Mangrove communities are experiencing dieback from natural and human-related causes throughout Queensland. In Moreton Bay, areas of mangrove dieback have been monitored over the last 20 years.
Mangrove dieback can have many causes such as weather, insects and disease, nutrients, pollution, climate change and pollution—find out more below.
Cause of dieback
Episodic climatic events such as heavy rainfall and prolonged flooding drown mangroves and cause extensive dieback. In 1974, the Brisbane River lost most of its mangrove community due to prolonged flooding from a severe rain depression after a cyclone.
A severe hail storm in 1999 damaged a large area of mangroves in Moreton Bay. This area has still not fully recovered. Changes in rainfall patterns due to drought affect the relative extent of mangrove and saltmarsh communities. Rainfall patterns might also cause sinking of sediments due to reduction in groundwater levels, oxidation of acid sulfate soils which underlie most mangrove areas, and collapse of soil profile.
Insects and disease
Heavy infestations of insects may defoliate mangroves and give the appearance of dieback. Fungal diseases can kill mangroves as happened to a community of river mangroves (Aegiceras) under the South-East Freeway in Brisbane during the summer of 2006. In the late 1970s, a soil fungus, Phytophthora cinnamomi, caused large areas of dieback around Gladstone, central Queensland.
At the mouth of the Brisbane River, mangrove dieback was thought to be caused by excessive nutrients. The nutrients led to a build-up of algal bunds on mangrove roots which caused water to pond and led to drowning.
Mangroves can also be affected by pollutants causing stress as photosynthesis may be affected or genetic defects and a greater susceptibility to disease. Oil can kill mangroves, lenticels covered in oil can no longer draw in air and the plant can suffocate.
Projected sea level rise due to climate change will add to the pressure on remaining mangrove communities as these may not be able to move inland due to barriers from foreshore developments, sea walls, revetments and other infrastructure on the coast.
Last updated: 22 March 2013
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Mangrove dieback , WetlandInfo, Department of Environment and Science, Queensland, viewed 6 August 2019, .