A project to save coral reefs from crown-of-thorns starfish (COTS) is celebrating a successful trial and a funding win. Robotic control could give reefs breathing space, allowing them to survive other threats.

COTS outbreaks have been estimated to be responsible for 40 percent of the coral decline on the Great Barrier Reef in recent decades, and many other reefs are similarly affected. Divers control the problem by injecting a lethal poison into the starfish, but can only cover so much territory. Enter COTSbot, an underwater robot Dr Matthew Dunbabin of the Queensland University of Technology has been training to take over the task.

Having established its seaworthiness last year Dunbabin has been training COTSbot to distinguish the crown-of-thorns from desirable reef dwellers. After months spent tethered to a boat, seeking approval from human supervisors for every starfish it wished to stab, COTSbot was recently allowed to roam free, attacking its enemies at will.

Already excited by recent successful demonstrations – COTSbot can cover up to 14 kilometers (8.7 miles) of reef a day, taking out hundreds of starfish without harming other species – Dunbabin and his colleagues received a further boost from the Google Impact Challenge Australia, which provides funding for non-profit innovators "using technology to tackle the world's biggest social challenges". Victory in the People's Choice category will give them, along with their partners at the Great Barrier Reef Foundation, AU $750,000 (US $570,000) to develop a more advanced version.

Dunbabin calls his vision a “Swiss army knife” of reef care, tracking bleaching events, and recording which species of corals are recovering and which are in danger. Improvements in battery technology could extend COTSbot's operating time, currently eight hours in calm water and four when fighting strong currents. Dunababin is also investigating solar recharging, but says fouling of the panels represents a challenge.

In the short term, Dunbabin sees COTSbot's role as augmenting human divers as they control outbreaks on high-value reefs, such as those closest to tourist centers or of exceptional environmental significance. He told IFLScience he eventually hopes mass production will bring costs down to the point where locals can afford their own bot, which they take with them when they visit their favorite remote reef.

In moderation the COTS prevent the fastest growing corals overrunning slower species. Unfortunately, they can breed at such an astonishing rate – the females release 65 million eggs each breeding season – that when human-induced disturbance gives them an opening, they turn reefs into wastelands. Natural predators can't keep up, making interventions like COTSbot essential.

Dunbabin conceded to IFLScience the recent massive heat-induced bleaching may indicate climate change and ocean acidification are overtaking COTS as threats. Nevertheless, abundant evidence suggests that reefs can often survive an individual menace, while succumbing when faced by multiple sources of stress.

Dunbabin hopes to make the list of dangers just that little bit shorter.