| A pumped-water storage reservoir is a special type of reservoir in which the stored water is pumped from with other watershed; it mainly functions for drinking water supply. In China, this type of reservoir can be found in coastal areas. Dajingshan Reservoir is one example in tropics. It is located in Zhuhai and supplies drinking water to both Zhuhai and Macao. The reservoir is an eutrphic water body, the mean chlorophyll a concentration is over 31.00 mg.m-3, the eutrophication has resulted in some problems in management of water quality. For this reason, a large scale Ecological Project (EP) was initiated to against the rapid development of eutrophication in 2006. This study focused on zooplankton in the reservoir to explore the community structure and population dynamics of the zooplankton and evaluate the effects of the EP on the reservoir ecosystem.The zooplankton of Dajingshan Reservoir has a tropical feature in biogegraphy, but differs greatly from other reservoirs in the same area. 55 species of zooplankton were observed, including Rotifera (9 families, 15 genera and 33 species, Cladocera (5 families, 8 genera, 11 species), and Copepoda (5 families, 9 genera, 12 species). Copepods were the dominant group, for both abundance and biomass; there were a few pelagic cladoceran species, they had a relatively high percent in biomass but a low percent in abundance. The reservoir is rich in rotifer species and abundance, but the rotifers represented a low percentage biomass. Limnoithona sinensis is the dominant species in zooplankton. This species is common in low salinity water, and it is brought in by pumping water from the other rivers affected by sea water. L. sinensis is small-sized, about 375μm for the adults, but has a highly adaptive ability. As an r-selective species, it has a strong invasion ability. It is important that the species has a high swimming speed to escape from fish predation. Bosmina longirostris is the dominant species in cladocerans, it can be found all over the year with a peak in autumn. The Shannon-Wiener diversity index of rotifers ranges from 0.34～0.76 dit, and from 0.17～0.83 for Evenness. The density of Brachionus calyciflorus is rather high, which indicates organic contamination. The dominant rotifer, Asplancha brightweIli blooms in winter and early spring, indicating that the reservoir was 13 mesosaprobic in that period.The zooplankton in the reservoir is mainly composed by small-sized species. The size of the rotifers is distributed between 50～200μm, and 200～400μm for crustaceans. Crustaceans with body-size over lmm are rare, maybe due to the strong negative effect on large body-size zooplankton by ffilter-feeding fishes, and in which they can significantly reduce the size of zooplankton on average. The standing crop of zooplankton was low, from 202.9μg.L-1～251.3μg.L-1in 2005 and 2006, relatively low compared to other water bodies in the same area. EP had remarkably effects on both the community structure and the dynamics of zooplankton. The biodiversity in the B zone of EP increased, especially that of cladocerans and copepods. Eutrophication was reduced in the B zone, with a low percentage of Cyanophyta and a low pH. The dynamics of the dominant species changed remarkably. Limnoithona sinensis declined in both abundance and biomass. The dominant species in rotifers shifted from Asplancha brightwelIi to Brachionus calyciflorus. The dominant species in cladocerans, Bosmina longirostris tended to increase, while the total biomass of zooplankton in the B zone of EP decreased, compared to the first half year or to the water pumping outlet. This may be due to the fish swarming and reproducing in the B zone of EP, the abundant macrophytes provided food for the adults and a good shelter for their larvae.
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