中文摘要：

根据2012年8-9月在南海西北部海区的采样调查,对网采浮游植物的群落结构进行了研究.本次调查共检出浮游植物206种（包括变种及变形）,隶属于4门55属,其中硅藻门40属114种,占总种数的55.3％;甲藻门10属86种,占总种数的41.7％.浮游植物平均细胞丰度为66.67×104cells·m-3,硅藻平均细胞丰度为65.79×104cells·m-3,甲藻平均细胞丰度为0.88×104cells·m-3.优势种为伏氏海线藻Thalassionema franenfeldii、翼根管藻Rhizosolenia alata和菱形海线藻Halassionema nizschioides.调查海区的Shannon Weiner多样性指数（H ＇）平均值为2.67,高值区位于西沙群岛和调查区东部.对比分析浮游植物细胞丰度与环境因子可知,浮游植物细胞丰度高和种类多的区域,其水体营养盐含量也高,说明营养物质与该区浮游植物细胞丰度分布和群落结构密切相关.

英文摘要：

Net-phytoplankton community structure and abundance were preliminary studied on the basis of investigation in the northwest South China Sea from August to September, 2012. A total of 206 species were identified, belonging to 4 phyla with 55 genera, of which 55. 3% were Bacillariophyta（40 genera and 114 species） and 41. 7% were Pyrrophyta （10 genera and 86 species）. The average cell abundance of phytoplankton was 66.67× 104cells · m-3 , which was mainly contributed by diatom with mean value of 65.79 × 104cells · m-3. The mean value of dinoflagellates was only 0.88 × 104 cells · m-3. The dominant species were diatom such as Thalassionerna franenfeldii, Rhizosolenia alata and Thalassionema nizschioide. The average Shannon-Wiener diversity index of phytoplankton community was 2.67, and the high value occurred in the Xisha Islands and the east part of surveyed area. Distributive pattern of phytoplankton was much related with environmental condition. The water column with high phytoplankton abundance and species diversity often coincided with a high nutrient level particularly in upwelling zone. It suggests that nutrient may play important role in impacting the distribution of phytoplankton abundance and the community structure in this region.