Unprecedented mangrove dieback in Northern Australia

Thousands of hectares of mangroves on the Gulf of Carpentaria have suffered a severe dieback as a result of drying conditions and high temperatures.

Professor Norm Duke, spokesman for the Australian Mangrove and Saltmarsh Network, said around 7000 hectares of mangroves had been affected, which is more than nine percent of the mangroves in the area stretching 700km west from Normanton.

Professor Duke said the scale and speed of the dieback was unprecedented.

“We have seen smaller instances of this kind of moisture stress before, but what is so unusual now is its extent, and that it occurred across the whole southern gulf in a single month. What we are seeing is a natural process, but nature usually does this incrementally. Not with such severity. We have never seen this before.”

Aerial and satellite surveys have confirmed the scale of the dieback, after scientists heard anecdotal evidence in early 2016.

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Arial photographs show the scale of the dieback. Source: James Cook University

Dr Duke suggested that the severity of the event is likely a result of global climate change.

“The normal wet season in the region is four to five months long, with about 100mm falling in a month. But it seems there were 10 or 11 months in a row with rainfall below 50mm.”

“By all accounts, the climate is going to become more erratic, so we can expect these type of events to become more common.”

Given the scale of the dieback, Dr Duke called for a properly funded study, and a commitment to proper ongoing monitoring.

Mangrove forests play an important role in transferring organic matter and from the land to marine ecosystems. Notably, they provide shelter for fish and crustaceans, which in turn provide food for turtles and dugongs in the area.

“Some of the mangroves will recover, some won‟t. But there are already anecdotal reports of marine life dying and piles of dead seagrass washing up on the shore. If that‟s true then turtles and dugongs will be starving in a few months” Dr Duke said.

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