PLAGUE OF SEA STARS
As if the world’s coral reefs didn’t have enough problems — killer rising ocean temperatures, crazy bleaching events and oil slicks comprising 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 1.5 kilometres, 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 metres, or four or five animals on one patch of coral. We’ve swam distances of 1,500 metres to collect 100 animals.”
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 kilometres. 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.
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.
In the Maldives, divers buried the harvested sea stars in 30-centimetre-deep holes in the sand.
“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.”