The decomposing process of Ulva prolifera green tide was simulated in the outdoor pond to study laws of the nutrient release. Simultaneously, we carried out field investigation in the coast of Qingdao in June 2018, such as the Aoshan Bay, the outside of Aoshan Bay and the Shilaoren Beach, to monitor regularly the seawater quality. Simulation experiment results showed that the concentrations of nitrogen and phosphorus nutrients were increasing significantly during the decomposition of Ulva proliferas and dissolved organic and particulate states are the main forms of nitrogen and phosphorus nutrients. The concentrations of dissolved organic nitrogen (DON), particulate nitrogen (PN), dissolved organic phosphorus (DOP) and particulate phosphorus (PP) nutrients in the water of 5 g/L biomass experiment were much higher than original water. Field investigation results showed that the nitrogen and phosphorus nutrients contents in the seawater reduced to the minimum gradually due to the absorption of the green tide. And then, as the decomposing of the Ulva prolifera green tide, the contents of nitrogen and phosphorus nutrients in the sea water were gradually increasing. Aoshan Bay was most affected by the Ulva prolifera green tide, it was even inferior to the second-class water quality standard. PN and PP were the main forms of nutrients in the investigation area, this situation was most obvious in the Aoshan Bay (PP, 2.02 μmol/L). Compared with Aoshan Bay, the seawater exchange capacity of the Shilaoren Beach was strong, and it was intercepted and salvaged in time after that the Ulva prolifera green tide was docked, which was less affected by the decomposing of Ulva prolifera green tide. With the accumulation and decay of the Ulva prolifera, the nutrients content and structure of the sea area changed significantly, which had severe impact on the stability of the phytoplankton community, which may cause secondary disasters of red tide. Therefore, we must promptly clean up the Ulva prolifera gathered near the coast of Qingdao to reduce the impact on nearshore seawaters in the southern Yellow Sea.

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.

Green tide caused by Ulva prolifera recurrent for 12 consecutive years by 2019 has become one of the most serious ecological disasters in the Yellow Sea. Based on the current scientific understanding of the Yellow Sea green tide and the control countermeasures, three key processes were identified during the early stage, i.e., the attachment and growth of U. prolifera micropropagules on the aquaculture facilities, the detachment of the epiphytic U. prolifera from the rafts and forming the floating biomass, and the floating U. prolifera in the Subei Shoal entering the offshore area and forming the large scale green tide. The specific control countermeasures were proposed according to the three key processes including: new material and technology studies to prevent the attachment and growth of the green algae, monitoring the recycling of the aquaculture facilities and to prevent the disposal of attached green algae on the intertidal flat, and the interception and collection of floating green algae in the major waterways in the Subei Shoal. This integrated strategy will help to provide ideas and technical supports for the scientific source control and management during the early stage of the Yellow Sea green tide.

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.

Coral reef is one of the most diverse ecosystem in the ocean, and benthic shellfish is an important component of this ecosystem. We used the SCUBA diving line intercept transect quantitative method to investigate the community status and characteristics of benthic shellfish in the coral reef area of Weizhou Island, Beibu Gulf, covered 6 sites. Sectional benthic shellfish were qualitatively and quantitatively collected in the fall (October 2015) and spring (May 2018). The species composition, abundance, biodiversity index and so on were analyzed. Based on the two survey results, 128 species of benthic shellfish were found in the coral reefs of Weizhou Island, belonging to 1 family, 1 genera, 3 species of Polyplacophora, and 25 families, 46 generas, 68 species of Gastropoda, and 22 families, 31 generas, 57 species of Bivalvia. Dominant species are Parahyotissa numisma, Beguina semiorbiculata, Thais echinata, Trochus maculatus, Euplica versicolor, Barbatia obliquata, Atrina verxillum, Cantharus cecillei, Cerithium dialeucum, Drupa margariticola. We recorded 2 class, 14 family, 43 species in quantitative transects in spring of 2018 and the total species, biomass, Shannon-Wiener index, Margalef index and Pielou index are 3.39 ind./m², 86.94 g/m², 3.31, 3.50 and 0.37. By comparing and analyzing the ecological indices of benthic shellfish in different years, the shellfish biomes in the coral reefs showed good succession development during 2015 to 2018. The shellfish community in the coral reef area of the South China Sea may be affected by both the intensity of anthropogenic disturbance and latitude. This study provided valueable data to rationally develop and utilize marine biological resources, biological protection and ecological restoration for the coral reef ecosystem in the Weizhou Island.

To elucidate the characteristics of macro-fouling communities on discus buoys, an assessment was conducted on 4 buoys deployed in offshore waters southeast of the Zhujiang River Delta and the northeastern Beibu Gulf, respectively. The abundance and biomass of macro-fouling organisms colonizing the side of buoys were 400.00−78 296.00 ind./m² and 659.42−62 276.00 g/m², respectively, whereas those on the bottom were 412.00−66 585.00 ind./m² and 1 861.60−60 784.00 g/m². At most stations, the abundance and biomass of macro-fouling organisms on the bottom of buoys were higher than on the side. The diversity index (H′) on the bottom of buoys ranged from 2.39 to 3.06, the richness index (d) from 4.02 to 6.98 and the evenness index (J′) from 0.88 to 0.91; and those on the side of buoys were from 0.64 to 2.79, 1.10 to 4.89 and 0.58 to 0.96, respectively. Both of the H′ and the d on the bottom of buoys were higher than on the side. According to the results of Hierarchical Cluster Analysis and Non-metric Multi-Dimensional Scaling, the macro-fouling communities of buoys could be clustered into 4 groups at 30% similarity. Of them, the communities on the bottom of the buoys could be basically clustered into a group while those on the sides varied with locations. Moreover, one-way Analysis of Similarities and Similarity Percentages-Species Contributions not only indicated that the macro-fouling community structure differed significantly between the side and bottom of the offshore buoys but also highlighted that the cirripedians and cnidarians made the greatest contribution to the difference. Overall, macro-fouling organisms preferentially colonized the bottom of discus buoys rather than the side.

According to two years (2018−2019) spring plankton surveys in the Zhoushan coastal waters, the zooplankton community structure (species composition, abundance of dominant species) were investigated, the canonical correspondence analysis (CCA) was used to study spring interanuual difference of zooplankton community and causes of their dynamics, the mechanism of community dynamics were discussed according to our results.The results show that the study region is divided into three groups according to cluster analysis of sea surface temperature (SST) and sea surface salinity (SSS): Hangzhou Bay water masses (Area I), upwelling water masses in Zhoushan Island (Area II), and water masses in Zhoushan offshore area (Area III). Water mass groups have significant influence on the composition of zooplankton community. The main species contributing to the difference between the three water masses in spring 2018 and spring 2019 (contribution rate >10%) are Calanus sinicus. The contribution species of the same water mass in two years were: Tortanus derjugini (56.91%) and Labidocera euchaeta (12.34%) in Area I, Calanus sinicus (72.64%) and Muggiaea atlantica (13.35%) in Area II, Calanus sinicus (41.93%) and Noctiluca scintillans (22.94%) in Area III. CCA shows that the first CCA axis (CCA1) and the second CCA axis (CCA2) explained 46.14% of the accumulated variance of the dominant species of zooplankton and 97.82% of the species-environment accumulated variance in spring 2018 and spring 2019. CCA1 mainly reflects the spatial difference between the offshore water mass and the Hangzhou Bay water mass. CCA2 mainly reflects the interannual difference between the stations in 2018 and 2019. Salinity is the main factor influencing the spatial difference of zooplankton community structure in spring, while temperature and chlorophyll a concentration are the main factors controlling the interannual difference of zooplankton community structure in spring.

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 data obtained from bottom trawl investigation in the Haizhou Bay and adjacent waters in 2018, a mass-balance model for the Haizhou Bay ecosystem was constructed by Ecopath with Ecosim software, consisting of 26 functional groups. Using Ecopath model, we evaluated the trophic structure, trophic impact relationship and ecosystem characters of the Haizhou Bay to provide a theoretical basis for the implementation of ecosystem-based fisheries management. The result showed that in this ecosystem trophic levels of functional groups varied from 1.00 to 4.19, and the range of fish trophic level was wide, ranging from 3.22 to 4.19. Phytoplankton and molluscs were in important nutritional positions in the ecosystem facing with the pressure from both the primary producers and predators. The evaluation of the ecosystem structure and function showed that the total primary production/total respiration (TPP/TR) was 7.096, total primary production /total biomass (TPP/B) was 56.866, the connectance index (CI) and system omnivory index (SOI) were 0.429 and 0.204, indicating that the Haizhou Bay ecosystem was in an immature, unstable state and was susceptible to external disturbances. Through the study of the Haizhou Bay and its adjacent waters ecosystem model, we analyzed the nutrient structure and phylogenetic status of the sea area, which would provide a theoretical basis for the sustainable utilization and scientific management of fishery resources in the Haizhou Bay.

In this paper, the net primary productivity (NPP) of the northern islands of Miaodao Archipelago in 2005, 2010 and 2017 was estimated by using ArcGIS10.2, ENVI5.1, SPSS26 and other software based on the classic CASA model, and analyzed the spatial-temporal heterogeneity of NPP from the perspectives of season, individual of island, landscape type, terrain gradient, and then analyzed the spatial-temporal heterogeneity of the landscape pattern of the five northern islands in 2005, 2010 and 2017. The relationships between them and the reasons were discussed. The results showed that: the total NPP for the five northern islands of Miaodao Archipelago was 7 520.54 t/a in terms of carbon; the mean density of NPP was 406.07 g/(m²·a) in terms of carbon; the distribution of NPP showed a significant spatial-temporal heterogeneity; the order of the average area of each landscape type from largest to smallest was coniferous forest, broad-leaved forest, construction land, grassland, arable land; the mean density of NPP from largest to smallest was broad-leaved forest, coniferous forest, arable land, grassland, construction land; the mean density of NPP of each landscape increased first with the increase of slope and height difference, and then decreased slowly; the aspect had a great influence on the NPP of forest, and the mean density of NPP of half shady slope is the largest; the annual mean density of NPP of different terrain gradients decreased with the time; the high value of NPP appeared in the mountainous area, and the low value of NPP is mainly in the flat area; due to the natural geographical conditions and the plant growth strip, the distribution of NPP was influenced by season, geographical location and landscape type.