The Baffling, Gruesome Plague That Is Causing Sea Stars to Tear Themselves to Pieces
"They twisted their arms together," a marine biologist said, "and they'd pull and pull and pull, until one of them came off... It was horrific. They weren't just dying. They were tearing themselves to pieces."
Photos by Molly Matalon and Damien Maloney
Allison Gong is a marine biologist, so she knows perfectly well that a sea star has no blood, brain, or central nervous system. Still, she can't help thinking of the stars in her lab as pets. "Because of my weird personality," she told me, "I form an emotional attachment, even though obviously they can't reciprocate."
This attachment has deepened during the 20 years that she has worked in the Long Marine Laboratory at the University of California, Santa Cruz, where she exhibits the stars to undergraduates in her marine-biology classes. (One of her first lessons: The term "starfish" is a misnomer, because stars are not fish.) Until recently, Gong had 15 stars in her care: eight bat stars, five ochres, one leather, and a rainbow. She had developed a daily routine. Nearly every morning she entered her lab at 8:30 AM and saluted her menagerie with a cheerful "Hey, guys!" She checked "to make sure everybody's fine": If a star was climbing off the table, for instance, she'd prod it back into the water, with a gentle reprimand: "Guys! You know you need to get back in there." She recorded the temperature of the water, which is piped in from the shallows of Terrace Point, the reef on which the Long Marine Lab is situated; from the lab's windows it is common to see cresting dolphins, back-paddling sea lions, and breaching humpback whales in the surf below. Finally, Gong fed the stars frozen squid or lake smelt that she carefully diced into small, digestible bites. None of the stars, which typically live about 35 years in the wild and can survive more than three times as long in captivity, had ever died. At least not of natural causes. Some years ago Gong accidentally dropped a tank on a star, crushing it. "I thought it would recover, but it didn't. I felt bad about that."
Gong was therefore unprepared for the discovery she made during Labor Day weekend in 2013. No sooner had she greeted her charges ("Hey, guys!") than she realized that "somebody had died." The bat stars, aggressive scavengers, had glommed together in a single ball—an ominous sign. Gong peeled them off, one by one, until she found what they had been consuming: the corpse of an ochre sea star, their tablemate for the past five years.
Two days later she noticed that some of the other stars in the water table did not look well. "Their behavior was a little off," she said, putting it mildly. Some of their arms were twisted around their stomachs, as if the animals were trying to hug themselves. Healthy stars, especially ochres, have a rough texture and a firm consistency. But these looked "kind of mushy," like deflating party balloons. "It got to the point where I was afraid to open the door," she said. The next day a disturbed lab assistant reported that one of the stars had lost an arm. When Gong returned the day after that, the table looked "like an asteroid battlefield." The stars were squishy and pockmarked with pullulating white lesions. Sometimes their guts spilled out of the lesions. More arms had detached. The arms continued to crawl, disembodied, around the tank.
It is not uncommon for many species of sea stars to shed their arms in times of stress. When a curious child picks up a star out of a tide pool by one of its limbs, for instance, the star may jettison that arm in an effort to escape and regenerate it later. But Gong quickly understood that this was different. Her stars weren't merely shedding their arms. They were tearing them off. They were tearing them off the way a man, lacking access to a sharp tool, might tear off one of his own arms: by using one arm to wrench the other out of its socket. "They twisted their arms together," Gong said, "and they'd pull and pull and pull, until one of them came off. Then the arm walks away because it doesn't know that it's dead. It was horrific. They weren't just dying. They were tearing themselves to pieces."
It seemed at first that the sickness affected only the ochre stars. But soon the rainbow star began showing symptoms. Gong arrived one morning to find it ripping off one of its five arms. She left the lab to feed other animals, and by the time she returned, 40 minutes later, it had ripped off two more. The leather star and the last of the ochres liquefied a few days later. The bat stars did not, however, appear to be affected—at least not negatively. For them, the mass death of their tablemates was a bonanza. They gorged on the corpses.
Today they are the only stars remaining in the lab. "It's the stuff of nightmares," Gong said. "I had never seen anything like that. I'd seen animals die, but it's just a one-off. Something dies, and you get on with your life. But there was no getting on."
Anxious to figure out what was going on, she inquired next door at UCSC's aquarium, the Seymour Marine Discovery Center, which also draws its water from Terrace Point. The aquarists told her that they had noticed mysterious signs of disease in their own collection, which included a pair of sunflower stars, one of the largest star species in the world. A sunflower star can have as many as 24 limbs, each extending the length of a meter. Before long, the two sunflowers were losing their arms too. "They're so big that when they start pulling off their arms, it's bad," Gong said. "It's really bad. It looks like they've been butchered." The aquarists removed the sunflowers from public display so that children visiting the museum wouldn't scream.
In the neighboring building, Peter Raimondi, the chair of UCSC's Ecology and Evolutionary Biology Department, had begun to suspect that whatever was killing the sea stars was not confined to Terrace Point.
Raimondi had recently found himself undergoing an unexpected and not entirely desirable career shift: He had been thrust into the role of sea star detective. Though he is a marine biologist who divides his time between analyzing data and conducting research trips along the Pacific Coast, Raimondi is not entirely ill suited to the part. There is a private-investigator quality to his round, inquiring face, active eyes, and urgent, impatient voice. He wore sandals and cargo shorts when I met him in March, but in a fedora and distressed suit he'd bear more than a passing resemblance to Jake Gittes.
Raimondi's conversion is not as unusual as it might seem. Scientists are increasingly being made into investigators, as the world they study has come to resemble a crime scene. We are witnessing the greatest loss of life in planetary history, what scientists have dubbed the Sixth Extinction. Unlike the previous five extinctions, this one is caused not by vast natural processes but by human behavior. The current rate of extinction across all species is approximately a thousand times faster than the historical average. The reasons are various but most prominently include the warming of the atmosphere and the scrambling of ecosystems caused by human activities, which enable the infiltration of invasive species, the spread of disease, and the dwindling of natural habitats. Most of the species we lose expire without our noticing. For every Martha—the last surviving passenger pigeon, which died in a cage at the Cincinnati Zoo in 1914—there are thousands of other species that vanish anonymously, far from human view, their extinction only noted by human beings belatedly, species like the Liverpool pigeon, the Alaotra grebe, the Mexican grizzly bear, the Texas wolf, and many others that we did not even identify until they were gone for good. But those who devote their lives to examining the natural world notice this loss. Nobody knows their beats better than they do. They are the first to the scene and are the most highly equipped to understand the threats that face the animals they study. In the cases of many species, they are the only ones who care.
Raimondi, for instance, may know more than anyone alive about the condition of sea stars along the Pacific Coast.
For the past decade he has served as the principal investigator at MARINe, the Multi-Agency Rocky Intertidal Network, an ambitious effort to monitor coastal marine life. Every year, a team of researchers visits close to 200 sites between Graves Harbor, on the Alaskan panhandle, and Punta Abreojos, in Baja, Mexico. They take censuses and record observations about more than a thousand species, including at least 15 sea stars. The database is online and open to the public. The idea is to document the population sizes and environmental conditions along the coast, so that if something unusual happens, it can easily be measured. No such comprehensive, systematic monitoring system existed in the United States before MARINe, and to this day there is only one similar system, in the Great Barrier Reef. In most of the world we don't really know, with any accuracy, which marine species live where. The oceans remain a wilderness. We understand that we are changing its composition in dramatic ways, but we do not know exactly how.
In spring 2013, Raimondi began receiving reports of high levels of sea star wasting syndrome. Wasting is a generic term that describes symptoms of physical deterioration, which in the case of sea stars can include splotchiness, sores, deflation, and the jettisoning of limbs. Any number of insults, both environmental and pathogenic, can lead to wasting. It is not uncommon for a diver or tide-pooler to observe an individual sea star with symptoms. It's the echinodermatous equivalent of coming down with a very bad flu. About 1 percent of stars will exhibit wasting symptoms at any given time. But when a high percentage of animals succumb, it means something is wrong. It is the difference between a bad case of the flu and an epidemic.
This is what Raimondi began to observe himself in late March of that year. First, a marine-water-quality specialist at the University of Washington reported that every sunflower sea star observed on the coast of Vashon Island showed signs of wasting. In late April, a research technician at Oregon State noticed wasting symptoms in the ochre stars at the Tokatee Klootchman natural site in Carl G. Washburne Memorial State Park. In late June, researchers observed wasting ochre stars at Sokol Point, on Washington's Olympic Peninsula. In August, Raimondi himself found wasting ochres while on a research trip to Kayak Island, a remote island in the Gulf of Alaska 60 miles from the nearest town. He realized then that something strange was going on.
Throughout the fall the sightings increased in number and virulence. The Seattle Aquarium's veterinarian, horrified by the sight of the sick stars, quarantined them and doused them with antibiotics; when that failed, she began to euthanize every star that showed signs of the sickness. The geographic range of the events was startling. Mottled stars died at the Anchorage Museum in Anchorage, Alaska, and Pacific blood stars died at Point Loma in San Diego. The sea star population of Terrace Point, in Long Marine Laboratory's backyard, crashed almost entirely. Nor was the epidemic limited to the tidal zone; divers saw wasting stars in subtidal reefs, and crabbers even found wasting stars in pots pulled up from depths of 300 feet. "One or two percent—that's not a big deal," Raimondi told me. "But when you start seeing twenty to thirty percent or higher—in some cases it was all of them—then you know that something much different is occurring."
Nobody knew exactly what to call it. Was it a die-off? A plague? A population crash? An extinction event? Scientists began referring to it as "the Wasting."
Gong may have never witnessed anything like it, but Raimondi had. In 1982, while a graduate student at UC Santa Barbara, Raimondi observed firsthand the effects of the strongest El Niño episode of the 20th century. Temperatures in the Pacific Ocean spiked by as much as ten degrees Fahrenheit. Sea stars, among other affected marine creatures, died off in massive numbers from wasting syndrome. This occurred again after the 1997–98 El Niño, with one study putting wasting rates among sea stars as high as 56 percent at certain locations. Warm water seemed to be the common variable; various localized wasting events had occurred in Southern California during warmer-than-average years. Temperature rise is also believed to have contributed to other recent marine die-offs: the sudden collapse of the Long Island Sound lobster fishery in 1999, the mass bleaching of coral reefs in the Caribbean in 2010, the death of thousands of pelicans in the beaches of northern Peru in 2012, the recent mass starvation of sea lions in Southern California, and the discovery of as many as 100,000 Cassin's auklet corpses this winter along the Pacific Northwest coast. But by the summer of 2014, Raimondi could be certain that the Wasting was the most widespread marine mortality event he had ever seen.
Yet this time, warmer water didn't appear to be responsible. It is true that, after a 12-year-period of relatively low temperatures, the water off the Pacific Coast has become significantly warmer in the past several months. But the Wasting began nearly a year before this recent warmer phase, with the first observations coming in the Pacific Northwest, as far north as Alaska, where the water is especially cold. "If we were seeing it in Alaska," Raimondi told me, "then we figured it was unlike anything we'd seen in the past."
It also was happening more quickly than he had ever witnessed. "That's the part that surprised me the most," he told me. "It was so sudden and so complete, and in so many different species." Never before had he seen disembodied arms walking around. Or sunflowers "exploding." Nor had he ever seen a ghost star. Wasting tends to be a gradual process, as the star deteriorates over the course of days or weeks. But the Wasting can attack with such sudden ferocity that some of the stars rot in place. Their soft tissue dissolves and decomposes, devoured by fuzzy white bacteria, but the star's hard white spicules—their spines, which are made of calcium carbonate—remain. This leaves behind a ghostly impression of the star; it is, quite literally, a chalk outline.
"It was creepy," said Raimondi, using a term one doesn't typically hear from biologists. The Wasting has that effect. It makes scientists, who tend to choose their words with severe caution, speak like teenagers. In conversations they kept using words like "shock," "horror," and "nightmare."
Researchers investigate the cause of a mortality event in much the same way that the CDC tracks a deadly outbreak or a criminal detective tracks a serial killer. It's not enough to know who has died. You have to know the sequence in which they died. You must trace the violence back to its source. But Raimondi couldn't detect any apparent pattern. The stars died at different rates. Some became ghost stars within hours, some took a week to succumb, and still others managed to recover. It was utterly unpredictable. If the epidemic was caused by warm water, then why had it gotten worse during the winter? It did not appear to be caused by pollution, which tends to be localized, because it was occurring everywhere. And if it was caused by a pathogen, then why didn't it appear to spread outward from some point of origination, instead of hopping around? In the middle of some of the most devastated sections of the coast, they found pockets of healthy starfish. In unaffected areas, they found pockets of wasting. It struck in warm water and cold water. There was no sense to it. Raimondi even questioned whether the Wasting was actually an example of wasting syndrome. Perhaps it was something different altogether, something entirely unprecedented.
Cameramen from CBS, NBC, and CNN began trailing Raimondi when he went on his regular research expeditions. Boats containing journalists would appear in the bay. The British tabloids ran articles with headlines like MYSTERY AS MILLIONS OF STARFISH WASH UP DEAD ON WEST COAST and MYSTERIOUS PLAGUE CAUSES STARFISH TO RIP OFF THEIR ARMS—AND SCIENTISTS DON'T KNOW WHY. One ecologist called the Wasting "the most extensive and devastating disease of marine invertebrates that has happened."
The press attention, though distracting, had its benefits. Thousands of alarmed citizens began to investigate unsurveyed stretches of the Pacific Coast, logging their observations on a new Sea Star Wasting map that Raimondi created. Participation increased in groups like the California Academy of Sciences' Citizen Science program, and Reef Check, which trains amateur divers to conduct species surveys. The data accumulated—wasting was even detected on the northern Atlantic Coast—and Raimondi's Wasting map grew increasingly detailed, but still no pattern emerged.
Amateur gumshoes wrote him with their theories. Many blamed global warming, or acidification, which occurs as oceans absorb higher levels of carbon dioxide. A particularly determined, conspiratorial set blamed the Fukushima nuclear crisis—a hypothesis that was swiftly dismissed by scientists. Others blamed power lines along the coast for bombarding reefs with electromagnetic radiation. One man claimed that Christmas trees had caused the Wasting. He believed that fir trees, farmed in Alaska, carried with them some kind of bacteria lethal to sea stars; when they were shipped in tankers to Southern California, he said, they shed their poisonous bacteria into the water.
Donna Pomeroy, a retired wildlife biologist who for the past 20 years has lived across the street from Pillar Point reef in San Mateo County, is one of the citizen science volunteers who began to monitor her local star population, participating in monthly surveys of the reef with a group from the California Academy of Sciences. Right away she saw that the stars that normally clung to the rock ledges were peeling off. "It was pretty gross," she told me. "They looked as if they were made of wax and had been left too close to a heat lamp. The arms were literally dripping off. It's my backyard. I'm protective of it. It's sickening."
Around the same time she also started to notice, in startling abundance, a Pepto-Bismol-colored mollusk called the Hopkin's rose nudibranch. "It used to be that we'd go several years without seeing the Hopkin's rose. Seeing one was a thrill. But now the reef was covered with hundreds of them. Something bizarre was happening."
"It was like walking into a redwood forest and finding candy canes growing out of the branches," said Mary Ellen Hannibal, an environmental writer who participates in regular surveys for the California Academy and is writing a book about citizen science.
"The nudibranchs are gorgeous," Pomeroy said, "but it's scary to see these changes happen so fast, so dramatically. There's a bigger picture, and we don't know what it is."
Catherine Lyche, a junior at Monterey's Santa Catalina School, had a particular attachment to sea stars; she would "scream with joy" when she found them on tide-pooling trips with her school's Marine Ecology Research Program. So she was disturbed last spring to find stars that were wrinkled, armless, and decomposing. "Even my teacher didn't know what was causing it," said Lyche. "That was troubling."
Her classmate Katie Ridgway was startled when she couldn't find any sea stars on a trip to the local Asilomar reef. A year earlier the stars had been everywhere. "It was like, wow—why is this happening? Did I do something to cause this?" On a school break she returned to Seattle, where she grew up, and found that the reef she used to explore as a child in Puget Sound was also devoid of stars. "It made me wonder if ten years from now, when I've graduated from college, if I come back here or to Seattle, is this still going to be a constant concern? If it continues, and water rises, and another virus affects another organism, what's going to happen by the time I have kids?"
"No one was able to see it coming," said Lyche. "If we're not able to predict something as significant as this, what else don't we see coming?"
There are 10 million viruses in a drop of seawater. It would therefore seem unlikely that scientists would be able to determine the pathogen responsible for the Wasting. But a breakthrough came in November of last year. Ian Hewson, a Cornell microbiologist who studies aquatic viruses, detected high levels of a previously unidentified virus in tissue samples taken from sick stars. His team named the culprit SSaDV, an acronym for "sea star–associated densovirus" ("densovirus" describes a small virus that tends to infect insects and crustaceans). When scientists injected SSaDV into healthy stars, the animals developed wasting symptoms. News reports trumpeted SCIENTISTS SOLVE MYSTERY OF WEST COAST STARFISH PLAGUE, but Raimondi, who co-authored the paper that announced the discovery, is at great pains to explain that this isn't so.
That is because the virus has also been detected, albeit in smaller quantities, in many healthy sea stars, sea urchins, sand dollars, and marine worms—in 24 species so far. It has been found in mud on the ocean floor. It has even been discovered in museum specimens as old as 1942, which means that stars have been carrying this virus for at least seven decades, and perhaps much longer. A librarian at Stanford came upon an 1898 report about Narragansett Bay by a biologist named Hermon C. Bumpus, who observed: "I have noticed on certain lots of star-fish... what appears to be a disease, attacking the skin first and not infrequently eating its way through the body."
Why had this particular virus, which appears to exist everywhere and has for decades if not centuries, suddenly become fatal to sea stars? Was the virus opportunistic, attacking only when an animal's immune system was depleted, the way that a person without a jacket might be more susceptible to catching cold? If so, what conditions had depleted so many stars? The mystery, it turned out, had not been solved at all. It had only deepened.
In late February I conducted my own amateur investigation of the intertidal zone with Melissa Redfield, a member of Raimondi's research team. During low tide, Redfield and I walked ten minutes east of the Long Marine Laboratory to Natural Bridges State Beach. The reefs there are composed of Santa Cruz mudstone, a brown sedimentary rock, slippery with algae, and soft enough that sea urchins can burrow cubbies into it. A mother and her two children were spying beneath ledges and in wells for marine life. They yelled every time they spotted a hermit crab, a purple sea urchin, or a sea anemone with neon-green tentacles. A family of Japanese tourists did the same. A solitary woman kneeled facing the ocean and played a plaintive song on a recorder.
I could not see any sea stars no matter how closely I searched, but Redfield began to spot them almost immediately. She called me over to a location near the edge of the tide; I lay with my belly on the mudstone, craning my neck to peer beneath a rock ledge, with Redfield shining a flashlight, and still it took me a full minute to see the star, so expertly was it camouflaged. She kept finding additional stars, most of them colored violet and some purplish pink, hiding in crevices and, in one case, beneath a sea urchin. After a half hour, she had found about a dozen ochre stars. Most were the size of a quarter or smaller; the largest was the size of an adult's hand. All appeared healthy except for one of the larger stars. It was missing an arm and had a white lesion at the base of one of the remaining arms.
This has been a familiar pattern along the Pacific Coast this winter. As the Wasting has persisted, stars have disappeared almost completely in many locations. In others, stars survived a brush with the epidemic and seemed to recover, as if having developed immunity—only to be wiped out months later. Raimondi estimates that between 1 and 10 million stars have died so far. In the intertidal region alone, the mortality rate averages about 75 percent. But smaller sea stars have been observed at a number of sites in which the larger ones have vanished. "It's like a forest fire," said Rich Mooi, curator of invertebrate zoology and geology at the California Academy of Sciences. "The forest burns down and then the seedlings come." Most of these smaller stars are not newborns, however. Sea stars grow very slowly; by the time they are large enough to be observed, they are probably several years old. This means that the stars we observed at Natural Bridges were not babies but survivors.
This raises another question. Are these smaller stars actually immune to the Wasting, or are they simply too small to contract the disease? The virus may be benign in small quantities, only to become fatal once it multiplies sufficiently. If so, the seemingly healthy stars may reach a certain size, only to drop dead shortly thereafter. Or they may contract the disease as adults. We have no better idea of the stars' fate than they do. "I've never seen anything like this in my lifetime," Redfield told me. "It's hard for me to think of the big picture. I don't want to think about the big picture."
"Is it a onetime event or a harbinger of worse to come? You wonder whether there's been some big change that will irreversibly damage the ecosystem." –David Horwich
Raimondi today finds himself in the position of an investigator who has intimate knowledge of his suspect—the killer's tendencies, eccentricities, and modus operandi—who knows everything about the suspect, that is, except his true identity. Raimondi believes that the densovirus is probably the killer. But it is powerless alone; it requires accomplices. These might include warmer water, hypoxia, pollution, and ocean acidification—though not necessarily all of them at once. Then again, the entire densovirus hypothesis might be wrong. He wonders whether there might be correlation without causation. In that case the densovirus would be a secondary infection, an opportunistic predator taking advantage of an immune system that has been debilitated by some other stronger, unknown force.
It is also unknown what effect the Wasting will have on the fragile tidal ecosystems along the Pacific Coast. Sea stars eat mussels and sea urchins; might mussel beds, without the presence of this predator, extend their territory, expanding into lower depths? Might sea urchin populations surge? If so, that will have its own consequences. Urchins devour kelp, which provides nutrients and protection to a wide range of sea life. When urchins multiply too greatly in one area, kelp forests turn into kelp deserts. This leads to a phenomenon called "urchin barrens": surreal marine wastelands devoid of life apart from a sea carpet of purple-spiked urchins.
The urchin population does appear to be growing, though it is unclear whether the absence of sea stars is responsible. Even so, there is also concern that the urchins might not be as healthy as they appear: Raimondi has recently received reports of mass wasting among sea urchin populations. He does not know whether the same densovirus is responsible, but it looks familiar. "It's a lot like the early days for sea stars," he told me.
Yet Raimondi—unflappable, seasoned, sober—said he is not especially concerned. "A lot people ask me, 'Are they going to go extinct? Is there going to be a catastrophe? Is the whole ecosystem going to collapse?' The answer is no. I've seen this before, and the system recovered."
Some of the younger scientists and volunteer surveyors I met were less sanguine. They have been traumatized by observing in their own lifetime extinction events and environmental calamities that are unprecedented in the history of human civilization. The idea that the sea stars might be evidence of some decisive, more profound transformation of the marine ecology does not seem to them so far-fetched.
"Pete [Raimondi] sees it as a big experiment," said Jan Freiwald, a marine ecologist who is the director of Reef Check California, when I met him at his office at the Long Marine Laboratory. "He takes himself out of it. But we just don't know how big the effects might be. It worries me. The saddest thing is when you see the other sea stars eating one that is wasting. You think, No, don't do it!"
"It makes you feel sad," said David Horwich, a Reef Check volunteer who was one of the first divers to detect the Wasting. "Is it a onetime event or a harbinger of worse to come? You wonder whether there's been some big change that will irreversibly damage the ecosystem."
"It feels apocalyptic," said Mary Ellen Hannibal. "Whatever is going on with the sea stars has the sense of an immersive event that's not visible to the eye, that's pulling species out from underneath."
All that Raimondi can do now is monitor the juvenile stars closely, to see whether they will recover or die off like the rest. In this task, he will rely heavily on the vast network of citizen volunteers who have mobilized in response to the crisis. "We can only go to a certain number of sites," he said. "But so many people go to tide pools. That's a huge amount of data. We're getting a ton of reports from casual beachcombers in places we've never been." The problem is that the juvenile stars, which can be smaller than a pinkie fingernail, are exceedingly difficult to see. For this reason some of the most successful observers have not been marine scientists but small children.
"Parents have bad knees," said Raimondi. "They're not going to get down on the reef. But kids are super curious, they have great eyesight, and they're low to the ground." Some of the most valuable sightings have come from children as young as three years old, trailed by their parents as they scramble across the reefs. Preschoolers make excellent detectives. They are avid and indefatigable. They are deeply persistent. It is almost as if they're worried that these are the last stars they will ever see.