Diversity Of Living Coccolithophores In The Western Pacific Ocean

Living coccolithophores(LCs)are regarded as a group of unicellular phytoplankton coverd by calcite structure.They are important primary producer and marine biogenic inorganic carbon maker in the ocean,which play significant roles in global biogeochemical cycle of carbon.In addition,they also have influence on ocean albedo,ocean heat retention,cloud albedo and global sulrfur cycle.In the autumn of 2017 and 2018,we used microscopic observations of LCs in the Western Pacific Ocean(0?21 °N,120?13° 0E)to investigate their community structure,biodiversity,estimates of coccolith caicite and coccolithophore carbon biomass,Canonical Correspondence Analysis(CCA)and community assembly.In summer 2017,a total of 28 taxa of coccospheres and 19 types of coccoliths were identified from 161 samples.The abundance of coccospheres and coccoliths ranged from 0 to 26.8×103 cells/L and from 0 to 138.5×103 coccoliths/L,averaged at 4.2×103 cell/L and 10.9×103 coccoliths/L,respectively.Gephyrocapsa oceanica,Florisphaera profunda,Emiliania huxleyi,Umbilicosphaera sibogae,Gladiolithus flabellatus and Umbellosphaera tenuis were dominant species.High abundance of LCs was observed around mesoscale eddies,especially the Halmahera Eddy.Abrupt abundance increases of coccoliths and coccospheres in vertical variation presented patchy or "bull's eye" distribution.And coccosphere species occupied different depth.The average values of Shannon index and Pielou index were 1.39 and 0.70,respectively.The average values of coccolith caicite and coccolithophore carbon biomass were(0.197±0.280)?g C L-1 and(0.140±0.232)?g C L-1,respectively.Our study indicated that coccolithophore community in the survey area can be clustered into four groups.And the whole surveyed area could be divided to three parts warm-eddy region dominated by Gephyrocapsa oceanica,warm-eddy and none-eddy region dominated by Florisphaera profunda.In summer 2018,132 samples were obtained from 22 stations.Thirty-one species were indentified,including 28 taxa of coccospheres and 21 types of coccoliths.The abundance of coccospheres and coccoliths ranged from 0 to 0-19.2×103 cells/L and from 0 to 0-61.5×103 coccolith/L,averaged at 2.9×103 cell/L and 5.2×103 coccolith/L,respectively.Gephyrocapsa oceanica,Florisphaera profunda,Emiliania huxleyi,Gladiolithus flabellatus Umbilicosphaera sibogae,and Algirosphaera robusta were dominant species.Highest coccosphere abundance in DCM layer higher than others,which was six times as it in the surface layer.The horizontal distribution of coccosphere were dispicted by two dominnat species,G.oceanica and F.profunda.At section E130,coccosphere were concentreated at the depth of 25 to 150 m along the water column at 2-6°N.The average values of Shannon index and Pielou index were 1.24 and 0.73,respectively.The average values of coccolith caicite and coccolithophore carbon biomass were(0.089±0.118)?g C L-1 and(0.066±0.089)?g C L-1,respectively.And highest concentrations of them were found in DCM layer.The whole surveyed area could be divided to three parts as that in 2017The abundance of coccoliths and coccospheres were respectively 2.10 times and 1.47 times that in 2018.There was little difference in species richness between the two years.G.oceanica,F.profunda,E.huxleyi,U.sibogae and G.flabellatus were common dominant species in the two years,whose abundance in 2018 were lower than that in 2017,except for F.profunda.Here advanced ecological models were used to figure out the effects of environmental variables and spatial limitation on the coccolithophore community assembly.Results showed that spatial limitation could be key factors in LC distribution and community assembly.Significant Distance-Decay Relationship(DDR)were observed in species composition similarity in two years(P<0.001).And it was more obvious in 2017 than that in 2018.Similarity DDR was in inverted U-distribution at depth.The abundance of LCs was mainly controlled by temperature,salinity,sampling depth and a group of nutrientsWestern Pacific Warm Pool,as an important ocean carbon stock,controls the global circulation of carbon,nitrogen and other life elements in the WPO and even global ocean through the biological pump in its central waters.However,there was no report about the LC community in this area before.The current field study widened the dataset of LCs in western Pacific Ocean and favored later research on carbon cycle in the western Pacific.