浮游动物大小不一，采用不同网目孔径的浮游生物网采样得到的浮游动物种类组成和丰度有差别。为了了解使用不同网具采样对南海北部浮游动物分析的影响，于2007年8月在南海北部采用网目孔径为505μm(大网)和160μm(中网)两种网具进行了浮游动物采样。虽然两种网具对个体较大的浮游动物(水母类、磷虾类、毛颚类等)的捕获率差别不显著，但是大型网捕获的个体较大的浮游动物种类数较中型网捕获的多；对于个体较小的浮游动物，尤其是小型桡足类，大型网的捕获效率远远低于中型网，差异显著；其中对于13种主要小型桡足类[锥形宽水蚤(Temora turbinata)、瘦拟哲水蚤(Paracalanus gracilis)、丽隆水蚤(Oncaea venusta)等]种群，其中网捕获的丰度之和为大网之和的11倍之多。由此可见，两种网具是可以互补的。聚类分析结果表明，尽管两种网具捕获的浮游动物种类组成不同，但浮游动物的群落结构相似，即无论大型网或是中型网采集的浮游动物，都能被分为近岸和远岸两个类群。

Zooplankton is a categorization spanning a wide range of organism sizes. Different mesh sizes of the plankton net used in zooplankton research can lead to different results. In order to understand whether the zooplankton community structure has been altered by different mesh sizes of the plankton net in the northern South China Sea, we investigated the catching efficiency in August 2007 using two plankton nets of different mesh sizes. The mesh sizes of large and medium nets are 505 and 160 μm, respectively. The results show that the capture efficiencies of the two nets are not significantly different for large size zooplankton, such as medusae, euphausiids, chaetognathes, and so on. Species of larger zooplankton caught by the large net are higher than those by the medium net. The difference between the two plankton nets was mainly due to the loss of small-size copepods in the samples collected by the 505 μm mesh net. The abundance of 13 dominant small copepods (Temora turbinate, Paracalanus gracilis, Oncaea venusta, and so on) caught by the medium net was 11 times of that by the large net. It suggested that two plankton nets can compensate each other. In addition, although species composition of zooplankton differed in samples collected by nets of different mesh sizes, the zooplankton communities from the two nets are similar under cluster analysis. Zooplankton communities from both nets can be divided into onshore and offshore groups, either with large or medium size plankton net.