中文摘要：

报道了2004年夏季南海北部18个大面测站浮游植物的调查结果.应用Utermoehl方法初步鉴定出浮游植物4门74属159种,平均细胞丰度为（115.05±438.89）×10^3个/L（n=91）,其中硅藻在物种丰富度和细胞丰度上占绝对优势;其次为甲藻.主要优势种为柔弱伪菱形藻Pseudo-nitzschia delicatissima、旋链角毛藻Chaetoceros curvisetus、皇冠角毛藻Chaetoceros diadema、具齿原甲藻Prorocentrum dentatum和冰河拟星杆藻Asterionellopsis glacialis.调查区浮游植物表层细胞丰度的平面分布从沿岸向外海迅速减少,高值区分布在广东沿岸和珠江口附近海域.同1999年同期资料相比,浮游植物细胞丰度增加1倍,但平面分布趋势相同.调查区浮游植物垂直分布总体特征是由水体表层到底层,细胞丰度逐渐减少.细胞丰度密集区位于水体表层,但是只有S2断面出现了次表层最大值现象,其垂直剖面分布同叶绿素a、铵盐、溶解氧以及盐度密切相关.整个调查区浮游植物的多样性程度是低的.

英文摘要：

The investigation in the northern South China Sea （18°-25°N, 110°-118°E） in summer 2004 on phytoplankton was carried out with samples taken from 18 grid stations and the results are reported in this paper. A total of 161 taxa belonging to 74 genera of 4 classes were identified by Utermoehl method, in which diatoms were predominant and coexisted with dinoflagellates, silicoflagellates, and cyanobacteria. The average cell abundance of phytoplankton was （ 115046 ± 438891 ） cells/L （ n = 91 ）. The dominant species were Pseudo-nitzschia delicatissima, Chaetoceros curvisetus, Chaetoceros diadema, Prorocentrum dentatum and Asterionellopsis glacialis, etc. among them Pseudo-nitzschia delicatissirrta is most dominated. The average cell abundance of phytoplankton in surface water reduced rapidly from coastal zone to open sea. A high abundance of phytoplankton occurred in coastal seawaters of Guangdong Province and in the Zhujiang （Pearl River） Estuary. Compared with the historical phytoplankton data, the cell abundance of our survey doubled that of summer 1999, but horizontal pattern of the cell abundance was similar. Vertical profiles of cell abundance in survey area showed that, with the increase in depth, the cell abundance decreased rapidly. Subsurface maximum cell abundance found only at Section 2, cell abundance in the other stations was high in surface layers. Pearson Correlate Analysis of phytoplankton cell abundance with environmental factors showed that the phytoplankton abundance correlated positively to the ammonia, chlorophyll a and dissolved oxygen, and negatively correlated to the salinity. The Shannon-Wiener biological diversity index and Evenness of phytoplankton community in survey area were low.