Spatial Distribution Pattern And Community Assembly Of Planktonic Ciliates In The South China Sea

Planktonic ciliates are single cell eukaryotes with cilia in the body surface,distributing widely in aquatic habitats with diverse species.As an important predators of pico-and nano-phytoplankton as well as preys of meso-zooplankton and larva,ciliates play vital roles in transferring material and energy from the microbial loop to the traditional food chain.Previous researchs on ciliates diversity were mainly via morphology methods or traditional molecular methods,which may underestimate low abundance taxon.High-throughput sequencing is convenient,fast,low coast and sensitive to low abundance groups.Sequencing based on rRNA can remove interferences of extracellular nucleic acids and dead cells,re:flecting the real sample composition.The South China Sea is the largest marginal sea in China,located in tropical and subtropical waters.Researches on the diversity and composition of ciliate in South China Sea mainly focused on the photic zone,while distribution of ciliate in the aphotic layer and the mechanism of different distribution were rarely involved.In this research,we explored ciliate diversity,community composition and distribution patterns of ciliate in the water column,and discussed the mechanism that influence different distribution of ciliate.Results were as follows:(1)The dominant groups of planktonic ciliates in northeastern and mid-region of the South China Sea were Spirotrichea,Oligohymenophorea,Colpodea,Phyllopharyngea.Prostomatea,Litostomatea and Heterotrichea were secondary dominant groups.In northeastern area relative abundance of Phyllopharyngea was larger than Colpodea,it was reverse in mid-region basin of the South China Sea.Colpodea has higher relative abundance in the photic zone than the aphotic zone,while Oligohymenphorea is reverse.(2)The diversity of ciliates had different spatial distribution patterns.In northeastern area,ciliate diversity is significant higher in north than south.In mid-region basin,ciliate diversity increased at first and then decreased with depth,reaching the highest diversity 300 in 5 meters of station 14,the lowest diversity is 86 in 4000 meters of station 43.In general,ciliate diversity in the northeastern area was significantly higher than the mid-region area.In the northeastern area ciliate diversity was correlated with distance.In the mid-region area,ciliate diversity was correlated with depth.(3)The community structure of ciliate in northeastern area is clearly divided into two groups,and the south group and north group both can be distinguished in different depth.In the mid-region area,ciliate community structure can also be distinguished in different water depth.The community structure is significantly correlated with geographic distance,depth,temperature and oxygen in the northeastern area.In the mid-region area,the community structure was correlated with depth,temperature,salinity,oxygen and the abundance of PNF,NF and bacteria.(4)Dispersal limitation was the main ecological process for ciliate in both areas.There was no obvious variation in depth in north station of the northeastern area.In the south station,dispersal limitation is higher in aphotic zone than photic zone,heterogeneous selection was reverse.Undominated decreased with depth increase.The mid-region area was similar to south station of the northeastern area.Dispersal limitation was higher in the aphotic zone than in the photic zone,while heterogeneous selection was first decrease then increase with depth.Undominated was increased at first then decreased with depth.The above studies had systematically studied the differences in the distribution and community assembly of ciliate in the South China Sea both in the horizontal direction(north-north and central sea areas of the South China Sea)and vertical scale(from the surface to the bottom).Which revealing the diversity,community distribution and the mechanisms that cause the distribution patterns of ciliate in the northeastern and mid-region of the South China Sea.This work fills in the research gap of the ecological distribution of ciliate in the South China Sea,and enhances the understanding of ciliate distribution patterns and community assembly in the aphotic zone.