Cooperative Fish and Wildlife Research Units Program: Georgia
Education, Research and Technical Assistance for Managing Our Natural Resources

The dominant fish species within impounded coastal wetlands in the southeastern United States may be different from the species that dominate natural marshes. We tested the hypothesis that resident fish assemblages inhabiting impounded coastal wetlands in South Carolina would differ from resident assemblages in natural marshes of the southeastern United States. We used rarefied species richness, Shannon’s H’ diversity, J’ evenness,used Morisita’s Index of Similarity and the Percent Similarity Index to compare resident fish assemblages from two three years of impoundments fish samples to 12 open-marsh resident fish assemblages from previously published studies in North and South Carolina. Fish assemblages in impoundments were sampled with rotenone, and assemblages in natural marsh habitat were sampled with rotenone and seines. Comparisons yielding an index similarity index ≥ 0.50 were deemed moderately similar and those with an index ≥ 0.75 were deemed very similar. Fifty-three percent of the among-impoundment comparisons (Morisita’s Index) were at least moderately similar, whereas 67% of impoundment-natural marsh comparisons were moderately similar. The best-fitting model for describing the observed similarity indicesMorisita’s Indices contained only a difference in tidal influence. A difference in tidal influence between the compared assemblages caused a 63% decrease in the index of similarity. Species richness and diversity were greater in impoundments than natural marshes, but evenness was similar between habitat types. Our results support the hypothesis that resident fish assemblages in impounded wetlands and natural marshes are different, and in our system, a lack of tidal influence drives this difference.