Effects of disturbances on large-river mussel assemblages

Abstract

Data from more than 10 years of quantitative sampling from stable gravel shoals in large rivers of the central US were used to test effects of specific disturbances (passage of commercial navigation vessels, the flood of 1993, and introduction of Corbicula fluminea) on native freshwater mussels (Family: Unionidae). Although many lotic species of Unionidae have been eliminated from large rivers because of degraded water quality, poor land use practices, and large-scale navigation projects, the resulting fauna appears to tolerate many disturbances. For example, high density populations of C. fluminea had no effect on unionid density at two shoals in the lower Ohio River. The record flood of 1993 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 temporal trend. In a barge turning basin that was dredged in 1976, density 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 regardless of current traffic levels. The mussel fauna now inhabiting large rivers, dominated by thick-shelled species tolerant of reduced water velocity and increased sedimentation, appears to be quite resilient to many natural and man-induced disturbances. © 1998 John Wiley & Sons, Ltd.