Algal Community Dynamics Within the Savannah River Estuary, Georgia Under Anthropogenic Stress

Abstract

Estuaries are naturally dynamic ecosystems mixing fresh and marine waters, while consistently varying in depth and discharge due to diurnal tide shifts. Anthropogenic alterations impacting the Savannah River are expected to change the hydrology of the ecosystem and effect algal community structure and composition. The Savannah Harbor Expansion Project began recently with the aim of widening and deepening the river by more than a meter. It is anticipated that tidal height, influx of salt water, and sedimentation rates will be affected, which will disturb algal communities upstream. Baseline data from the Savannah River mudflats were obtained in 2011 as part of a biodiversity assessment. Algal community indices were also examined and related to species alterations in the community. Living algal species were classified as freshwater, marine, or brackish in addition to planktonic, epipelic, and epipsammic. Live diatoms were replaced by filamentous cyanobacteria representatives like Phormidium and green filamentous algae. There was a decrease in abundance of live chain-forming marine plankton species potentially due to sediment accumulation. Species richness within the diatom communities analyzed in clean material decreased (mean = 40 ± 6.6 standard deviation to 26 ± 4.6) and the 95% confidence interval narrowed when before and during dredging was compared. Cymatosira belgica Grunow remained as the dominant species with an average of 38% relative abundance at low tide and 33% relative abundance at high tide. With exposure to dredging and increased sediment deposition diatom communities showed significant change due to potential increase in turbidity and lower light availability.