What Determines Who is Where in Atlantic Coastal Plain Streams?

Atlantic coastal plain (ACP) streams exhibit pronounced environmental variation over time and space, yet influences of these dynamic conditions on fish community composition are poorly understood. We hypothesized that (1) ACP fish communities would be more influenced by local- than landscape-scale habitat conditions, but that (2) at the landscape scale, biogeographic factors such as basin, ecoregion, and stream size would be more influential than anthropogenic land use. We tested hypotheses with fish-community, local-habitat, and landscape data collected for two summers at wadeable ACP streams in the Ogeechee, Altamaha, and Savannah basins of Georgia. Species richness varied among sites from 5 to 24 species, and primarily was influenced by one landscape (stream size) and three local factors (woody debris, pH, and width:depth ratio). In contrast, multivariate assemblage composition primarily was influenced by local factors (woody debris, pH, depth, and water velocity). Sites sorted into two distinct groups, characterized either by “fluvial” or “non-fluvial” fish communities. The faunal and environmental characteristics of these site-groups were highly persistent, despite significant inter-annual variation in regional discharge patterns. Our findings suggest that ACP fish communities primarily are structured by local habitat conditions, which are strongly interdependent with local hydrology. This information helps refine predictions about the potential biological effects of channelization, water abstraction, and climate change in ACP streams