Crown of Thorns predators key to control: scientists
Published Friday April 17 2015, 2:15pm
A new experiment showing fish devouring Crown of Thorns Starfish (COTS) on Great Barrier Reef has drawn attention to the role of overfishing in outbreaks of the starfish, with another expert saying that more biological controls are the way forward in controlling Crown of Thorns populations.
Each Crown of Thorns starfish can grow to the size of a dinner plate, eat six square metres of coral a year and is covered in poisonous spines.
Outbreaks send millions of the creatures swarming over the Great Barrier Reef, with the starfish identified as one of the greatest immediate threats to Reef health.
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The experiment by the Australian Research Centre (ARC) Centre of Excellence for Coral Reef Studies, saw several specimens of the starfish staked to the seafloor near coral bommies to test the response of the surrounding fish.
The fish devoured the Crown of Thorns in a matter of hours, leaving nothing but their poisonous spines behind.
Crown of Thorns have few natural predators and are usually rejected by fish as prey, with only a few species of marine creature such as the large Triton’s Trumpet gastropod actively hunting them.
Although the results can be taken to indicate that overfishing might contribute to Crown of Thorns outbreaks, researchers acknowledge that by staking down the starfish in the open they have exposed them to more predators than usual.
One of the most voracious eaters of the starfish in the experiment was the starry pufferfish, which is not normally targeted by commercial or recreational fishermen.
Anne Clarke heads up the Crown of Thorns control project at the Cairns-based Reef and Rainforest Research Centre (RRRC) and said that while puffer fish will eat wounded starfish they probably couldn’t be used to control healthy specimens.
“Pufferfish are very effective at cleaning up wounded starfish - and the starfish do get wounded and they do get diseases that weaken them and make them vulnerable,” Ms Clarke said.
“If you wanted to say overfishing was leading to COTS outbreaks, it’d be a long bow to draw because pufferfish aren’t targeted by fishermen.”
Ms Clarke said many other biological management techniques - using naturally-derived methods to kill or control the starfish - are proving effective against Crown of Thorns outbreaks.
“Biological controls are something the research community is looking at very strongly at the moment,” Ms Clarke said.
“The bio-salts developed at JCU and used for injection right now are one way that we’ve found of inducing mortality without damaging the surrounding environment.
“There’s also natural diseases that affect the starfish and we’re looking at ways of taking advantage of that.”
“Another really interesting area that we’re investigating is the effect of compounds released by the Triton’s Trumpet- the ‘smell’ of the the Triton sends Crown of Thorns into flight mode and they hurry away from it as fast as possible.
“This has a lot of potential because it might be possible to set up a slow-release mechanism of this compound, almost like an air freshener, that could be used to protect the high-value reefs.
“This would free up control resources to tackle outbreaks at seeder reefs where the populations of Crown of Thorns really get going first.”
