It is likely to be the worst instance of climate-related dieback of mangrove forests ever recorded. 7,400 hectares of the trees withered and died along a 1,000-kilometre stretch of the Gulf of Carpentaria in an ‘unprecedented and deeply concerning’ event. Scientists have pinned the blame squarely on El Niño.
‘Essentially they died of thirst,’ says Norman Duke, ecologist at James Cook University who has led an investigation into the cause of the dieback. According to his report, the trees had been weakened by four years of drought and were then probably killed off by the high temperatures and the low sea levels of last year’s El Niño. This coincided with the world’s worst recorded coral bleaching, which impacted 25 per cent of Australia’s Great Barrier Reef. Says Duke:
‘We’ve learnt that mangroves, like coral reefs, are vulnerable to changes in climate and extreme weather events.’
The Gulf’s mangroves are considered to be some of the most pristine of their kind. Although remote, they serve as an essential part of the tidal ecosystems and industries such as prawn and mudcrab fisheries. The trees’ semi-submerged roots buffer the coast from storms and floods, while providing shelter for marine animals. Meanwhile, they are capable of taking in large amounts of carbon dioxide relative to their size – carbon that returns to the air if the trees die.
Australia has 11,000 square kilometres of mangroves, with the most significant portions growing along the eastern, the northern and the northwestern coasts. Usually the biggest threat to mangroves is coastal development and clearing, however, dieback shows how much damage the climate and future El Niño events can do.
Duke is using the problem to sound the alarm for the Gulf’s coast: ‘It’s time we spared a thought for the struggling northern seafood industry and seriously considered the other implications, for now and in the future, of increasing mangrove dieback.’
This was published in the May 2017 edition of Geographical magazine.