In the cold waters off Alaska, scientists have discovered a warning sign that could help save sea stars before they die by the billions. University of Vermont researchers have identified early immune biomarkers in sunflower sea stars—markers that appear long before the gruesome melting begins. The breakthrough, published in the Proceedings of the Royal Society B, represents the closest look researchers have ever had at how sea stars respond to the wasting disease that has devastated Pacific populations since 2013.
Lead author Andrew McCracken, a doctoral student in biology at UVM, describes sea star wasting disease as both sad and gruesome. "The starfish melt and literally walk away from their limbs," he says. "I have seen them pull themselves apart." The disease affects more than a dozen species, but none have suffered as severely as the sunflower sea star—giants that once dominated Pacific waters from Mexico to Alaska but now exist nowhere south of Washington state.
For over a decade, scientists struggled to understand the enemy. Only recently did an international team including McCracken identify a bacterial culprit: Vibrio pectenicida, the first driver pinpointed in more than ten years of hunting. McCracken's advisor, Melissa Pespeni, had long suspected the sea star microbiome held answers. Her previous research found shifts in the microbiome before visible wasting appeared—and she was right.
In 2016, a postdoctoral researcher in Pespeni's lab collected tissue samples from living sea stars in Alaska, beyond reported outbreak zones. Diver teams gathered samples from both healthy populations and those experiencing symptoms. Using this tissue, McCracken decoded which genes activated in response to exposure. The results revealed immune responses and microbiome shifts in sunflower sea stars before lesions or other physical signs emerged. The team even detected early changes in the sea stars' catch-collagen system—the mechanism that lets them tighten their grip on rocks and stiffen their bodies. When that system fails, sea stars lose rigidity, develop lesions, and ultimately disintegrate.
"We found some markers showing that early on, before you even see lesions, before they are losing arms, we are seeing differences in how they are regulating those systems," McCracken explains. For Pespeni, the real power lies in integrating both the host's response and which microbes are present and in what abundance—a combined approach that brings the mechanism into sharper focus than ever before.
The implications are significant. By understanding how the disease progresses and identifying which microbes play roles, scientists may uncover resistant phenotypes—individual sea stars or species with natural defenses worth studying. "If we can hone in on those early interactions more, I think we can discover more about the mechanism itself," McCracken says. "We are in the early stages of figuring out how this works, which we need to know to be able to do anything about it."
Sunflower sea stars are more than ecological curiosities. As one of the primary predators of sea urchins, they help maintain balance in kelp forest ecosystems. Without them, sea urchin populations can explode, devouring kelp forests that countless other species depend on. The work happening in Vermont labs today—decoding the earliest whispers of disease—may give these vanished giants a chance to return to their homes along the Pacific coast.