A decline in recent decades in the status of Rana temporaria in the British Isles has been attributed to a number of factors, mostly relating to increased urbanization. Acidification has recently been suggested as a factor which could affect R. temporaria populations in certain areas.
The effects of acid water and aluminium on the embryonic development of R. temporaria were investigated using eggs obtained by artificial fertilization from frogs caught in two widely separated areas; an upland area (acidic ponds) and a lowland area (circumneutral ponds). The eggs were kept in artificial soft water at either pH 4.5 or pH 6.0 and with aluminium concentrations covering the range measured in water from the acidic ponds.
The survival of embryos to normal free-swimming larvae was not affected by water pH in the absence of aluminium. Increasing aluminium concentrations reduced the survival of lowland embryos in circumneutral water, but upland embryos were unaffected. However, in acidic water the survival of embryos from both areas decreased with increasing aluminium concentrations. Embryos which did not survive either died early in development, or developed gross abnormalities, or were constricted in the perivitelline membrane and failed to hatch. The body length of surviving larvae was decreased by both increasing aluminium concentrations and low pH, probably owing to a reduction in growth rate rather than development rate. The body length of larvae from upland ponds was decreased less than that of lowland larvae in acidic water, suggesting a greater acid tolerance in embryos from acidic ponds.
Reduced embryo survival, sublethal effects, such as reductions in embryonic growth rate, and indirect ecological effects may affect recruitment to the adult population in acid ponds. It is not possible to predict from the present data what effects these results of acidification may have on regional population because the acid tolerance of embryos varies widely within regions.