The Impacts of Revetted Banks on Fish and Macroinvertebrate Assemblage Composition and Diversity in a Regulated Coastal Plain River

Although replacement of natural vegetated banks with armor riprap can have detrimental effects on lotic ecosystems, evidence suggests that riprap can also increase aquatic diversity in previously degraded systems.  The goal of our study was to determine what impacts riprapped banks have on fish and macroinvertebrate assemblages in the Pearl River, a southeastern river with a long history of anthropogenic modification.  We collected fishes via electrofishing from armored and natural banks at five regions during fall 2011, winter 2012, and summer 2012.  We also collected macroinvertebrates with introduced substrates in fall 2011.  Richness was analyzed with rarefaction curves, whereas seasonal abundance and evenness were analyzed with ANOVA.  Differences in assemblage structure were assessed with PERMANOVA.  Fish and macroinvertebrate richness did not vary between bank types.  However, fish abundance and evenness were higher at riprapped banks during the summer, and fish assemblage composition varied during base flows in the summer and fall.  Macroinvertebrate abundance, evenness and assemblage structure also varied between bank types in the fall.  Our results imply that, at base flows, riprapped banks in the Pearl River support unique aquatic assemblages, possibly due to a lack of natural heterogeneous habitat.