EFFECTS OF WATER LEVEL ON ZOOPLANKTON COMMUNITY DURING “PLATE-SHAPED LAKE ENCLOSED IN AUTUMN” IN A SUB-LAKE OF THE POYANG LAKE

" Plate-shaped Lake Enclosed in Autumn” is a fishing method used by fishermen in the Poyang Lake. According to seasonal water level, fishermen use artificial gates to control sub-lake water level for fishing. This study analyzed the zooplankton community structure during the " Plate-shaped Lake Enclosed in Autumn” and discussed the impact of water level and other possible influencing factors on the zooplankton community structure. From 9th November, 2014 to 4th January, 2015, we conducted 8 times qualitative and quantitative zooplankton acquisitions from seven sampling sites in the open water area of Dahuchi Lake, a sub-lake located in the Poyang Lake National Nature Reserve. A total of 77 species of zooplankton were identified, which consisted of 53 species of Rotifera, 10 species of Cladocera and 14 species of Copepoda. During the " Plate-shaped Lake Enclosed in Autumn” fishing process, the specie richness of zooplankton gradually decreased with the decrease of water level. The diversity index of zooplankton also showed a decreasing tendency. Zooplankton density and biomass increased first and then decreased. However, the density variation of dominant species in zooplankton has obvious species differences. The density of Asplanchna priodonta and Limnoithona sinensis gradually increased during " Plate-shaped Lake Enclosed in Autumn”. The density of Polyarthra vulgaris, Mesocyclops leuckarti, Bosmina longirostris and Copepod nauplii continuously decreased. Redundancy analysis (RDA) showed that several environmental factors such as water level, conductivity, water temperature, dissolved oxygen and nutrient had significant effect on the zooplankton community structure with the strongest effect by dissolved oxygen. In addition, according to the information of fishing catch during " Plate-shaped Lake Enclosed in Autumn”, we propose that the decrease in planktonic fish caused by fishing activities can impact zooplankton density.