Abstract

We investigated the changes in the community structure of Cladocera before and after dredging in West Lake, Hangzhou, including their abundance, biomass, diversity, and dominant species. Samples were collected at four sampling stations (fromⅠto Ⅳ) in West Lake before dredging(in 1995) and after dredg-ing(in 2003), and regression analyses between biomass of Cladocera and water quality parameters were conducted. The result showed that from 1995 to 2003, the annual average density of Cladocera increased from 1.86 individuals/L to 4.53 individuals/L , while the biomass increased from 0.051 mg/L to 0.093 mg/L ; however, Margalef biodiversity indices decreased from 10.39 to 4.33. Some small-sized species, such as Bosmina longirostris, Bosminopsis deitersi,and Moina micrura, increased in abundance, whereas Diaphano-soma leuchtenbergianum, the previous dominant species, was replaced by Bosmina longirostris at Station Ⅰand by Moina micrura at Station Ⅲ. The annual average biomass of Cladocera was negatively correlated with Chlorophyll-a (R2= 0.7102, P<0.01), total phosphorus (R2= 0.5276, P<0.01) and pH values, but posi-tively correlated with water transparency at all stations. Diaphanosoma leuchtenbergianum, Bosmina longi-rostris and Bosminopsis deitersi were more abundant at StationⅠwith lower trophic level, whereas Moina micrura was more abundant at Stations Ⅱ, III and Ⅳ with higher trophic level, indicating that differencesin trophic levels are responsible for the heterogeneous distribution of Cladocera in West Lake.