A crown-of-thorn sea star starts to consume coral on the Great Barrier Reefs. (Khaled Bin Sultan Living Oceans Foundation)

As if the world’s coral reefs didn’t have enough problems — killer rising ocean temperatures, crazy bleaching events and oil slicks comprised of sunscreen from sunbathers that denude them, they are now under attack by hordes of thorny sea creatures.

That’s what some scientists are calling an explosion of voracious crown-of-thorns sea stars in Maldives that are eating coral reefs with mouths in their stomachs. For some reason — no one quite knows what — their numbers have grown out of control. Where once divers would see one or two eating coral across about a mile, they’re now seeing 100. And a single sea star can produce 50 million eggs per year, scientists said.

“Their population is exploding in numbers that haven’t really been seen in the Maldives before,” said Alexandra Dempsey, a coral ecologist for the Khaled bin Sultan Living Oceans Foundation. “They can be clumped in an area with 60 to 80 animals within 20 meters, or four or five animals on one patch of coral. We’ve swam distances of 1,500 meters to collect 100 animals.”


The crown-of-thorns starfish, Acanthaster planci, is a large, multiple-armed starfish that usually preys upon hard, or stony, coral polyps. (Jürgen Freund/iLCP)

The result is a list of major headaches for humans and nature. For Maldives, which took in nearly a billion tourism dollars in 2010, it threatens the economy because coral lures about 800,000 vacationers per year. For coral, it’s the ultimate sacrifice, say scientists who’ve reported a killing field of bleached reefs that stretches for miles. For fish and other animals — sponges, eels, reef sharks, angelfish, it means the loss of their homes, breeding areas and nurseries.

“Once the fish lose their home and they have nowhere to live,” Dempsey said, “they’re going to start to die off, affecting the food chain and larger fish.”

An organized harvest launched by the foundation Oct. 14 to Nov. 3 netted more than 7,000 animals. “We are … saving hundreds of corals for each starfish that we take off the reef,” said Andrew Bruckner, the chief scientist for the foundation.

Sea stars that climb on coral and leave them dead aren’t the only worry. The gigantic El Niño stretching across the Pacific Ocean is warming waters to temperatures coral can’t stand. When it reaches a certain threshold, basically getting too hot, they lose their ability to photosynthesize, break down, die and turn bleach white.


A diver bags a crown-of-thorn sea star from the Great Barrier Reef. (Khaled Bin Sultan Living Oceans Foundation)

The hard part of a coral reef is actually a skeleton upon which a fine, sometimes almost microscopic creature lives. The prickly crown-of-thorns prefers to eat fast-growing coral that make reefs more resilient so that they recover from events such as El Niños. When they’ve chewed up fast-growing coral, they gobble boulder coral, the huge formations that give reefs their photogenic pop and take hundreds of years to grow.

So the foundation launched an effort to remove as many crown-of-thorns as they possibly could starting in October and ending this month. It placed an all-points-bulletin for certified scuba divers to help, but when they arrived in Maldives, only divers associated with resorts joined them.

Dempsey and Bruckner dove and were astonished to see thousands of sea stars in places they had never seen them. There was a similar outbreak in the mid-1980s, but nothing like this. There have also been outbreaks in Japan and on the Great Barrier Reef, where Australians spend more than $1.5 million each year to remove them, Bruckner said.

Bruckner and Dempsey carried plastic pipe to push them off coral and bags to carry them away. The plan was easier said than done.

Sea stars really suck. They actually clamp on coral reefs using limbs with thousands of tiny suckers. Those limbs are an evolutionary miracle, or nightmare in this case. Cut one off and it will not only grow back, but it will become another crown-of-thorns sea star. That’s comic book villain kind of scary.


(Khaled Bin Sultan Living Oceans Foundation)

“It’s much more exhausting than one would think,” Dempsey said. “We’re on scuba, of course, and the stars can be found from from five meters to 30 meters down.” Most were eight to 10 meters deep, she said. “They’re incredibly strong. If you don’t get them on the first try, they try to hide and get away.”

The whole time, divers are fighting ocean currents and waves. They struggled to grab them from underneath the coral and in nooks between. They swam off with 40 to 50 in one bag, sea stars heavy with body weight mostly comprised of water. Dragged out of the ocean, a bag could weigh 50 pounds.

Divers dug a foot-deep hole in the sand and buried them.

“It is vital that the starfish are not returned to the water as they can recover very easily and return to feeding on coral,” Bruckner said.

“Traditionally we would never have believed that removing starfish would be the appropriate measure,” he added. “We must stress that we do not like killing any animals, and we do regret killing these starfish. But because coral reef ecosystems are out of balance, and humans are causing imbalances in nutrients that increase the survival of crown-of-thorns larvae, then we see this as the only feasible option.”


(Khaled Bin Sultan Living Oceans Foundation)

(Khaled Bin Sultan Living Oceans Foundation)

(Khaled Bin Sultan Living Oceans Foundation)

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