The tide pools near Botanical Beach on Vancouver Island used to pulse with life—brilliant purple and orange sea stars clinging to rocks, their arms reaching into swirling waters. When I visited there in 2014, the scene was dramatically different. The stars were literally melting before our eyes, their tissue dissolving into the water, leaving behind only ghostly white fragments.
“It was like walking through a graveyard,” marine biologist Dr. Julia Sanders told me, her voice still catching when describing that period. “One week they’d be healthy, the next they’d be falling apart. Nothing in my career prepared me for that kind of mass mortality event.”
What Sanders and other scientists were witnessing was sea star wasting disease (SSWD), one of the largest marine wildlife die-offs ever recorded. The mysterious condition decimated more than 20 species of sea stars along North America’s Pacific coast, from Alaska to Mexico. Some areas lost more than 90% of their sea star populations in just weeks.
Now, nearly a decade later, Canadian researchers have made a groundbreaking discovery that may finally explain what triggered this ecological disaster.
A team from the University of British Columbia has identified that sea star associated densovirus (SSaDV)—a virus previously suspected in the die-offs—works alongside bacterial communities to create a “one-two punch” that overwhelms sea star immune systems.
“This isn’t just about identifying a virus,” explains Dr. Emma Chen, lead author of the study published in Science Advances. “Our research shows that ecological collapse often comes from complex interactions. The virus weakens the sea stars, but it’s the secondary bacterial infection that delivers the fatal blow.”
Walking along the same beaches today, I notice small signs of recovery. Juvenile ochre stars cling to sheltered rock crevices, their tiny arms barely the size of my pinky finger. But the ecosystem remains fundamentally altered.
Sea stars are keystone predators—meaning they have outsized impacts on their environments relative to their abundance. They control mussel populations that would otherwise dominate the intertidal zone. Without stars, these areas transform.
Indigenous communities along the coast have been noting these changes for years. Tribal ecological knowledge keeper Mark Williams from the Tsimshian Nation described to me how the absence of sea stars has cascaded through traditional harvesting areas.
“Our people have always seen the stars as guardians of the shore,” Williams said during a community monitoring project I attended last year. “When they disappeared, everything changed—more mussels, fewer chitons, different seaweeds. The whole system is speaking to us.”
The Canadian discovery hinges on the relationship between virus and bacteria. Using advanced genetic sequencing and tracking viral load in healthy versus diseased sea stars, researchers identified how bacterial communities changed dramatically in infected individuals.
“We found that as viral loads increased, the diversity of gut bacteria plummeted, while potentially harmful bacterial groups proliferated,” Chen explained. “It creates a perfect storm for tissue degradation.”
The Health Canada Ocean Protection Division has been monitoring the situation, noting that while the disease doesn’t affect humans directly, it serves as an indicator of marine ecosystem health.
What makes this research particularly significant is how it might help predict and potentially mitigate future marine disease outbreaks. Climate change has warmed coastal waters along British Columbia by nearly 1°C since the 1950s, according to Environment and Climate Change Canada data. This warming creates additional stress on marine organisms, potentially making them more susceptible to infections.
“Understanding the trigger mechanisms for these kinds of mass mortality events is crucial as our oceans continue warming,” says marine ecologist Dr. Sarah Paulson from the Pacific Marine Analysis and Research Association, who wasn’t involved in the study. “This Canadian research provides a framework for investigating other marine disease outbreaks.”
Recovery efforts now focus on maintaining habitat quality and monitoring remnant populations. In some areas, sea stars are making modest comebacks, though nowhere near their previous numbers.
The research also highlights the value of long-term ecological monitoring. The Hakai Institute, a scientific research organization on British Columbia’s Central Coast, has been tracking sea star populations since before the outbreak, providing crucial baseline data.
“Without knowing what was there before, we can’t fully understand what we’ve lost,” explains Hakai researcher Dr. Lin Zhao. “And without understanding the mechanisms behind these diseases, we can’t prepare for future outbreaks.”
For coastal communities dependent on healthy marine ecosystems, the stakes couldn’t be higher. Fishing guide Ellie Thompson showed me how the changes have rippled through her small business near Tofino.
“Tourists used to come specifically to see the incredible diversity in our tide pools,” she told me as we picked our way across slippery rocks. “The stars were always the highlight. Now I’m teaching about resilience and recovery instead.”
As I watch a small group of purple sea stars in a protected cove—survivors or perhaps descendants of survivors—I’m struck by both hope and concern. These animals have persisted through an ecological catastrophe, but the seas they inhabit continue to warm and acidify.
The Canadian research breakthrough doesn’t just solve a scientific mystery; it reminds us that ecological health often hangs in a delicate balance. As oceans warm and marine diseases proliferate globally, understanding these complex interactions becomes increasingly urgent—not just for sea stars, but for all of us who depend on healthy seas.
