Studies on the effects of calcium bicarbonate concentrations on the biology of biomphalaria pfeifferi (Krauss) (Gastropoda: Pulmonata)

Summary

• 1. The intrinsic rate of natural increase, r_m, of the planorbid snail Biomphalaria pfeifferi, was estimated in a series of culture media with differing concentrations of calcium bicarbonate. These gave a range from very soft to distinctly hard water.

• 2. r_m values were obtained from cohorts of snails from two widely separated streams, in different catchments, and these were compared with results obtained by Williams (1970b) from a third stream. All three were near Salisbury, Rhodesia, but they had markedly different calcium bicarbonate concentrations.

• 3. Snails from all three demes gave a similar pattern of r_m values and highest values were obtained from a culture water containing 12 mg/l of calcium as Ca⁺⁺, and 35 mg/l bicarbonate as CaCO₃, here classified as water of ‘medium’ hardness. This was in spite of the fact that two of the demes came from distinctly harder water.

• 4. Apart from this overall similarity the three demes showed differences in egg-laying and survivorship patterns.

• 5. The significance of these results is discussed.