What's eating the starfish? Mystery rot threatens populations on both coasts

Leather sea star eating a dying mottled sea star.
A healthy leather sea star eating a dying mottled star. Donna Gibbs

A grisly disease is decimating starfish populations on both North American coasts. From Orange County to Alaska, and along the rocky shores of New England, leggy echinoderms are shedding their limbs and "melting" away. 

No cause has been identified yet, but researchers are calling it the "sea star wasting syndrome."

"Their flesh deteriorates and there’s nothing to hold them together," said Donna Gibbs, diver and taxonomist at the Vancouver Aquarium, who also referred to the remains as "goo piles." "That’s as technical as it gets right now," she told NBC News. 

Donna Gibbs
The shed limbs of a sunflower sea star near Popham Island, British Columbia, in September 2013. Donna Gibbs

Up in Canada's Howe Sound and lower down near Seattle in the Puget Sound, divers started noticing fatalities in the sunflower sea stars — brilliant orange 3-foot wide adults with up to 24 arms — in September. But on the East Coast, this year's dying is a second chapter to a die off that started in 2010, when piles of starfish remains would tumble onto New England beaches, brought in by the waves. 

"A year after that we started seeing animals that have been exhibiting this 'wasting disease.' It appears to have [been] developing over the past few years," Gary Wessel, a professor at Brown University who is investigating the disease, told NBC News.

Starfish — also called "sea stars" — are ancient creatures, whose ancestry dates back almost half a billion years. They've seen a lot, and have a robust immune system. Periodically, their numbers swell, and they get sicker quicker, and the population is pruned to its usual size. Die offs have been recorded off the California coast in 1983 and 1997.

What's different this year is the speed at which the mystery ailment is zipping through starfish populations, leaving tattered limbs and spilled guts in its wake. Just this summer, divers in the Pacific Northwest saw thriving starfishes stacked like pancakes, but were startled to find them missing once the cooler weather set in. "They were so many — and now there’s just a bunch of goo left," Gibbs said. 

The first visible sign of the disease is a lesion that appears on a starfish arm. The arm then turns white, and the animal sheds it, perhaps wising up to the spreading disease. But by then, it's usually too late. Instead of growing a new arm (starfish shed limbs routinely) the wound stays open and the digestive organs peek out. The other arms can then begin to swell, and within a few days the rest of the body softens and falls apart. 

At the University of Rhode Island and Brown University, researchers are watching as the disease spreads through sea stars in tanks. "When we start seeing sea stars dying in one tank, it was a matter of a week before everybody was dead in that tank," Marta Gomez-Chiarri, who is collecting evidence and reports from across the world about dead starfish sightings, told NBC News. Most starfish die from the disease, but a few bounce back. 

The lab casualties indicate that the likely suspect is a bacterium or a virus rather than a chemical or environmental factor in the ocean, Brown's Gary Wessel said. Wessel and his students have recorded that the disease is contagious between animals, and between species of sea stars as well. 

His working theory is that a combination of stressors, both environmental (a change in ocean temperature) and pathogenic (a new bacterium or virus) may be to blame. The disease is unlikely to affect humans or other larger marine life, he said. 

Fall and spring temperatures seem to be trigger factors for the Rhode Island sea stars. Students at Gomez-Chiarri's lab collected sea star specimens in the summer, but didn't see the rot set in until three weeks ago, she said. Gomez-Chiarri believes that a change in ocean temperatures might make the starfish a little more vulnerable to whatever's eating them.

Not many people keep track of starfish numbers, which makes it difficult to identify shifting trends. So for now, the researchers are facing more questions than answers. Among them: Where did the disease begin? Is it the same bug on both coasts? How does it travel? "The spread — that’s a little bit scary for me," Wessel said. 

Nidhi Subbaraman writes about science and technology. You can follow her on Facebook, Twitter and Google+