IUCN Red List of Ecosystems, Mangroves of the South-west Australian Shelf

Mangroves of the South-west Australian shelf is a regional ecosystem subgroup (level 4 unit of the IUCN Global Ecosystem Typology). It includes the marine ecoregions of Great Australian Bight, Houtman, Leeuwin, South Australian Gulfs, and Western Bassian. The South-west Australian shelf mangrove province mapped extent in 2020 was 198.8 km2 across, representing 0.1% of the global mangrove area. The biota is characterised by one species of mangrove. Mangroves in this province are confined to sheltered shores of large embayments like the Gulf of Saint Vincent and Spencer Gulf, and protected bays, like those on the Eyre Peninsula. Low rainfall generally corresponds with the scarcity of estuaries, with limited freshwater, nutrients and sediments entering the sea. Mangroves are mostly found seaward of saltmarshes and often interspersed with seagrass beds and mudflats. They range from extensive and dense forests to sparse and isolated stunted trees at more extreme settings. Today the South-west Australian shelf mangroves cover 5% less than the estimated area in 1970. However, the mangrove net area change has been -2.3% since 2007. If this trend continues an overall change of -3.4% is projected over the next 50 years. Furthermore, under a high sea level rise scenario (IPCC RCP8.5) ≈-12.0% of the South-west Australian shelf mangroves would be submerged by 2060, although landward migration may occur. Moreover, 0.3% of the province’s mangrove ecosystem is undergoing degradation, with the potential to increase to 0.9% within a 50-year period, based on a vegetation index decay analysis. Overall, the South-west Australian shelf mangrove ecosystem is assessed as Least Concern (LC).