Effects of mercury on the life table demography of the rotifer Brachionus calyciflorus under different algal food (Scenedesmus obliquus) densities

In aquatic ecosystems, mercuric compounds are considered to be highly toxic to a great variety of aquatic biota ranging from bacteria to fishes. In the present study, the effects of different concentrations (0, 2.0, 6.0, 10.0, 14.0 and 18.0μg·L−1) of Hg2+ on the life table demography of Brachionus calyciflorus were investigated at three densities (1.0×106, 2.0×106 and 4.0×106cells·mL−1) of Scenedesmus obliquus. The results showed that compared to the controls, Hg2+ at 14.0 and 18.0μg·L−1 significantly decreased both the average lifespan and the life expectancy at hatching, Hg2+ at 2.0–18.0μg·L−1 shortened the generation time, and Hg2+ at 18.0μg·L−1 decreased the net reproductive rate of B. calyciflorus cultured at 1.0×106cells·mL−1 of S. obliquus. Increase in algal food level reduced the negative effects of high concentrations of Hg2+ on survival, reproduction and population growth of the rotifers. Hg2+ at 6.0μg·L−1, and 6.0 and 18.0μg·L−1 increased the intrinsic rate of population increase of the rotifers cultured at 1.0×106 and 2.0×106cells·mL−1 of S. obliquus, respectively. But Hg2+ at 18.0μg·L−1 decreased the intrinsic rate of population increase of the rotifers cultured at 4.0×106cells·mL−1 of S. obliquus. Significantly nominal concentration–response relationships existed between Hg2+ concentration and each of all the five life history variables of B. calyciflorus cultured at 1.0×106cells·mL−1 of S. obliquus, the generation time of the rotifers cultured at 2.0×106cells·mL−1 of S. obliquus, as well as the intrinsic rate of population increase of the rotifers cultured at 4.0×106cells·mL−1 of S. obliquus. Among all the life history variables, generation time was the most sensitive to mercury pollution. Since algal levels chosen in the present study are much higher than those available in natural waters, except in eutrophic water bodies, the effects of mercury on survival, reproduction and population growth of the rotifers in natural waters may be more severe than those extrapolated from the present study.