RESUMO
Based on samples collected in the waters around Nansha Islands from August 25 to September 28, 2011, the characteristics of net phytoplankton community and their relationships to environmental factors were investigated. A total of 113 species, belonging to 34 genera of 3 phyla were identified, among which 57.5% belonged to Pyrrophyta and 40.7% belonged to Bacillariophyta. Ceratium in Pyrrophyta had the most species accounting for 30.1% of the 113 species. The average abundance of net phytoplankton was 2.12 x 10(4) cell x m(-3) and high abundances were encountered in the complex gyre adjacent to Reed Tablemount and in the Cyclonic Gyre adjacent to Wan'an Tan. Trichodesmium in Cyanophyta was the dominant functional group, taking up 77.0% of the total net phytoplankton abundance. Trichodesmium thiebautii, T. erythraeum and Pyrocystis noctiluca were the major dominant species. The dominant species varied with locations. Cyanophyta widely dominated at stations 3, 5, 6 and 10-14, Pyrrophyta were the dominant phytoplankton in the central locations at stations 4 and 7-9, while Bacillariophyta dominated only at the southernmost stations 1 and 2. The values of Shannon index and Pielou evenness index of net phytoplankton community were 3.10 and 0.62, respectively. The salinity, water temperature, contents of ammonium, nitrite, phosphate and silicate, as well as mesoscale gyres and the west Nansha coastal current were the important environmental factors affecting the characteristics of net phytoplankton community. The ordination plots by canonical correspondence analysis could well display the characteristics of net phytoplankton community and their relationships to environmental factors.
