Wednesday, 18 May 2016

Queensland's dying mangroves may contribute to global warming

Queensland's mangrove ecosystem dying in secret


15 May, 2016

The proverbial canary in the coal mine of the Queensland ecosystems went off months ago and we missed the calls.

There have been large scale diebacks of mangrove trees in the Gulf of Carpentaria for months and scientist have only just noticed as they are in the most remote areas of Queensland.

Scientists are not exactly sure what happened up there but they know the damage is extensive and unprecedented.

James Cook University Professor and spokesman for the Australian Mangrove and Saltmarsh Network, Norm Duke, said they were only guessing at what happened, but he had some prevailing theories.

"It is coincident with a very hot dry period in northern Australia, in some ways it is coincident, in the same season at least, with the dieback of corals on the east coast.

"We don't have any other indications of major events up there, the only other kinds of things that could cause such a wide area of mangrove death would be a large oil spill, very large, or a cyclone, or a tsunami.

"But there's been nothing like that the, only the dead mangroves."

Mangroves protect shorelines from erosion, stopping sediment going offshore. Professor Duke liked to think of them as coastal kidneys because they clean the water that comes from the land and goes into the sea.

"That's absolutely essential for ecosystems such as coral and seagrass, the rely on clean water and mangroves do the filtering on the coast.

"Mangroves are also fish habitat and nursery and the fishermen are telling us their catches have dropped in the Karumba area for example."

Karumba sits on the Gulf of Carpentaria coastline to the east of Burketown.

Mangroves play another role in the ecosystem, carbon storage, not only do they store carbon within, they keep it trapped underground in their extensive root network, Professor Duke said.

"They can store up to five times or more carbon than a normal forest and if they are dying like this they will release the carbon into the atmosphere and contribute further to global warming."

The Australian Mangrove and Saltmarsh Network has no funding and is relying on Google Earth imaging and concerned locals for their information.

"We're hearing from indigenous rangers in the Northern Territory, WWF and other organisations that may be able to support an initial field survey," Professor Duke said.

Prawn and barramundi fisheries are a large industry in the Gulf and the decline of the trees will also signal the decline of those fisheries.

"The worst case is they all die, the shore line starts to erode, the sediment becomes mobilised and they redeposit elsewhere.

"There will be a lot of muddy water and there will be a decline in fishery values associated with the areas."

Professor Duke said the loss of the mangroves would totally disrupt the ecosystem, smaller fish would not have safe habitat and the whole food cycle will deteriorate.

"One the trees have died, they can only grow back from seedling which may take 20 to 30 years before you get a functioning forest again," he said.

"The problem with sea edge is you've got waves, currents and storms, It's very difficult in some circumstances for plants to get started."

Professor Duke said the ownership of the mangroves fell under the purview of the state government.

"Mangroves in the state of queensland are protected species, there's a state government obligation for protection."


Just like the Great Barrier Reef, Australia’s mangroves are dying too; Mangrove death may contribute to global warming


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