Study On The Seasonal And Spatial Variation Of Phytoplankton Around Marine Ranching Area Of The Northern Yellow Sea

In this study,the Utermohl method was used to conduct a four-season ecological survey of the coastal marine ranching water and its surrounding waters in the northern Yellow Sea(121.51°E-122.03°E,37.46°N-37.63°N)in north Yantai.A monthly survey of hypoxic periods was conducted based on the hypoxic phenomenon in this area.The following results were obtained by studying the spatial and temporal distribution of phytoplankton species,cell abundance,dominant species and the influence of hypoxia:1.In 2016,a total of 39 species of 24 genera in 4 phytoplankton families were identified,among which the species of diatoms were the most(25 species&15 genera),accounting for 64.10%of the total species.In 2017,a total of 39 species,22 genera and 3 phytoplankton species were identified,among which the species of diatoms were the most(29 species&15 genera),accounting for 74.35%of the total species.The abundance of phytoplankton in winter in 2016 and 2017 is much higher than in other seasons.In 2016,the seasonal changes of phytoplankton abundance in surface and bottom layer were the same(winter>autumn>summer>spring).In 2017,the seasonal changes of phytoplankton abundance the seasonal changes of phytoplankton abundance were slightly different from that of the bottom layer.At the surface,phytoplankton abundance was in order winter>summer>autumn>spring;while in the bottom layer,the order was winter>summer>spring>autumn.The main dominant species in winter of 2016 and 2017 were Thalassiosira subtilis,Thalassiosira rotula and Thalassiosira pacifica,among which Thalassiosira subtilis was in absolute dominant position,while the common dominant species in spring,summer and autumn was Coscinodiscus asteromphalus.The diversity index in 2017 was generally higher than in 2016,and that in the bottom layer was significantly higher than in the surface layer.2.In this study,it's found that in May to September of 2016 and June to August of 2017,there were different degrees of hypoxia happened in the surveyed sea areas.In 2016,hypoxia was more serious,and its impact on phytoplankton was more significant.The hypoxia phenomenon in 2016 gradually aggravate from May to August.In May,only a mild hypoxia occurred in few stations.Dissolved Oxygen(DO)mass concentration in the low oxygen station was between 4.5 mg/L to 5 mg/L.Low-oxygen phenomenon occurred in all stations in August,and the DO concentration of most stations was between 1 mg/L to 3 mg/L;the hypoxia phenomenon in September relieved compared with August.The DO mass concentration of each station significantly increased.In 201 7,the hypoxia phenomenon gradually exacerbated from June to August,and the mass concentration of DO at most stations in June was between 4 mg/L to 5 mg/L.The mass concentration of DO at most stations in August was between 1 mg/L and 3 mg/L.Through comprehensively analyzing the phytoplankton and hypoxia status in this sea area,it is found that the phytoplankton abundance in low oxygen sea area is significantly lower than that in non-low oxygen sea area.With the continuous increase of the degree of hypoxia and the continuous decrease of the mass concentration of DO,the proportion of dinoflagellates in phytoplankton abundance was also gradually increased.Based on comprehensive analysis of various data,the adaptability of dinoflagellates to low oxygen environment was stronger than that of diatoms.