Changes in mangroves at their southernmost African distribution limit. (5th January 2021)

• Record Type: Journal Article
• Authors: Adams, Janine B.; Rajkaran, Anusha
• Is Part Of: Estuarine, coastal and shelf science. Volume 248(2021)
• Publication Date: 2021-01-05
• Subjects: Climate change -- Intermittently closed estuaries -- Range expansion -- Avicennia marina -- DPSIR; Estuarine oceanography -- Periodicals; Coasts -- Periodicals; Estuarine biology -- Periodicals; Seashore biology -- Periodicals; Coasts; Estuarine biology; Estuarine oceanography; Seashore biology; Periodicals; 551.461805
• DOI: 10.1016/j.ecss.2020.107158
• Languages: English
• ISSNs: 0272-7714

Abstract

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. Many of the small estuaries are temporarily closed to the sea for different periods thus limiting recruitment. An increase in the intensity of freshwater floods will scour banks and completely remove mangroves. It is important that these dynamic responses are understood and incorporated into management plans so that mangrove forests can be better protected and conserved. Graphical abstract: Image 1 Highlights: Mangroves occur in 32 estuaries along the east coast of South Africa. Extent is small (<2000 ha) but mangroves are important for biodiversity conservation. Mangroves have been lost from 10 small estuaries due to catchment and mouth disturbance. Harvesting for wood and cattle browsing are growing human pressures. Extreme events such as flooding and mouth closure cause mangrove die-back.