Study On The Benthic Microeukaryotes Diversity In Subtropical Intertidal Sediments

Microeukaryotes are single cell eukaryotes that are composed of large quantities of species differing in cell sizes,shapes and functions.Microeukaryotes can act as primary producers,consumers and decomposers,playing key roles in driving biogeochemical cyclings of marine ecosystems.Traditionally,morphological methods based on microscopic identifications were limited to specific groups and it is rather difficult to study all groups of microeukaryotes simultaneously which constrained the studies on the ecology of microeukaryotes.High throughput sequencing(HTS)has been applied to the study of microbial ecology including microeukaryotes in recent years,and a variety of habitats has been investigated.However,there are only a few studies focusing on microeukaryotes in the sediments,most of which were from specific environments such as hydrothermal vents,coastal seas and lakes rather than intertidal sediments.18S rDNA(ribosomal DNA)gene has been widely used to infer the community structure of microeukaryotes.However,the copy numbers of 18S rDNA gene differ significantly in microeukaryotes and DNA can exist for a long time in the extracellular environments,the community compositions of micro-eukaryotic assemblages may be twisted from the real one when rDNA is used.Our study focused on benthic microeukaryotes diversity at typical intertidal zone in Fujian province by sequencing the hyper-variable V4 regions of SSU rRNA transcripts through HTP method.The current work aimed to reveal the spatial and temporal distribution pattern of benthic microeukaryotes,and to figure out the factors shaping the patterns observed.Our study includes two parts,one part focusing on benthic microeukaryotes in different sampling months,depths,and areas covered by different vegetation in the Zhangjiang estuary mangrove,and the other focusing on benthic microeukaryotes at different sites in Xiamen intertidal zone during different seasons.The results are as follows:Part one Benthic microeukaryotes diversity in the Zhangjiang estuary mangrove sediments(1)Community composition:At super-group or phylum group level,Stramenopiles are the most abundant and account for 86.67%of all sequences followed by Alveolata which accounts for 7.75%,and Archaeplastida,Hacrobia,Apusozoa and unidentified microeukaryotes collectively are less than 0.2%.At genus level,the most abundant top 10 genera all belong to bacillariophyte,accounting for 59.12%of all sequences.Unidentified raphid-pennate are the most abundant genus accounting for 12.56%of total sequences,followed by Navicula which account for 10.88%.(2)Alpha diversity:mean Richness and Shannon indices increase with sampling depth and reach the maximum at mudflat area and in December,2015.For the Richness index,the mean value reaches the lowest at ecotone and in October,2015,and the mean value of the Shannon index reaches the lowest at Spartina area and in August.Richness index positively correlated with sampling depth and negatively correlated with lutein concentration,while Shannon index positively correlated with salinity and NH4-N concentration,negatively correlated with lutein and chlorophyllb concentrations.(3)Beta diversity:benthic microeukaryotes community dramatically differ in sampling months and are shaped by different overland vegetation,however there is no significant difference among benthic microeukaryotes communities from different sampling depths.Season(sampling month)is the primary factor explaining the variance of the composition of microeukaryotes,and together with overland vegetation type,they can explain 55.04%,61.81%and 44.81%of the variance of microeukaryotes,the abundant and the rare biosphere respectively.Part two Benthic microeukaryotes diversity at different sites in Xiamen intertidal zone(1)Community composition:At super-group or phylum group level,Stramenopiles are the most abundant and account for 91.66%of all sequences,followed by Alveolata and Rhizaria which accounts for 3.13%and 2.68%,and Apusozoan,Hacrobia,Archaeplastida together with unidentified microeukaryotes collectively are less than 0.3%of the sequences.At genus level,the most abundant top 10 genera all belong to bacillariophyte,accounting for 76.2%of all sequences.The Navicular are the most abundant group accounting for 20.98%of total sequences,followed by Gyrosigma which account for 14.55%.(2)Alpha diversity:Richness index range from 1064 to 2841(average 1886.5),and Shannon index range from 4.09 to 5.89(average 5.89).Richness index negatively correlated with cadmium concentration.(3)Beta diversity:benthic microeukaryotes community,especially the rare biosphere,dramatically differ in sampling seasons.Factors such as pH,peridinin,fucoxanthin,cadmium concentration and sampling season are significantly correlated with benthic microeukaryotes community,while cadmium concentration,fucoxanthin and sampling season can explain 33.89%,35.66%and 32.76%of the variance of microeukaryotes,the abundant and the rare biosphere respectively.