Thousands of hectares of Australia's mangroves dead

An area of dead mangroves in the Gulf of Carpentaria, which lost 9 per cent of its mangroves in just one month.
An area of dead mangroves in the Gulf of Carpentaria, which lost 9 per cent of its mangroves in just one month.PHOTO: AGENCE FRANCE-PRESSE

Severe drought the likely cause of massive 'dieback' in just a month

SYDNEY • Thousands of hectares of mangroves in Australia's remote north have died, scientists said yesterday, with climate change the likely cause.

Some 7,000ha - or 9 per cent of the mangroves in the Gulf of Carpentaria - died in just one month, according to researchers from Australia's James Cook University, the first time such an event has been recorded, reported Agence France-Presse.

The so-called dieback - where mangroves are either dead or defoliated - was confirmed by aerial and satellite surveys and was likely to have been the result of an extended drought period, said Dr Norm Duke, a mangrove ecologist from James Cook University.

"This is what climate change looks like. You see things push the maximums or minimums... What we are looking at here is an unusually long dry season," Dr Duke said.

"The reason that there's dieback now is because of this drought. Droughts are normal, but not so severe, and that's the difference," he said.

PICTURE OF CLIMATE CHANGE

This is what climate change looks like. You see things push the maximums or minimums... What we are looking at here is an unusually long dry season.

DR NORM DUKE, a mangrove ecologist from James Cook University.

The mangrove forests play an essential role in the region's ecosystem, said Dr Duke. They were nurseries for many fish species. "But we also think of them as kidneys - as water filters and purifiers," he said, reported The Guardian.

They act as massive reservoirs of carbon storage, storing up to five times more carbon than normal forests within themselves and deep inside their extensive root network, reported The International Business Times. If the mangroves die in such large numbers, this will release carbon into the atmosphere and cause global warming.

Dr Duke said the remoteness of the damaged area was a huge inhibitor to solving the problem, reported The Sydney Morning Herald.

Explaining the damage to the ecosystem as a result of the dieback, he said: "One of the mangroves' roles is that they prevent erosion of mud banks and as they've died, a lot of the sediment is going to be released and make the water dirtier and that will kill seagrass and coral."

"If it involves seagrass, then the implications extend much more broadly, you're talking about turtles and dugongs, but we don't know for sure," he said, adding that shellfish that rely on the mangroves for shade had already died in large numbers.

Dr Duke said researchers believe the event took place in the semi-arid region in late November or early December last year, reported Agence France-Presse.

"The dieback occurred synchronously across 700km in one month," he said, which is about the distance between Sydney and Melbourne. He added that "by all accounts, the climate is going to become more erratic, so we can expect these types of events to become more common".

Some of the mangroves suffering dieback were defoliated, meaning they were not yet dead but had lost their leaves, and could recover. But most "won't recover, and will be dead", with satellite images matching ground surveys, said Dr Duke.

A version of this article appeared in the print edition of The Straits Times on July 12, 2016, with the headline 'Thousands of hectares of Australia's mangroves dead'. Print Edition | Subscribe