Crown-of-thorns starfish are one of the greatest threats to Australia's Great Barrier Reef, and a team of researchers have a robot that's going to fight back.

The starfish species, which is native to the Indo-Pacific region, feeds on coral and a serious outbreak can have a devastating impact on reef health. Some estimates suggest the organism has accounted for a 40% decline in coral cover in the World Heritage-listed site.

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A crown-of-thorns starfish feeding on coral in Komodo National Park, Indonesia. Image: Ullstein Bild

The anti-crown-of-thorns starfish robot, or COTSbot, was developed by Matthew Dunbabin and Feras Dayoub of the Queensland University of Technology.

Dunbabin, a robotics expert, said he had been thinking about the project for many years, but was held back by the available methods of eradicating the starfish.

Previously, human divers needed to inject every tentacle of the starfish to kill it, he explained, but last year, James Cook University came up with a single shot injection system. "From a robotics perspective, it became a lot better for us. We could start to consider it a robotics problem."

The COTSbot comes equipped with a pneumatic injection arm that will deliver a fatal dose of bile salts to the crown-of-thorns starfish.

Matthew Dunbabin and Feras Dayoub with the COTSbot. Image: QUT

Looking like a mini-submarine, the water-going robot uses the latest advances in machine learning and image recognition to make sure it's only targeting the pest starfish and not touching coral. The vision system is autonomous, Dunbabin said, but if it has any doubts, the machine takes an image of the unknown item and sends it back to the lab for a human to have the final say.

As well as detecting starfish, the COTSbot's cameras can be used for obstacle detection. It comes equipped with sonar and a doppler velocity log, which helps it navigate in a straight line and determine how far it is from the sea floor. At the surface, it can also use GPS.

Image: QUT

Dunbabin said he had designed the robot to have minimal environmental impact. It's battery powered and won't spill fuel, and is also buoyant so it floats to the surface if the power source shuts down. "We've always built robots that would have negligible environmental impact, even if we lost them," he said. "Even the injection system has multiple levels of safety built in ... the bile salts themselves have no known environmental impact."

The machine is still in the testing phase. In trials on the reef, the robot will be given a mission but remain connected to researchers by a tether. If it detects a starfish, and if the team gives permission, the injection will go ahead.

The COTSbot should be able to search the reef for up to eight hours at a time, with the ability to deliver more than 200 shots.

After deploying its test vehicle, the team hope that success in the field will generate enough interest that the machines can be deployed at scale across the Great Barrier Reef. "I've always been interested in ... how we can upscale what I can do as a person for the environment with robots," Dunbabin said.