bioGraphic celebrates the discovery, at long last, of the phenomenon behind a mysterious wave of rather horrific sea star deaths on America’s Pacific Coast. Now, researchers are trying to figure out how to use that information to end the largest marine die-off ever known:
I’m here because this team believes it has unraveled a monumental mystery. In 2013, sea stars began dying along North America’s West Coast, victims of a plague known as sea star wasting disease. The condition first surfaced in the Pacific Northwest, where scientists and scuba divers noticed sea star arms flexing and corkscrewing in tight spirals before tearing off and shimmying away like dancers in some macabre ballet. Grisly lesions, white and splotchy, spread like gangrene across their surfaces. Internal organs seeped from open wounds. Bodies would bloat and then deflate, the muscles dissolving in soupy puddles that left behind flattened sheaths of flesh. These, too, eventually decayed until all that remained were ghostly silhouettes, a sickly residue on the seafloor.
Within months, the disease had spread thousands of kilometers in each direction, from Baja California to the Gulf of Alaska. The body count quickly reached the millions. After a few years, it topped several billion. At least 26 species were affected. And although the carnage has since slowed—in part because there are fewer of the invertebrates left to kill—it’s ongoing. Yet for more than a decade, scientists haven’t been able to figure out what’s causing it.
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Now, after four years of work and endless rounds of RNA sequencing, [Hakai Institute’s Alyssa] Gehman and her team think they’ve found the real culprit: the causative agent, in science speak, behind perhaps the worst marine die-off in modern history. But given the false leads of the past, Gehman will settle for nothing less than certainty. That’s why she’s testing, and testing again. And that’s why I’m here to watch.
She nudges me closer as a colleague cracks open another container. Inside, a 16-armed sunflower star (not all have five) the color of a faded basketball clings to one wall. This, like the others, is a healthy baby sunflower star, the species hit hardest by wasting. They range in color from sunbeam to lavender and can move the length of a king-sized bed in two minutes flat. To me, though, this particular specimen already looks dead.
Then it suddenly comes to life. Its arms peel off the container walls and fold like a swimmer in a flip turn. It floats belly up, its tiny tube feet wriggling, the mouth at its center agape. Despite lacking a brain or even a head, this creature somehow seems to grasp that the removal of the container’s lid means Gehman’s team is about to feed it. Anticipation of the pending smorgasbord revs the sea star’s nervous system as much as opening the kibble drawer excites my dog. I find it charming; Gehman goes even further. “We love these animals,” she says.
And sea stars’ ecological importance supersedes their capacity to delight. They’re so essential that the term “keystone species” was first coined about them; research shows that removing sea stars from intertidal food webs lets other invertebrates take over, which often mow down kelp forests or driving out species such as chitons, limpets, anemones, and barnacles. Sea stars generate such outsized influence, in other words, that their collapse is reshaping coastal waters in severe and disturbing ways.
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[Cornell marine scientist Drew] Harvell knew that mass die-offs in nature, even among sea stars, are not uncommon. For years, as an expert in marine diseases, she’d used this UW facility to track outbreaks of other illnesses. This epidemic, though, wasn’t restricted to a limited geographic region; it extended almost the length of the continent. It wasn’t limited to one or two species, but affected more than two dozen. And it was clear that whatever unknown pathogen was killing sea stars had a co-conspirator: heat.
In 2013, around the time Harvell was alerted to the die-offs, an enormous patch of warm seawater had begun to form across a swath of the eastern Pacific Ocean, at first in the Bering Sea and the Gulf of Alaska. The Blob, as it came to be called, initially spread hundreds of kilometers across and hundreds of meters deep. In time, this overheated pool expanded to cover more than 1,600 kilometers (1,000 miles) in every direction. It stretched 90 meters (300 feet) down, held seawater that was as much as 3.9 degrees Celsius (7 degrees Fahrenheit) hotter than normal, and upended an entire universe.
Warm-water species like ocean sunfish appeared off Alaska. Nazca boobies more common to Central America started showing up in California’s Farallon Islands. Millions of Pacific Northwest seabirds died because their ocean food was suddenly nowhere to be found. Dozens of whales washed up dead, too. And then sea stars collapsed.
“This thing was like nothing we’d ever seen,” Harvell says. “Nobody ever expected something of this magnitude.”
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In 2020, after prior attempts failed, The Nature Conservancy decided to finance one more effort to determine the cause of death. With additional support from the Hakai Institute, the organization agreed to pay for Gehman’s research. Soon after, she received her first shipment of healthy stars from Puget Sound. Her team slowly exposed them to a slew of contaminants: the tanks of sick and dying stars; seawater housing ill stars; ground-up flesh from dead stars; sick stars’ internal fluids. In each case, the healthy stars died, usually within a week. When the team heated ground-up tissue and bodily fluids from sick stars to kill pathogens before injecting the mixture into healthy stars, none got sick. That confirmed that a microorganism, and not heat alone, was to blame. But what kind of organism?
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Now, in August 2025, after another year-and-a-half of work confirming and reviewing their findings, Gehman and her team have published a peer-reviewed study in the journal Nature Ecology & Evolution identifying Vibrio pectenicida, a saltwater-loving bacterium that works its way into sea star fluids, as the likely “dominant pathogen responsible for sea star wasting disease.” Gehman’s team has tracked down the killer.
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“We think that if these guys can get past this pandemic, [past] their sensitivity to this disease, they have a pretty decent chance of potentially persisting in the wild,” Jason Hodin tells me from his lab at Friday Harbor, a few hundred meters from where I’d met Harvell. Hodin, a senior research scientist at UW, is standing in the rain outside a small building up a hill from a faded dock. He’s showing off a maroon-tinged sunflower star named Martha. It’s the size of a grizzly bear’s head, “and it’s not done growing,” he says.
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You can read more of Gehman’s research here, in Nature Ecology & Evolution.