The effect of substrate on burrowing in freshwater mussels (Unionidae)

The burrowing behaviour and rates of burrowing on sand, clay, mud, and gravel were determined for three species of freshwater mussels, Lampsilis radiata (Barnes), Anodonta grandis Say, and Elliptio complanata (Solander). Burrowing is achieved by a series of probing and digging movements by the foot, alternating with adduction or closing of the valves, and foot contraction, which cause the valves to be forced downwards into the substratum. Overall burrowing abilities were superior in sand in comparison to gravel in all three species, and E. complanata burrowed more rapidly than the other species in clay, sand, and gravel. Righting was not accomplished in soft liquid mud but burrowing was achieved by frequent, rapid adduction of the valves. Although righting by both E. complanata and A. grandis in a clay substratum was slower than in either sand or gravel, both species burrowed more rapidly in clay. Although there were differences in burrowing abilities between species and in the four substrata tested, the ultimate success in burrowing by all three species suggests that substrate is not the direct causal factor affecting local distribution of freshwater mussels.