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.