The effects of acidification on life-history traits of the freshwater clam Musculium partumeium (Say, 1822) (Bivalvia:Pisidiidae)

This study examines the effects of acidification on growth, survivorship, and natality of the fingernail clam, Musculium partumeium. Six groups of newborn clams (parents), collected in either October (replicate 1) or January (replicate 2), and their offspring (F₁) were maintained in river water kept at a pH of 3, 4, 5 or 6 with the addition of H₂SO₄. A control (no acid added) had an average pH near 7. Generally, growth and survivorship were poor in treatments of pH 3 and 4. Maximal growth occurred at a pH of 5, which approximates that of the stream from which these clams were collected. Also, clams maintained at a pH of 5 generally had the highest gross and net reproductive rates and the youngest age at first reproduction, leading to maximum values of r (intrinsic rate of increase) for clams maintained at pH 5. Usually the F₁ generations had greater survivorship than their parents and under adverse conditions could attain greater shell lengths. Life-history traits in M. partumeium appear to be sensitive to changes in environmental pH and populations of these clams may be able to acclimate to changing pH regimes over time, i.e., from one generation to the next.