Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

Ph.D. in Biological Science



First Advisor

Clifford A. Ochs

Second Advisor

Susan Adams

Third Advisor

Greg Easson

Relational Format



Dams and their impoundments block movement of stream organism and change stream physiochemical properties, which subsequently changes biological assemblages and creates barriers to gene flow. While changes in species assemblages and gene flow have been assessed for numerous impoundments and stream organisms, no study has assessed the effects of large impoundments on crayfish assemblages and population genetic diversity and connectivity. I examined the physiochemical, biological, and genetic effects of impoundments on crayfishes. Between May 2015 and August 2017, I sampled multiple sites up- and downstream of three impounded streams, and along the lengths of two unimpounded streams, in the Bear Creek and Cahaba River drainages in Alabama, USA. First, I assessed the most effective sampling methods for collecting crayfishes in high gradient southern Appalachian streams. A combination of kick seining and electroshocking were most effective at collecting crayfishes, with higher species richness and decreased sampling biases when using both methods. Once effective methods were established, I assessed the effects of impoundments and their subsequent changes to crayfish assemblages and their habitats. Impoundments altered crayfish assemblages up- and downstream of impoundments. Crayfish abundances and species diversity were lower in impounded than unimpounded streams. Assemblages up- and downstream of impoundments were similar, but in unimpounded streams, gradual shifts in dominant species occurred from up- to downstream. Assemblage differences between impounded and unimpounded streams were associated with more stable temperature and flow regimes, decreases in crayfish refuge habitats (i.e., aquatic vegetation, interstitial space), and increased abundances of predatory fishes in impounded streams. Nonetheless, with distance downstream of impoundments, crayfish assemblages began to recover and resemble unimpounded stream assemblages. Impoundments also impacted gene flow and genetic structure of crayfishes. Impounded streams’ crayfish populations were genetically isolated, and unidirectional downstream gene flow, or no gene flow, was detected between up- and downstream populations. The degree of impact of impoundments on gene flow was species-specific, with intrinsic biological and life history characteristics, such as dispersal ability and physiological tolerance, determining the degree of impact. With already declining crayfish populations, decreases in species and genetic diversity due to impoundments can decrease the persistence of hundreds of crayfish species in thousands of impounded streams. These changes in crayfish populations can cause cascading effects throughout stream ecosystems by altering the numerous ecosystem services provided by crayfishes.

Included in

Biology Commons



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