DISTRIBUTION OF BENTHIC FORAMINIFERA AND THECAMOEBIANS IN RESPONSE TO SALINITY IN THE SAVANNAH RIVER ESTUARY, SAVANNAH, GA

Populations of benthic foraminifera and thecamoebians at the sediment surface can be correlated with existing environmental conditions so that assemblages extracted from historic sediments can be used to reconstruct estuarine conditions of the past. Past studies have found a strong correlation between relative abundance of species and salinity. The purpose of this study was to survey the sediments of the Savannah River Estuary to determine changes in relative abundances of benthic foraminifera and thecamoebians with salinity. Sediment surface samples were obtained from the Savannah River at nine sites ranging from the mouth of the river where the average salinity was 23.9 ppt to the upper estuary at 36 km upriver where the average salinity was 2.9 ppt. Both calcareous and agglutinated foraminifera as well as thecamoebians were present in the samples and their relative abundances varied with distance up river. Calcareous foraminifera of genera Cibicides, Elphidium, and Ammonia were dominant at the mouth of estuary and represented 75.5 % of the total population. Agglutinated foraminifera of genera Ammobaculites and Saccammina were dominant at 23.7 km upriver and represented 86.0 % of the total population. Thecamoebians were dominant at 36.1 km upriver, with genera Difflugia and Centropyxis making up 92.5 % of the population. The change in dominant populations is likely the result of salinity decreasing with the transition from lower to middle to upper estuary.