| Both Feilaixia Reservoir and Jiantan Reservoir are typical riverine reservoirs with a short retention time. Feilaixia Reservoir was filled in 1999 and Jiantan Reservoir was a new one filled in 2007. Community structure and distribution of zooplankton in the two water bodies were investigated in 2006 and from 2006 to 2007, respectively. 21 species of zookplankton were identified in Feilaixia reservoir, among which there were 11 species of Rotifer, 6 species of Copepods and 4 species of Cladocera species. Zooplankton abundance ranged from 1.73 ind.·L-1 to 166.08 ind.·L-1, dominanted by Copepods and followed by Rotifers. Before flood season came, zooplankton abundance was much higher than in the other periods because of longer retention time. 49 species of zookplankton were identified in Jiantan reservoir, among which there were 31 species of Rotifer, 4 species of Copepoda species and 14 species of Cladocera species. Zooplankton abundance ranged from 0.02ind.·L-1 to 98.7 ind.·L-1. Rotifera was the dominant group with dominant species of Keratella and Asplanchna, followed by Copepods. In Jiantan Reservoir, digging sand in a large scale, especially near the sampling sites of Tanwu, Xiacun, Ruhu and Hengli, which led to high turbidity and affected zookplankton grazing. At the other two sampling Sites- Dam and Shuiwenzhan, polluted water from Xizhijiang River provided rich food for the zooplankton, Zooplankton at here was much more than at the other sites, compared with the other types of reservoirs in the same region, the zooplankton abundance in the two reservoirs were low due to the high water flow velocity. Jiantan Reservoir was a newly constructed water body, it was filled in the early of 2007. The species composition and abundance of zooplankton didn't differ strongly from in 2006. However, Feilaixia Reservoir is a relatively mature water body. It has a different pecies composition and abundance of zooplankton from Jiantan reservoir.Diaphanosoma dubia is one of the dominant species in most tropical water bodies. However, whether food or temperature plays a key role in its dominating remains unclear. In order to study the effects of algal food and temperature on the growth and reproduction of D. dubia and to understand the possible causes for this small animal to be one of the dominant species in the tropical water bodies, a series of laboratory eaperiments were carried out. Five organic carbon concentrations of Chlorella pyrenoidosa usded in feeding culture of the animals were: 0.05 mgC·L-1 , 0.1 mgC·L-1, 0.3 mgC·L-1, 0.6 mgC·L-1 and 1.0 mgC·L-1, respectively. Six organic carbon concentrations of Microcystis aeruginosa were 0.5 mgC·L-1,1.0 mgC·L-1,2.0 mgC·L-1, 4.0 mgC·L-1,6.0 mgC·L-1,8.0 mgC·L-1. In the grazing behahavior experiment, Five organic carbon concentrations of C. pyrenoidosa were 0.1 mgC·L-1,0.3 mgC·L-1,0.6 mgC·L-1 and 1.0 mgC·L-1, organic carbon concentrations of Microcystis aeruginosa were 0.5,1.0,2.0, 4.0mgC·L-1. Three temperatures were 23℃,26℃and 29℃.The survival rate was quite low and no reproduction at the C. pyrenoidosa concentration of 0.05 mgC·L-1. The somatic growth rate and longest body length increased with the organic carbon concentrations of C. pyrenoidosa, the longest body length was 1.087mm, 1.125mm, 1.225mm and 1.313mm, respectively. Food concentration showed no significant effect on embryonic and juvenile development periods, lifespan and the number of the cumulative eggs for each adult. The size at maturity and the mean number of eggs per brood both increased with the increasing organic carbon concentrations of C. pyrenoidosa, but the duration of reproduction decreased. The intrinsic rate of increase increased with the increasing organic carbon concentrations of C. pyrenoidosa. The net reproduction rate and the intrinsic rate of increase showed peak values at the food concentration of 0.6 mgC·L-1. Under the highest food concentration of 1.0 mgC·L-1, the generation time was shortest and the intrinsic rate of increase was closed to the peak value. When fed with different concentrations of M. aeruginosa, the survival rates of D. dubia decreased with the increasing organic carbon concentrations. No reproduction was observed at the high concentration. When fed at different temperatures, D.dubia grew faster at 26℃and 29℃than at 23℃, but the lifespan and longest body length were reduced. Temperature showed a significant effect on embryonic and juvenile development periods, lifespan and the number of the cumulative eggs for each adult. When fed with 1.0 mgC·L-1 C. pyrenoidosa, the grazing rates varied in 24 h, being highest in the first 7h, and then decreased. The grazing rate increased with the increasing organic carbon concentrations of C.pyrenoidosa and M. aeruginosa.Small size, transparent body and quickly moving, low threshold food concentration, adaption to high temperature favor the D.dubia to dominate in tropical water bodies.
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