Community Composition And Spatio-temporal Distribution Of Bacterioplankton And Microbial Eukaryotes In The Surface Waters Of The Bohai Sea And The Yellow Sea

Microorganisms play an important role in the biogeochemical cycles of marine ecosystems.Human activities affect the coastal environment,leading to a series of ecological problems such as eutrophication and harmful algal blooms.The nitrogen-rich and phosphorus-limited nutrient structure is an important feature of waters in the Yellow Sea and Bohai Sea water.The specific nutrient stoichiometry,together with physical oceanographic dynamics(e.g.,an intrusion of Yellow Sea Warm Current in winter)in these regions,may affect the composition,abundance,spatial and seasonal changes of microorganisms in the waters.However,large-scale studies on bacterioplankton and planktonic eukaryotic microbes in the Yellow Sea and Bohai Sea were rare.This work is an integrated research of planktonic microbes in eutrophic coastal oceans by appling high-throughput sequencing,flow cytometry and quantitative PCR techniques.The research content and results are as follows:(1)A total of 140 surface water samples were collected in autumn(November)and spring(April)in 2014 at the Bohai Sea,northern Yellow Sea,central Yellow Sea and southern Yellow Sea.A total of 20 sites(10 spring and 10 autumn)were investigated using high-throughput sequencing 16S rDNA and quantitative PCR.The results showed that the?-diversity of bacteriplankton was high and varied greatly;the two-way ANOVA analysis showed that the seasonal and regional(among the Bohai Sea,the North Yellow Sea,the central Yellow Sea,and the southern Yellow Sea)effects were not significant for?-diversity;?-Proteobacteria(3%-79.7%,relative abundance),?-Proteobacteria(1.9%-24.3%),Bacteroides(2.3%-47.8%)and Cyanobacteria(0.8%-84.7%)were dominated in the community;NMDS and ANOSIM statistical tests showed that the community structure of bacterioplankton differed significantly between these two seasons,but there was no significant difference among the four regions;RDA analysis showed that temperature,salinity and N:P were the most important environmental factors structuring the bacterioplankton community in the surface water of the Yellow Sea and Bohai Sea.Correlation analysis showed a marginally significant association between the16S rDNA copy numbers of bacterioplankton obtained by molecular methods and bacterial cell numbers(R~2=0.31,P=0.079),Synechococcus,a dominant group in bacterioplankton community,showed a strong correlation(R~2=0.70,P<0.001)between cell abundance and 16S rDNA copy number.Moreover,we also used the PICRUSt software to predict the geochemical functions of bacterioplankton in the surface waters and found that the assimilated sulfur potential was much higher than the nitrogen and sulfur metabolism.(2)Based on the above 20(spring and autumn each with 10)water samples from the Yellow Sea and Bohai Sea,the high-throughput sequencing based on 18S rDNA was used to explore the community composition and spatio-temporal distribution patterns of microeukaryotes.The results showed that the?-diversity of microeukaryotic communities in surface water was high and varied greatly among samples;Alveolata(63.7%),Archaeplastida(23.5%),Stramenopiles(8.7%)and Opisthokonta(2.6%)were the dominant in terms of the relative abundance of rDNA sequences.Two-way ANOVA showed that seasonal and region-wise variations were neither significant nor correlated with any environmental factors measured in this study.ANOSIM test found that the community structure was significantly different between these two seasons and among these four regions.Temperature was the most important environmental factor that driving the microeukaryote community spatio-temporal variations.