Beaver and Mill Dams Alter Freshwater Mussel Habitat, Growth, and Survival in North Carolina Piedmont Streams

Freshwater mussels are imperiled indicator species, perform key ecosystem services, and serve as basal resources in stream foodwebs. Increasing beaver populations and mill dam removals may have consequences on freshwater mussel growth and survival. Therefore, I examined the effects of beaver and mill dams on mussel resource availability and quality by measuring total suspended solid (TSS) mass and C:N values. I complemented stream survey data with a common garden experiment conducted in the upper Tar River Basin of North Carolina. I found that mill impoundments significantly increased mussel food quality, species richness, and growth of mussels in mill tailraces (p < 0.05). In contrast, mussels growing in streams with beaver impoundments did not experience elevated food resources or growth. Mussel mortality was twofold higher across all beaver reaches compared to mill reaches. Patterns in mussel growth and survival were positively correlated with increased TSS (<250 um) mass and %N. My research shows that discontinuities in the flow continuum alter stream energetic pathways with dramatic consequences for the growth and survivorship of freshwater mussels. Quantifying costs and benefits of restored connectivity to taxa across multiple trophic levels and addressing effects of wetland ecosystem services should be considered when prioritizing restoration projects.