This study aims to understand the characteristics and variability in the β diversity of fish community and its influencing environmental factors in the Haizhou Bay, which was rich in fishery resources in history but seriously declined in recent years due to overfishing and environmental pollution. The data were collected from fishery resource surveys conducted in the Haizhou Bay and its adjacent waters from 2013 to 2017 using bottom trawl in autumn. β diversity was measured by Sørensen dissimilarity index using pairwise and multiple-site methods. Additionally, β diversity was divided into turnover and nestedness components and the results were analyzed visually by violin plots. On this basis, the generalized dissimilarity modelling (GDM) was used to analyze the relationship between β diversity and its components with environmental factors. The results of this study showed that the β diversity of fish community and its components fluctuated remarkably among survey years, the fluctuation was larger in the shallow water, less for the deep water, and remained at a relatively stable level regarding the whole sea area. The proportion of the turnover component in β diversity was basically maintained at more than 80%. The component of turnover was significantly larger than that of nestedness, implying the changes of fish community in the Haizhou Bay were dominated by turnover. The salinity and chlorophyll concentration of seawater were the main factors influencing β diversity and its turnover component, and the accumulated deviance explained rate of salinity and chlorophyll were 28.05% and 23.33%, respectively, the influence of water temperature was weak. The environmental factors selected in this study had a low explanatory rate for the nestedness component, which was only 1.52%. Our results implied that the characteristics of fish community have been driven by the environment, and the community development can yield corresponding adaptive to environmental changes. The process of changes in β diversity of fish community may be complex. For instance, salinity and chlorophyll concentration affect the prey density of fish and thus affect β diversity, however, more influencing factors have not been evaluated. Further studies on β diversity and its components are necessary to understand the mechanism of changing characteristics of fish community, and to provide scientific reference for the establishment of marine reserves as well as the optimization of marine conservation strategies.

Cynoglossus semilaevis as a representative species of Pleuronectiformes, is an important marine economic fish in Chinese coastal areas. The abnormal body color of C. semilaevis has been perplexing the practitioners for a long time. There are many reasons leading to abnormal body color, among which the genetic factors are thought to be the most fundamental reasons. The present researches on hypermelanosis of the blind side of C. semilaevis mainly focus on environment, nutrition, physiology, cloning of known pigmental genes and so on, while the digging of new funtional genes is still lacking. In this study, skin samples with different colors of C. semilaevis are selected for transcriptome sequencing. Through GO and KEGG functional enrichment and comparative analysis of different genes, differential expressed genes are screened in six melanogenesis-related KEGG pathways and the top ten genes are verified by qPCR. In this study, we find five functional genes with significant changes in the hypermelanotic skin on the blind side of C. semilaevis, which refer to txndc, alox15b, ptgs2, ptgis, and atp1a2a (p<0.05). The expression levels of txndc, alox15b, ptgs2, and ptgis genes in the melanization group are higher than those in the control group. In terms of function, three of these five genes are related to arachidonic acid (AA) to some extent. This provides theoretical support for the hypothesis that nutritional regulation related to unsaturated fatty acids may be involved in the molecular mechanism of abnormal body color in C. semilaevis.

According to the bottom trawl survey data of fishery resources in the offshore waters of Shandong from 2016 to 2017, the spatial autocorrelation and spatial heterogeneity of demersal fish in the offshore waters of Shandong were examined by using spatial autocorrelation indices and variogram. The results showed that there were significant spatial aggregation patterns and spatial autocorrelation in the demersal fish in the offshore waters of Shandong. The spatial autocorrelations were strong in spring, summer and winter, and weak in autumn. From the perspective of spatial distribution, the areas of high relative abundance index of demersal fish were mainly located in the southern waters of Shandong in spring and summer, and areas of high relative abundance greatly decreased in autumn and winter, while the areas of low value were mainly in the Laizhou Bay and adjacent waters in four seasons. The parameters of variogram showed that there was a strong nugget effect in autumn, and the spatial heterogeneity of random part accounted for 76.0% of the total spatial heterogeneity. The spatial heterogeneity of random part in spring, summer and winter only accounted for 26.2%, 27.7% and 23.6% of the total spatial heterogeneity. In the spatial autocorrelation and spatial heterogeneity of demersal fish showed seasonal variation in the offshore waters of Shandong, which was to some extent related with changes in environmental factors such as water temperature.

According to the seasonal fishery resource survey data from 2016 to 2017 in the adjacent waters of Changshan Islands, two-stage generalized additive model is used to examine the spatio-temporal distribution of Paralichthys olivaceus abundance and its relationships with relevant factors. The results show that the abundance of P. olivaceus exhibites obvious seasonal variation, and the abundances in spring and autumn is higher than those in winter and summer. In spring and autumn, it mainly distributes in the waters of 120.5°−122.5°E; and in summer and winter, it moves to the waters with suitable water temperature. The occurrence probability of P. olivacvacus is mainly affected by season, bottom salinity and bottom temperature. The probability of occurrence is relatively high at the salinity of 31. The relative abundance of P. olivaceus are mainly affected by bottom salinity and depth, and the relative resources is higher at the depth of 33 m. The spatio-temporal heterogeneity of the abundance distribution of P. olivaceus is affected by multiple factors in the adjacent waters of Changshan Islands.

Trichiurus haumela is one of the major commercial fish populations in the Beibu Gulf of the northwestern South China Sea. It is of great significance to estimate population parameters and assess the stock status of T. haumela for the fishery management in the Beibu Gulf. Based on the biological data of T. haumela collected in the Beibu Gulf from 2006 to 2016, the asymptotic length (L_inf), the optimal length-at-first-capture (L_{c_opt}), relative mortality (M/k and F/k), exploitation rate (E), and relative biomass (B/B₀) are estimated using the length-based Bayesian biomass estimation method (LBB). The results show that the L_inf is 44.4 cm, the mean of L_{c_opt} is 28.5 cm, the mean of M/k and F/k are 1.32 and 2.76, the F/M is 2.20 and the E and B/B₀ are 0.67 and 0.16, respectively. The anal length of the first gonadal maturation (L_50%) is 28.63 cm fitted by Logistic models. The results show that the current stock of T. haumela in the Beibu Gulf is over-exploited, the extant biomass is relatively low, the length-frequency tendes to simplification and miniaturization.

The study of spatial patterns of fish populations provides reference for reasonable utilization and management of fishery resources, which depends greatly on the quality of data collected from well-designed surveys. So appropriate sampling designs are essential in fishery-independent surveys, which can greatly affect the accuracy and applicability of the survey results. Computer simulation study is conducted to investigate the effects of sampling design on the spatial pattern of fish populations based on the data collected from bottom trawl surveys in the southern waters off Shandong Peninsula in four seasons from 2016 to 2017 in this study. Four sampling methods, including simple random sampling (SRS), systematic sampling (SYS), stratified random sampling (StRS) and stratified systematic sampling (StSS) with four levels of sample sizes are considered as potential sampling designs in this simulation study. The effects of different sampling designs on the estimation of mean crowding index and poly block index (PBI) for Conger myriaster and Enedrias fangi are examined. Relative estimation error (REE) and relative bias (RB) are used to measure the performances of different sampling designs. The results show that the simulated values of spatial pattern indices from SYS and StSS are closer to the “true” values, and the performances of SRS and StRS are relatively poor. The REE of estimation of spatial pattern indices for target fish populations decreased significantly with sample size. The original spatial pattern of fish populations has a certain effect on the estimation of spatial pattern indices. The precision of estimation of PBI decreased with the increase of the “true” values of spatial pattern indices, with PBI being overestimated when it is high. Different sampling designs have a certain effect on the estimation of spatial pattern indices of fish populations, and the degree of population aggregation also affected the analysis results. Therefore, the spatial pattern indices of target fish populations could be incorporated into the survey goals in sampling designs to improve the fishery-independent surveys with multiple objectives.

In order to further interpret the community structure of nekton and explore the ecological process of community structure changes, community structure of nekton in the Minnan sea area are analyzed based on the niche preemption model (NPM), broken stick model (BSM), overlapping niche model (ONM), dominance pre-emption model (DPM) and random assignment model (RAM) a total of 5 species abundance pattern models. The results show that there are 192 species of nekton in the Minnan sea area, including 132 species of fish, 31 species of crab, 13 species of shrimp, 10 species of cephalopod, 6 species of stomatopod. The fitting effect of NPM in the abundance distribution of nekton is better than that of ONM, the dominant species have dominant position and species niche do not overlap in Minnan sea area. From the open sea to the coastal area, the distribution pattern of nekton abundance changes from DPM to NPM, the simulation result of NPM is worse, and the simulation result of BSM is better, the status of dominant species decreased, the number of species increased, and species abundance distribution tendes to uniform.The fitting effect of DPM on the abundance distribution of nekton is better than that in the deep fishing area. With the increase of latitude, the fitting effect of the abundance distribution of nekton is better gradually, the dominant position of dominant species gradually increased, the number of species become less, and species abundance distribution tendes to unevenness, however, the fitting effect of DPM on the species abundance distribution of nekton in shallow fishing areas is poor, and the dominant position of dominant species gradually declines, the number of species becomes more, and species abundance distribution tendes to uniform. Therefore, niche preemption model is suitable to study the abundance distribution patterns of nekton in the Minnan sea area.

The Bohai Sea and Yellow Sea are continental shelf areas with high production of dimethyl sulfide (DMS). Field investigation of DMS in this area is helpful to accurately assess its amount released from the ocean and its negative feedback on global climate change. Both model-based and direct measurement methods are based on DMS concentration in surface seawater and lower atmosphere, respectively, so advanced detection technology plays a decisive role in the accurate flux estimation. Gas chromatography, mass spectrometry, chemiluminescence and satellite remote sensing are commonly used observation techniques. At this paper, a method based on benzene-assisted photoionization positive ion mobility spectrometry (BAPI-PIMS) for in-situ observation of DMS in seawater is proposed. Combined with dynamic gas stripping and on-line water removal Nafion tube sampling system, the interference of environmental water vapor is eliminated. Under the optimal conditions, the linear range based on the two DMS product ions is 0.10−120 nmol/L, and the detection limit is as low as 0.065 nmol/L. Then the demonstrated method is applied to field detect DMS in the Bohai Sea and northern Yellow Sea, and the concentration of DMS in surface seawater ranged from 0.08 nmol/L to 0.96 nmol/L, while the air-sea exchange flux ranged from 0.12 μmol/(m²·d) to 17.75 μmol/(m²·d). Lastly, the difference between DMS detected on field and in lab and the main impact factors are discussed via the correlation analysis and canonical correspondence analysis, and results show that nutrients and phytoplankton community are the main factors during the seawater preservation, indicating the important significance of field observation method established currently for accurate evaluation of DMS release from the ocean.

In order to study the relationship between daily increment of statolith and environment of neon flying squid (Ommastrephes bartramii) for different cohorts in the North Pacific during feeding ground, we explore the relationship between daily increment of statolith microstructure and environmental variables by gradient forest method (GFM) and generalized additive model (GAM) based on the samples collected in the North Pacific from 2010 to 2016. The results show that the life cycle of O. bartramii is about one year. The age of the autumn cohort ranges from 165 d to 345 d, and the age of winter-spring cohort ranges from 95 d to 271 d, respectively. Sea water temperature at the depth of 100 m (Temp_100), sea surface temperature (SST), sea surface salinity (SSS) and mixed layer depth (MLD) are the key environmental variables for the daily growth of autumn cohort. Temp_100, MLD, sea surface height (SSH) and chlorophyll a concentration (CHL) are the key environment variables for the daily growth of winter-spring cohort. GAM analysis shows that the daily increment width of statolith is significantly correlated with the key environmental variables selected by GFM (p<0.01). Key environmental variables of different cohorts suggest that the growth of O.bartrarnii is significantly affected by water temperature and prey abundance.

Based on the investigation data of zooplankton in the sea area near the north operation area in the Lanshan Port of Rizhao Port in May (spring) and October (autumn) 2015, the community structure characteristics of zooplankton was analysed in this paper. The results showed that 20 species and 7 taxa of zooplankton were found in the two seasons, including 12 species and 4 taxa in spring and 19 species and 6 taxa in autumn, the average abundance of zooplankton were 128.1 ind./m³ in spring and 103.3 ind./m³ in autumn, the average biomass (wet weight) were 1 129.9 mg/m³ and 954.3 mg/m³, the average Shannon-Wiener diversity index (H'), Margalef’s species richness diversity (D) and Pielou’s evenness index (J) were 2.39, 0.85, 0.87 in spring, respectively, and 2.01, 1.21, 0.62 in autumn, respectively. In spring, the dominant species were Sagitta crassa, Calanus sinicus, Labibocera euchaeta, Acartia pacifica, Pleurobrachia globosa, while in autumn, the dominant species were Acartia pacifica, Doliolum denticulatum, Sagitta crassa, Labibocera euchaeta. Cluster analysis showed that the zooplankton in the investigation area could be divided into three groups. This study could provide important basic data for further study of zooplankton community structure in the coastal waters of Rizhao.