A James Cook University scientist has discovered why there was an unprecedented dieback of mangroves in the Gulf of Carpentaria in early 2016 – the plants died of thirst.
As explained in findings published today in the Journal of Marine and Freshwater Research, Dr Norman Duke, leader of JCU’s Mangrove Research hub, headed an investigation into the massive mangrove dieback, using aerial observations and satellite mapping data of the area dating back to 1972, combined with weather and climate records.
Dr Duke said they found three factors came together to produce the unprecedented dieback of 7400 hectares of mangroves, which stretched for 1000 kilometres along the Gulf coast.
“From 2011 the coastline had experienced below-average rainfalls, and the 2015/16 drought was particularly severe. Secondly the temperatures in the area were at record levels and thirdly, some mangroves were left high and dry as the sea level dropped about 20cm during a particularly strong El Nino.”
Dr Duke says this was enough to produce what scientists regard as the largest recorded incident of its kind, and the worst instance of likely climate-related dieback of mangroves ever reported.
“Essentially, they died of thirst,” he said.
Dr Duke said scientists now know that mangroves, like coral reefs, are vulnerable to changes in climate and extreme weather events.
He said the mangroves of Australia’s Gulf region have experienced relatively little anthropogenic impact and are considered the least altered mangrove ecosystems in the world.
“So the relative dominance of climate influences in this region is of critical interest to world observers of environmental responses to climate change.”
Dr Duke said the area is sparsely populated, with passing fisherman and scientists conducting unrelated work the first to notice the dieback.
“It took 4-5 months to come to the attention of mangrove tidal wetland specialists and managers. Our response to this event further involves training and equipping Indigenous rangers and local community volunteers to build local partnerships for rigorous and repeated shoreline assessments.”
Dr Duke said it was important not to be caught out the same way again, describing the dieback as a wakeup call for action on shoreline monitoring.
He called for a national shoreline monitoring program commensurate with Australia’s global standing.