Changes in mangroves at their southernmost African distribution limit

Abstract

Mangroves in South Africa occur at one of the most southerly locations in the world, which provides a unique opportunity to study their dynamic responses to anthropogenic and natural perturbations. The exposed high-energy South African coastline restricts mangroves to 32 sheltered estuaries of which 18 (56%) are predominantly open to the sea. A large area of mangrove (47% of the country total) occurs in the uMhlathuze Estuary – a novel ecosystem formed by the creation of an artificial mouth. A Drivers-Pressures-State-Impacts-Response (DPSIR) framework was applied to understand factors of change and highlight governance and management responses. The largest mangrove area (440 ha) was lost during the construction of Durban Bay harbour. Mangroves (~7 ha) no longer occur in 10 small KwaZulu-Natal estuaries as a result of catchment and mouth disturbance. In the Eastern Cape, pressures are escalating in the form of harvesting for wood, cattle browsing and changes in mouth condition. Climate related warming and an increase in CO2 are positive conditions for mangroves to expand their distribution to higher latitudes but this will depend on propagule dispersal between estuaries and the availability of suitable habitats.