Distribution of Salt-Marsh Foraminifera in Two South African Estuaries and the Application as Sea-Level Indicators

The global mean sea level is rising as a result of climate change and is likely to affect millions of people. It is essential to understand and quantify regional relative sea-level variability to be able to predict future changes. Proxy evidence is necessary for extending our understanding of past sea-level changes beyond the industrial era, and salt-marsh foraminifera have become an important tool for reconstructing late Holocene sea-level changes. In South Africa, little is known regarding the distribution of salt-marsh foraminifera and their use as sea-level indicators, thereby limiting their application in sea-level research. This study therefore describes the distribution of living and dead surface foraminifera from two study sites along the SE South African coastline. The full surface dataset has been compiled from 139 samples that are used to describe the contemporary distribution of salt-marsh foraminifera. Cluster analysis is used to define four biozones; high marsh, middle marsh, low marsh, and mudflats. In the high marsh, where environmental conditions reach the survival threshold, a greater abundance of agglutinated foraminifera occurs. In the low-marsh zone, where subaerial exposure is restricted and environmental conditions are usually stable, a greater diversity of calcareous species occurs. The tidal mudflats have the highest diversity of calcareous assemblages with some agglutinated taxa present. Distributions of living foraminiferal populations are similar to the population distributions of dead foraminifera at both sites in the low-marsh and mudflat zones. In the high-marsh zones, however, the living-to-dead ratio and distributions are different, which could be a result of different influences of environmental variables along with seasonal variations. This study provides insights into foraminiferal distributions along the SE coastline of South Africa, which will be useful for interpreting late Holocene sea-level changes.