Effects of Small Dams on Freshwater Bivalve Assemblages in North Carolina Piedmont and Coastal Plain Streams

Small dams represent one of the most widespread human alterations to North American streams, yet effects on bivalve assemblages are understudied. Dams are quickly being removed and prioritizing dams for removal presents a challenge for resource managers also tasked with preserving imperiled taxa. My study examined effects of dam condition (intact, breached, relict) on bivalve assemblages in North Carolina river drainages (Tar, Neuse, Roanoke) from 2009-2011. I sampled bivalve assemblages within three 150-m reaches associated with each dam. I found that streams with small intact dams support more mussels, higher richness, and greater numbers of imperiled species compared to streams with breached or relict dams. Mill reaches of intact dams had higher mussel abundance (density and CPUE) compared to up- and downstream reaches. Mill reaches of intact dams had larger Elliptio complanta compared to up- and downstream reaches, suggesting mussels in mill reaches exhibit rapid growth and larger sizes relative to conspecifics in other reaches. Small dams may stabilize/moderate upstream landuse effects and provide mussels with enhanced food resources. My data suggest that un-controlled dam removals may have negative consequences for mussels and restoration projects need to assess ecological trade-offs between species-specific costs and benefits of decisions regarding imperiled taxa.