Multiple environmental stressors confine the ecological niche of the rotifer Cephalodella acidophila

Abstract

The planktonic food web in extremely acidic mining lakes is restricted to a few species that are either acidophilic or acidotolerant. Common metazoans inhabiting acidic mining lakes with a pH below 3 include rotifers in the genera Cephalodella and Elosa. The life history response of Cephalodella acidophila to three environmental key factors, pH (2, 3.5, 5.0 and 7.0), temperature (10, 17.5 and 25 °C) and food concentration (10 000, 35 000 and 50 000 algal cells per mL), was investigated in a full factorial design using life-table experiments. The effect of each of the three environmental variables investigated on the rotifer life cycle parameters (life span, fecundity and population growth rate) differed. C. acidophila is a stenoecious species with a pH optimum in the range 3-4 and a comparably high food threshold. Combining the laboratory results with field data, we conclude that C. acidophila is severely growth limited in its natural habitat. However, low pH alone is not harmful as long as temperatures are moderate to warm and food is abundant. The population of C. acidophila in the field is maintained mainly due to release from competitors and predators.

Keywords: Cephalodella acidophila; acid lakes; life-table experiments; pH; rotifers.

Fig. 1

Life cycle parameters of Cephalodella acidophila in response to pH, temperature and food levels. (a, e, j). Average life span of females; (b, f, j) cumulative egg production per female; (c, g, k) net reproductive rate R₀; (d, h, l) population growth rate r. Experimental temperature is indicated on top of each column. Bars denote standard errors.

Fig. 2

3D mesh plots of the net reproductive rate (juveniles female⁻¹) of Cephalodella acidophila in response to pH, food level and temperature.