Salt marsh at the tip of Africa: Patterns, processes and changes in response to climate change

Abstract

This study developed a conceptual understanding of climate change responses of salt marsh in open and closed estuaries and outlined changes in terms of implications for ecosystem services. Changes in salt marsh cover in South Africa were described in relation to prevailing pressures. Salt marshes occur in the sheltered estuaries distributed along the ~3000 km coastline. Supratidal salt marsh occurs at elevation greater than 1.5 m amsl and are dominant in the cool temperate (5328.28 ha) and intertidal salt marsh in the warm temperate region (2093.31 ha). Although small in total extent (14 955 ha), salt marshes play a central role in biodiversity conservation because they provide critical habitat for migratory fish and birds. Approximately 43% of salt marsh habitat has been lost due to encroaching development and agriculture from the 1930s to 2018. In addition, salinisation and desiccation resulting from upstream freshwater abstraction reduces freshwater inflow, which extends periods of mouth closure in temporarily closed estuaries causing inundation and flooding of salt marsh. Predicting the combined effects of multiple stressors (increase in storm surges, floods, droughts and reduced river flow) is critical to conserve these important habitats. Research and monitoring to understand salt marsh responses is ongoing because the interface between the subtropical and warm temperate coastal regions of South Africa is expected to be affected by mangrove range expansion. This study is globally relevant as little is known about southern hemisphere salt marshes in Africa and data are needed for comparative purposes.