2007年8月10—29日对南海北部41个站位进行了浮游植物群落结构的调查。调查结果表明, 共发现浮游植物5门80属216种(包括变种、变形、未定种), 调查期间南海浮游植物以硅藻为主, 占所有物种数的64.81%, 占总浮游植物细胞丰度的89.11%; 甲藻次之, 占所有物种数的30.56%, 占总浮游植物细胞丰度的10.62%; 蓝藻门的红海束毛藻Trichodesmium erythraeum在许多站位也占有相当的比例。绿藻和一些淡水的蓝藻只在珠江口附近的站位才被检出。主要优势种为海链藻Thalassiosira sp.、菱形海线藻Thalassionema nitzschioides、中肋骨条藻Skeletonema costatum、微小原甲藻Prorocentrum minimum和裸甲藻Gymnodinium sp.。从平面分布来看, 南海北部在珠江口外围和台湾浅滩海域存在2个浮游植物丰度高值区。表层和次表层浮游植物的平面分布格局差异很大, 表层浮游植物的丰度平均为25.21×103个•L?1, 高值区在珠江口附近海域; 次表层浮游植物丰度平均为9×103个•L?1, 高值区在台湾浅滩海域。调查区域的浅水站位(<200m)的浮游植物丰度远高于深水站位(>200m)。从垂直分布来看, 浮游植物的细胞丰度基本上自上而下随水深的增加而逐渐降低, 最大丰度在10m水层。深水站位与浅水站位的浮游植物垂直分布结构有很大的差异。硅藻类在浅水站位中基本随深度的增加而减少, 但在10m处出现最大值; 而在深水站位则存在次表层(75m)最大值的现象。甲藻类在浅水站位中随深度增加显著减少, 而在深水站位的75m以上其分布比较均匀。越靠近外海, 浮游植物中硅藻所占的比例越小, 硅甲藻比率大的海区一般具有高的生产力和较高的浮游植物丰度。调查海区表层和次表层的浮游植物Shannon-Wiener指数的平均分别为2.8和3.0, 生物多样性高的区域分别位于珠江口、粤东近海和海南的东部近海, 浅水站位的浮游植物多样性指数远高于深水站位。

We investigated the abundance and species composition of phytoplankton community in the northern South China Sea (110°－120°E, 18°－23°N) from 10th to 29th August 2007, using 208 samples taken from 41 sampling stations. A total of 216 species belonging to 80 genera of 5 classes were identified. Diatoms contributed to 64.81% of the total phytoplankton species number and 89.11% of the total phytoplankton cell abundance; followed by dinoflagellates, which accounted for 30.56% of total phytoplankton species number and 10.62% of the total phytoplankton cell abundance. The dominant species were Thalassiosira sp., Thalassionema nitzschioides, Skeletonema costatum, Prorocentrum minimum and Gymnodinium sp.. Trichodesmium erythraeum that belonged to Cyanophyta was also commonly found at many survey stations. High phyto-plankton cell abundance was located in the Pearl River Estuary and in Taiwan Shoal. The horizontal distribution pattern of phytoplankton abundance was different in the surface and sub-surface waters. In the surface water, the average abundance of phytoplankton was 25.21×103cells•L?1 with a high value near the Pear River Estuary; while in the sub-surface water, the aver-age abundance was 9×103cells•L?1 with a high value in the Taiwan Shoal. On the whole, phytoplankton abundance was lower at deep-water stations (>200m) than at shallow-water stations (<200m). In general, the vertical profiles showed that total phytoplankton abundance presented a peak at 10m and then decreased with increasing water depth. The vertical distribution patterns of phytoplankton abundance also appeared to be different between deep-water and shallow-water stations. Diatoms abundance decreased with increasing water depth at the shallow-water stations, but formed a maximum peak at sub-surface (75m) of the deep-water stations; dinoflagellates abundance significantly decreased with increasing water depth, but evenly distributed in the water above 75m at the deep-water stations. The ratios of diatom to dinoflagellates showed a decline ten-dency approaching to the pelagic region. Higher productivity and phytoplankton abundance regions corresponded with a larger ratio of diatom to dinoflagellates. At the survey stations, the average Shannon-Wiener diversity index of phytoplankton com-munity was 2.8 in the surface water and 3.0 in the sub-surface water. High phytoplankton biodiversity located in the Pearl River Estuary and the coasts of Guangdong and Hainan provinces. The diversity of phytoplankton at the shallow stations was far enriched than that at the deep-water stations.