Crown-of-thorns culling effective for suppressing outbreaks on Great Barrier Reef

New research has found that targeted surveillance and culling of crown-of-thorns starfish (CoTS) can effectively suppress outbreaks to protect coral reef health and resilience on the Great Barrier Reef.

While crown-of-thorns starfish (Acanthaster cf. solaris) are native to the reef, outbreaks are a major driver of coral mortality and reef degradation on top of other stressors such as coral bleaching.

The new study found timely and sufficient control efforts during CoTS outbreaks resulted in a sixfold reduction in starfish numbers and a 44% increase in coral cover across impacted regions.

CoTS expert, Morgan Pratchett, a professor of marine biology and aquaculture at James Cook University who was not involved in the research, told Cosmos: “there needs to be early and concerted culling effort to effectively protect corals during an emerging CoTS population outbreak”.

“Critically, we are now seeing the start of the fifth documented CoTS outbreaks in the far northern Great Barrier Reef, and despite acknowledged importance of early intervention, there is yet to be any culling undertaken at reefs where there have been elevated densities identified throughout the period since 2021.

Underwater photograph of a thorny purple-coloured starfish attached to a coral
A crown-of-thorns starfish. Credit: Morgan Pratchett

“I still maintain that the best hope we have of containing population outbreaks of CoTS and protecting coral across the entire Great Barrier Reef is to stop the initiation of outbreaks. We now have the methods in place to detect the early initiation of population outbreaks, but this is yet to be matched by complementary approaches to culling CoTS.”

The new study, published this week in the journal PLOS ONE, uses data from the Australian Institute of Marine Science’s (AIMS) Long-Term Monitoring Program to validate the CoTS Control Program.

According to Pratchett, the study “demonstrates localised benefits of early and concerted culling to not only protect, but facilitate, recovery of corals”.

But CoTS outbreaks do not occur in a vacuum, they happen alongside other stressors such as mass coral bleaching events caused by elevated sea temperatures.

Photograph of a man snorkelling under water next to a large crown-of-thorns star fish
Morgan Pratchett and a crown-of-thorns starfish. Credit: supplied

Pratchett says that while the “current paper shows that effective and timely culling can have significant benefits for reef ecosystems, [it] is only part of the management responses needed to ensure the future health of the Great Barrier Reef.

“The extent and severity of mass coral bleaching will increase with ongoing greenhouse gas emissions, and we need urgent and immediate actions to minimise the future effects of global climate change,” says Pratchett.

“Given inevitable delays in reducing emissions and stabilising climatic conditions, researchers and managers must simultaneously contribute to reducing local stressors on coral reefs. On the GBR and throughout the western Pacific the other major cause of coral loss are recurrent outbreaks of CoTS, and the most effective and direct way to minimise coral loss is through targeting culling.”

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