Distribution Patterns Of Microeukaryotic Community Between Sediment And Water Of The Yellow River Estuary

Although microprokaryotes have an extraordinary diversity than that of microeukaryotes,the role of microeukaryotes in ecosystems is indispensable.Estuaries are one of the most diverse and productive ecosystems in the world.Being located at intersections of land and sea,they are highly vulnerable to environmental change and human activities owing to being adjacent to inland regions and coastlines.And microorganisms are sensitive to environmental fluctuations.Therefore,microbial communities could be used to evaluate the state of estuarine ecosystems.Sediment and water have always been closely tied in aquatic systems.However,little information regarding the full extent of microeukaryotic composition in both the two habitats did we know especially in estuaries.In this study,we collected representive samples of sediment and water from the Yellow River estuary in Kenli,Dongying,Shandong Provence in October 2012 and analyzed the microeukaryotic abundance,diversity,community structure and their relationships with environmental factors between sediment and water in the Yellow River estuary by fluorescence quantitative PCR?qPCR?and454 high-throughput sequencing.The main results were as follows:?1?Microeukaryotic abundance detected by qPCR analysis showed that the microeukaryotic 18S rRNA gene abundance in sediment samples ranged from 1.03×10⁶to5.48×10⁷copies/g DW with an average of 1.45×10⁷copies/g DW.Nevertheless,microeukaryotic 18S gene abundance varied from 3.01×10⁴to 1.25×10⁶copies/mL?5.61×10⁵copies/mL for average?in water samples.In all,significantly?Wilcoxon rank-sum test,P=0.008?higher 18S rRNA gene abundance was detected in sediment samples than water.?2?Eukaryotic microorganisms in sediment and water samples performed by 454 high throughput sequencing showed that the OTU number in sediment?78-136?was higher than water?75-105?in each site except D site.Chao1 index were higher in water?195-304?compared with sediment samples?98-386?except A site.Shannon diversity index was significantly?Wilcoxon rank-sum test,P=0.032?higher in sediment than in water.In all,the diversity of microeukaryotes in the two habitats did not indicate clear trend.?3?Based on the results of 454 high throughput sequencing,the eukaryotic microbes were analyzed at different taxonomic levels.The microeukaryotic community at phylum level could be clustered into two separate branches except single sample WE,a sediment branch?SA to SE?and a water branch?WA to WE?.Metazoa?0-45.3%?,Fungi?23.15%-47.15%?,Streptophyta?1.1%-35.2%?,Ochrophyta?6.3%-19.2%?,Cercozoa?1.6%-15.9%?and Dinophyta?1.65-78.02%?were more abundant in sediment.The dominant phyla in water were Dinophyta?1.65-78.02%?,followed by Metazoa?0-45.3%?,Ochrophyta?1.4%-20.3%?,Cryptophyta?1.1%-6.3%?,Chloroplyta?1%-9.1%?,Cercozoa?1.1%-4.7%?,Fungi?0-8.5%?and Katablepharidophyta?0.3%-2.7%?.In all,differences indeed existed between sediment and water.The result showed that the two habitats absolutely had significant?ANOSIM,P=0.027?differences of microeukaryotic community composition according to similarity analysis.?4?Although there were indeed differences between sediment and water,co-existed microeukaryotic taxon was also found in the study according to the OTU-based results:OTU92 represented class Dothideomycetes.?5?According to Pearson correlation analysis,the microeukaryotic microorganisms detected in sediment were much less sensitive to environmental factors compared with water.The microeukaryotic taxa in sediment were only significantly?P<0.05?correlated with dissolved oxygen,TN and Dep,while more environmental factors were significantly correlated?P<0.05?with microeukaryotic microorganisms in water,such as pH,salinity?Sal?dissolved oxygen?DO?,NO₃^-,NH₄⁺,TP and so on.In addition,co-occurence types among microeukaryotes could also be found in sediment and water samples.The results showed that the network relationships among water eukaryotic microorganisms were more complex,while relatively simple in sediment.As such,we have provided baseline data to support further research on estuarine microeukaryotes in both sediment and water,which was useful for guiding the practical application of ecosystem management and biodiversity protection.