HYDROGEOLOGIC PARAMETERS THAT CONTROL CRAYFISH DISTRIBUTION ON A BARRIER ISLAND ALONG THE COAST OF GEORGIA

Crayfish are freshwater decapod crustaceans capable of building complex burrow systems. While crayfish are commonly found to exist in freshwater, a few species have been reported to tolerate saline environments. This study investigates the occurrence and distribution of crayfish on Sapelo, a barrier island in Georgia. We investigate the geochemical, geophysical, and hydrogeological parameters that control the spatial distribution of crayfish on the island. Geochemical data (temperature, dissolved oxygen, conductivity, pH and ORP) were collected using a YSI 556 and Solinst probes. Groundwater parameters were measured in-situ using previously installed piezometers. Soil samples were collected using an open-faced auger. Geochemical parameters were analyzed for nitrates, chlorine, iron and phosphates using a HACH colorimeter. Ground Penetrating Radar (GPR) was utilized to determine the subsurface stratigraphy of burrowing crayfish populations and the surrounding areas. Electrical Resistivity (ER) was utilized to delineate boundaries of the crayfish populations as well as identifying areas affected by saltwater intrusion on the barrier island. Crayfish were collected in surface water, using a dip net, while burrowing crayfish were collected by excavation. Most of the water on Sapelo Island was found to be brackish as opposed to being fresh or saline. Primary burrowers were found at two sites and evidence of their presence at a third site. Secondary burrowing crayfish were found in three roadside ditches. While secondary burrowers were found in freshwater, primary burrowers were only found in brackish water. Multiple species, including one that had not previously been recorded on Sapelo Island, Procambarus advena, was documented. Preliminary results also indicate little difference in hydrogeologic, geochemical and subsurface characteristics between sites inhabited by burrowing crayfish and those without crayfish. Additional research, that includes in-situ slug testing, is being carried out to better understand the spatial distribution of burrowing crayfish on the island.