In recent years, the water quality of the Liaohe Estuary has been declining, and a large input of nitrogen has increased the burden on the environment. The denitrification process releases nitrogen from sediments into the atmosphere in the form of N₂O and N₂, which reduces the nitrogen load in the estuarine ecosystem. In this study, quantitative PCR was used to determine the levels of four denitrification functional genes narG, nirK, norB and nosZ present in the surface sediments of the Liaohe Estuary. The narG gene, which dominates nitrate reduction, was found to be the most abundant. The nirK-type denitrification functional gene was sequenced by high-throughput sequencing. The results showed that the genus of denitrifying bacteria in the Liaohe Estuary was mainly Devosia, Phaeobacter, Alcaligenes, Pseudomonas. The abundance of denitrification function genes is mainly affected by sediment properties, except that norB gene is significantly related to many environmental factors. The community structure and diversity of nirK type denitrifying bacteria are mainly affected by salinity, pH, dissolved oxygen and ${\rm {NO}}_2^- $ contents. The effects of environmental factors on the abundance and community structure of denitrifying bacteria were studied. The results provided a theoretical basis for alleviating the fate of nitrogen elements in the eutrophication of Liaohe Estuary.

Neon flying squid Ommastrephes bartramii is a cephalopod species of economically importance distributed in the North Pacific Ocean. Because of short lifespan, their abundances mainly depend on the recruitments and the marine environment during their early life stages will directly affect the recruitments. Using fishery data collected by Chinese squid-jigging fleets in the Northwest Pacific Ocean from 2004 to 2015 and the sea surface temperature (SST) of spawning and feeding grounds, which were divided into different numbers of subareas, correlation analysis and random forest model were used to screen out the subareas that CPUE has significant relationships with Ps (the proportion of favorable-SST in spawning grounds) of spawning grounds and Pf (the proportion of favorable-SST in feeding grounds) of feeding grounds during spawning and feeding periods. The Ps and Pf were used as input variables of the neural network model to forecast recruitments based on spawning ground and feeding ground, respectively, and the advantages and disadvantages of the model and forecast accuracy were analyzed. The results show that the schemes of dividing spawning ground into 5°×5° and feeding field into 2.5°(longitude)×4°(latitude) were optimal. The ranges of subareas selected by random forests are largely consistent with those selected by correlation analysis, both random forests and correlation analysis can identify potential subareas associated with CPUE, and both have forecasting accuracy of >90%. However, the subareas selected by the random forest are better and the forecast accuracy is higher than those selected by correlation analysis. In addition, the model based on the spawning ground is more accurate and stable than that based on feeding ground.

In this paper, the time series analysis model ARIMA (1, 2, 0) was applied to simulate and predict the stock of small yellow croaker (Larimichthys polyactis) based on the monitoring catches data of canvas stow net in the southern Yellow Sea from 2003 to 2014 and verified by the monitoring catches data of 2015 and 2016. The results showed that the simulated and actual values for the catch yield from 2003 to 2014 were correlated significantly (p<0.05) and the correlation coefficient was 0.881. The relative error between predicted and actual value in 2015 and 2016 were respectively 6.73% and 22.75%, the overall relative error was 14.74% and the regression equation fitted the real situation better, which illustrated that the time series analysis model ARIMA (1, 2, 0) can be applied to simulate the catches trend of L. polyactis and predict the catch stock, especially superior in short-term forecasting. However, in any case the fixed model of L. polyactis is not always suitable for all data analysis, and the values of p, d and q in ARIMA model are considered to be variable according to different time series. Therefore, the optimal values of p, d and q should be determined based on the guidance and analysis of relevant theories in order to avoid copying directly the fixed model.

Volatile halocarbons (VHCs) produced in the oceans are important carriers for chlorine, bromine, and iodine to enter into the atmosphere. Marine algae can produce VHCs that have an ozone-depleting potential. Marine microalgae in particular have been shown to be major contributors of VHCs in the atmosphere. However, little is known about the influences of environmental factors on the production of VHCs by marine microalgae. In this study we examined the influence of different light intensities (20 μmol/(m²·s), 70 μmol/(m²·s) and 140 μmol/(m²·s)) and nitrate concentrations (1 mg/L, 5 mg/L, 10 mg/L and 50 mg/L) on the growth of Prorocentrum donghaiense and Phaeodactylum tricornutum and the releases of four VHCs (CH₃I, CH₂Br₂, CHBr₂Cl and C₂HCl₃) by these two microalgae. Unialgal cultures of these two kinds of microalgae were conducted in axenic and sealed glass vessels. The VHCs were extracted and analyzed by gas chromatography coupled to purge-and-trap preconcentration system. The releases of VHCs by these two microalgae were affected by light intensity and nitrate concentration, while their influences on different VHCs were various. The release of CH₃I was significantly affected by light intensity and nitrate concentrations. Within a certain range, the amount of CH₃I released from the two microalgae raised with the increase of light intensity. Moreover, our results showed that increasing the nitrate level above 5 mg/L could promote the production of CH₃I by these two microalgae.

The qualitative and quantitative analyses on betaine lipids of microalgae were conducted by means of the quadrupole flight time ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-Q-TOF-MS) using electron spraying ionization. As a result, 133 betaine lipids including 53 DGCC, 41 DGTS and 39 DGTA were identified from 14 species of microalgae in four major phyla. DGCC was the dominant betaine lipid in dinoflagellates and haptophytes, while DGTS was the main betaine lipid in chlorophytes. There were two main types of betaine lipid in diatoms: DGCC in centric diatom and DGTA in pennate diatom. The differences of fatty acid of betaine lipid in marine microalgae were only observed at the phyla and class levels, but at lower taxonomic levels the differences were less stable. DGCC existed in diatoms, dinoflagellates and chlorophytes, which contained C14−C18 saturated and unsaturated fatty acids and C20 and C22 polyunsaturated fatty acids. The difference in DGCC is that saturated C14−C18 fatty acids existed in dinoflagellates, while the fatty acids of odd carbon numbers C19 occurred only in diatoms. The results of description and molecular characterization of betaine lipid in microalgae can be served in future investigation in chemotaxonomy, physiology, ecological role of microalgae and functional properties of these phosphorous-lacking polar lipids.

The sea surface temperature(SST), salinity(SSS), dissolved oxygen (DO), chlorophyll a(Chl a) and surface partial pressure of carbon dioxide(pCO₂) was determined by underway measurement system in the Qiongzhou Strait in summer 2011 and 2014, and the spatiotemporal variations of pCO₂ were analyzed and its control factors were explained. The averages of pCO₂ in surface sea water were (516±29) μatm and (533±15) μatm, sea-air CO₂ fluxes were (8.4±1.7) mmol/(m²·d) and (4.5±0.4) mmol/(m²·d) in summer 2011 and 2014, the Qiongzhou Strait acted as strong atmospheric CO₂ source and was more higher than the adjacent and similar sea areas. The upwelling forced the CO₂-enriched subsurface water to intrude the surface water and elevated pCO₂ in the east mouth, also promoted biological productivity and absorbed CO₂ from sea water, and also made the pCO₂ drop and DO rise sharply in the vicinity of west mouth in summer 2011. The upwelling was weak in east mouth and vertical mixing was strong along ship-track in summer 2014, the distributions of pCO₂ and DO were obviously different from that in summer 2011. Narrow channel effect was significant in the middle of Qiongzhou Strait, high water transportation speed with strong mixing resulted in weak photosynthetic activity, they altogether maintained high pCO₂ in summer 2011 and 2014.

Mangrove growing on the tidal flat is of important value for the estuarine plant community compositions and coastal protection against wind and wave. This study aims to explore the spatial distribution pattern and associated influencing factors of estuarine mangrove based on the soaking and sinking experiment of aboriginal Aegiceras corniculatum embryo and observations on water salinity, plant community structure and geomorphology of the tidal flat along the estuaries of Nanliujiang River and Dafengjiang River. Our results show that the distribution pattern of mangrove along Nanliuujiang River and Dafengujiang River estuaries exhibits a mode of “pure mangrove (e.g. mixture of Aegiceras corniculatum, Kandelia candel, Sonneratia apetala)→mixture of mangrove and semi-mangrove (Hibiscus tiliaceus, Clerodendrum inerme Gaertn)→mixture of mangrove, semi-mangrove and non-mangrove→mangrove mosaic→sparse mangrove seedlings” from sea to land. However, mangrove at the landward limitation of the Dafeng River estuary is characterized by a mixture of mangrove, mangrove seedlings and semi-mangrove. Besides, the time length of mangrove socking dominates the spatial distribution pattern of the estuarine mangrove while the time length of landward transport of tidal current affects the extreme location of the mangrove landward growth. A suitable tidal flat is an essential condition for the mangrove development and growth.

Based on the data of pH and environmental parameters from 2011 to 2017, using the method of grid statistics and time-space matrix, contrastive analysis of pH in each environmental unit and the correlation of pH and environmental factors were studied. Furthermore, the differences of relevant factors affecting different seasons, regions and water levels were analyzed. The results showed that: (1) during from 2011 to 2017, the spatial distribution of pH was relatively stable in the Bohai Sea, the average value of surface pH in environmental units was from 7.95 to 8.38, the bottom was from 7.89 to 8.35, the absolute variation of average value was 1−1.5 standard deviations; (2) the time series of pH in each environmental unit tend to change synchronously, but there were differences among the units due to the different spatial distribution, the distribution characteristic of surface pH in winter was consistent with the saline; (3) there was a significant positive correlation between pH and chlorophyll a content in the Bohai Sea, and the surface pH varied seasonally, which was obviously consistent with distribution and variation characteristics of chlorophyll a, therefore, biological factor played an important role in regulating the pH of surface water; (4) the low value region of pH in Bohai Sea bottom in August was consistent with the formation of hypoxic zones by regional water stratification, and it was found that the bottom pH was positively correlated with dissolved oxygen; (5) the characteristic information of acidification indicators was further displayed by gridding processing technology and time-space matrix analysis method, which provided a good technical support for long-time scale analysis and research under climate change.

The photosynthetic active radiation (PAR) plays a significant role in regulating ocean primary productivity, so it may indirectly affect the abundance and spatial distribution of cephalopods. In this study, we examined the relationship between photosynthetic active radiation and Ommastrephes bartramii stocks in the Northwest Pacific Ocean, and evaluated the impacts of the anomalous climatic environments on the squid stocks, based on the fishery data during 2006−2015 obtained from the squid-jigging Science and Technology Group of Shanghai Ocean University and the remotely satellite data of PAR. The results indicated that catch per unit effort (CPUE), latitudinal gravity center (LATG), PAR and its spatial distribution exhibited significant monthly variation. From July to November, the suitable range of PAR was 36−39 E/(m²·d) in July, 33−36 E/(m²·d) in August, 24−27 E/(m²·d) in September, 18 E/(m²·d) in October and 12 E/(m²·d) in November. The most favorable PAR was 36 E/(m²·d), 33 E/(m²·d), 27 E/(m²·d), 18 E/(m²·d), 12 E/(m²·d), respectively, from July to November. The results showed that a significant positive relationship (p<0.05) was found between CPUE and PAR, and further a significantly positive correlation (p<0.05) was found between CPUE and the monthly percentages of suitable PAR accounting for the whole fishing ground. Meanwhile, the LATG varied with the mean latitude of the most preferred PAR in each month. Finally, under the anomalous climatic environments, the CPUE in the La Niña years is higher than that in the El Niño years, which may be caused by the higher PAR in the La Niña years. Our findings indicated that the PAR strongly affected the abundance and spatial distribution of O.bartramii in the Northwest Pacific Ocean.

For the wave model, we combine the variational multiscale method with the free surface captured technology, and decompose various physical quantities of the wave model into “coarse” scale and “fine” scale following the variational multiscale method, and introduce the stabilization structure to eliminate numerical pseudo oscillation. Finally, the total variational multiscale equation of coupling “coarse” scale and “fine” scale is solved to simulate the water wave oscillating freely in a cycle and wave propagation. The numerical results show that the numerical results is accurate, and the method eliminates the spurious oscillations, and simulate correctly the phenomenon of periodic changes of water waves oscillating freely and wave propagation.