Density, Shell Use and Species Composition of Juvenile Fiddler Crabs (Uca Spp.) at Low and High Impact Salt Marshes on Georgia Barrier Islands

Coastal wetlands offer refuge for juveniles of many species, with protection often coming in the form of dense vegetation. Human impacts have led to a 67% loss of coastal wetlands worldwide in the past 300 years, thus decreasing available refuges. There are no studies that show what affect this has on fiddler crabs (Uca spp.), a key species in salt marsh habitats. The present study looks at how human impacts are affecting juvenile fiddler crab densities, shell use, and species compositions. This study was conducted at 3 low and 3 high impact sites on Tybee and Skidaway Island, Georgia. Six collection trips were completed from June to August 2010 to each of the 6 sites. During each trip ten quadrats (1m 2 ) were placed at each site, and juvenile fiddler crab densities, Littoraria irrorata shell availability, and percent shell use were recorded. In the lab, juvenile fiddler crab carapace width and sex were determined and multiplex PCR was used to identify juvenile fiddler crab species. Juvenile fiddler crab densities were lower at high impact sites, while shell availability and shell use were similar at both low and high impact sites. Juvenile fiddler crab sizes and sex ratios did not differ between low and high impact sites on the substrate, nor did the sex ratios in shells. However low impact sites had significantly larger juvenile fiddler crabs found in shells as compared to high impact sites. Species compositions differed between low and high impact sites on the substrate and in shells, with an increase in Uca pugilator and U. minax at high impact sites. Impacts to salt marshes can cause a decrease in available refuge for juvenile fiddler crabs which could lead to higher mortality rates and an overall decrease in juvenile fiddler crab densities. Fiddler crabs are important in aerating the soil, soil drainage, and decomposition rates. A change in fiddler crab densities and behavior can have an adverse affect to the salt marsh and could lead to the loss of an important ecosystem