Climate change blamed for huge mangrove die-off

Climate change has triggered a massive die-off of mangroves along the northern coast of Australia, according to scientists at the country’s James Cook University.

Professor Norm Duke, who is also the spokesman for the Australian Mangrove and Saltmarsh Network, said in a statement on the university’s website that the scale and magnitude of the loss appeared “unprecedented and deeply concerning”.

Mangrove swamps are important ecosystems – the forests and coastal wetlands absorb up to 50 times more carbon than tropical rainforests by area.

The mangroves help marine life thrive. They are home to a wide variety of fish, crab and shrimp and serve as nurseries for many fish species.

The dense roots of the trees also help to protect the coastline by trapping sediments flowing down rivers and from the land. This helps to prevent coastal erosion, and by filtering out the sediments the forests also offer protection to coral reefs or seagrass meadows situated just off shore.

The large-scale die-off of the mangroves was discovered at an international wetland conference in Darwin.

A detailed scientific survey is yet to be done, but Duke said hundreds of hectares of mangroves were dying in two locations on the coast of the Gulf of Carpentaria – at Limmen Bight in the Northern Territory and Karumba in Queensland.

“The dieback occurred synchronously across 700km in one month,” Duke said –  that is about the distance between Sydney and Melbourne. 

The waters of the region are pristine, which led Duke to the conclusion that the die-off was due to climate change.

Certainly over the past few years, the seawater in the region had been warmer than usual and the rainfall has been more erratic.

The death of the plants is particularly concerning given the recent large-scale bleaching event seen on the Great Barrier Reef.

Duke told The Guardian news publication that following the death of the forests, there were 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,” he said.

Unfortunately, there is very little monitoring of these mangroves in areas where very few people live.

Duke said it was essential that monitoring efforts were scaled-up as a matter of priority to help scientists quickly isolate and manage dieback events such as those seen in the gulf.

He said that the next step in the investigation into the Gulf of Carpentaria dieback would be to start field investigations to determine the cause and begin appropriate management measures.