Body size and population growth of Brachionus patulus (Rotifera) in relation to heavy metal (copper and mercury) concentrations

Abstract

The effect of different sublethal concentrations of Cu^{+ 2} and Hg^{+ 2} was evaluated on the population growth and morphometry (body width and postero-lateral spines) of Brachionus patulus. When exposed to Cu^{+ 2} at lower concentrations (i.e., 2.5% and 5.0% of LC₅₀), the population growth of B. patulus did not differ significantly from controls, while at the corresponding conditions, Hg^{+ 2} had adverse effects. The rate of population increase (r) varied from 0.13 to 0.28 per day, depending on the metal type and its concentration in the medium. In general, increase in metal concentration decreased the rate of population increase. When the daily growth rate was plotted as function of population density over the entire growth phase, a significantly inverse relation was obtained for controls and in treatments containing lower concentrations (2.5 and 5% of LC₅₀) of heavy metals. However, under higher metal concentrations, the relation between population density and the daily growth rate became non-significant. Morphometric data showed that Cu caused larger bodied individuals, while the opposite effect was resulted due to Hg^{+ 2}. Postero-lateral spines of B. patulus were also significantly influenced by the concentration of Cu^{+ 2} or Hg^{+ 2}. Thus, compared to controls, there was reduction in the spine length, at low concentrations of Cu^{+ 2}, but at all the four tested levels of Hg^{+ 2}. Our data suggested that in addition to the population growth rate, morphometric measurements need to be considered for understanding the impact of heavy metals to brachionid rotifers.

Keywords:

• Lorica size
• spine length
• heavy metal
• growth rate
• population dynamics

Acknowledgments

We thank PAPIIT-IN201907 (UNAM, Mexico) for financial support.

Notes

*** = p <

* = p < 0.05.