Factors Affecting Feeding and Growth of Juvenile Freshwater Mussels (Unionidae)

Survival and growth rates of caged juvenile mussels were determined at five sites along a thirty kilometer reach of the James River over a six week period in summer. The juveniles were initially 7.5 mm long. Two species were compared: a habitat generalist (Potamilus alatus) and a small stream specialist (Lampsilis reeveiana). Suspended particles in the size range of 1-10 micrometer (a measure of food availability) increased progressively from upstream to downstream. Water temperature varied among sites and was lowest at the fourth most downstream site and highest at the most downstream site. Mussels were caged with or without access to the substrate, and both upstream and downstream of structure. Growth rate (length/time) was highest at the most downstream site and was strongly correlated with temperature but not with particle concentration. Both species responded similarly, but P. alatus had higher growth than L. reeveiana at all five sites. Juveniles in contact with substrate did not grow faster than those that were not in contact, suggesting that deposited particles were not an important food source. Juveniles caged upstream of structure (a partly buried cinder block) grew more slowly and had lower survival than those caged downstream of structure