Community Structure Of Picoplankton In The Coastal Waters Of Zhoushan And Correlation With Environmental Parameters

The ocean accounts for about 71%of the Earth's surface.In such vast ocean,microorganisms are everywhere.They are tremendously involved in atmospheric production,micro-food webs,and biogeochemical cycling of organic matter,and are an important part of marine ecosystem biomass and primary production.Picoplankton refers to plankton with a particle size of 0.22 to 2³?m.It mainly includes picoeukaryotes,planktonic bacteria,and viruses.It has the characteristics of high abundance,small size and easy to be ignored.Studying the diversity and community structure of picoplankton in different marine habitats can be helpful to better understand the relationship between microbes and environmental and/or biological factors,to further explore the temporal and spatial distribution of picoplankton and to fully grasp its ecological status.This paper revealed the diversity and community structure of picoplankton in the coastal waters of Zhoushan with high-throughput sequencing technology combined with flow cytometry counting method,and analyzed the relationship between picoplankton and environmental factors by RDA/CCA?RDA,Redundancy analysis;CCA,Canonical Correlation Analyses?.The main findings were as follows:According to the results of flow cytometry,the highest average abundance of picoeukaryotic organisms appeared in autumn?8.58×10⁵ cells/mL?.The differences of the average abundance among spring,summer,and winter was small?1.46-2.21×10⁵cells/m L?.The average carbon biomass of Zhoushan fishing ground in summer,spring,autumn and winter were 11.32,1.93,2.30 and 2.66 mg C/m³,respectively.Based on high-throughput sequencing of the 24 picoeukaryotes in four quarters of the study area,the seasonal variation analysis of their community structure and diversity was completed.A total of 856291 high-quality sequences were obtained,including 257 otus which is belonging to 40 phylums,68 families,99 orders,126 families and 140 genera.Different types of dominant species were observed in each quarter,Cryptomonadales_uncultured and Intramacronucleata occurred more frequently throughout the year.In this study,lefse multilevel species difference discriminant analysis was applied to find the dominant discriminant groups in each quarterly group,and Network analysis was used to observe the co-occurrence species in each season.Compared with traditional research methods,molecular biology method is indeed useful in discovering more marine microbial species.Results of correlation analysis between the structure of picoeukaryote community and environmental factors indicated that temperature and NO₃^-had strong positive correlation on the samples collected in summer.As to spring samples and DS5,NO₂^-presented a strong positive correlation with salinity,and PO₄^3-presented a negative correlation effect.PO₄^3-and PH presented a strong positive correlation effect on autumn samples and a negative correlation effect on summer samples.The results of bacteria diversity and community structure in different functional sea areas in Zhoushan archipelago in summer were as follows:the results of flow cytometry counting showed that the overall rank of heterotrophic bacteria abundance in all sea areas was:GQ>ZJJ>DJ>TH>LH>DS>SJM>JT.From the abundance index?Chao1,ACE?,the rank of bacteria abundance was:LH>JT>DS>SJM>DJ>ZJJ>GQ>TH.The average abundance of Synechococcus and heterotrophic bacteria in each sea area of Zhoushan archipelago was slightly higher than that in the adjacent waters of the Changjiang Estuary,approximately 10⁶ cells/mL,which had high biological carbon fixation capacity.The absolute predominant bacterial assemblages of DJ,GQ and TH was Flavobacterium,the absolute predominant flora of DS,JT,LH and SJM was?-proteobacteria,and the absolute predominant flora of ZJJ was cyanobacteria.This study demonstrated that?-proteobacteria were widely distributed in coastal areas,especially in areas where there is high concentration of organic particles due to human activities.Meanwhile,?-proteobacteria had an important association with the ocean's sulfur reduction process.The abundance of?-proteobacteria might significantly associate with petroleum hydrocarbon contamination,and Flavobacterium reacts rapidly during red tides.PICRUSt?v1.0.0 channel?was used to predict the bacterial function of each functional division area,overall speaking,the functional diversity and differentiation of bacteria in each target area was significant.