOM indicated that the UV radiation was responsible for the photodegradation of CDOM. The tyrosine-like component was more susceptible to photodegradation than the marine humic-like component. The results also indicated that photodegradation was the important removal route of CDOM in the western Pacific Ocean.

Biogenic elements are the basis of primary production in marine systems. Their cycles in marine environments are affected by various physical, chemical, and biological processes. Understanding the concentration distribution, structural characteristics, and influencing factors of biogenic elements are essential to understand the dynamics of marine ecosystems. In February 2019, a field investigation was conducted in the Shenhu Area of the northern South China Sea and seawater samples were collected to analyze dissolved inorganic nutrients. Combined with the hydrological environment parameters, such as temperature, salinity, chlrophyll a (Chl a), pH and dissolved oxygen (DO), the distribution and controlling factor of nutrient concentration and structure in the Shenhu Area were discussed. Concentrations of each nutrient in the seawaters from 0 m to 30 m were very low, and the nutrient concentrations gradually increased with the increase of depth. At the depth of about 3 000 m, the concentrations of dissolved inorganic nitrogen (DIN), phosphate and silicate reached 38.02 μmol/L, 2.71 μmol/L and 149.07 μmol/L, respectively. Temperature, pH and DO were significantly correlated with nutrients, indicating that environmental factors greatly affected the biogeochemical processes of nutrients. In addition, the concentration of nutrients in the northeast direction of the study area at a depth of 75 m was relatively low and showed a gradual increasing trend in the southwest direction, which may be related to the intrusion of Kuroshio water with high temperature, high salinity and low nutrients. Meanwhile, the difference between the conservative mixing concentrations calculated based on an end-member mixing model and the measured values of nutrients showed that, at 75 m depth, silicate and phosphate were consumed by biological activities, while nitrates were controlled by biological addition. With the increase of phosphate, the DIN at each site increased linearly, but the silicate increased with a power function, indicating that the regeneration rate and recycling efficiency were different for different nutrients. The ratios of N/P in the Shenhu Area showed opposite trends compared with the ratios of Si/N and Si/P. At 0−30 m, the N/P ratios were low and the Si/N and Si/P ratios were high. At 75 m, the N/P ratios increased along with the decrease of Si/N and Si/P ratios possibly because of different biological effects. Below 75 m, the N/P ratios gradually decreased to 14.44, while the Si/N and Si/P ratios gradually increased. All nutrient ratios remained stable below 1 000 m. The calculation results of the N−anomaly showed that nitrogen fixation in seawater above 300 m was stronger than denitrification, and denitrification below 300 m was enhanced. The distribution characteristics of the concentration and structure of nutrients in the Shenhu Area indicated that the Kuroshio intrusion and biological activities significantly affected the biogeochemical process of nutrients in this area.

Dissolved oxygen is an indispensable element for the survival of marine organisms. With the increase of human activities, the situation of hypoxia in the global coastal waters has become exacerbated, which is considered as an important factor threatening the health of the marine ecosystem. The vertical distributions of water temperature, salinity and density were investigated in the offshore area of Qinhuangdao from May to September in 2017. Additionally, the average monthly oxygen consumption rate was evaluated, and hence the mechanism of hypoxia and acidification was discussed. The results showed that the water column in the studied area was vertically homogenous in May, and no obvious difference for dissolved oxygen (DO) between the surface and bottom layers, with the value larger than 8 mg/L. From June to August, the pycnocline presented in the mid of the water column. In this period, DO and pH in bottom water gradually decreased, and reached 2−3 mg/L for DO and less than 7.8 for pH in the end of August, suggesting significant hypoxia and acidification in this area. However, DO and pH in bottom water sharply increased in September, after the pycnocline disappeared. The result indicated that hypoxia and acidification of Qinhuangdao offshore waters are seasonal. DO was significantly correlated with chlorophyll a and pH, indicating that the hypoxic and acidified processes in the offshore area of Qinhuangdao were local. The evaluated oxygen consumption rate, based on the box model, in bottom water and sediment ranged from 951 mg/(m²·d) to 1193 mg/(m²·d) (mean: 975 mg/(m²·d)) from June to August in 2017. Comprehensive analysis showed that water stratification was the prerequisite for the occurrence of hypoxia and acidification in Qinhuangdao offshore waters, and DO consumption caused by organic matter decomposition was an important reason of hypoxia and acidification in bottom water.

In order to investigate long-term variations of deep sea currents and temperature in the east of the Luzon Strait, a submarine mooring system was made at 19.75°N, 126.75°E from May 2015 to May 2016 in the Philippine Sea. The vertical distribution of ocean currents and its temporal variation characteristics are analyzed in the paper. Several features show that: (1) In the upper layer (100～160 m) , the average current velocity is about 12.5 cm/s with average flow direction oriented northwest; in the middle layer (810 m), the average current velocity is about 2.6 cm/s with flow direction oriented westward; in the deep layer of 1 550 m and 2 560 m, the average current velocity is small and less than 1 cm/s whereas that in 4 040 m is about 2.3 cm/s and oriented southwest. (2) The kinetic energy of the upper layer is one to two orders of magnitude compared with the middle and the deep layers. In the deep layer, the total kinetic energy and average kinetic energy in the 4 040 m layer is the largest, with smallest total kinetic energy and eddy kinetic energy in the 2 560 m layer, and with smallest averaged kinetic energy and largest eddy kinetic energy in the 1 550 m layer. Meanwhile, eddy kinetic energy is larger than averaged kinetic energy in all the layers. (3) The wavelet analysis shows that ocean current exhibits a low-frequency oscillation period of 81～85 d in layers shallower than 2 560 m, while the current at 4 040 m shows 51 d oscillation period.

In responding to deadly drowning accidents, China's first operational attempt on the rip current hazard prevention for coastal tourism was carried out by the National Marine Hazard Mitigation Service (NMHMS). A great number of recreational beaches in South China are found developing littoral sand bars and rip currents. Present paper, which is part of the nation-wide work, investigate the mechanism, characteristics, and evolution sandbar-induced rip current at three most visited beaches employing multi-techniques as complementary tools. The alongshore sandbar morphology, shorelines, and rip currents are highly dynamic with seasonal variations evidenced by the morphodynamic calculation and the satellite image interpretation. Unconventional contrary seasonal evolution of the rip current is identified at Qing’ao Bay with higher risk in cooler seasons. The rip current shows high sensitivity to the sandbar group pattern, the wave height, and the incident direction according to the phase-resolving hydrodynamic modelling. The wider rip channel between sandbars generated larger rip size compared to narrower gaps, but is not necessarily accompanied by stronger flow velocity. The rip current might be totally absent in small channels when majority of water flows out through neighboring broader pathways. The flow velocity is demonstrated proportional to the wave height and inversely proportional to the incident angle. Alongshore currents dominated over rip currents as the wave incident angle reached 10°−30° in the numerical simulation. It is verified in the field observation that the rip current is most hazardous at low tide when shallower water depth intensifies the topographic effect on waves and currents. The study result provides useful reference for the engineering mitigation and public warning of beach rip hazard. In near future, long time observation for specific sections of shoreline would be conducted to accumulate enough statistics for the rip current prediction and risk governance.

To evaluate the wave simulation capacity of the sea ice dissipation source terms in the third-generation wave model WAVEWATCH III V5.16, a nested wave model covering the area from Beaufort Sea to Mackenzie River Estuary is established to simulate the storm waves under the effect of Arctic storms from August 1st to September 31st, 2014. Simulated significant wave heights are calibrated using the measurements from SWIFT buoy. Results show that in the absence of ice data (i.e., with default model settings), in the areas near the ice edge, where wave energy is strongly controlled by sea ice, the performance of IC1 ice source item is the best, of which the results are more in line with the specific ice conditions in the Beaufort Sea.