The importance of mangroves

Mangrove systems are critical to coastal ecosystems, helping both plants and animals survive.

Many juvenile larger predators, like sharks, and other marine animals like turtles, grow up in mangroves, protected by their root system.

So when mangroves in the Gulf of Carpentaria began to dieback at an unprecedented rate in early 2016, scientists rushed to discover why.  A total of 7400 hectares of mangroves, which stretched for 1000 kilometres along the Gulf coast, had been decimated.

Dr Norman Duke, leader of JCU’s Mangrove Research hub, headed the investigation into the massive mangrove dieback.  They used aerial observations and satellite mapping data of the area dating back to 1972, combined with weather and climate records.

Their findings?  Three factors that contributed to the mass dieback.

So, what killed the mangroves?

“From 2011 the coastline had experienced below-average rainfalls, and the 2015/16 drought was particularly severe,” Dr Duke said.

He said this, combined with record high temperatures and a drop in sea level during a particularly strong El Niño had left mangroves high and dry.

Essentially, Dr Duke said, the mangroves died of thirst.

“This event is being regarded as the largest recorded incident of its kind, and the worst instance of likely climate-related dieback of mangroves ever reported,” he said.

“Mangroves in Australia’s Gulf region have experienced relatively little impact from human pollution and are considered the least altered mangrove ecosystems in the world.  Given this, the relative dominance of climate influences in this region is of critical interest to world observers of environmental responses to climate change.

“We now know that mangroves, like coral reefs, are vulnerable to changes in climate and extreme weather events.”

A call for action on shoreline monitoring

Dr Duke said the investigation also foregrounded the necessity of shoreline monitoring in the Gulf region.

“The area is sparsely populated, meaning it took 4-5 months before the dieback came to the attention of mangrove tidal wetland specialists and managers,” Dr Duke said. “Passing fisherman and scientists conducting unrelated work the first to notice the dieback.”

He said in response to this event, Indigenous rangers and local community volunteers should be further trained and equipped to build local partnerships for rigorous and repeated shoreline assessments.

“We cannot afford to be caught out like this again! The Gulf dieback has been a wakeup call for action on shoreline monitoring.

“We urgently need a national shoreline monitoring program commensurate with our global standing. We have the specialists, we have the resources, and we know there is interest and concern amongst the Australian public.”

To read the entirety of Dr Duke and his team’s findings, see the latest edition Journal of Marine and Freshwater Research published earlier this month.



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