EFFECTS OF DISTURBANCES ON LARGE-RIVER MUSSEL ASSEMBLAGES

Data from more than 10 years of quantitative sampling from stable grav el shoals in large rivers of the central US were used to test effects of specific disturbances (passage of commercial navigation vessels, th e flood of 1993, and introduction of Corbicula fluminea) on native fre shwater mussels (Family: Unionidae). Although many lotic species of Un ionidae have been eliminated from large rivers because of degraded wat er quality, poor land use practices, and large-scale navigation projec ts, the resulting fauna appears to tolerate many disturbances. For exa mple, high density populations of C. fluminea had no effect on unionid density at two shoals in the lower Ohio River. The record flood of 19 93 in the upper Mississippi River had no measurable effect on mussels at three locations; species richness (22-25), density (45.3-60.3), and percentage of juveniles (11-26%) varied among years but showed no tem poral trend. In a barge turning basin that was dredged in 1976, densit y of recently recruited Amblema plicata plicata was not significantly different from density at a reference site for six of nine study years indicating that recruitment is proceeding at a similar rate regardles s of current traffic levels. The mussel fauna now inhabiting large riv ers, dominated by thick-shelled species tolerant of reduced water velo city and increased sedimentation, appears to be quite resilient to man y natural and man-induced disturbances. (C) 1998 John Wiley & Sons, Lt d.