IUCN Red List of Ecosystems, Mangroves of The Agulhas

Abstract

Mangroves of the Agulhas is a regional ecosystem subgroup (Level 4 unit of the IUCN Global Ecosystem Typology). It includes the marine ecoregions of Agulhas Bank and KwaZulu-Natal that extend along the South African eastern coastline. The extent of the Agulhas mangroves in 2023 is 23.0 km2, representing 0.02% of the global mangrove area. Mangroves in this province are limited to 31 estuaries which provide sheltered conditions as mangroves do not occur along the open coastline. The biota is characterized by three species of true mangroves, and 88 associated animal species. The Agulhas province mangroves are classified as terrigenous sedimentary. Natural drivers of extent and distribution include sedimentation, floods, mouth dynamics, storm surges, marine sediment deposition and propagule distribution. The ecosystem is threatened by anthropogenic pressures including urban and industrial development, harvesting for wood, livestock browsing and trampling, restriction of tidal exchange by infrastructure, freshwater abstraction causing estuary mouth closures and lower salinity, and pollution (plastics, heavy metals, oils, fungal pathogens, and coal dust). Under climate change, an increased frequency of tropical storms poses additional risks to mangrove survival due to sediment deposition, estuary mouth closures and back-flooding. The mangrove net area change has been positive since the 1970s (+51.5%), mainly due to flow modifications and an artificial mouth opening in the Mhalthuze Estuary, which contributes ~62.5% of the total mangrove area. Natural regeneration of mangroves has occurred in some estuaries previously impacted by mouth closure related to sea storms. There are also signs of a poleward shift to southern latitudes. However, the ecosystem has collapsed in 11 estuaries since the 1930s due to development, mouth closures and inundation of mangrove stands along with sediment deposition following floods. Similar losses are expected to increase under predicted climate change scenarios. Since mangrove stands are limited laterally by development, future sea-level rise will result in permanent losses. Overall, the status of the Agulhas mangrove ecosystem is assessed as Endangered (EN).