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24 November: Genetics reveal extent of killer seastar population explosions

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24 November 2015

Scientists have taken a major step towards understanding how and why deadly plagues of coral-eating crown-of-thorns seastar (COTS) break out across the Great Barrier Reef, thanks to novel research from the Australian Institute of Marine Science (AIMS).

For the first time, scientists have developed a genetic technique that significantly advances the detection of COTS offspring (called ‘larvae’). Using this technique, scientists will be able to test theories about COTS outbreaks, which can devastate coral reefs.

“On the Great Barrier Reef, COTS may be responsible for over 40% of recent coral loss,” explains lead author, Dr Sven Uthicke. “Until now the number and distribution of their offspring was impossible to detect with any accuracy, but by looking for their genetic ‘fingerprints’ we can identify whether their larvae are actually present in the water.”

Last summer, Dr Uthicke and his team tested their technique on water samples collected from the Great Barrier Reef shortly after a major COTS breeding event, known as ‘spawning’.

“To our surprise, we were finding COTS larvae in almost every water sample we took between Cairns and Cooktown. Some had apparently travelled more than 100 km, which supports previous models that predicted COTS larvae could move rapidly on ocean currents.”

“Based on our findings, numbers of COTS larvae were thousands of times greater than the number of adult COTS present in the same region – which may suggest that just killing off adults will not be enough to stop an outbreak.”

“Nonetheless, we should still concentrate on keeping COTS populations under control where we can, for example, to keep tourism sites attractive for visitors to the Great Barrier Reef.”

But although the initial findings are concerning, there is reason to be optimistic.

“We plan to carry out a number of short-term surveys to try to pinpoint exactly when the COTS are spawning, and under which conditions they can survive and spread. By homing in on these issues we will be able to understand precisely what is driving them and, hopefully, come up with solutions to stop it happening in the future,” says Dr Uthicke.

The paper “Outbreak of coral-eating Crown-of-Thorns creates continuous cloud of larvae over 320 km of the Great Barrier Reef” by S. Uthicke, J. Doyle, S. Duggan, N. Yasuda and A. D. McKinnon appears in the journal Scientific Reports (


Further information, please contact:

Dr Sven Uthicke, AIMS Principal Research Scientist, +61 (07) 4753 4483 or +61 (0) 447 825 604 (AEST, GMT+10)

Catherine Naum, AIMS Communication Manager (acting), +61 (07) 4753 4409 or +61 (0) 408 741 236 (AEST, GMT+10)