Dynamic Changes Of Phytoplankton In The Spring And Autumn Of The Bohai Sea And The Summer And Autumn Of The Yellow Sea

In this article,four investigations were carried out in the Bohai Sea in Spring(October),Autumn(may),and the Yellow Sea and the Yangtze river estuary waters in the Summer(August)and Autumn(October)in 2014,including chemical and biological,a comprehensive survey.It studied phytoplankton species composition,cell abundance and distribution,dominant species and their spatial distribution,seasonal succession community diversity and community structure.Through analyzing the reasons for the differences in phytoplankton community structure and comparing with the historical data,we can grasp the succession rules and trends of phytoplankton community,understand accurately the ecological environment status of the surveyed sea area,provide the basic data of fishery resources in the Yellow Sea and Bohai Sea and provide data support for the prevention and control of the ecological environment.According to the survey,there were obvious seasonal changes in the phytoplankton community in the Spring and Autumn of the Bohai Sea in 2014.In 2014,two voyages of Bohai Sea identified a total of 100 species of phyla,45 species and 45 genera,including diatoms,82 species of 36 genera,accounting for 82%of the total species,and 17 species of 8 genera of dinoflagellate,accounting for 17%of total species,one species of the genus Chrysophyta.From the number of phytoplankton species,the number of species in Spring is significantly smaller than that in Autumn,and the ratio of diatoms to dinoflagellate species is different.The ratio of diatom to dinoflagellate in Spring is 7:1,and the ratio of diatom to dinoflagellate in Autumn is 5:1.In terms of phytoplankton cell abundance,it is higher in Spring than that in Autumn.The diatom phytoplankton in both seasons has an absolute advantage in cell abundance and is the main group of phytoplankton in the Bohai Sea.In Spring(May),the total cell abundance of phytoplankton ranged from 1.08×104cells/m3 to181×104 cells/m3,with an average of 25.5×104cells/m3.In Autumn(October),the total cell abundance of phytoplankton ranged from 0.71×104cells/m3 to 72×104 cells/m3,with an average of 13.9×104 cells/m3.The abundance of diatom cells in Spring was dominant.The ratio of diatom to dinoflagellate was 12:1.The diatom dominance in autumn decreased,and the abundance of dinoflagellate cells increased significantly.The ratio of diatom to dinoflagellate was 2:1.In terms of the dominant species of phytoplankton,diatoms have higher dominance in Spring,and the dominant degree of dinoflagellates is prominent in autumn.The dominant species for the spring survey voyage are Chaetoceros densus,Guinardia striata,Paralia sulcata and Noctiluca scintillans,and the dominant species of the Autumn survey voyage are Coscinodiscus asteromphalus,C.wailesii,Paralia sulcata,Ceratium fusus and Noctiluca scintillans.In terms of the level and distribution of phytoplankton community diversity,diversity level is lower in Spring than that of Autumn,and the stability of community structure in Spring is poor.Due to the overproduction of single dominant species,the local sea area diversity is reduced.The low value areas in Spring are distributed in the central Bohai Sea and the Bohai Strait.The low value areas in Autumn are distributed in the Liaodong Bay and the Bohai Strait.The survey of two voyages in the Summer and Autumn of the Yellow Sea in 2014 also found that there were significant seasonal differences in phytoplankton community.A total of 193 species of 63 genera and 4 genus of phytoplankton were identified,including Bacillariophyta,118 species of 44 genera,accounting for 61.14%of the total species,and 72 species of 16 genera of the Pyrrophyta,accounting for 37.3%of the total species.There are 2 species of 2 genera of the Chrysophyta and 1 species of 1 genera of the Cyanophyta.In terms of species number,the total number of species in Summer is slightly larger than that in Autumn,the proportion of diatoms and dinoflagellate species is basically the same,the ratio of diatom to dinoflagellate in summer is 1.6:1,and the ratio of diatom to dinoflagellate in Autumn is 1.9:1.The number of dinoflagellate species in Summer is slightly higher.From the abundance of phytoplankton cells,the total cell abundance of phytoplankton in Summer is much lower than that in Autumn,and the Summer is between 0.03×104cells/m3 and 1362.03×104cells/m3,with an average of 38.9×104cells/m3.The degree is between 0.01×104 cells/m3 and 27729.8×104 cells/m3,and the average is 758.03×104 cells/m3.The abundance of diatom cells is lower in Summer than in Autumn;the abundance of dinoflagellate cells is higher in Summer than in Autumn.Summer diatoms and dinoflagellates were basically flat in cell abundance,the ratio of diatom to dinoflagellate was 1.1:1;the diatom dominance in Autumn increased significantly,the abundance of dinoflagellate cells decreased significantly,and the ratio of diatom to dinoflagellate is 199:1.From the perspective of dominant species of phytoplankton,the dominant degree of Summer dinoflagellates is higher,and the superiority of diatoms in Autumn is higher.The dominant species in Summer are Rhizosolenia styliformis var.styliformis,Ceratium fusus,Ceratium tripos,Noctiluca scintillans and Pyrophacus steinii.The dominant species in Autumn are Chaetoceros lorenzianus,Thalassionema frauenfeldii and Thalassionema nitzschioides.In terms of the level and distribution of phytoplankton community diversity,the two voyages in Summer and Autumn are not much different.In terms of spatial distribution,the horizontal distribution of phytoplankton community in the Yellow Sea in Summer and Autumn is uneven,and the Summer is characterized by high level of diversity in coastal waters,low level of diversity in Haizhou Bay and Jiangsu offshore waters,and diversity of coastal waters in Hangzhou Bay is low;it shows that the level of diversity in the coastal waters is high in Autumn,the level of diversity is low in the offshore waters of Jiangsu and the offshore area of Hangzhou Bay.Compared with the historical data,the phytoplankton community in the Yellow Sea and Bohai Sea has obvious species succession,and the dominant position of Chaetoceros has decreased.The hornweed in Dinoflagellate has gradually emerged and has become the main dominant species of phytoplankton community.Its prosperous period generally occurs in the summer and autumn of each year.The phytoplankton community structure is gradually controlled by diatoms to diatoms and dinoflagellates.This succession is a response of phytoplankton to changes in the external environment.The impact of such changes on the balance of marine ecosystems and fishery resources remains to be further investigated and demonstrated,and attention should be paid.