‘Natural buffer’: Could this tiny red crab help protect the Great Barrier Reef?

The red decorator crab could be a secret weapon in the fight against crown of thorns starfish.
The red decorator crab could be a secret weapon in the fight against crown of thorns starfish. Copyright University of Queensland
By Charlotte Elton
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This killer starfish is destroying the Great Barrier Reef. A tiny crab could change all that.

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Scientists fighting to save the Great Barrier Reef have discovered a new secret weapon - a tiny red crab.

The Great Barrier Reef is one of the natural wonders of the world.

But many of its reef-building corals have been devoured by plagues of toxic crown-of-thorns (COTS) starfish.

A little red crab could help to stop that.

The red decorator crab - or ‘Schizophrys aspera’ - has a voracious appetite for the juvenile starfish, research from the University of Queensland has shown.

“It’s one of the best predators of COTS we’ve seen and could be a natural buffer against future outbreaks on the reef,” said lead researcher and PhD candidate Amelia Desbiens.

How bad is the crown of thorns outbreak on the reef?

The Great Barrier reef has declined rapidly over recent decades. Last year, a joint report from the UNESCO World Heritage Centre and International Union for Conservation of Nature recommended that the reef “be inscribed on the List of World Heritage in Danger”.

Underwater heatwaves and cyclones - driven in part by runaway greenhouse gas emissions - have devastated some of the 3,000 coral reefs that make up the Great Barrier Reef.

Crown of thorns starfish are yet another threat. These predators were responsible for about 42 per cent of the decline in coral cover between 1985 and 2012, the Australian government estimates.

These starfish have up to 21 arms, more than 600 ovaries, and hundreds of toxin-tipped thorns. Each one can eat 10 square metres of coral a year - and there are millions of them.

Thanks to their thorny spikes, they are invulnerable to most predators - but not all.

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The Great Barrier Reef is threatened by coral bleaching, climate change, and invasive species.canva

Why is the crab so good at beating crown of thorns starfish?

University of Queensland researchers tested the appetite of more than 100 species of crabs, shrimps, worms, snails, and small fish.

“The red decorator crab was by far the most consistent predator consuming COTS in 89 per cent of the feeding trials,” she said.

“We were surprised by its voracity – each red decorator crab devoured more than five COTS per day while most other species barely ate a single one.”

This appetite could explain why some reefs escape outbreaks while nearby coral are decimated.

The research could pave the way for a program to protect the reef, said senior author, Dr Kenny Wolfe.

“This preliminary study sets us on the right path to resolving the role naturally existing predators could play in controlling COTS outbreaks,” he said.

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