Shell Etching on Clams from Low-Alkalinity Ontario Lakes: A Physical or Chemical Process?

Abstract

Elliptio complanata (Unionidae: Bivalvia) were sampled from sites of low and high water turbulence in four Ontario lakes that varied in pH (6.0–7.5) and alkalinity (22–243 μeq∙L−1). External shell etching on each clam was quantified using an image analysis digitizer system. Within-lake variation in shell etching was contrasted using a log–log analysis of covariance approach. Clams exposed to higher turbulence regimes (and large sediment particles) were significantly more etched than low-exposure clams (P < 0.05). Approximately 52% of the total shell etching variability resulted from within-lake differences between high- and low-exposure clams. The remaining variation was accounted for by differences among individual clams. Shell etching in these lakes appears to be primarily a physical process probably related to water turbulence. Etching was not related to variation in lake water chemistry and thus is likely not influenced by lake acidification.