In the autumn of 2014, a comprehensive survey of hydrology, chemistry and biology in the Bohai Sea was carried out. The structure characteristics of phytoplankton community in the Bohai Sea were studied. The historical data were combined to analyze the formation of phytoplankton community structure. Three classes, including 42 genera, 96 species were found in the survey. Among of them, diatoms are the main species, with 34 genera and 79 species, accounting for 82% of the total species; 16 species of 7 genera of the dinoflagellates account for 17% of the total species; and 1 species of 1 genera of the Chrysophyta. Among them, the genera of Chaetoceros has the most species, a total of 17 species, followed by the genera of Coscinodiscus, a total of 13 species. The total cell abundance of phytoplankton is between 0.71×10⁴ cells/m³ to 72.15×10⁴ cells/m³, with an average of 13.88×10⁴ cells/m³. The cell abundance ratio of diatom to dinoflagellate is 2∶1. The abundance of diatoms in the Laizhou Bay is significantly higher than that in other sea areas. The cell abundance of dinoflagellates in the central Bohai Sea is significantly higher than that in other sea areas. The dominant species of phytoplankton are mainly Coscinodiscus asteromphalus, C. wailesii, Paralia sulcata, Ceratium fusus and Noctiluca. Scintillans. Horizontal distribution of phytoplankton community diversity in the Bohai Sea is uneven in autumn, and the diversity of local sea area is reduced due to the overproduction of single dominant species, the low value areas in autumn are distributed in the Liaodong Bay and the Bohai Strait. Compared with the historical data, the phytoplankton community in the Bohai Sea have obvious species succession. The genara of Ceratium has gradually emerged, its dominance in the central Bohai Sea and Liaodong Bay have surpassed the genara of Chaetoceros and Coscinodiscus. The phytoplankton community structure transforms from dominating by diatoms to dominating by diatoms and dinoflagellates.

Benthic diatoms are important primary producers in estuarine mudflat system, and the spatial and temporal changes in the communities can significantly impact the productivity of benthic fauna in the estuary. In this study, the ecological parameters in the estuaries of Daliao River, Hangu River and Huanghe River along the Bohai Sea coastline were surveyed and the related environmental factors were discussed, aiming to understand the seasonal variations and spatial differences of benthic diatom communities. The results showed that the species diversity index and absolute abundance of benthic diatoms were the highest in autumn, and the dominant species displayed obviously seasonal succession. The diatom absolute abundance in the estuaries of Daliao River and Hangu River were significantly higher than that of Huanghe River Estuary. The coarser sediments and significant phosphorus limitation in the Huanghe River Estuary are main reasons for the low diatom abundance. The correlation analysis between the benthic diatom communities and environmental factors indicated that the changes of temperature and nutrient concentration have significant effects on the seasonal pattern of the benthic diatom communities, while the sediment size, tidal range and runoff of the three estuaries are more important to explain spatial differences.

To investigate the spatial and temporal distribution of dinoflagellate cysts in surface sediment of Meizhou Bay, surface sediment was sampled at 7 stations in Meizhou Bay in May 2018 (spring), August 2018 (summer), November 2018 (autumn) and February 2019 (winter) for analysis of dinoflagellate cysts. In total, 42 species representing 6 groups, and 2 uncertain taxa were identified. The species number and abundance of heterotrophic species were higher than those of autotrophic species, and among them the species number and abundance of the protoperidinioid group were the highest. Seasonal difference was not obvious: the species number ranged from 34 to 38, and the abundance varied from 397.8 to 569.5 cysts/g with the annual average of 448.0 cysts/g. The species number and abundance of species at stations near the industrial zone were lower than those near the aquaculture area. There were 16 dominant species, among which the protoperidinioid group had an absolute advantage, but the dominance degree of all these dominant species was not large. Diversity index, richness index and evenness index were high, with the annual average of 3.45, 1.55 and 0.92, respectively. Compared with historical data, 19 new cysts were recognized, but the abundance was not much different. It should also be noted that a total of 6 toxic dinoflagellate cysts were found in the waters of the Meizhou Bay. Although the annual abundance was not high, there is still a risk of toxic red tides, which should be taken seriously.

Currently, the global nitrogen and phosphorus cycles are out of balance due to anthropogenic activities which produce a large amount of reactive nitrogen and phosphorus annually. The incremental N and P are mainly derived from production and application of synthetic N fertilizers, manure application, large areas of cultivated leguminous crops that could fix atmospheric N₂, and NO_x emitted from fossil fuel combustion. It should be noted that crop and livestock production systems are the major cause of human alteration of the global N and P cycles. Increased human sewage and fertilizer application in agricultural production have significantly raised the inputs of N and P nutrients to coastal ecosystems leading to a global spread of eutrophication. Most of these inputs are transported to the coastal ocean via river runoff and atmospheric deposition. More than half of the incremental N and P loads are related to anthropogenic sources. The Baltic Sea and East China Sea present typical eutrophication condition in developed country and developing country respectively. The mitigation strategies should focus on dual nutrient strategy for successful N and P reduction, including reduction of leaching and runoff from agricultural fields, growing perennial crops, effective application of fertilizers, and planting winter cover crops.

In this study, 40 groupers belonging to 10 genera of the subfamily Epinephelinae from Western Pacific were collected, and partial sequences of 16S rRNA gene and COI gene were amplified and determined. The molecular phylogenetic relationships were constructed and analyzed using maximum likelihood method. The results showed that the length of COI gene was 651 bp, encoding 227 amino acids. While the consensus sequences of 16S rRNA gene were 566 bp, with certain base insertion and deletion. The sequences of 16S rRNA gene were more conserved than those of COI gene. The phylogenetic tree of the 10 genera of the subfamily Epinephelinae was constructed and the results showed that Plectropomus was first separated and rooted at the base of the tree, indicating its evolutionary status was most primitive. 6 species from Plectropomus were clustered as a monophyletic group. Aethaloperca was close to Cephalopholis, which tightly clustered together. Variola was located between Plectropomus and Cephalopholis. Epinephelus was located at the top of the tree, indicating its advanced evolutionary status. The species from Epinephelus in the tree were clustered as two parallel branches, instead of a monophyletic group; Cromileptes, Triso, Hyporthodus, Anyperodon and Promicrops could not form an independent branch but cluster together with species from Epinephelus, indicating their close relationship within Epinephelus and some species might belong to Epinephelus.

Based on the bottom trawl surveys in the Haizhou Bay and adjacent waters during spring and autumn of 2011 and 2013−2018, the performance of regular GAM and PCA-GAM was compared, and the distribution of Cynoglossus joyneri in this area was predicted. The predictive ability and fitting effect of the two GAMs were evaluated by cross-validation. The results showed that the goodness of fit and prediction effects of PCA-GAM were better than those of regular GAM. In spring and autumn, the abundance of C. joyneri in the southern waters was higher than that in the northern waters, and the abundance in the near-shore shallow waters was larger than that in the deep waters. The higher water temperature in the coastal waters of the southern Haizhou Bay was conducive to the development of gonads for the spawning groups during spring and autumn. The lower salinity was conducive to the growth and development of fish eggs and larvae. At the same time, the abundant prey resources in the coastal waters provides a large amount of food for it after spawning period. In this study, two GAMs were used to predict the resource distribution of C. joyneri in the Haizhou Bay in spring and autumn of 2018. The results showed that the predicted abundance by PCA-GAM were more consistent with the actual catches, and the performance of PCA-GAM was better than the regular GAM. This study provides a new method for studying the spatial distribution of marine organisms in the future.

Illex argentinus was a short life cycle species. Its resource abundance is susceptible to changes in the marine environment, especially in its early life history stage. According to the production statistics of the Chinese squid jigging fleet during 2003−2016 in the Southwest Atlantic and the sea surface temperature (SST) of the spawning ground from satellite remote sensing, the correlation analysis method was used to select the featured area representing SST changes during the spawning season (June) of I. argentinus. Based on the assumption that the ratio of optimum SST range to the total area (Ps) of the spawning ground of I. argentinus is positively correlated with the abundance index (catch per fishing unit, CPUE, t/ship), the optimum spawning area and suitable sea water temperature range of I. argentinus were traced back, and a variety of multivariate linear prediction models of abundance index based on the environmental factors were established. The correlation analysis shows that there are significant correlations between SST and CPUE in two consecutive sea areas (Area 1, Area 2) in June. They are 42.5°−44°S, 57.5°−59°W (Area 1) and 39°−39.5°S, 45°−46°W (Area 2) respectively. The inferred spawning area of I. argentinus ranges from 37.5°S to 44°S and 41.5°W to 51.5°W, and the optimum SST in the spawning area is 16°C to 17.5°C. The SSTs of two featured areas (Area 1, Area 2) and Ps in the inferred spawning area are used to establish four types of multivariate linear prediction models of abundance index (ICPUE), the results show that the fourth model containing the featured areas and Ps in the inferred spawning area is superior to the other 3 models, and its prediction model of abundance index is ICPUE=1.390 4×Ps+0.261 9×SST_{Area 1}+0.096 2×SST_{Area 2}−3.248 0.

Dosidicus gigas is an important fishing target by Chinese squid-jigging fisheries, which is widely distributed in the Southeast Pacific Ocean. Its population is largely affected by climatic and environmental conditions on the fishing ground. In this study, we calculated the habitat suitability index (HSI) on the fishing ground of D. gigas in the Southeast Pacific Ocean off Peru from January to December during 1950 to 2015 based on sea surface temperature (SST) and the anomalies of sea surface height (SSHA), and variability in the environmental variables and habitat quality were further analyzed under the warm and cold phases of the Pacific Decadal Oscillation (PDO). The results suggested that PDO showed cold, warm and cold phases from 1950 to 2015. The anomalies of SST (SSTA) and SSHA during the cold PDO were significantly lower than those during the warm PDO. The cross correlation analysis suggested that both the SSTA and the SSHA were significantly positively correlated with the PDO index. However, and the HSI values on the fishing ground of D. gigas were significantly negatively correlated with the PDO index, SSTA and SSHA. During the cold PDO, the water temperature became cold, and the SSH decreased, these changes led to enlarged areas of suitable SST and SSHA for D. gigas, therefore, the favorable habitats largely increased. However, during the warm PDO, the water temperature became warm, the SSH elevated, whereas the ranges of suitable SST and SSHA contracted, all these changes resulted in the decrease of the suitable habitat of D. gigas. Our findings suggested that PDO regulated the environmental conditions on the fishing ground of D. gigas off Peru, and further significantly affected the habitat quality and suitable ranges of the habitat.

According to the demersal trawling survey data in the Haizhou Bay and its adjacent waters in autumn of 2011 and 2013−2018, we studied the habitat suitability of Saurida elongata, using biotic and abiotic factors data, such as bottom water temperature, bottom salinity, water depth, resource density, bait biology, collected synchronously. The weight of each environmental factor was determined by using the model of boost regression tree (BRT), and the habitat suitability index (HSI) model was established by using arithmetic mean method and geometry mean method respectively, and the optimal model was determined by cross validation. The results show that the most suitable bottom water temperature range for the Saurida elongata to inhabit in fall was 17.5−18℃, the most suitable bottom salinity range was 31.3−32, and the most suitable water depth range was 24−37 m. Three main bait organisms were selected as biological factors, namely, Loligo spp., Metapenaeopsis dalei and Amblychaeturichthys hexanema. The HSI model was established with the bottom water temperature, bottom salinity and water depth as the influencing factors. The results show that the feed factors contributed most significantly to the total deviation of spatial distribution, followed by the water depth and bottom water temperature. Through cross validation, it is found that the weighted HSI model with arithmetic mean method algorithm has lower Akaike Information Criterion (AIC). The results show that the most suitable habitat (HSI≥0.7) of Saurida elongata in autumn was 34.5°−36°N, 119°−121°E, among which 35°−36°N was the most suitable habitat, and the HSI increased from near shore to sea.

Based on the macrobenthos materials samples collected in August 2009, October 2009, May 2010 and August 2010 in the Laizhou Bay, the present study analyzed species composition, abundance, biomass, community structure and compared with historical data of macrobenthos. The results suggested that 272 species of macrobenthos were identified in the research region, including 122 species of Polychaetea, 64 of Crustacea, 46 of Mullusca, 18 of Echinodermata, 9 of Pisces and 13 of other groups. The total average abundance was (1102.56±216.32) ind./m², average biomass was (28.16±8.45) g/m², Polychaetes were the most dominant groups in the abundance and Mollusks were dominant in the biomass. Regarding the spatial influence on macrobenthos, low values of abundance and biomass usually appeared in stations outside of the Huanghe River Estuary in the west of the bay, but high values occurred in the central of Bohai Sea. Regarding the temporal influence on macrobenthos, significant seasonal variations in the abundance and biomass were observed. The dominant species were distinct, the relative important species were Sternaspis sculata, Glycinde gurjanovae and Alvenius ojianus. Compared with the historical data, the species composition and dominant species had showed an obvious miniaturization trend.