Effect of pH, iron and aluminum on survival of early life history stages of the endangered freshwater pearl mussel, Margaritifera margaritifera

Abstract

Glochidium larvae and juveniles of the endangered freshwater pearl mussel Margaritifera margaritifera may be sensitive to low pH and metal exposure, but to our knowledge, no tolerance tests have been performed. Therefore, we exposed glochidia, fish-attached glochidia, and juveniles of the pearl mussel to low pH and increased iron (Fe) and aluminum (Al) by using realistic pH (6.0–4.5), Fe (0.5–2.0 mg L−1), and Al (0.25–1.0 mg L−1) levels periodically observed in this study site. Survival of glochidia decreased with decreasing pH, increasing Fe, and increasing Al, as well as with increasing Fe + Al concentration in a 72 h exposure. All glochidia died within 24 h in pH 4.5 and Fe 2.0 mg L−1. When infected trout, Salmo trutta, were exposed to increased Fe and Al from 4 days before to 76 days after infection, the numbers of encysted glochidia did not differ from unexposed control fish. In juvenile mussels, a slight decrease in survival was observed in lowered pH and increased Al and a combination of Al + Fe in a 168 h experiment. Results indicate that episodes of low pH and high metal concentrations may harm glochidia and potentially contribute to local decline of M. margaritifera.