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CTV News
5 hours ago
- CTV News
Canadian researchers solve 12-year mystery of sea star wasting disease
Sunflower sea stars (pycnopodia helianthoides) and sea vases (ciona intestinalis) are seen in the waters in Rivers Inlet, B.C., in an undated handout photo. THE CANADIAN PRESS/Handout - Hakai Institute, Bennett Whitnell (Mandatory Credit) A team led by researchers in British Columbia has solved the mystery of a gruesome disease that has killed billions of sea stars along the Pacific coast of North America, more than a decade after the die off. Melanie Prentice, the lead author of a new study, recalls a moment of 'not really believing it' when researchers found a strain of bacteria that was abundant in diseased sea stars and absent in healthy ones. 'My initial reaction was like, 'Okay, so I've done something wrong,'' she said. Prentice said the team spent months trying to disprove their findings, ultimately confirming they had cracked the code of the disease. They found the bacterium Vibrio pectenicida is a clear cause of sea star wasting disease. '(It's) a question that researchers have been trying to answer for about 12 years, so we're beyond thrilled,' said Prentice, a research associate at the Hakai Institute and the University of B.C. department of earth, ocean and atmospheric sciences. The paper detailing the four-year research project and its findings were published online in the peer-reviewed journal Nature Ecology & Evolution on Monday. Alyssa Gehman, who helped launch the project in 2021, described the disease as 'gruesome,' causing sea stars to develop lesions, lose their arms and 'disappear into mush' about a week or two after exposure to the pathogen. It has been especially deadly for sunflower sea stars, killing about six billion of the species that can sprout 24 arms and span up to a metre. The giant sea stars are now considered functionally extinct across much of their former range off the coast of the continental United States, with losses exceeding 87 per cent in the 'northern refuges' where they still persist, the study said. The collapse has had cascading impacts, including widespread losses of ecologically, culturally and economically important kelp forests. 'I think we didn't really appreciate how important they were until we lost them,' Prentice said, describing the orange, purple or brown sunflower stars as a 'keystone' species with an outsized impact on their ecosystem. The giant sea stars are top predators, striking fear into other invertebrates. 'Almost everything that lives on the ground underwater runs away from them when they're coming,' said Gehman, a marine disease ecologist at the Hakai Institute and an adjunct professor at the University of B.C.'s Institute of Oceans and Fisheries. They keep sea urchin populations in check, in turn ensuring the health of help forests that provide habitat and food for numerous other species. The devastation of the sunflower sea stars has caused a 'total ecosystem shift,' Prentice said, transforming biodiverse kelp forests into 'urchin barrens.' The bacterium that causes sea star wasting disease had remained elusive for more than a decade since sea stars were first observed dying in large numbers in 2013. The same bacterium has been known to attack scallop larvae. Prentice said the breakthrough came after the research team switched from examining diseased tissues to focusing on the sea stars' coelomic fluid, likening it to the blood of the sea star. Earlier research had involved running the tissues through tiny membrane filters that would have excluded bacteria, which are typically larger than viruses, she explained. The Hakai Institute team started by replicating the initial experiments, but they weren't able to cause disease in healthy sea stars, she said. 'We were doing everything we could and we were just never ever able to cause disease, and so to us that suggested that the pathogen is larger than a virus.' However, after pivoting to coelomic fluid, which Prentice described as 'essentially sea water,' the researchers did trigger disease in healthy sea stars. 'That suggested that the pathogen was in that fluid, and so then we just end up working with a much cleaner, easier tissue type to investigate,' she said. From there, Prentice created a list of all the different microbial species found in wasting sea stars and compare it against the healthy stars in the lab. 'I finally got to a place where I generated these different lists and it was very evident right away that there (were) tons of different Vibrio species within our wasting sea stars and we weren't really seeing that in our healthy sea stars,' she said. Prentice said she then filtered the genetic data to look at each strain of Vibrio bacteria, which led to their eureka moment with Vibrio pectenicida. 'We just saw it in every single wasting sea star sample, and then we looked at our controls and it was just not in any of them,' she said. Prentice said other researchers had wished her 'good luck' when she joined the project, but there was skepticism over whether they would solve the mystery. It felt 'incredible' to be part of a discovery that could help make a meaningful difference in the recovery of sea stars and their ecosystems, she said. Gehman, too, said she wasn't sure the project would result in a singular answer. 'I thought it would be complicated. I thought there would be multiple things relying on other things,' she said. 'This was much clearer than I was expecting.' The discovery allows researchers to turn their efforts to deeper questions, including the possible role of warming ocean temperatures and the potential to breed sea stars in captivity to promote disease resistance and spur recovery, she said. The disease now appears to be seasonal, with outbreaks occurring in the warmer months, suggesting temperature may be a factor, said Gehman, adding she will soon conduct temperature experiments to investigate further. 'Does Vibrio pectenicida grow faster at warmer temperatures and the sea star can sort of survive at the growth rates at cooler temperatures, but when you get to warmer temperatures, they can't, is that what's happening?' The findings could help researchers understand where sea stars may struggle or survive with climate change in the future, Gehman said. Prentice said there are 'remnant' populations of sunflower stars along the B.C. coast, and its 'very possible' some could be more resistant to the wasting disease. She said finding and selectively breeding sea stars with a higher capacity to fight off the disease could produce 'superstar' sea stars for reintroduction in the wild. 'It seems like science fiction sometimes, but people are working on it,' she said. This report by Brenna Owen, The Canadian Press, was first published Aug. 4, 2025.
Globe and Mail
5 hours ago
- Globe and Mail
Breakthrough in mysterious sea star wasting disease offers hope for recovery of critically endangered creatures
Sunflower sea stars were once everywhere along the Pacific coast. Big, colourful and many-armed, they could be spotted at low tide clinging to rocks as if painted there by Vincent Van Gogh. Then came a devastating sickness that turned healthy sea stars into mounds of decaying mush. Known as sea star wasting disease, the mysterious syndrome is estimated to have killed billions of individuals since it emerged in 2013. More than 20 species have been affected, with sunflower sea stars among the hardest hit. Their numbers have plummeted by 90 per cent and the species is listed as critically endangered by the International Union for the Conservation of Nature. Now the cause of the contagion has been found: It is a bacterium – a member of the vibrio family – whose relatives include pathogens associated with seafood-borne illnesses and with cholera. The breakthrough, reported Monday in the journal Nature Ecology and Evolution, marks a turning point in the quest to understand why sea stars are dying. It may also aid efforts to help populations recover. 'The exciting thing about it being a bacteria is that it makes it possible for us to isolate and grow it,' said Alyssa Gehman, an adjunct professor at University of British Columbia and a marine disease ecologist at the Hakai Institute, whose lab spearheaded the work. And since the strain can be cultured, it also means that Dr. Gehman and her colleagues have been able to report their discovery with an unusually high degree of confidence. While the researchers employed the tools of modern molecular biology to arrive at their conclusion, their approach was essentially one developed by medical pioneers in the 19th century to pinpoint the cause of infectious disease. 'It's very clean work, very thorough,' said Blake Ushijima, a marine microbiologist at the University of North Carolina Wilmington who was not involved in the discovery. He said that while the disease cannot be removed from the environment, knowing its cause raises the possibility that captive populations of sea stars can be protected from it and then successfully reintroduced. The find also sheds light on a long-suspected connection between sea star disease and climate change. Because vibrio bacteria tend to be more active in warmer water, rising ocean temperatures along the Pacific coast may account for why the disease has become so rampant. The outcome has wreaked havoc on ocean ecosystems. Sea stars are voracious hunters. In their absence, sea urchin populations have exploded and led to severe overgrazing of kelp forests that provide crucial habitat for other species. Dr. Gehman said that when she first undertook the project in 2020 with funding from The Nature Conservancy of California among other sources, she felt the complexity of the disease would likely preclude finding a definitive cause. But she thought she could help to move the field forward. 'We didn't expect to get to the place we did,' she said. Much of the work was conducted at the United States Geological Survey Marrowstone Field Station, located near the entrance to Puget Sound. The station includes facilities where sea stars can be kept in quarantine without risk of contamination or of infection being released back into the ecosystem. It began by setting up a baseline group of specimens that were isolated long enough to be reliably disease free. These were subjected to a series of 'challenge experiments' to determine under what circumstance disease would spread. Dr. Gehman said that from the outset, she and her colleagues considered all possible causes, including marine viruses and contagious forms of cancer. An important step forward came when the researchers learned they could spread the disease by injecting a body fluid from a sick to a healthy sea star. Known as coelomic fluid, the material ceased to be infectious once it was heat treated, pointing to the presence of a live pathogen. Infection was also blocked when the fluid was passed through a filter that should have allowed viruses to pass through. It was by systematically combing through the genetic contents of the coelomic fluid that researchers eventually zeroed in on a bacterial cause. This was a Herculean task since sea stars, like many organisms, host a vast and diverse microbiome. They can also be colonized by secondary infections that are not responsible for the disease but are present alongside it. It was during a meeting in early 2024 that the team first noticed how the DNA of one particular bacterium among myriad of suspects was consistently appearing in their genetic readouts. It was called Vibrio pectenicida, a species known to attack scallop larva. Dr. Gehman and research scientist Melanie Prentice were on a Zoom call with Grace Crandall, a PhD student at the University of Washington who conducted the challenge experiments, when the researchers suddenly realized they might have hit upon the answer. 'It was a moment of eerie quiet as we were all looking at each other,' Dr. Prentice said. 'Part of me was thinking, can we have some streamers coming from the ceiling or something?' But to confirm their suspicions the team needed a diseased specimens to work with and transmit diseased fluid – not easy to find during the winter months. They quickly put out the call and heard back from a colleague who was dealing with an outbreak in his lab. 'It's about a four-hour drive plus ferry from the University of British Columbia where we were, so we just hopped in a car and drove straight there,' Dr. Gehman said. 'We arrived at 9 p.m. and sampled the stars in the dark with headlamps.' Using the sample material, the group conducted a battery of controlled tests which confirmed their initial suspicions. The results consistently pointed to Vibrio pectenicida as the single definitive cause. The bacteria is now cultured and available for further research. That includes studies across different species to look for differences in response to the disease and the potential for finding individuals with some innate resistance. Scientists also hope to trace the recent evolution of the bacteria by looking at preserved tissue samples. All of this can inform recovery strategies for bringing back the threatened sea stars. 'This discovery has been so critical and so important,' Dr. Prentice said, 'But the most exciting part about it is all the stuff that it's allowing us to do next.'
CBC
6 hours ago
- CBC
Giant sea stars are melting away — and now scientists know why
Canadian scientists say they've finally identified what is likely causing giant colourful sea stars in the Pacific Northwest to literally waste away: It's bacterium from the same family that causes cholera in humans.
