A comparison of the fish communities in managed and unmanaged wetlands in coastal South Carolina
Robinson, Kelly Filer
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Estuaries are among the most productive habitats in the world and serve as habitat for many resident and marine-transient fishes. Along the southeastern coast of the United States, thousands of acres of estuarine marsh were ditched, drained, and impounded in the late eighteenth century for rice cultivation. Although many of these impoundments now are subject to tidal inundation, about 28,000 ha of impoundments remain intact in South Carolina. Most are managed via water level manipulation to promote the growth of food plants for migratory waterfowl. Studies of the fish communities within impounded wetlands have documented reduced access to these habitats, unfavorable abiotic factors, and reduced population exchange with adjacent unaltered environments. In this dissertation, I present results of studies that 1) provided estimates of summer production of fish guilds in three study impoundments along the Combahee River, SC, 2) determined the optimal impoundment management strategy for maximizing export of YOY spot from the Combahee River as well as the factors that most influence spot export, and 3) compared the resident fish communities of two mesohaline impoundments with resident fish communities of open-marsh habitats. In Chapter 2, I provide an estimate of secondary production that is removed from the trophic relay and demonstrate that the study impoundments provide poorer quality habitat than do open marsh habitats. In Chapter 3, I present my findings that spot export can be best maximized by changing the way water flows through the trunks to minimize ingress and maximize egress. Also, impounded wetlands had relatively little effect on YOY spot export; whereas, export was most sensitive to juvenile settlement densities and natural mortality within the estuary. In Chapter 4, I show that resident communities within the study impoundments differed from resident communities from open-marsh habitat; and the lack of tidal influence was the driving factor. Overall, the study impoundments provided suboptimal habitat for fish communities and altered the estuarine resident community structure. Because these structures occupy a small proportion of the marsh landscape in the Combahee River, they do not adversely affect the overall population dynamics of at least one marine-transient species (i.e., spot).