In June 2013, Steven Fradkin stumbled upon a grisly scene at Starfish Point in Washington, northwest of Seattle. About one in four of the park’s namesake animals were contorted and covered in white lesions. The seriously sick starfish were crumpled and sagging, their internal organs beginning to rupture through their skin. But that wasn’t what really stuck with Fradkin, when I spoke to him a year later. What really affected him were the arms that had ripped loose from the animals’ bodies. “There were individual arms just roaming around in a Walking Dead kind of way,” he says.

Three months after Fradkin’s group noticed the disease in Washington, divers found dying starfish north of Vancouver, Canada. By September the disease had been spotted in the Puget Sound and down the Pacific coast into Oregon and California. By the summer of 2014, it had spread to Alaska and Mexico. The illness, dubbed starfish wasting syndrome, proceeds quickly. First, the lesions appear. Then the arms begin to rip off and the lesions spread. In the last phase of the disease, the starfish’s internal organs begin to emerge from the lesions. The starfish are reduced, finally, to goo — within the course of a few days. Even sea stars in captivity aren’t safe; in aquarium tanks where water is drawn from the sea, they’re dying. More than 20 species are dying on the West Coast; incidents have also been reported in Rhode Island and North Carolina. It’s almost a year and a half since the initial discovery. The starfish are still dying. We don’t know how many; our best guess is in the millions. Scientists now believe a virus is to blame — one that’s been in the ocean for at least 70 years. So why did it become a problem now, and what does it mean for the ocean at large?

Starfish are gluttonous predators, eating everything from sea snails to urchins — even other starfish. Their tube feet, outfitted with adhesive cells and a hydraulic system, are powerful enough to rip openings into limpets and mussels. The starfish then ejects its stomach through its mouth, which is located on the underside of the animal (its anus faces the heavens). The stomach can fit through openings as small as a hundredth of a millimeter, and it brings with it powerful digestive juices that dissolve any creature unlucky enough to be caught. Digestion takes place outside the starfish; once the prey has been dissolved, the stomach processes the nutrient-rich broth left over, and then is withdrawn back inside the tough skin. the starfish ejects its stomach to eat The coastal sea star Pisaster ochraceus, known for its bright purple and orange hues, has been the paradigm of a keystone species since 1966, when the ecologist Robert Paine published his classic paper in The American Naturalist. Paine removed sea stars by hand from tide pools for two years and found that when the sea stars vanish, so do a lot of other things. Before the sea star removal, 15 species were found in the area; after, only eight. Entire populations of algae vanished, and other species, like the limpet, migrated away in search of food. Three years later, he coined the term "keystone species" in a paper that broadened his 1966 findings. The concept has been used to manage species diversity ever since. The coastal sea star Pisaster ochraceus, known for its bright purple and orange hues, has been the paradigm of a keystone species since 1966, when the ecologist Robert Paine published his classic paper in The American Naturalist. Paine removed sea stars by hand from tide pools for two years and found that when the sea stars vanish, so do a lot of other things. Before the sea star removal, 15 species were found in the area; after, only eight. Entire populations of algae vanished, and other species, like the limpet, migrated away in search of food. Three years later, he coined the term "keystone species" in a paper that broadened his 1966 findings. The concept has been used to manage species diversity ever since. Pisaster isn’t the only keystone species affected by the current die-off. The sunflower sea star, Pycnopodia helianthoides, is often bright pink or purple and lives in the intertidal zone; it’s another keystone species, and an even more bloodthirsty predator. They can radiate 16 or more arms and are large enough to catch and eat fish. In the absence of prey, they simply shrink and wait for their next meal. Pycnopodia move at the relatively rapid pace of 3 feet per minute, keeping urchins in check, along with clams, abalone, snails, and other sea stars. "They’re the Ferrari of sea stars," says Ben Miner of Western Washington University in Bellingham. "You’d expect immediate changes, like within a couple months, just from the absence of Pycnopodia." Keystone species help maintain an ecosystem by eating quickly-reproducing prey species like urchins and mussels — keeping populations low. Without the sea stars, the urchin population explodes; bad news for the kelp forests and everything in them. Giant kelp can grow to 150 feet underwater at a speed of two feet a day, but their weaknesses are their holdfasts, which are sort of like tree roots. The holdfasts are home to brittle stars, prawns and snails, among other creatures. Urchins like to eat the kelp holdfasts. Without them, the rest of the kelp drifts off in the tides. In this way, urchins can devour forests, which, higher up, are also home to fish, including several types of commercially-important rockfish, according to the National Oceanic and Atmospheric Administration. "We’re getting indications it’s worse underwater, and that these systems may respond in a bad way," says says Pete Raimondi, a marine biologist at the University of California-Santa Cruz. "It completely changes the community if there’s no kelp, especially with respect to fish. They use kelp as a structure for recruitment and refuge." Pycnopodia’s absence may also lead to more lingcod, which grow to about 5 feet and 80 pounds. They lay eggs in nests, which are essentially massive embryos attached to the ocean floor, Miner says. The nests are a favorite of Pycnopodia. Lingcod are good at cleaning water, so if their numbers increase, the water quality may change. Though the lingcod boom sounds good — more sportfish, cleaner water — they also have an effect down the food chain. Lingcod mature into aggressive predators, eating other fish, squid, octopi, and crab; more of them is bad news for their prey. The die-off is Paine’s experiment writ large: here is what the Pacific Coast looks like without sea stars.

One of the groups tracking the spread of the die-off is the Multi-Agency Rocky Intertidal Network or MARINe, an organization comprised of teams from several universities. They monitor more than 200 sites, including the one I visit on March 26 with a team of researchers from the University of California, Santa Cruz. We drive a little way up the coast on Highway 1, until we arrive at Scott Creek, a site the team has sampled since 1999. Seven species are counted here twice a year, including Pisaster. It’s gray and windy at Scott Creek; I don’t get the sense that it’s raining so much as that the sky is spitting on me. I suit up in boots and a waterproof jacket, which is already damp. The researchers are wearing waterproof coveralls. We park our cars on the bridge over Scott Creek and climb down to the beach, wading through the creek, which is rushing dangerously close to the tops of my boots. When we finally arrive at the sites, which are mostly mudstone, low tide is a few hours away. The nooks and crannies starfish like to hide in are still either submerged or being pounded by surf, so we begin by taking a count of the local sea weed. A starfish survey of the Santa Cruz area. Scott Creek is the northernmost red pin. Explore the data → After about an hour, the tide pools are exposed. The researchers stretch industrial-looking tape measures and tie them off on bolts embedded in the rock. Then we spread out, marking the sections where we start our counts with yellow chalk. The researchers wearing waders take the areas closest to the surf; I am farther back on the mussel bed, and part of my job is to shout "wave" when one’s coming in, so no one will be surprised or, god forbid, swept away. My boots crunch on the mussel bed. Maya George, the leader of the expedition, has brought a foam pad to kneel on, so the mussels won’t cut into her legs. We all begin looking for starfish. Or sea stars, I should say. No one’s rude about it, but the marine biologists refer to the starfish exclusively as sea stars. They gently make a point of saying "sea stars," right after I have called the animals starfish. Because, of course, sea stars are echinoderms, not fish. By the end of the day, I find myself saying "sea star" more and "starfish" less. The few sea stars we do find are nestled into crannies and cracks on the rocks. When someone sees one, they shout the species name, along with the estimated size. So for instance, "I’ve got a Pisaster, 100" translates to a starfish that’s about 100 millimeters in size. If possible, the researchers gently pull the animals free of their nooks. They examine them, and take photographs, particularly of some that appear to have lesions. They’re minor, though: stage 1. Everyone’s in a remarkably good mood, despite the fact that we’re not finding many starfish. In 2000, when starfish monitoring began, researchers found 163 Pisaster individuals. The species’ population peaked in the fall of 2008, when researchers found 393. After hours looking through the tide pools, we’ve found 33. At least two showing signs of the disease.

This isn’t the first time starfish have died en masse. In 1978, the Gulf of California-dwelling sea star, Heliaster kubiniji, began showing white lesions on its body. The gulf sea star figures in John Steinbeck’s The Log from the Sea of Cortez: "The ferocious survival quotient excites us and makes us feel good," Steinbeck writes of the difficult habitat where it lives. Tough though they might be, the gulf sea stars were quickly overwhelmed. The sickness was attributed to an influx of warm water, says Raimondi. Then it happened again, another die-off, this time in 1997 in southern California. This time, the culprit was thought to be warm waters from an El Nino event. Pycnopodia vanished, and sea urchins ate into the kelp forests nearby. This of course upset the fish that use kelp forests as their homes. The sea star populations in that part of southern California still haven’t recovered. But the current die-off is different. Not only is it bigger, it doesn’t seem to be linked to water temperature. Where other die-offs had slowed down when the waters cooled, this time, the sea stars kept dying through the winter of 2013-2014. Something else had to be happening.

A starfish survey of Washington State, where the wasting syndrome was first discovered. Explore the data → In October 2013, after hearing of the Vancouver die-offs, Seattle aquarium staff veterinarian Lesanna Lahner sent divers to examine local sea star populations . The results were grim: about 40 percent of the sea stars under the aquarium’s pier were sick. By November, the three species that usually lived under the pier were gone. Then, the stars in the display tanks started dying. She tried treating the animals with antibiotics, in the hopes they had a bacterial infection; they wasted away all the same. "We’ve lost hundreds," Lahner says. "We lost the majority of sea stars at the Seattle Aquarium." In sea stars, dropping an arm is a common response to injury, but in this disease, it appears to be linked to the lesions. Lahner began euthanizing the sickest animals — though some do recover from small lesions, once a sea star has lost several arms and parts of its gut are eviscerating, there’s no hope left. Lahner assumes the sea stars are suffering, although starfish don’t have a centralized nervous system and no "brain" per se. A nerve ring — around the mouth — in the body of the sea star connects to the radial nerves, which run down each arm. The deaths in Seattle provided clues. The aquarium doesn’t filter water from the ocean, in order to try to maintain a bacterial environment that’s as close to natural as possible. But the system could also give a pathogen a way into the tanks. Researchers including Lahner, Miner, Fradkin, Raimondi, and Ian Hewson, a specialist in ocean viruses at Cornell— a group Hewson refers to as "the sea star mafia"—began to collaborate in October 2013 to find a cause for the deaths. Scientists, including Lahner, began sending Hewson samples of starfish; more than 460 sea stars, some sick and some healthy. "We kept Fed-Ex in business with dead stinking packages of sea stars," he said. Researchers in his lab sliced off bits of the animals’ arms and put them in a blender with some water — then used a technique called PCR to amplify the bits of DNA floating around in the blender. By doing that, they could start figuring out what was living on or in the starfish. They describe their findings in a paper published November 17th in the Proceedings of the National Academy of Sciences. A starfish survey of the Los Angeles area.Explore the data → Testing ruled out possible culprits: fungi, protozoans, and several species of bacteria. Using material from the blender that had been filtered to exclude all but virus-sized particles, they began inoculating healthy sea stars. The healthy stars that were inoculated began to display symptoms of sea star wasting disease; if the material was boiled before the sea stars were exposed, they didn’t get sick. Genome technology suggested that a densovirus, a type of virus, was to blame. But the virus may be only part of the story. Not only were some of the sick sea stars testing negative for the virus, some of the healthy ones were testing positive. And here’s another weird thing: the lesions, the first symptom of the disease, didn’t show higher levels of the virus — it didn’t seem to be causing them. "These ecosystems are dirtier and more complicated than terrestrial ones," Raimondi says. Even figuring out that a pathogen might have been involved was difficult. When scientists looked at the lesions, they didn’t find heavier loads of the virus, Hewson says. What they did see was that the bacteria there are the same that occur in healthy sea stars, there’s just more of them. Starfish are covered in millions of bacteria; usually they live harmlessly on the animals’ skin. There are some clues the virus may be affecting the sea stars’ immune system, by affecting a type of cell in the animal that ordinarily engulfs and consumes bacteria, Hewson says. That may create conditions where the bacteria that are ordinarily benign can compromise the sea stars. The virus has been around for at least 72 years But the same virus destroying the sea stars now was also present in samples of healthy sea stars held in museum collections from 1942 — meaning it’s been around for at least 72 years. And in those stars, at least, it didn’t seem to cause illness. Something has clearly shifted, Hewson says. "Obviously, the oceans are changing, and in places becoming warmer and more acidic," Hewson says. Observations suggest that daytime low tides during periods with lots of sunlight seem to make it easier for sea star wasting disease to spread. That might mean the virus spreads better in warm water. It may also explain the lesions, if they're caused by bacteria. Bacteria grow better in the heat, too. The virus probably isn’t the whole story, both Lahner and Raimondi say. Lahner took sea stars that were disintegrating at 54 degrees Fahrenheit and cooled their water to 50 degrees. "They all went from falling apart, having their viscera hanging out, to pretty healthy in a day," she says. "I came back, and they were like, ready for the cover of Vogue. They were perfect." So temperature may play a role in the animals’ ability to recover as well. The north Pacific basin, on average, has warmed by about half a degree centigrade from 1955 to 2013, according to data from the National Oceanic and Atmospheric Administration. "That’s kind of a scary number," says Andy Allegra, a NOAA data specialist. "It’s very large."

And that’s not all. The oceans absorb carbon dioxide — about half of what’s released into the atmosphere. When the carbon dioxide interacts with the water, it makes the water more acidic, especially near the surface. Ocean water over the past 300 million years has been slightly basic. Data on pH levels hasn’t been recorded as dutifully as temperature, but a long-running station sampling the Pacific, published in 2009, found "a significant decreasing trend" in pH over the course of 20 years, meaning it’s becoming more acidic. Acidification has been shown to slow sea stars’ growth, suggesting it stresses the animals. Lahner borrowed some mathematicians to analyze the data around two die-offs in and underneath the Seattle Aquarium. There were 20 variables, but only two showed a strong association: pH and dissolved oxygen content. Lahner and others are trying to tackle the question of acidity now. "I totally think climate change is involved," Lahner says. "I just don’t have evidence yet." "I totally think climate change is involved. I just don’t have evidence yet." It’s also true that there had been a boom in the starfish population before the die-off, Hewson says. In Vancouver, before the die-off, the starfish were so overpopulated that local divers were in danger of creating underwater avalanches by toppling piles of them. An abundance of sea star hosts makes it easier for a virus to spread, since the animals are more likely to come in contact with each other. The farther the virus spreads, the more opportunities it has to mutate and become more virulent. There is one piece of good news: viruses do not generally wipe out their entire host population, Hewson says. To do so would be counterproductive. Of course, that assumes the virus is the cause of the die-off, and no one’s proved that yet. The scientists seem to be shaking out into three camps, Raimondi says: the ones who think sea star wasting is environmental, those who think it’s caused by a pathogen, and a third group, who thinks —as he does — that it’s both.

Steve Fradkin, the man who first discovered the die-off, is sanguine about potential disruptions to the food web. Yes, mussel beds will probably become more dominant, he says. But they provide habitats for other organisms, too. "It’s different than normal, sure," Fradkin says. "But that doesn’t make it a horrible place." His attitude on this point is noticeably more relaxed than Miner’s and Raimondi’s, both of whom expressed worry about how the starfish’s absence might affect other species. We don’t know what’s going to happen, Fradkin reminds me. Not yet. Maybe we won’t notice an impact beyond the absence of the vividly-colored starfish from West Coast beaches. What does worry him, though, is that the starfish are serving as the ocean’s version of canaries in a coal mine. Starfish are usually pretty hardy. Pisaster is preyed upon by seals and birds, but they usually only pick off an arm or two, which the animals can easily regenerate. "Anything that can damage this thoroughly tough animal, short of the ‘acts of God’ referred to in insurance policies, deserves respectful mention," write Edward Ricketts, Jack Calvin, and Joel Hedgpeth in the classic 1939 book Between Pacific Tides. If this rugged creature is dying in such large numbers, what else might be next? "The world appears to be changing faster than it had been," Fradkin says. He hesitates to chalk up the wasting event to climate change. But he does worry all the same. "This is a proxy and a parable for what else can happen. If it’s happening to sea stars, it’s probably having other effects elsewhere."

Scientists can’t inoculate sea stars against the disease; they’ll have to recover on their own. Fortunately, starfish also reproduce when the water’s warm. The animals simply release their eggs and sperm into the water, a process known as broadcast spawning; before this happens, their gonads may account for 40 percent of the sea star’s weight. They also spawn when they’re stressed; a last-ditch burst of energy leads to a quick burst of reproduction before they die. During the El Nino event in 1997, that’s exactly what happened. "Evolutionarily, maybe that’s a good thing," says Carol Blanchette, a biologist at the Marine Science Institute at the University of California-Santa Barbara. There’s a slight delay between spawning and seeing baby sea stars, though. After the sperm and eggs meet in the ocean, the sea star larvae are microscopic, measuring less than a millimeter in length. These larvae then must grow into "new recruits," or baby starfish. In the 1997 die-off, the increase in new recruits after the sea star deaths wasn’t seen by biologists until 1999 and 2000 — that is, when the baby sea stars were large enough to see with the naked eye. "The world appears to be changing faster than it had been" Some sites are starting to see recruitment pulses, says Santa Cruz’s Raimondi. The period when they would have spawned corresponds to the start of the disease, he tells me. They’re about the size of thumbnails now. I perk up. It’s the first good news about the die-off I’ve heard in months. "We have some sites with huge pulses of babies coming in, I mean, really massive pulses," Raimondi says. "At one of the sites, we’ve seen more babies in the last three or four months than in the last 15 years combined." But even this good news comes with a caveat. If the culprit is a virus, there’s a reserve of it lurking in sea urchins and the ocean sediment. That disease reservoir means that if the die-off is caused by the virus, it might not end. Even if the sea stars aren’t spreading it among themselves, they may still catch it from their prey.