SEASONAL VARIATIONS OF CRUSTACEAN ZOOPLANKTON COMMUNITY STRUCTURE IN THE MIDDLE REACHES OF THE HUAIHE RIVER

Seasonal dynamics of community structure of crustacean zooplankton were studied throughout 2007. Twenty-four species were recorded, including eight genera and thirteen species for cladocerans and nine genera and eleven species for copepod. Two peaks of cladoceran density were observed in April and September, (28.2±21.6) ind. /L and (40.8±10.1) ind. /L, respectively. The dominant species were D. cucullata and B. fatalis, respectively. The predatory copepod were C. vicinus vicinus, M. leuckarti and T. Taihokuensis, and their peak densities occurred in April, May and June, respectively. The relationship between predatory copepod density and Daphnia density was significant (r=0.541, n=48, P0.01). S. dorrii and L. sinensis were dominant species in May and August, respectively. The maximum edible phytoplankton (≤20 μm) biomass appeared in April and then declined rapidly, while inedible phytoplankton (>20 μm) biomass increased from April and peaked in July. Redundancy analysis (RDA) showed that mid-spring decline of Daphnia density was related to the feeding pressure of predatory copepod (especially C. vicinus vicinus) and seasonal variation of phytoplankton biomass.