Influences of Local and Regional Environmental Factors on Atlantic Coastal Plain Stream Fish Communities

Atlantic coastal plain (ACP) streams are complex and unique ecosystems that support a diversity of fishes and other organisms, yet the environmental features that regulate fish assemblage structure are poorly understood in these systems. Based on limited previous studies, we hypothesized that (1) ACP fish assemblages would be more influenced by local than regional habitat conditions, (2) at the regional scale, historical biogeographic factors such as basin, physiography, and stream size would be more influential than contemporary factors such as anthropogenic land use, and (3) regardless of habitat conditions, fish assemblage variation would be greater among mainstem than headwater sites. We addressed these hypotheses using preliminary univariate and multivariate analyses of fish-assemblage, local-habitat, and land-use data collected in summer 2016 from paired sites (headwater vs. mainstem) in 13 wadeable ACP streams in the Ogeechee, Savannah, and Altamaha river basins. We captured over 4200 individual fish, of 49 different species. The four most commonly occurring and numerically abundant species were Redbreast, Pirate perch, Redfin pickerel, and Bluegill; these species made up 52% of all individuals collected. Richness varied among sites from 6 to 25 species, and appeared to be influenced by a combination of landscape (stream size, physiography, and land use), and local factors (large woody debris and dissolved oxygen). As hypothesized, headwater sites exhibited greater assemblage similarity than mainstem sites, regardless of basin boundaries. However, neither local nor landscape features predominantly drove assemblage variation, much of which was unexplained by measured variables. We discuss possible mechanisms for these patterns and avenues for further study.