High and Dry: Regional Drought Regimes Regulate Fish Community Structure in Appalachian Mountain Streams

Habitat contraction and desiccation during drought can represent natural and pervasive disturbances to stream fish communities. In the southeastern United States, climate models predict increased occurrence and magnitude of drought in the future, but the ecological consequences of these projections remain unclear. We used long-term fish community data from Little River, TN and Cataloochee Creek, NC in Great Smoky Mountains National Park to assess relationships between drought and fish community dynamics. We used population estimates derived from three-pass depletion samplings to calculate trajectories in Bray-Curtis distances between samples collected from Little River (3 sites, 1987-2004) and Cataloochee Creek (4 sites, 1986-2004). Convergence in community structures across all sites in both streams correlated with a moderate drought during 1998, which simultaneously stimulated species-specific population growth (e.g., Longnose Dace, Rhinichthys cataractae) or collapse (Rainbow Trout, Oncorhynchus mykiss). In Little River, drought subsided and communities returned to a state of dynamic equilibrium within two years. In Cataloochee Creek, prolonged drought sustained an alternative fish community state characterized by Longnose Dace dominance along the river continuum. Our findings highlight the disruptive capacity of drought in high elevation streams and suggest drought magnitude and duration are associated with the extent of change to fish communities.