Study On Microeukaryotic Diversity In The Southwest Indian Ocean

Microeukaryotes have extremely high diversity and complex ecological functions,,which is an indispensable part of the marine ecosystem.Different from the photosynthesis ecosystem,the deep-sea hydrothermal fields are mainly powered by chemosynthesis.Compared with prokaryotes,the study on the molecular diversity of microeukaryotes in deep-sea hydrothermal fields is seriously lagging behind.In this study,samples were collected from the Longqi(LQ),Tiancheng(TC)and Tianzuo(TZ)hydrothermal fields in the Southwest Indian Ocean.The composition of microeukaryotic communities and environmental driving factors were studied using fluorescence microscopy observation and high-throughput sequencing approaches.The main results are as follows:(1)As the depth increases,the abundance and biomass of heterotrophic nanoflagellate(HNF)and pigmented nanoflagellate(PNF)decrease,with the size fraction of 2-5 μm as the predominant group.The abundance of HNF below 1000m in LQ is significantly higher than that in TC,TZ and KP,but there is no significant difference in the abundance and biomass of HNF and PNF in different deep-sea hydrothermal fields.There is a relatively low abundance of PNF in the deep-sea hydrothermal area,with an abundance of 3±1 cells ml-1.Overall,the abundance and biomass of HNF and PNF were negatively correlated with depth,and positively correlated with salinity,temperature and bacterial abundance.The abundance and biomass of HNF and PNF have a strong coupling relationship with temperature and bacterial abundance.(2)The a diversity of microeukaryotes from hydrothermal fields is significantly higher than the bathypleagic samples(depth below 1000m),and there are significantly higher a diversity estimates in bathypelagic than surface(4m)water,mesopelagic water(depth between 200 to 1000m(including 1000m))and DCM(Deep chlorophyll maximum)depth.The relative abundance of Spirotrichea and Mamiellophyceae in the LQ hydrothermal fields are relatively high;the unclassified Metazoa and Polycystinea in the TC and TZ hydrothermal fields also had relatively high abundance of sequences,respectively.With higher relative abundance of unclassified Metazoa in the hydrothermal fields than that in the non-hydrothermal area,and Embryophyceae in the non-hydrothermal area than that in the hydrothermal fields.In the hydrothermal area.main unique microeukaryotes were belonged to Rhogostoma sp.(Cercozoa)、Flabellula sp.(Lobosa)和 Syndiniales-Group-Ⅱ-Clade-6,-10,-11 and-12 sp.(Dinoflagellata)may be unique microeukaryotes to hydrothermal fields.Density,depth,temperature and the abundance of 2-5μm HNF are the main factors affecting the structure of the microeukaryotic community in the Southwest Indian Ocean.