Population level indicators of stress: Effects of two heavy metals (copper and mercury) on the growth of Lecane quadridentata (Ehrenberg, 1830) (Rotifera: Lecanidae)

Abstract

We quantified the population level responses of Lecane quadridentata exposed separately to five different concentrations of Cu (0.3125, 0.625, 1.25, 2.5 and 5.0 μ g/L as CuSO₄) and Hg (0.0844, 0.1688, 0.3375, 0.675 and 1.35 μ g/L as HgCl₂) at 23°C and under an algal food density of 1 × 10⁶ cells/mL of Chlorella vulgaris for 24 days. We derived peak population densities and the rate of population increase (r) per day in both controls and in heavy metal treatments. In general, the population growth of L. quadridentata decreased with increasing concentration of Cu or Hg in the medium. The growth was similar in controls and in the lowest tested concentration of Cu (0.3125 μ g/L), whereas in Hg treatments, even at the lowest tested concentration (0.0844 μ g/L), there was a drastic decline of rotifer densities. The peak population densities in controls were 63± 5 ind./mL, whereas in heavy metal treatments, they ranged from 1 to 58 ind./mL depending on the concentration. The rate of population increase also decreased with increasing concentration of Cu or Hg. In general, the r varied from +0.23± 0.01 to -0.12± 0.02, depending on the metal type and concentration. The differences in the population level responses of L. quadridentata to Cu and Hg were interpreted in terms of relative toxicity of the chosen heavy metals. Since our study showed that peak population density was also sensitive to metal stress, we recommend the use of this variable together with the rate of population increase in ecotoxicological evaluations.

Keywords:

• Copper
• rotifera
• heavy metal
• population dynamics
• chronic toxicity

Acknowledgements

We thank Prof. Roberto Rico-Martínez and an anonymous reviewer for helpful comments on our contribution. This work was supported from the project PAPIIT IN201907 (UNAM, Mexico).

Notes

*** = p < 0.001