This tiny red crab could save the Great Barrier Reef from coral-eating venomous starfish, say researchers in Australia.

University of Queensland scientists have identified natural predators which could help fight outbreaks of the destructive crown-of-thorns starfish (COTS) on the reef. The red decorator crab - or Schizophrys aspera - was by far the most consistent predator, consuming COTS in 89% of the feeding trials, which tested more than 100 species of crabs, shrimps, worms, snails and fishes.

PhD candidate Amelia Desbiens 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.

“It’s one of the best predators of COTS we’ve seen and could be a natural buffer against future outbreaks on the reef. We also saw 10 other species of crabs eat juvenile COTS fairly consistently, while other animals, including the short-tailed latirus sea snail and the iridescent fireworm, were less enthusiastic eaters.”

According to the Great Barrier Reef Foundation, in normal numbers on healthy coral reefs, COTS are an important part of the ecosystem. However, as they can eat their way through 10 square metres of coral in a year, when they appear in outbreak proportions they decimate a reef.

Coral rubble or dead coral is the preferred home of juvenile COTS, so the researchers searched for and collected potential predators that had, until now, flown under the radar. They then introduced juvenile COTS to the predators in small tanks and observed their feeding behaviour over several days.

Desbiens said it had been suspected that the presence of specific predators could explain why some reefs escape COTS outbreaks.

“Few animals successfully eat adult COTS but they are vulnerable when young because they are small and lack toxic spines to defend themselves.

"This makes it the perfect time for predators to strike and it is an opportunity for researchers and managers to understand a natural process that could reduce COTS numbers. COTS are mass-reproducers and can develop into large populations so it’s vital we find a way to deal with outbreaks quickly.”

Senior author Dr Kenny Wolfe said, "We’d like to conduct broader surveys on the Great Barrier Reef across areas with and without outbreaks to evaluate whether the presence of this crab can help predict the chance of COTS gaining a foothold.

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