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01.22.2026
# How to Kill a Million Sea Stars
Synthetic pheromones offer a promising new means of controlling troublesome crown-of-thorns starfish.
###### Story by Annie Roth
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For decades, crown-of-thorns starfish (COTS) have been rampaging out of control. These pizza-sized sea stars are native to the Indo-Pacific region, including along Australia’s Great Barrier Reef, but their insatiable appetite for coral, dwindling roster of predators, and high reproductive capacity mean that a small population can quickly multiply to plague proportions, devastating struggling reefs. Across the Indo-Pacific, conservationists at war with COTS have developed a range of special weapons and tactics to take them on. But these stubborn starfish are extremely hard to kill. Not only are they covered in venomous spines that make them difficult for divers to handle, they also release toxic slime when threatened, which can harm surrounding marine life. COTS are resilient, too. As with other sea stars, an entirely new individual can pop into existence from what was once a severed limb. And thus, just as Mickey Mouse’s desperate act of chopping a magical broomstick gives rise to an army of clones in Disney’s _Fantasia_, slicing and dicing crown-of-thorns starfish can do more harm than good.
To date, scientists have come up with several ways to safely slay these starfish and protect coral ecosystems, but they all involve killing them one by one, which is time-consuming, costly, and not particularly effective when an outbreak can number in the millions of individuals. But an international team of researchers has recently developed a new way to help control COTS—one that co-opts the animals’ own communication systems to lure them to their deaths.
The trick, according to the recent research from scientists in Australia and Japan, is to release synthetic starfish pheromones into the water. In laboratory trials, at least, the scientists found that pheromones can lure large numbers of COTS to one place so they can be bumped off en masse. This new method, the researchers say, has the potential to make culling crown-of-thorns sea stars vastly more efficient and cost-effective.
On a healthy coral reef, COTS help maintain the balance of the ecosystem, says Scott Cummins, a molecular biologist at Australia’s University of the Sunshine Coast and a coauthor of the new study. But when people destabilize the environment by overfishing the starfish’s predators, or when pollution and nutrient runoff trigger an algal bloom, the starfish can quickly become an existential threat.
A single female COTS can release more than 200 million eggs a year. What’s worse, an adult COTS consumes enough coral every year to strip bare a roughly 10-square-meter (110-square-foot) chunk of coral reef, which is about the size of a small bedroom. That may not seem like much, but with millions of sea stars at work, a healthy reef can be reduced to rubble in a matter of weeks. This is what almost happened near the small Japanese island of Okinawa roughly 40 years ago, when divers were forced to remove more than 1.5 million starfish by hand to keep the reef from being overtaken.
Since then, scientists have been looking for better ways to cull COTS. Recent advances have included killing the invertebrates by injecting them with vinegar or lime juice, which slowly turns them to mush and saves conservationists the hurdle of handling the spiny starfish. Scientists have even developed an autonomous underwater vehicle, known as the RangerBot, designed to dole out death. But these approaches still require conservationists to track the starfish down one by one.
Cummins’s new strategy, of using the starfish’s own pheromones to draw them in close, came from years of studying sea slugs—invertebrates with poor vision that primarily communicate through chemical signals. The work led Cummins to discover that many other marine species, including COTS, also release small proteins known as peptides into the water to communicate, using these signals to meet up and coordinate activities like mating. “If you can understand how an animal communicates, you might be able to manipulate their behavior,” Cummins says.
Having identified the specific peptide that causes the sea stars to swarm, Cummins and his colleagues created a synthetic version. Laboratory trials with their pheromone—dubbed “ _Acanthaster_ attractins” for crown-of-thorns’ scientific genus, _Acanthaster—_ caused adult sea stars to beeline toward the pheromone. And not only is Cummins’s synthetic pheromone effective, it’s also entirely nontoxic.
This new approach, says Maria Byrne, a marine biologist at Australia’s University of Sydney who was not involved with the study, “holds great promise” for efforts to control COTS. “However,” she adds, because coral reefs are chemically complicated places, with lots of species releasing all sorts of scents and signals, a real coral reef, unlike a lab, is already rich with “chemicals that the crown-of-thorns starfish may respond to. So it will be important to conduct field trials to see how the chemical works in nature.”
Cummins hopes to begin field trials along the Great Barrier Reef soon. Australians “have been fighting against [COTS] for 50 years,” Cummins says. Though more research is needed before field trials can begin, Cummins is looking forward to what comes next. “It’s an exciting time,” he says.
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# Annie Roth
Annie Roth is an award-winning science journalist, filmmaker, and children's author who enjoys telling stories about animals and the people who study them. Her work has appeared in _National Geographic_ , _T_ _he_ _New York Times_ , _Science Magazine_ , and many other publications. Roth writes best when a cat is sitting on her lap.
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###### Topics
Conservation Coral Reefs Ocean Predators Seastars Wild Life
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