Coral-eating starfish threaten the Great Barrier Reef in Australia / A new invention is designed to curb its spread.

CANBERRA, Visually, the prickly starfish with its dazzling colors fit well into the colorful Australian coral reef. But living together does not go smoothly. Crown thorns threaten one of the most biodiverse ecosystems on earth. To stop their spread, divers have so far killed the animals with lethal injections – without much success. Now, inventors have created a robot to take up the fight against the starfish.

Queensland University of Technology researchers have developed so-called Rangerbots, which are similar to mini-submarines, in collaboration with Google and the Great Barrier Reef Foundation. The underwater robot can be navigated by tablet through unclear coral reefs to track thorn crown stars there. Then the device shoots a lethal injection of vinegar or bile salt on the starfish. The reef should remain intact.

The yellow underwater hunter can detect the thorny starfish with a reliability of 99.4 percent, says its inventor Matthew Dunbabin. "We trained the Rangerbot to differentiate marine life and recognize the coral-eating crowns of thorns." The 15-kilo and 75-centimeter robot can dive for up to eight hours per battery charge and can also be used at night, even in waters with sharks and crocodiles. In addition, the robot recognizes, according to Dunbabin, other dangers for coral reefs such as coral bleaching or silting.

The Crown of Thorns is extremely voracious

Also Anna Marsden, managing director of the Great Barrier Reef Foundation, places great hopes in the high-tech sea drone. "Food and livelihoods of more than a billion people depend on coral reefs, and they risk losing everything if these important ecosystems are not protected." Protecting the Great Barrier Reef is a huge and expensive task because of its immense size and complexity.

The area off Australia's northeast coast is the largest coral region in the world: on an area almost as large as Germany, about 2,900 reefs provide habitat for millions of marine life. Every year more than two million tourists come.

In the past, sedimentation, sea acidification and coral bleaching affected the reef. According to a study, the Great Barrier Reef lost half of its coral between 1985 and 2012. Forty percent of it fell victim to the voracious crowns of thorns.

Several million of them are currently in the region, says Sven Uthicke from the Australian Institute of Marine Science. According to Uthicke, only climate change makes corals worse. Thorny crowns, which are among the largest starfish in the world, are not real pests: in smaller numbers they help to preserve the coral variety, because they eat the fastest growing species. But as soon as more than about 15 crowns of thorns per hectare, they eat up the corals faster than they can regrow.

Researchers see two reasons for the current thorn crown plague: First, their natural enemies disappear like star-puffer fish. On the other hand, the increasing input of agricultural nutrients into the sea causes algae to proliferate – the main food of thorn-crown larvae. In previous programs, the crowns of thorns are individually killed by lethal injection – a complex process, with which the plague is difficult to get a grip on. The little killer robots will now kill the coral-eating echinoderms faster and more efficiently.


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