The Influence of Habitat Structure on Fish Assemblage Composition in Southeastern Blackwater Streams

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Abstract
We quantitatively sampled fish assemblages and measured habitat structure in upper coastal plain streams of the central Savannah River drainage, South Carolina. Fish species abundances ordinated in principal component space based on 15 habitat variables were arrayed along gradients of velocity and stream size (depth and width) and their covariates such as substrates and cover. The majority of species centroids oriented toward slower, deeper habitats with depositional substrates and cover. Size classes within some species were well separated, indicating change in habitat use with age, whereas others clustered closely, indicating consistent habitat use through ontogeny. In an ordination based on species distributions and abundances (detrended correspondence analysis) species again oriented among velocity and stream size gradients. Although taxonomically related species had distinct optima, most genera and families clumped into similar regions, indicating a phylogenetic component to assemblage composition. A Mantel comparison of species ordinations on PCA and DCA axes resulted in high and significant concordance, indicating that these independent techniques produce the same conclusion regarding response of fishes to habitat parameters. Much site-to-site variation in composition of coastal plain fish assemblages can be attributed to variation in habitat structure, primarily current velocity and stream size.