9 Jan 2019


Scientists fear the combination of persistent coral eating crown-of-thorns starfish outbreaks and more frequent coral bleaching are a ‘perfect storm’ that could leave the Great Barrier Reef unable to recover.

The concern is raised in a new WWF-Australia report, by Dr Udo Engelhardt*, which urges a crackdown on the “excessive, and often illegal”, use of industrial fertilisers that trigger outbreaks.

WWF-Australia Reef water quality spokesperson Sean Hoobin said Dr Engelhardt’s report should drive renewed urgency to ban outdated high polluting farm practices.

“The Reef is under unprecedented pressure. It may bleach for the third time in four years this summer. Over this same period the fourth major COTS outbreak has been underway – accelerating the loss of the Reef’s coral cover."

“To save the Reef we must lead on global action to address climate change, but only Australian governments can address major local impacts like farm pollution, and it is critical they act now,” Mr Hoobin said.

Dr Engelhardt’s main findings include:

  • The 4th recorded COTS outbreak, which started in 2010, is much more widespread than previous outbreaks with up to a 50% increase in the number of reefs affected
  • High levels of fertiliser run-off may be leading to continuing favourable COTS recruitment conditions which in turn lead to more ongoing outbreaks
  • Field observations following mass bleaching in the Seychelles showed the surviving corals were being eaten by starfish reducing the abundance of heat-resistant coral critical to the reefs’ long-term survival.

Dr Engelhardt said he was concerned about the double whammy of COTS outbreaks occurring straight after bleaching.

“This is the worst-case scenario because you’re losing those few corals that are showing signs of adaptation to climate stress, and if you lose those due to starfish predation you’ve lost your insurance policy down the track."

“If we improve water quality we have every chance of reducing this ongoing cycle of COTS outbreaks and therefore give the Reef a fighting chance,” Dr Engelhardt said.

Other findings of the report include:

  • Starfish densities may be lower because there is less coral for them to eat following mass bleaching and cyclones, but even at reduced densities they can decimate reefs
  • Outbreaks have been recorded in the northern and southern parts of the GBR which aren’t usually impacted
  • The central GBR region remains the most seriously affected, with outbreaks in an estimated 90% of mid-shelf reefs during the current episode
  • Science has established a clear link between fertiliser pollution and COTS outbreaks
  • The use of industrial fertilisers must be far more effectively regulated and controlled with a stronger enforcement of existing laws urgently required
  • COTS monitoring should be scaled up and include fine-scale surveys which find juvenile starfish hiding during the day. This method can detect an outbreak up to two years before it develops and provides critical data.

* Dr Udo Engelhardt, Director of Reefcare International Pty Ltd, is a senior researcher with 30 years’ experience in dealing with the COTS phenomenon


The 1st recorded COTS outbreak episode was from 1962 to 1974

The 2nd recorded outbreak episode was from 1979 to 1991

The 3rd recorded outbreak episode was from 1993 to 2006

The 4th started in 2010 and is still underway