The Combined Effects of Zinc and Alga on the Life Table Demography of Anuraeopsis fissa and Brachionus rubens (Rotifera)

Abstract

In this work the combined effects of zinc and Chlorella on the demography of two co-occurring planktonic rotifers (A. fissa and B. rubens) were evaluated. Chlorella absorbed a significant (about 35%) quantity of zinc from the medium within the 24 h period. The age-specific survivorship curves of A. fissa and B. rubens showed increased mortality rate with increasing zinc concentration in the medium (0 to 0.5 mg L−1), at the two Chlorella levels (0.5 × 106 and 1.0 × 106 cells mL−1). In controls, both the rotifer species showed enhanced survival at higher food level (1.0 × 106 cells mL−1). Low food level (0.5 × 106 cells mL−1) and higher concentration (0.25 and 0.5 mg L−1) of zinc resulted in a steep fall in the survivorship. Regardless of Zn concentration and food level, A. fissa had a shorter average lifespan, lower gross and net reproductive rate, and rate of population increase than B. rubens. The maximum offspring production on a given day in controls for A. fissa was about 2 female−1, which was reduced to half when exposed to 0.5 mg L−1 of Zn. At both food levels, A. fissa exposed to Zn at 0.5 mg L−1 had negative population growth rates. The highest population growth rate (0.94 day−1) was observed for B. rubens in controls at 1.0× 106 cell mL−1 of Chlorella. The present data showed that A. fissa was more sensitive to zinc toxicity than B. rubens. Combination of high vulnerability to metal toxicity and low population growth rate, A. fissa in zinc contaminated waterbodies could be possibly more adversely affected than B. rubens.