中文摘要：

根据2004年2月在南海北部海域陆架区的采样调查,对南海北部Utermohl浮游植物的群落结构进行了研究.初步研究结果表明,本次调查共发现浮游植物5门106属198种（不包括20种未定种）.调查期内,南海浮游植物以硅藻为主,甲藻次之,以颗石藻为主要组份的金藻和固氮蓝藻也占有相当的比例,绿藻仅在珠江口个别站位被检出.菱形海线藻（Thalassionema nitzschioides Grunow）、佛氏海线藻（Thalassionema frauen feldii（Grunow） Hallegraeff）、贺胥黎艾氏颗石藻（Emiliania huxleyi（Lohmann） Hay et Mohler）、柔弱伪菱形藻（Pseudo-Nitzschia delicatissma Heiden）、长海毛藻（Thalassiothrix longissima Cleve et Grunow）、海洋桥球石藻（Gephyrocapsa oceanica Kamptner）、具齿原甲藻（Prorocentrum dentatum Stein）、具槽帕拉藻[Paraliasulcata（Ehrenberg） Cleve]和旋沟藻（Gyrodiniumspirale Bergh）为群落的优势种.南海北部浮游植物以广温、广布型为主,其次是暖水性种,热带、亚热带和冷水性种都较少.调查区浮游植物的细胞丰度介于3.8-2 810.3个/cm^3,平均值为206.4个/cm^3;浮游植物垂直分布总体特点是密集区位于水体表层,由水体表层到底层,细胞丰度逐渐减少;表层浮游植物细胞丰度的平面分布高值区位于调查区珠江口南部和南部海域.浮游植物群落的多样性分析显示调查海域中部的多样性较高,近岸和外海区则较低.应用典范对应分析（CCA）发现盐度和光照的梯度分布是影响南海北部浮游植物物种分布格局最重要的因素,磷酸盐和温度的梯度分布也起一定的作用.根据CCA的分析结果,将海区浮游植物物种划分为5个组,分别为：Ⅰ.高温度、高盐度、高光照和低营养盐组;Ⅱ.高温度和高光照组;Ⅲ.高磷酸盐和硅酸盐组;Ⅳ.低光强高盐度荫生物种组;Ⅴ.高硝酸盐组.

英文摘要：

They were presented that the phytoplankton species composition and cell abundance data based on the investigation in northern South China Sea（17°-23° N,111°-117° E） which was carried out from 8 th February to 4th March 2004 with 149 samples taken from 30 grid stations.A total of 195 taxa（not include uncertain species） belonging to 110 genera of 5 phyla were identified by Uterm hl method,in which Bacillariophyta were predominant and coexisted with Dinophyta.Chrysophyta which was mainly composed of coccolithophores and diazotrophs Cyanophyta were also common found in survey area.Few Chlorophyta were checked out at two stations near Zhujiang（Pearl River） Estuary.The dominant species in turn were Thalassionema nitzschioides Grunow,Thalassionema frauenfeldii Hallegraeff,Emiliania huxleyi（Lohmann） Hay et Mohler,Pseudo-nitzschia delicatissma Heiden,Thalassiothrix longissima Cleve ＆ Grunow,Gephyrocapsa oceanica Kamptner,Prorocentrum dentatum Stein,Paralia sulcata（Ehrenberg） Cleve and Gyrodinium spirale Bergh,etc.Most of phytoplankton taxa found in survey area was cosmopolitan species,warm-water species are also common,there were just few trophic-water,subtrophic-water or cold-water species.The cell abundance of phytoplankton ranged from 3.8-2 810.3 cells/cm^3,the average was 206.4 cells/cm^3.Phytoplankton cell abundance were concentrated in surface water and reduced rapidly from surface layer to the bottom.Two high phytoplankton cell abundance regions can be discriminated at southern waters of Zhujiang Estuary and southern part of the survey area, this two high phytoplankton cell abundance regions were mainly caused by higher nutrients concentrations and ecotone respectively.The Shannon-Wiener diversity indices and Pielou＇s evenness of phytoplankton community were high in centre of survey area.Canonical correspondence analysis（CCA） was applied to explore the relationship between phytoplankton species and environmental parameters,the results showed that salinity and photosynthetically activ