BENTHIC FORAMINIFERA DENSITY AND DISTRIBUTION IN THE SAVANNAH RIVER ESTUARY AND ACROSS THE GEORGIA SHELF

The distribution and density of benthic foraminifera was determined for surface sediments extending from the inner reaches of the Savannah River estuary across the Georgia shelf in conjunction with water column and sedimentary parameters. The goal was to identify preferred salinity ranges of benthic foraminifera in this coastal environment for potential use in salinity reconstructions. The estuarine salinity regime has been altered significantly by harbor deepening to support the local port and further deepening is being considered to allow even bigger cargo ships access to Georgia Port Authority terminals in the inner estuary.

A modified box corer and grab sampler were used to collect subtidal surface sediment samples from the mouth of the Savannah River estuary to 36 km upstream in Aug. 2007 and July 2008 and across the Georgia shelf on June 2007 and Dec. 2008. Rose Bengal stain was used to distinguish live from dead foraminifera. On the shelf, higher densities of live foraminifera were found in the summer than in winter. Highest densities of foraminifera were found at the river mouth with reduced values upstream and off-shore. Moderately high densities occurred on the mid-shelf with lower densities on the inner- and outer-shelf. Significant benthic primary production occurs in the relic sands of the South Atlantic Bight and reduced foraminifera densities off-shore may be influenced by lower light availability at the greater water depths causing reduced benthic primary production and reduced thus reduced food availability. Similarly, benthic primary production may be reduced on the inner-shelf due to more turbid coastal waters.

The relative abundance of Cibicides and Elphidium were the most abundant genera for both lower estuarine and shelf samples. Elphidium was most abundant in the mid-shelf samples, while Cibicides was slightly more prevalent on the inner shelf. The relative abundance of Quinqueloculina increased steadily offshore to greater than 20%. Calcareous foraminifera were dominant in the lower estuary and made up 80 to 100% of the assemblage at salinities above 13.8 ppt and were all but absent at salinities below 10.2 ppt. Agglutinated foraminifera, in particular Saccamina, dominated the upper estuary samples with the thecamoebian Centropixus prevailing in the two lowest salinity samples.