Influence of Land Use on In-Stream Substrate and Single-Metric Fish Indicators in South Carolina Coastal Plain Streams

The South Carolina Department of Natural Resources initiated a statewide stream assessment (SCSA) in 2006 to evaluate the status of aquatic resources throughout the state, to understand how aquatic species composition varies across the landscape, and to study how human activities can disrupt the processes linking terrestrial and aquatic systems. The identification and prediction of land use impacts on stream habitat and biological communities constitutes an essential, basal component of South Carolina aquatic resources management. However, there remains a sparsity of studies concerning land use change and subsequent effects on stream habitat and fish assemblages within South Carolina’s coastal plain. We utilized data from 79 wadeable streams across three coastal plain ecobasins (sampling region based on EPA level IV ecoregion and major drainage basin), including the ACE Carolina Flatwoods, the Pee Dee Carolina Flatwoods, and the Pee Dee Atlantic Southern Loam Plains to evaluate relationships among regional catchment land use, instream substrate habitat, and four fish metrics. This preliminary analysis used path analysis to evaluate a) the relative importance of large wood habitats to coastal plain fishes, and b) the relative influence of regional (catchment land use variables) versus local (in-stream substrate habitat variables) influences on coastal plain fish metrics. Model results indicated that the relative pattern and strength of relationships between fish metrics and habitat / catchment land use were dependant upon the type of biological data used. Simple fish metrics richness and Shannon diversity showed positive, direct relationships with large wood occurrence, and indirect positive relationships with regional catchment land use, i.e. minimal forest loss. Large wood acts as an intermediate response variable between landscape disturbance and simple fish metric response. As natural forested coastal plain landscapes are lost, declines are observed in the occurrence of large wood, and cumulatively these terrestrial and habitat disturbances result in decreased richness and diversity of coastal plain fish assemblages. Complex metric guild breadth (a measure of functional diversity) was approximately equally influenced by regional land use (agrarian land use change over time) and local habitat (large wood), suggesting that the structure of coastal plain fish assemblages is determined by factors operating at multiple spatial and temporal scales. In contrast, complex endemic abundance (abundance of Atlantic slope coastal plain endemic species) showed diminished strength of relationships with large wood and stronger, direct relationships with catchment-level landscape variables, minimal forest loss, and reversion of land from active row-crop agriculture to passive grassland/pasture. Observed reductions in endemic taxonomic groups were more strongly associated with larger spatial and temporal-scale phenomena than with local in-stream habitat conditions. These results indicate that landscape perturbations active at larger spatial and temporal scales may play a greater role in the actual distribution of endemic coastal plain fishes than local habitat conditions.