Australia is amassing an army of giant starfish-fighting snails

Last year, we reported on an innovative plan by Australian marine scientists to use the scary smells of giant triton snails to scare off the deadly starfish that are threatening the Great Barrier Reef. At the time, the idea had scientific support, but it was hindered by one major problem: researchers hardly know anything about these snails. Now that's about to change, as the Australian government announced this week that it will be funding a triton breeding programme specifically to help defend the reefs.

A crown-of-thorns starfish in the waters off Lizard Island on the Great Barrier Reef. Image: Ryan McMinds/Flickr

Crown-of-thorns starfish (COTS) are intimidating creatures. Growing up to 80 centimetres (32in) across, with as many as 21 arms, and covered in hundreds of poisonous spikes, they are among the most formidable predators of the Great Barrier Reef system, and they love to eat coral. Meal-time for a COTS involves enveloping coral polyps with its extended stomach and digesting them slowly. One starfish can clear out more than five square metres of coral in a year, and with an estimated ten million of these coral-eaters on the prowl, they pose a serious threat to a marine ecosystem that's struggling to stay healthy at a time of serious environmental upheaval.

Enter the Pacific triton, or giant triton. These predatory snails can grow more than half a metre (two feet) long, and of all the tasty critters in the sea, they have a special place in their stomachs for crown-of-thorns starfish. They're so good at hunting their many-armed prey, in fact, that the mere smell of a triton in the water will send the COTS scattering as fast as their tiny tube-feet will carry them. Researchers have long wondered if these snails could be useful in mitigating the threat of the starfish on the Great Barrier Reef.

But giant tritons aren't in a great position to help. They reproduce slowly, eat only a few starfish per week at best, and after years of being hunted for their pretty shells, are extremely uncommon.

"We don't really know anything about them, what they eat, whether they're nocturnal or not," said Cherie Motti, leader of the new triton breeding programme, "and this is the first real attempt to breed them."

It took two years of searching, but the Australian Institute of Marine Science (AIMS) managed to collect eight giant tritons, and over the past month, they have produced over 100,000 tiny snail larvae. The researchers are hoping these newborns can help them learn all there is to know about the life cycle of these squishy saviours. Then, their hope is to unleash the snails upon the reef and let them do what they do best: keep the starfish at bay.

Crown-of-thorns starfish aren't normally a problem for the Great Barrier Reef. They're native to Indo-Pacific waters and their appetite tends to keep fast-growing corals in check, allowing slower-growing species to keep up, which helps to maintain a diverse reef ecosystem. But recent years have seen record declines in the reef. The combined effects of climate change and El Niño have created unusually warm waters, leading to widespread coral bleaching, and leaving coral unable to rebound normally from threats like tropical storms and hungry starfish.

Over the past three decades, the coral cover of the Great Barrier Reef has been cut in half, and recent AIMS research found that starfish activity is directly responsible for more than 40% of that loss.

The current main approach to fighting off the starfish is culling by direct injection of approved chemicals, including bile salts and vinegar. But not only is this method expensive and time-consuming – it requires divers to seek out starfish one at a time – it's also rather intrusive.

"If we can have a natural predator doing the job for us (killing the starfish), it will be the best outcome," Motti said.

The researchers hope that the tritons will be able to do a much more efficient job by breaking up starfish spawning assemblages. COTS are expert breeders: a single female can produce 65 million eggs in one breeding season. If the presence (or just the smell) of the snails can scatter the COTS, this could prevent the birth of millions of new tiny terrors with minimal effort – possibly even without all that many starfish having to be consumed.

In May of this year, more than 70 experts gathered in Townsville, Australia for the Managing for Resilience Summit to discuss responses to threats to the Great Barrier Reef. Among the plans laid out was an increased emphasis on combatting the effects of the COTS.

"There is still a long way to go. We hope to learn more this year and within two years have [snail] babies growing happily," Motti said.