42 
Charles R. Blem and Leann B. Blem 
as well as the great number of egg masses found in the Chesterfield 
County pond, indicate that natural reproduction was successful there. 
One hypothesis is that such success may represent evolution of acid 
tolerance as a result of long exposure to low pH in this pond (e.g., 
Tome and Pough 1982, Cook 1983). However, there is another plausible 
explanation. While low pH can have direct effects upon amphibian 
larvae (Pough 1981, Freda and Dunson 1984), external cation 
concentration may be the source of the damage (Hall and Likens 1981, 
Freda and Dunson 1985; but see Dale et al. 1985). In most natural 
waters, decreases in PH would increase the amount of free aluminum 
(and other cations) available to aquatic organisms (see Hall and Likens 
1981, Clark and Hall 1985). Decreasing pH may then cause mortality by 
the increase in toxic aluminum, rather than by direct pH effects. 
Aluminum has long been known to be detrimental to fish, particularly 
their eggs and larvae (Freeman and Everhart 1981, Schofield 1980), and 
it appears to have a similar effect on amphibian larvae (Clark and Hall 
1985). 
Our tests of aluminum toxicity (Table 3) support the hypothesis 
that aluminum is harmful to spotted salamander eggs. It should be 
noted that addition of Al (S0 4 )2 decreased the pH of the aquaria media 
slightly as a result of the addition of S0 4 ions (Table 3). The extent of 
the extra acidity was only slight; this was not expected to affect egg 
mortality because we found no significant correlation between mortality 
and pH in the pH range of 4.2 to 4.8 (Table 2). Very small amounts of 
aluminum increased mortality of larvae to the point that we estimate (by 
extrapolation) that total mortality should occur at increases of 0.28 ppm 
aluminum. This is similar to levels of toxicity for brook trout ( Salvelinus 
fontinalis) eggs at similar pH’s (Hall and Likens 1981). This by no 
means proves a causal relationship between aluminum concentration 
and egg mortality, but does suggest that the hypothesis deserves further 
testing. 
Acidity of many temporary ponds in the coastal plain and eastern 
piedmont of east-central Virginia is near the minimum tolerance levels 
for spotted salamander embryos /larvae (see Pough 1976). Only one 
larva survived any of our tests in which the pH was 4.0 or less, and 
mortality in excess of 50% was observed in aquaria at pH’s of 4.3 to 4.4 
or less. This indicates that only a slight further acidification of local 
temporary ponds in east-central Virginia may result in total extirpation 
of the species from the area. 
Hatching success of spotted salamanders in acidic pools depends on 
at least two factors. The first is the volume of the egg mass. However, in 
the present study, there was no obvious relationship between mortality 
rate and size of the egg mass. We excluded both very small and large, 
