Australia is home to 7% of the world’s mangroves, with the majority located in the tropical regions.
During the summer of 2015–16, one of the worst mangrove dieback events ever recorded devastated around 7400 hectares of mangrove forests along more than 1000 km of Gulf of Carpentaria coastline.
Field visits suggest that a relatively low percentage of trees have recovered and most are dying or dead, but there is no current formal assessment of the condition of affected forests and what proportion are recovering. There is also little understanding of the patterns of impact across the extent of dieback – in some areas, all mangrove species in all tidal elevations have been affected but in other areas only some species in specific locations have been affected. The dieback was not discovered for nearly five months, and individual reports did not recognise the scale of the event, demonstrating shortcomings in coastal monitoring capability. A better understanding of extent, patterns, condition, trend and the likely cause of dieback-affected mangroves is informing monitoring and management responses.
The dieback event has caused concern amongst local communities and industry bodies such as commercial and recreational fishing groups that rely on many ecosystem services provided by mangroves. The wider national and international community are also concerned about the dieback event due to its scale, diverse impacts and possible link to climate change.
Biodiversity is likely to have been significantly impacted by the dieback. For example, epibiont communities – the small plants and animals that live on mangrove trunks and aerial roots – have been shed, and leaf litter supplies, an important part of aquatic food chains, have almost ceased.
Of the affected mangroves, approximately 200 km are shoreline mangroves whose death would expose the coast to erosion and storm surge effects causing extensive geomorphic and ecological disturbance.
Field work is covering the entire dieback zone along southern Gulf shorelines from Weipa in the east to the Gove Peninsula in the west with more detailed ongoing monitoring near Karumba, Burketown, Borroloola and Numbulwar townships. The fieldwork discovered major dieback areas between Pormpuraww to Numbulwar.
Duke, N., Field, C., Mackenzie, J., Meynecke, J. & Wood, A. (2019). Rainfall and its possible hysteresis effect on the proportional cover of tropical tidal-wetland mangroves and saltmarsh–saltpans. Marine and Freshwater Research, 21/02/19. https://doi.org/10.1071/MF18321
Harris T, Hope P, Oliver E, Smalley R, Arblaster J, Holbrook N, Duke N, Pearce K, Braganza K, Bindoff N. 2017. Climate drivers of the 2015 Gulf of Carpentaria mangrove dieback. Earth Systems and Climate Change Hub Technical Report No. 2, NESP Earth Systems and Climate Change Hub, Australia.
Norm Duke, James Cook University
0439 191 952
This project is also being supported by the Tropical Water Quality Hub, the Marine Biodiversity Hub and the Earth Systems and Climate Change Hub of the Australian Government’s National Environmental Science Program.