On a dark, drizzling January evening in 2014, Alyssa Gehman headed out to the Olympic Peninsula in Washington state to catch the midnight tide. There, in the bitter winter darkness, she caught a sea star in the beam of her headlamp. It wasn’t looking so good.
Gehman, then a graduate student earning a doctorate in disease ecology, had heard about a mysterious illness sweeping through the Pacific coast’s iconic invertebrates. But this was the first time she had seen sea star wasting disease for herself: white lesions splattered across an ochre sea star. A single knobby plum arm abandoned on the rocks.
Gehman experienced a deep sense of loss. Sea stars were “one of the first animals I fell in love with,” said Gehman, now a marine disease ecologist at the Hakai Institute in British Columbia. “It’s a part of how I chose to be a scientist.”
Since sea star wasting disease caught widespread attention in 2013, it’s reshaped Pacific ecosystems, killing billions of the invertebrates along the coast. Among the casualties are the region’s rich kelp forests, which contribute upwards of $52 billion to the global economy and sequester nearly a megaton of carbon from the atmosphere every year.
Conservationists and researchers have struggled to tackle the illness, in part because, for many years, no one was sure of the cause. Now, more than a decade later, Gehman is part of a team of scientists that believe they’ve found the answer. According to a recent paper published in Nature, the bacterium Vibrio pectenicida is the culprit.
After 12 years of scientific dead ends, “it’s just shocking that we took that long to find a Vibrio,” said Gehman. Others, though, are less convinced.
The long search is a familiar story. Since the 1980s, researchers have recorded several major epidemics in marine invertebrates. They often take years, if not decades, to identify the cause—and even then, questions remain.
The slow pace comes at a cost. “We lost 5 billion sunflower sea stars, at least,” said Gehman. Without knowing what is behind a disease, “there’s just a bunch of things that one cannot do when you don’t know what it is.”
Divers were among the first to notice that something was wrong. In September 2013, marine photographer Neil McDaniel reported that sea stars north of Vancouver were diseased. His images show sea stars that look deflated. Their arms had fallen off; their internal organs hung outside their bodies. Some stars collapsed to the sea floor, dissolved into piles of goo.
Sea star wasting disease is “a gruesome thing, so it was evident immediately that something weird was going on,” said Melanie Prentice, an evolutionary ecologist at the Hakai Institute and the University of British Columbia. Prentice is a co-author on Gehman’s recent paper.
Later research suggested that the first cases appeared along the Washington coast. From there, it spread south to Baja California, and north into Canada and Alaska. It even killed sea stars on display in the Seattle and Vancouver aquariums, which pumped in water directly from the ocean. Some of these stars had been on display for more than forty years.
The condition’s spread suggested it was caused by an infectious agent rather than a pollutant or environment stressor. As early as 2014, scientists had discovered signs of sea star wasting disease in at least twenty species across the Pacific coast. Sunflower sea stars—large predators that feed on sea urchins—were particularly vulnerable, losing nearly 90 percent of their pre-pandemic population in northern waters. The species went virtually extinct elsewhere.
With sunflower sea stars suddenly all but gone from their home range, sea urchin numbers exploded, and the hungry urchin hordes descended upon kelp forests. One study in British Columbia found that sea star wasting disease led to a 311 percent increase in the population of medium-sized sea urchins and a 30 percent decrease in kelp density over two years.
The scale and suddenness of the devastation shocked ecologists and the public alike. Where had sea star wasting disease come from? Could scientists stop it?
Lacking answers, a coalition of about two dozen scientists jumped into action. “It was a very frantic effort,” recalled Ian Hewson, a marine scientist at Cornell University. “There was a lot of pressure to identify something that was causing it.”
It would prove to be an uphill battle.
New diseases pop up all the time. Scientists are generally pretty good at sussing out the cause of illness in people. For instance, it took less than a month for the World Health Organization to get a genetic sequence of SARS-CoV-2 after the first cases appeared in Wuhan, China.
But researchers tend to move more slowly when it comes to marine epidemics, even when those illnesses affect commerce. It took fifteen years to identify the bacteria behind abalone withering syndrome, which—along with overfishing—has critically threatened several species of commercially fished sea snails on the West Coast. And researchers have yet to identify the cause of an illness affecting Atlantic lobsters that first appeared in the 1980s.
That’s partly because scientists know relatively little about what makes marine life sick. In fact, the word “disease” and “parasite” hardly appeared in marine biology textbooks before the 2000s, said Kevin Lafferty, a disease ecologist at the US Geological Survey in Santa Barbara, California.
“Invertebrate pathology is in its infancy,” said Harilaos Lessios, a marine biologist at the Smithsonian Tropical Research Institute in Balboa, Panama. Trying to work out the cause of these illnesses, he said, is a bit like “trying to determine the causes of cholera in the 1800s.”
More to Explore
Weird and Wondrous Sea Cucumbers
This is a problem for scientists and conservationists. Knowing what causes a disease is often the first step for mitigation. For instance, in the Florida Keys, the discovery that a bacterium found in human wastewater was behind white pox disease in elkhorn coral led to sewage system upgrades.
But researchers working on sea star wasting disease simply didn’t have much to work from. Microbes in marine invertebrates like sea stars are “desperately undersampled,” said Hewson.
When sea star wasting disease appeared in 2013, Hewson’s lab took the lead on finding the microbe behind the epidemic.
For a moment, it seemed like his team had found it: They identified an unusual concentration of densovirus on most—but not all—sick stars. Injecting densovirus from these stars into healthy stars made them sick, a finding his team published in a 2014 paper. It seemed that the mystery was solved.
Then, Hewson recalled, “that whole story fell apart very rapidly.”
There’s another reason why it takes so long for researchers to find answers when it comes to marine epidemics: Few people are working on these questions. Disease was such an afterthought in ecology, said Lafferty, that “in the ’80s, I would show up at these meetings to talk about marine diseases, and they’d put me in the miscellaneous section.”
In 1983, Lessios witnessed a mass die-off in sea urchins in the Caribbean that wreaked havoc on the local ecosystem. The cause of the epidemic has never been identified, though scientists have since identified pathogens behind a more recent sea urchin epidemic in the region.
“If humans die, people get upset and they finance research,” said Lessios. “When sea urchins die, even if they’re important for the ecosystem, it’s hard to convince anybody to give you money.”
Sea star wasting disease is a rare example of a fast and coordinated response to a marine epidemic. Around 2013, Hewson was part of an email chain of around twenty researchers working on the problem. But even then, Hewson and his team were the only people on the project trying to discover the instigating pathogen.
After Hewson thought his team had found the virus in 2014, something peculiar happened. Sea stars they injected with densovirus failed to get sick for two years’ worth of experiments. Eventually, Hewson was forced to conclude that they’d misinterpreted the data and, starting in 2018, the team refuted most of their findings. For the next few years, Hewson considered alternatives to his densovirus theory. Maybe sea star wasting disease was caused by algae? Heat waves? Ammonium? Nothing seemed to add up.
In 2021, Hewson shifted his focus on other projects. “I got so frustrated, honestly, of trying to find a cause,” he said. Eventually, he “came to the conclusion that it wasn’t actually a pathogenic disease at all.”
In the end, the cause of sea star wasting disease wasn’t discovered in a lab, but in a meeting.
Gehman managed to secure funding to further the search in 2021, which is how in January 2024, she found herself comparing data on microbes with Prentice, the evolutionary ecologist. Both healthy and sick sea stars carried a ton of Vibrio bacteria—which was expected, since the genus is found all over the ocean. But Gehman suggested breaking down the Vibrio data by species.
There, in the sick table, was the odd man out: Vibrio pectenicida.
“There was a moment of silence,” Prentice recalled. “It was just kind of a bizarre moment of being like, it can’t be this obvious.”
Later experiments appeared to confirm what Prentice’s genetic data suggested. Sunflower stars injected with a strain of V. pectenicida developed sea star wasting disease symptoms, while those injected with dead bacteria stayed healthy. Field testing revealed that the bacteria was present in sick sea stars and had also been around during a 2016 outbreak in Alaska.
When Gehman told a colleague about Vibrio, they facepalmed. “The fact that at the end of all this, like twelve years of research, we’re like, ‘actually, it was a Vibrio!’ I mean, it’s both surprising and totally not surprising.”
But not everyone is on board. When Hewson heard that Gehman’s lab were going with Vibrio as the causative agent of sea star wasting disease, “I rolled my eyes,” he said.
Weekly Newsletter
As Hewson pointed out: Many bacteria can make animals sick when they end up in places they don’t belong. It’s not clear to him whether the symptoms reported by Gehman—twisting limbs and lost arms—are a sign of sea star wasting disease, or simply a reaction to having Vibrio injected into what is effectively a sea star’s blood. “I think this is a stress response,” Hewson told Undark. “When they’re not happy, they lose their arms.”
Craig Nelson, a microbial oceanographer at the University of Hawai‘i at Manoa, agreed: “Ultimately I think the work cannot really demonstrate that this bacterium (Vibrio pectenicida) causes this disease,” he wrote in an email to Undark. “Basically any microbe can kill you if injected in high concentrations directly into your body.”
But Gehman defended her team’s work. “Just because other things might also cause disease of some kind,” Gehman wrote in an email to Undark, “does not mean that Vibrio pectenicida is not a causative agent” of sea star wasting disease. And during her team’s experiments, she said, the lab injected sea stars with fluids from healthy sea stars, which contain other bacteria. Only sea stars injected with Vibrio pectenicida, or with material from sick sea stars, showed signs of disease. And other researchers in the field say the work is solid. Vibrio pectenicida is “definitely involved,” said Lessios.
Regardless, it’s clear that the study has put sea star wasting disease—and marine epidemics more generally—briefly on the map. Along with mass media attention, Gehman has heard from conservationists and scientists who hope to build on their findings.
Discoveries like this one might help speed up the timeline for finding new marine pathogens in the future, said Gehman: “I hope we learn something from what I just did, and that we can make it a little faster.”
This article was originally published on Undark. Read the original article.
Support JSTOR Daily! Join our membership program on Patreon today.
