Botetourt County, Virginia

Pesticide Table for Freshwater Mollusks

Among the freshwater mollusks found in this area is the James River (Virginia) spiny mussel. This mussel is in the family Unionidae, a family restricted to North America. A far larger percentage of this family are imperiled than any other taxonomic (species) group.

Freshwater mussels can live up to 50 years. In the parasitic larval stage of the mollusk lifecycle it is dependant on fish within its habitat for nutrients and mobility. However, only a few host fish are known. Mature mussels bury themselves in the riffles and shoals and feed by siphoning phytoplankton and other plant matter from the water. Reverse siphoning is used to expell undigestible particles from the shell. Silt in the water can kill mussels by clogging their feeding siphons.

Major factors affecting mussel populations are alterations in temperature, waterflow, and siltation caused by stream damming and channeling. Agricultural runoffs and industrial practices have also affected the mussel habitat by degrading water quality and causing siltation. Because mussels are filter feeders, the effects of pollution are intensified due to the large quantities of water drawn through their siphons in the feeding process. Another significant threat to this species is the widespread and rapid population growth of the introduced zebra mussel. The zebra mussel not only competes with native species, but also attatches to them, adding so much weight that the native species cannot open to feed. In the past, commerial harvests contributed to the decline of freshwater mussels but this industry has since been reduced.

Matthews, J.R. (ed.), The Official World Wildlife Fund Guide to Endangered Species, Beacham Publishing Inc, Washington, DC. Vol II, pp. 955-956.