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Crown of thorns starfish could reach 60 million on GBR

An adult crown of thorns starfish can eat a dinner plate sized area of coral every day.
An adult crown of thorns starfish can eat a dinner plate sized area of coral every day. Jon Hanson

A NEW report commissioned by WWF Australia is warning the current crown of thorns starfish outbreak in the Great Barrier Reef could reach plague proportions. 

The report's author Dr Glen Holmes said crown of thorns numbers could reach 60 million, with devastating consequences for the reef. 

"It would be like a locust plague devastating vegetation," Dr Holmes said.

The outbreak has been underway for five years, with estimates putting current crown of thorns numbers between four and twelve million. 

Between 1985 and 2012, central and southern sections of the GBR lost over 60,000 hectares of live coral solely to crown of thorns.

 

Crown of thorns starfish outbreaks tend to follow this pattern. Primary outbreaks tend to occur between Cairns and Lizard Island before migrating south, feeding secondary outbreaks on well-connected reefs.
Crown of thorns starfish outbreaks tend to follow this pattern. Primary outbreaks tend to occur between Cairns and Lizard Island before migrating south, feeding secondary outbreaks on well-connected reefs. WWF

 

"To put that in perspective, that's the same as 60,000 football fields of coral eaten in less than 30 years," Dr Holmes said. 

An adult starfish can eat a dinner plate-sized patch of coral each day.

>> Report: moderate progress halting fertiliser run-off to reef

>> Great Barrier Reef about to suffer major bleaching

>> Attenborough draws attention to GBR at climate change summit

Crown of thorns are native to the Great Barrier Reef, but human influences have put increasing pressure on marine ecosystems. 

Research indicates outbreaks would naturally have occurred around once in 100 years, compared to today's rate of once every 14 to 17 years.

Around 400,000 crown of thorns have been removed from the Great Barrier Reef since 2012, but it's barely a dent in the millions devouring the reef. 

 

Increased levels of nitrogen, mainly from agriculture, is the main factor that drives outbreaks, as Crown of Thorns larvae feed on nutrients.  

This is why outbreaks often occur a few years after large flood events -- every time nutrient levels double, the number of crown of thorns larvae that survive to adulthood increase eight-fold. 

>> READ THE REPORT

Other factors include overfishing (which reduces crown of thorns' predator species), how close reefs are together and temperature increases from climate change. 

Research indicates nitrogen runoff will have to be reduced by 80% to bring crown of thorns back to their natural cycle.

The report recommends improving approaches to fertilising and educating growers on how to fertilise in the right place at the right time with the right amount to reduce excess.

"Achieving targets is well beyond the funds currently allocated by the government," the report says. 

The report is calling on governments to take action by:

  • Placing a cap on pollution to ensure new development does not result in more dirty water flowing to the Reef.
  • Support farmers to implement the latest practices which increase productivity and cut pollution.
  • Enforce laws for businesses who continue to pollute the Reef.
  • Invest to secure the farm practice and land use changes needed to deliver significant cuts to pollution.
  • Co-invest with industry in innovation to deliver the next wave of profitable pollution cutting practices.

Topics:  great barrier reef


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