The Effect of Dieoffs of Asian Clams (Corbicula fluminea) on
Native Freshwater Mussels (Unionidae) There is a great deal of
concern about the declining freshwater mussel fauna of North
America. Although deteriorating water quality and habitat
degradation may account for much of the decline, it has been
suggested that the exotic Asian clam, Corbicula fluminea, may be
having an effect on native unionids. Negative impacts may result
directly from competition or indirectly, because of Corbicula
population crashes that release ammonia and reduce dissolved
oxygen in the sediment. Laboratory tests were conducted to
determine the relative sensitivity of native mussel and Asian
clam life stages to unionized ammonia, and mussel glochidia were
the most sensitive (24-hr LC50 of 0.11 mg/L NH3-N). Juvenile and
adult mussels were similarly sensitivity, with average 96-hr
LC50's of 0.49 and 0.52 mg/L NH3-N, respectively. Adult C.
fluminea were the least sensitive, having an average LC50 of
0.80 mg/L NH3-N. The EPA standard t