Early channel evolution relates to fish community resource use in the Gulf Coastal Plains of North America

Recent work has highlighted the importance of complex, multi-threaded, sediment, and wood-retentive channels ("stage 0" channel morphology). Widespread channel evolution from a variety of perturbations threatens these crucial habitat types by shifting river channels to higher energy, more erosive environments. In this paper, we expand our understanding of the effects of loss of these resources with a quantitative, multi-decadal dataset of fish and habitats across National Forest sites in the Gulf Coastal Plains of Mississippi. Channel morphological analysis indicated a gradient from incised, wide, shallow channels with coarse substrates typical of advanced channel evolution processes to relatively unincised, narrower, deeper, more sediment, and wood-retaining channels typical of stage 0 conditions. Multivariate analysis of community-scale resource use suggested a gradient from communities which predominately use resources available in more erosive channels to those found in more stage 0-type channels. Regional constrained ordination, intra-watershed meta-analyses, and inter-watershed aggregate analyses all linked the channel morphology erosion gradient to community-scale resource use gradients. Measures of functional versus taxonomic diversity suggest a loss of functional but not taxonomic diversity. Our results demonstrate links between resource types available in channels and how communities structure themselves based on resource use. Further, our results suggest that this initial stage of channel evolution has a different outcome than later stages, which filter out habitat specialists in favor of generalist species. We integrate existing studies of fish community response to channel evolution with our data to build a broader understanding of the process and its ecological impacts in the Mississippi Embayment. Our results have implications for biodiverse and imperiled fish faunas globally.