长江河口浮游动物的种类组成、群落结构及多样性

于1999年枯水期(2—3月份)、丰水期(8月份)、2000年枯水期(2—3月份)对长江河口浮游动物采样调查，研究了长江河口浮游动物的种类组成、群落结构及多样性并初步探讨了三峡工程对长江河口浮游动物的影响及长江河口水环境的生物监测。调查共发现浮游动物87种，甲壳动物占绝对优势，共59种。在所有浮游动物中挠足类31种。其次为水母类，有9种，此外，枝角类、毛颚类各8种。3次采样浮游动物的优势种主要有河口半咸水种和近岸低盐种类如华哲水蚤(Sinocalanus sinensis)、火腿许水蚤(Schmackeria poplesia)、虫肢歪水蚤(Tortanus vermiculus)，真刺唇角水蚤(Labidocera euchaeta)等，还有长江径流带到河口的淡水种如近领剑水蚤（Cyclops vicinus vicinus)、英勇剑水蚤（Cyclops strenuus）、透明溞（Daphnia hyalina)等。一些浮游动物可作为水系指示种，其分布、数量反映了不同水系分布变化，长江河口浮游动物有；类水系指示种。通过对长江河口浮游动物群落聚类分析发现。1999、2000年枯水期浮游动物群落结构相似。可分为河口类群、近岸类群和近外海类群。1999年丰水期只形成近岸和近外海类群。浮游动物种类数由口门内向口门外方向有逐渐增加的趋势。浮游动物种类数由北向南变化趋势一致。大潮与小潮、涨憩与落强等潮汐作用对浮游动物影响往往因采样时间与区域等的不同而不同。对长江河口3次采样的物种多样性指数和均匀度指数进行了计算，结果表明：浮游动物多样性指数1999年枯水期最低，1999年丰水期最高。

The species composition, community structure and diversity of zooplankton in Changjiang estuary

Based on the data collected from three cruises during the dry (February to March,1999 and 2000) and the wet (August 1999) periods, the species composition, community structure and species diversity of zooplankton in Changjiang Estuary were determined. The study also aim to determine preliminarily the influence of Three Gorges Dam to the zooplankton community and the hydrodynamic environment in Changjiang Estuary . Results showed that 87 species in total was identified. Among them crustacean was the dominant group, contained 59 species. The zooplankton community composed of 31 species copepod,9 species of medusae, and 8 species of both cladocera and chaetognatha. The dominant species were from brackish estuarine and nearshore waters, such as Sinocalanus sinensis,Schmackeria poplesia, Tortanus vermiculus, Labidocera euchaeta, and from freshwater that flushed downstream via river runoff, such as Cyclops vicinus vicinus, Cyclops strenuus, Daphnia hyalina. Some zooplankton species can be used as the current system indicators. The fluctuation of their distribution and abundance reflect the change of hydrodynamic regime in their resident systems. In Changjiang Estuary,there are 5 current system indicators . Results of cluster analyses showed that the community structure during the dry period in 1999 was similar to that in 2000. Three groups were identified; estuarine, nearshore, and offshore groups. During the wet period, only 2 were found; nearshore and offshore groups. The species richness increased gradually from estuary towards open ocean. It also increased from north towards south. The influence of tidal cycle to the community structure varied with the sampling time (and date)and sites. Results of Simpson Diversity Index, Shannon-Weiner Diversity Index,and Evenness Index showed that the species diversity was lowest during the dry period and highest during the wet period.