Abstract: Spatial and temporal variation of ichthyoplankton community structure before and after impoundment of Three Gorges Reservoir (TGR) in the Yangtze River estuary and adjacent sea area(30°45′-32°00′N, 121°00′-123°20′E) was analyzed based on the samples at 40 stations during spring of 1999,2001,2004 and 2007. Through the study, 39 species, consisting of freshwater, brackish, coastal and marine varieties, were collected in trawl nets. The ichthyoplankton abundance degree in 2004 rapidly was decreased with 13.9% of 1999 and 4.3% of 2001, respectively, and appreciably increased in 2007. The dominant species comprised Engraulis japonicus, Coilia mystus, Allanetta bleekeri, Trachidermus fasciatu and Chaeturichthys hexanema. The dominance of Engraulis japonicus and Coilia mystus was reduced in 2004. There was significant dissimilarity within four year’s ichthyoplankton community structure, and the dissimilarity in 2004 was higher, comparied with 1999 and 2001. Similarity of percentage analysis showed that Engraulis japonicus and Coilia mystus represented the highest contribution in the community structure variation. Moreover, the similiarity index of ichthyoplankton was highest between 2004 and 2007 with the value 71.17%; Ichthyoplankton community diversity before and after impoundment of TGR was significantly different in the Yangtze Rive estuary, and the diversity after impoundment evidently decreased. A series of environmental disturbances, which happened in the Yangtze River estuary and adjacent water during 1999-2007, directly or indirectly caused the variation of ichthyoplankton community structure.

Key words: Yangtze River estuary  , ichthyoplankton ,  , community structure ,  , diversity