2.4.1 Mangroves

The Region’s mangrove forests are the most functionally and biologically diverse in Australia. Although plant diversity is low compared to other ecosystems, mangrove forests in the Region are diverse on a world scale.109,111 The Region is home to 44 mangrove species and hybrids,255 representing almost all the species found in Australia and around half of the global total.116 The number of mangrove species is a small fraction of the plants present in the Region, but these highly specialised plants, with their diverse shapes and structures, are enormously important for the ecosystem services they provide.255 The continued persistence of mangrove species is important for maintaining longstanding cultural connections for the Reef’s Traditional Owners.

Around half the world’s mangroves species are found in the Region

Large shifts in the extent of mangrove forests have not been observed over the past 5 years (Section 2.3.3), but less is known about their condition. Changes to mangrove forests driven by local climatic and geomorphological processes and by global climate change (Sections 2.3.3 and 6.3.2) can differentially affect individual mangrove species.123,256 For example, expansion of mangrove forest in the Howick Islands has involved successional replacement of colonising species with the dominant Rhizophora stylosa.123 As the climate changes, species with broader environmental tolerances may be at lower risk than those near the edge of their physiological limits, especially where farmland and built structures restrict their upslope migration.109 Warming is likely to allow some, but not all, mangrove species to expand their ranges southward and into areas currently occupied by other habitats, such as saltmarsh.109 There is currently no evidence of significant deterioration of populations of any of the Region’s mangrove species. 

Although continued warming and accelerating sea-level rise are expected to lead to future changes in the local distribution and condition of mangrove species, no substantial changes in the extent or diversity of mangroves have been observed over the past 5 years. 

An aerial shot of a river system meandering through lush mangroves.
Mangrove forests at Hideaway Bay. © Johnny Gaskell 2021
  • 109. Cooley, S.R., Schoeman, D.S., Bopp, L., Boyd, P., Donner, S., et al. 2022, Oceans and coastal ecosystems and their services, in Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change Cambridge University Press, Cambridge, UK and New York, USA, pp. 379-550.
  • 111. Joyce, K. 2006, Wetland Management Profile: Mangrove Wetlands, Department of Environment and Science.
  • 116. Duke, N.C. 2006, Australia's Mangroves: The Authoritative Guide to Australia's Mangrove Plants, University of Queensland, Brisbane.
  • 123. Hamylton, S., Kelleway, J., Rogers, K., McLean, R., Tynan, Z.N., et al. 2023, Mangrove expansion on the low wooded islands of the Great Barrier Reef, Proceedings Royal Society B 290(2010): 20231183.
  • 255. Duke, N. C., Larkum, A. W. 2019, Mangroves and seagrasses, in The Great Barrier Reef Biology, Environment and Management, ed. M.K. P. Hutchings O. Hoegh-Guldberg, Commonwealth Scientific and Industrial Research Organisation, Australia, pp. 219-228.
  • 256. Krauss, K.W., Cahoon, D.R., Allen, J.A., Ewel, K.C., Lynch, J.C., et al. 2010, Surface elevation change and susceptibility of different mangrove zones to sea-level rise on Pacific high islands of Micronesia, Ecosystems 13(1): 129-143.