Abstract: In order to understand the chronic toxicity of a pollutant to an organism in an aquatic environment with different food density, and screen out sensitive endpoints for monitoring Cd²⁺ pollution with rotifers as test animals, this paper studied the effects of different concentration (2.5, 5.0, 10.0, 20.0 and 40.0 μg·L^-1) Cd²⁺ on the life table demography of Bracionus calyciflorus at the Scenedesmus obliquus density being 1.0×10⁶, 3.0×10⁶, and 5.0×10⁶ cells·ml^-1. The results showed that at 25±1 ℃, the 24 h LC₅₀ of Cd²⁺ to  B. calyciflorus  was 37.7 μg·L^-1.  Compared with the controls at the same food density, when the S. obliquus density was 1.0×10⁶ cells·ml^-1, 20.0 and 40.0 μg·L^-1 of Cd²⁺prolonged the generation time of B. calyciflorus significantly, and 5.0 μg·L^-1of Cd²⁺ increased the percentage of  B. calyciflorusmictic offspring. When the S. obliquus density was 3.0×10⁶ cells·ml^-1, the Cd²⁺at all test concentrations except 5.0 μg·L^-1 decreased the percentage of mictic offspring; when the  S. obliquus density was 5.0×10⁶ cells·ml^-1, all test concentration Cd²⁺ had no effects on the life table demography (P>0.05). S. obliquus density had significant effects on the generation time, life expectancy at birth, net reproduction rate, percentage of mictic offspring of B. calyciflorus (P<0.05), Cd²⁺ concentration had significant effects on the generation timeand the percentage of mictic offspring (P<0.05), and the interaction of  S. obliquus  density and Cd²⁺ concentration had significant effects on the percentage of mictic offspring ( P<0.01).  Among all the studied parameters, the generation time and the percentage of mictic offspring were more sensitive to Cd²⁺ pollution under the algal densities of 1.0×10⁶ and 3.0 ×10⁶ cells·ml^-1, with the latter being the most sensitive.

Key words: Cd²⁺ concentration, Brachionus calyciflorus, Scenedesmus obliquus, life table demography, crustacean zooplankton, community structure, redundancy analysis, environmental factor.