Abstract:Living coccolithophores (LC) are important in marine ecology, biogeochemistry, and especially the carbon cycle. Our chief aim in investigating the geographic distribution of LCs has been to provide data to help understand their roles. We investigated LCs in the East China Sea (ECS) from 7 October to 5 November 2010. Seawater samples from CTD arrays were filtered through 25 mm cellulose mixed-ester membrane filters on board as soon as possible, and dried. Then a piece of the membrane was cut out and, using neutral balsam, mounted beneath a cover glass. The samples were observed with a polarizing microscope at 1000× magnification. Twenty-six taxa were identified at different depths from 108 samples in ECS, the dominant species being Emiliana huxleyi, Gephyrocapsa oceanica, Helicosphaera carteri and Algirosphaera robusta. The abundance of coccoliths and cells ranged from 0-76 cells/mL and 0-4500 coccoliths/mL, the average being 18 cells/mL, 613 coccoliths/mL, respectively. The distributed pattern of LCs and coccoliths in surface and bottom layers were patchy. The outer areas of the sea basin had more species but showed less abundance than the inner area. The highest abundance was found at a station supporting a diatom bloom. We further observed the distribution of: total coccoliths; total cells; coccoliths and cells of E. huxleyi and G. oceanica; and compared these distributions among PN sections (PNs, starts from the Changjiang River estuary (121.5°E, 31.5°N) to the south-east corner of Ryukyu (128.23°E, 27.45°N)), Coastal Current sections (CCs) and the Kuroshio Current sections (KCs). PNs supoorted the highest abundance except for the cells of E. huxleyi. The distributions of coccoliths and cells between CCs and KCs (except in the bottom-most layer) showed slightly higher abundances in deep than in surface water. At the KC stations, however, coccolithophorids thrived between 25m and 80m. Our observations suggest that water-column mixing, sediment resuspension and nitrate concentration affect the distribution patterns of both species numbers and individual species.