Kill Starfish Now to Save Great Barrier Reef—Scientists

A species of destructive starfish is being culled by researchers to save the Great Barrier Reef.

Crown-of-thorns starfish can decimate coral reefs, munching through up to 108 square feet of coral every year.

Now, according to a new study in the journal PLOS ONE, killing off these starfish can help the reef recover coral coverage significantly.

Crown-of-thorns starfish (COTS) are a large species of starfish that eat corals, so-named for their spiny appearance. They can grow up to about 3 feet across, and have up to 21 arms, coated in usually covered in toxic spines that can cause painful wounds.

There have been several outbreaks of these starfish on the Great Barrier Reef, each lasting between 10 and 15 years, with the first occurring in the 1960s. These starfish are considered a major ecological threat when their populations explode, often fueled by excess nutrients in the water which boost their larval survival rates.

"COTS are voracious coral predators and are prone to rapid exponential increases in their populations size, known as outbreaks. These outbreaks of COTS can decimate reefs and entire regions of coral reefs and are responsible for about 40 percent of all coral losses on the Great Barrier Reef," study co-author Samuel Matthews, a researcher at the Great Barrier Reef Marine Park Authority, told Newsweek.

"While COTS are a natural part of the system, outbreaks have been exacerbated by nutrient runoff and overfishing of key predators. With the increasing prevalence of mass coral bleaching, COTS Control is necessary to offset the corals lost due to climate change, and to buy time for coral reefs to adapt."

The researchers tested culling on several parts of the Great Barrier Reef, which is the world's largest coral reef system, stretching over 1,400 miles along the east coast of Australia. The Great Barrier Reef is highly vulnerable to climate change, as rising sea temperatures can lead to widespread coral bleaching, where corals lose their symbiotic algae and turn white, eventually leading to coral death. A fifth recorded mass-bleaching event was confirmed in March 2024.

Additionally, warmer waters are more favorable to crown-of-thorns outbreaks, as they enhance the development of the starfish larvae.

"Anthropogenically-driven disturbances are superimposing additional stressors upon the natural cycles of decline and recovery inherent to coral reef ecosystems major drivers of coral mortality on Indo-Pacific coral reefs are cyclones, coral bleaching events, and outbreaks of crown-of-thorns starfish," the researchers wrote in the paper.

The researchers killed the starfish by injecting them with vinegar or ox bile during dives, which also prevented them from releasing larvae into the water. Between 2012 and 2022, the researchers culled the starfish across 500 of the 3,000 reefs across the Great Barrier Reef.

They discovered that in culling areas, the reefs were seen to have a 44 percent increase in coral coverage, while in non-culling areas nearby, coral was continuing to be lost.

"Our research shows that if we start culling early on in an outbreak when numbers of COTS are still low, we are the most effective. It is also important to cull on the reefs that are the most important for spreading COTS and coral larvae around the entire GBR. By focusing on these reefs, we can both limit the spread of COTS outbreaks and help promote faster coral recovery," Matthews said.

"Recent research has suggested that if we were to double the capacity of the control fleet (from 5-6 vessels to 10-12) we would be able to protect most of the GBR from widespread coral loss from COTS. It is important to note, however, that COTS control is only able to buy some time for coral reefs to adapt to climate change. If global emissions are not drastically reduced in the coming years we will see more and more coral dying from bleaching which will reduce the positive impact that COTS control can have."

The researchers see this culling as a form of pest control to protect the reef and hope that this study proves that culling is an effective method of reducing crown-of-thorns outbreaks on the Great Barrier Reef and beyond.

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