Spatial-temporal Variability Of Living Coccolithophores Over The Tropical SCE&EIO

The geographic pattern and community structure of living coccolithophores,coupled with environmental parameters in South China Sea of summer and Eastern Indian Ocean during the spring monsoon were investigated by the present research.According to the biological sample,we concluded the coccolithophores community feature and the response analysis between coccolithophores and hydrological parameters,discussing the potential ecological function,mechanism and contribution.As the largest marginal sea over the tropical oceans,the Souch China Sea(SCS)is 3500,000 km2 with surface reversing wind systems.Typically low nutrient conditions spread over the surface water in the SCS with the intrusion of Kuroshio water branch.Mesoscale eddy is one of the most important physical phenomenon in the SCS and has remarkable effect on the oceanic current systems.Active eddy areas appeared northwest of Pacific ocean and SCS based on the information derived from the satellite.The most eutrophic cold eddy center located in Qiongdong area,where high chlorophyll a and primary productivity were generally higher than that in none-eddy area.This factor significantly controlled the biological production.As the ocean channel between the Pacific and Indian Ocean,the SCS is the transition region of monsoon so highly correlated with the climate change around the world.The eastern Indian Ocean is the major traffic artery to connect Asia and other continents,strongly influences the ecological environment.Indonesian throughflow is the critical link of the global thermohaline circulation through the passageway westwards of Pacific Ocean to the Indonesia.It has got attention from varied fields and modeling work for 30 years.As the major airflow channel,the Bay of Bengal and the equatorial eastern Indian Ocean can change the ecology and biogeography of the SCS.Water physical turbulence is relatively small during the inter-monsoon periods in eastern Indian Ocean therefore applicable to carry out series of investigations on the sea.The cell abundance and species number of coccolithophore samples were carried out under the polarized light microscope.222 coccolithophore samples were obtained by 56 stations in Qiongdong waters(18.09°-21.47°N,110.24°-116.01°E)during August 2012.34 living coccolithophore taxa was diagnosed.Coccolith species were dominated by Emiliania huxleyi,Gephyrocapsa oceanica,Umbellosphaera tenuis,Helicosphaera carteri,Coronosphaera mediterranea and Discosphaera tubifera;and the dominant species of coccosphere were E.huxleyi,G oceanica,Algirosphaera robusta,Florisphaera profunda and C.mediterranea.The cell abundance ranged 0-68.903(×10~3 cells/L)with an average 8.103(×10~3 cells/L).In the horizontal distribution of cell,high value appeared at east of Hainan and station SEATS;vertically,the subsurface layer(50-75 m)had a maximum value.After principle correspondence analysis(PCA)performed,RDA was applied to discover the relationship between nannoflora and local hydrologic condition,it turned out that N/P and PO43-co-limited the coccolith and coccosphere among many impact factors.30 taxa were identified from 143 samples collected in 56 stations of eastern Indian Ocean(-5°-18.05°N,79.99°-113.23°E)in April 2011.Dominant species were E.huxleyi,G.oceanica,F.profunda,Umbilicosphaera sibogae,A,robusta and H.carteri.Coccolith density ranged 0.26-376.065(×10~3 coccoliths/L)with an average 41.928(×10~3 coccoliths/L);coccosphere density ranged 0.329-63.802(×10~3 cells/L)with an average 12.445(×10~3 cells/L);coccolith density in the surface layer was 0.26-376.065(×10~3 coccoliths/L)with an average 67.513(×10~3 coccoliths/L)and coccosphere density was 1.019-62.706(×10~3 cells/L)with an average 10.960(×10~3 cells/L).22 taxa were identified from 200 samples collected in 30 stations of eastern Indian Ocean(-5°-18.05°N,79.99°-113.23°E):in April 2012.Coccolithophore community was mainly dominanted by species G.oceanic,E.huxleyi,F.profunda,U.irregularis and U.sibogae.Coccolith density was between 0.192-161.709(×10~3 coccoliths/L)with an average 22.658(×10~3 coccoliths/L);coccosphere density ranged 0.192-63.365(×10~3 cells/L)with an average 9.386(×10~3 cells/L);coccolith density in the surface layer was 0.202-134.915(xlO3 coccoliths/L)with an average 22.416(×10~3 coccoliths/L)and coccosphere density was 0.252-13.915(×10~3 cells/L)with an average 5.601(×10~3 cells/L).Only sporadic reports regarding coccolithophore study were carried out in the northern SCS.As well,biogeographic work in Indian Ocean was more localized lacking integral mode.Considering the unique role and important connection between the SCS and eastern Indian Ocean on nature,society and economy,it is greatly needed to study and compare the biology and oceanography between them.