Effects of Hydrologic Change on Stream Fish Assemblages in Alabama

Abstract

Alabama is home to the most diverse aquatic fauna in the United States. A major threat to this fauna is habitat degradation mediated by hydrologic alteration. Land cover changes contribute to disrupted flow patterns and volumes. Studies in streams in east Alabama found that hydrologic alteration shifted the assemblage structure from specialist endemics to generalist dominated. This study aimed to find if similar patterns were being repeated in other streams across Alabama’s physiographic regions. Streams in six watersheds were sampled for fishes contemporarily and compared to historic fish collections. Hydrologic and land cover data were compiled and analyzed. The assemblage data were analyzed using partial redundancy analysis (pRDA) constrained by hydrologic variables and controlled for watershed area. The impact of land cover was investigated using multiple regression. Evidence of assemblage change was found in most watersheds based on Morisita similarity. Hydrology significantly affected the fish assemblages in 4 of the 6 watersheds. Discharge Uphapee Creek, the most developed watershed, significantly decreased over the past 50 years. Land cover affected the fish assemblages in half of the watersheds. Where hydrology was most altered, the assemblage structure was generalist dominant and temporally variable. These watersheds had the least natural land cover. In Shoal Creek, a heavily forested watershed on Talladega National Forest, hydrologic variables were strongly correlated with precipitation, and the assemblages were stable over time and dominated by fluvial specialists. Land use and associated hydrology are critical components of watershed management and should be considered vital to conservation of Alabama’s aquatic biodiversity.