A Comparison of Resident Fish Communities in Managed and Unmanaged Coastal Wetlands in North and South Carolina, USA

Previous researchers have hypothesized that the dominant species within impounded coastal wetlands in the southeastern United States might be different from the species that dominate natural marsh habitat.  Based on this assertion and our own observations, we tested the hypothesis that the resident communities inhabiting mesohaline impounded coastal wetlands in South Carolina would be different from the resident communities in natural marshes along the southeastern coast of the United States.  We expected that differences in both tidal influence and salinity would drive any observed community-level differences.  We tested these hypotheses by comparing the resident fish communities sampled from two waterfowl impoundments along the Combahee River, SC, with resident communities of natural marsh habitats.  We used Morisita’s index of similarity to compare three years of impoundment fish samples to each other and to 12 open-marsh resident fish communities from previously published studies in North Carolina and South Carolina.  We considered comparisons yielding an index of ≥ 0.50 to be moderately similar and those with an index ≥ 0.75 to be very similar.  We used Akaike’s Information Criterion (AIC_c) to determine the linear model that best describes which variables (i.e., differences in salinity, tidal influence, and sampling method) influenced the observed community similarity indices.  About half (53%) of the among-impoundment comparisons were moderately similar, whereas a small fraction (6%) of the comparisons of impoundments to other communities were moderately similar.  Additionally, a quarter (27%) of the among-impoundment comparisons were very similar while a very small percentage (3%) of the impoundment-natural marsh comparisons were very similar. The best-fitting model for describing the observed Morisita’s indices of community similarity was the model that contained only a difference in tidal influence.  The results of model selection and averaging showed that a difference in tidal influence between the compared communities was the only descriptive variable, and that it caused a decrease in the index of similarity of more than half (0.63).  Our results support the hypothesis that resident fish communities in impounded wetlands differ from those in natural marshes, and in our system, a lack of tidal influence appears to drive this difference.