Distribution Patterns And Driving Factors Of Microbial Communities In Specific Areas Of The Bohai Sea,the Southern Yellow Sea And The Western Pacific

Marine microorganisms cover the three domains of life,i.e.Bacteria,Archaea and Eukarya,and play an important role in marine ecosystem.Exploring the spatial pattern of marine microbial diversity and its main controlling factors will deepen our understanding of the ecosystem processes in which marine plankton participate.In this study,using 16S r RNA and 18S r RNA gene high-throughput sequencing technology,we studied the distribution patterns and driving factors of microbial(bacterial,archaeal and microbial eukaryotic)communities in China coastal waters(the Bohai Strait,the southern Yellow Sea)and along the coastal-to-open ocean gradient(the central Bohai Sea-the southern Yellow Sea-the western Pacific).The main results are as follows:(1)The bacterial community in the surface waters of the Bohai Strait showed remarkable seasonal and spatial differences.In response to the dramatic changes of temperature and nutrient(NO₂-N and PO₄-P)levels between seasons,Synechococcus and unclassified taxa in Family I predominated in summer,while some oligotrophic taxa(e.g.,Pelagibacter,OM43 clade)are more abundant in winter.The spatial heterogeneity and patchiness of bacterial assemblages in the Bohai Strait had a weak correlation with the measured environmental factors(temperature,salinity and concentrations of inorganic nutrients)as well as the spatial factor(geographic distance),however,they showed a significant correlation with the phytoplankton community structure.Unclassified taxa within Vibrionaceae,Family I,Sva0996marine group and Surface 2,were closely linked to the abundant phytoplankton taxa Paralia sulcata,Noctiluca scintillans,and Coscinodiscus spp.The bacterial taxa that were distributed in patchiness,e.g.,SAR11 clade,unclassified taxa within Vibrionaceae and Sva0996 marine group,possess differentiated niches for utilization of organic matters.Besides,the distribution of OM43 clade was almost consistent with the area affected by the coastal current.In general,the spatial heterogeneity of bacterial communities were closely related to the heterogeneity of local environmental factors in the surface waters of the Bohai Strait,and the?-diversity of bacterial communities were influenced by the hydrodynamics.(2)The microbial community composition across three domains and their?-diversity were significantly different in the deep waters between the cold water mass region(CWMR)and the outer region(OR,the region of the Northern Jiangsu coast)of the southern Yellow Sea.The microbial?-diversity in the deep waters of the CWMR was significantly lower than that of the OR,which was mainly due to the weak water exchange between the inner cold water mass and the external water column,while the Shannon and Shannoneven diversity indices of microbial eukaryotic community were significantly higher in the deep waters of the CWMR than of the OR,suggesting the less disturbance on the microbial eukaryotic communities in the cold water mass.The greater depth,the higher levels of DO,salinity and PO₄-P concentration,and the lower water temperature and DIN concentration were responsible for the distinct microbial community composition in the cold water mass.Among these factors,water depth had the most significant effect on the microbial community structure,followed by water temperature.Close relationships were found between SAR11 Clade Ia and DO concentration,between Candidatus Nitrosopumilus,Pelagophyceae and water depth,salinity,and between Syndiniales,Bacillariophyta,RAD-B and DIN,Si O₃-Si concentrations.According to the microbial co-occurrence networks,the network structure in the deep waters of the CWMR was less complex than that in the deep waters of the OR,but the proportion of mutual exclusion relationship was higher than that in the OR,which could be attributed to the intensified competition for limited resources among microorganisms in the environment of the cold water mass.(3)By comparing the microbial communities across three domains in the central Bohai Sea,the southern Yellow Sea(the CWMR and the the region of the Northern Jiangsu coast)and the western Pacific(western area),we found that for bacterial and microbial eukaryotic communities,species richness(observed species,Chao,and ACE)and diversity(Faith's PD,Shannon,and Shannoneven)in the central Bohai Sea and the southern Yellow Sea were higher than in the western Pacific;for archaeal communities,species richness displayed a similar trend,but diversity displayed a reverse trend.Flavobacteriaceae,SAR11 Clade I,Cyanobiaceae,Nitrosopumilaceae,Syndiniales,Dinophyceae,etc.,had significantly higher relative abundances in the central Bohai Sea and the southern Yellow Sea.In contrast,Alteromonadaceae,Pseudomonadaceae,Marine group II(MGII)and Marine group III(MGIII)were more abundant in the western Pacific.The relative abundances of the oligotrophic taxa SAR11,SAR86 and SAR116 in the central Bohai Sea and the southern Yellow Sea were an order of magnitude higher than those in the western Pacific.Different sub-taxa within Flavobacteriaceae and Candidatus Nitrosopumilus were abundant in coastal areas and open ocean.Alteromonadaceae(29.4%)were relatively abundant at the depth of 1000?4000 m in the western Pacific,while Ascomycota(24.1%)and Basidiomycota(6.5%)were relatively abundant at the depth of 3000?4000 m in the western Pacific.In addition,the relative abundance of MGII in the surface waters of the western Pacific was up to 58.2%.Geographical distance,local physicochemical factors(temperature,salinity,DIN,PO₄-P,Si O₃-Si),and water depth all had significant effects(P<0.001)on the microbial community compositions in the three areas.Geographical distance had the greatest effect on bacterial community composition,while local environmental factors had the greatest effect on archaeal and eukaryotic community compositions;the effects of these factors on bacterial community composition were weaker than those on archaeal and microbial eukaryotic community composition.To sum up,at the meso scale,the spatial patterns of the bacterial community in the Bohai Strait and the microbial community across three domains in the southern Yellow Sea were more influenced by local environmental factors.At the large scale,both local and spatial factors were important in driving the spatial pattern of the microbial community.The relative importances of these factors were different to the three domains of microorganisms,and archaea and microbial eukaryotes had a stronger response to local environmental factors than bacteria.