Lake Yuandang, a shallow lake in the East Plain ecoregion of China, was originally part of Lake Dianshan; the deposition of sediments formed a reed beach at the junction between these two lakes one hundred years ago. The lake has become mildly eutrophic, due to increasing anthropogenic pressures. In the present study, nine ostracods(Cypretta turgida, Cypria kraepelini, Cypridopsis vidua, Cypris subglobosa, Dolerocypria taalensis, Fabaeformiscandona myllaina, F. subacuta, another Fabaeformiscandona sp. and Ilyocypris salebrosa) were found. None of these species are endemic species, and all are highly tolerant to variable environments. In an analysis of the dominance(Y) of the ostracods, four species(C. kraepelini, F. myllaina, F. subacuta and Fabaeformiscandona sp.) were found to have relatively high effective occurrence numbers and, among these, C. kraepelini was the most abundant and dominant species in Lake Yuandang. F. myllaina was originally reported in Japan and this is the first record of the species in China. Canonical correspondence analyses(CCA) showed that water depth was the most important predictor of ostracod occurrence, followed by total nitrogen, chlorophyll a, transparency and dissolved oxygen. Classified according to the habitat traits of zoobenthos, the ostracods in Lake Yuandang included swimmers(C. kraepelini and C. vidua), climbers(C. subglobosa and C. turgida) and sprawlers(the other five species). The sprawlers accounted for 56% of all the ostracods, which provided an indication of why the water depth played the most important role in determining the abundance and distribution of the ostracods in this shallow lake. Overall, the composition and abundance of ostracods could be influenced by the natural physicochemical factors, increasing human impacts, and be possibly influenced by the short history of this lake. This study expands our knowledge on the relationship between the community composition of ostracod and the evolutions of lake’s ecosystems.

Key words：Lake Yuandang; freshwater ostracod; water depth; anthropogenic pressure; dominance Y; habitat groups