August 5, 2025 - After a decade of watching a mysterious plague turn sunflower sea stars into formless goo, Canadian scientists have identified the killer: a bacterium known as Vibrio Pectinicida. The discovery, published in the journal Nature Ecology and Evolution, marks a critical first step toward reversing the catastrophic decline of this keystone species and restoring the vital ecosystems that depend on it.
The identified pathogen belongs to the same bacterial family that causes cholera in humans.
An Underwater Epidemic
The crisis began in 2013, when Sea Star Wasting Disease triggered a mass die-off along the west coast of North America, from Alaska to Baja California. The primary victim was the sunflower sea star, a vibrant, 24-armed predator.
The disease's progression is gruesome. Infected stars develop twisted arms that eventually detach and appear to "walk away from their bodies." Lesions form soon after, and the creatures quickly dissolve and die. "When it first happened, it was just fields and fields of puddles of dying sea star goo,"
The ecological toll has been immense. The paper estimates that over 87% of sunflower sea stars in the northern part of their range have been killed, with some estimates putting the total number of deaths at 5.7 billion. In their southern habitats, the species is now considered functionally extinct.
For years, the cause of the disease remained elusive as multiple theories were disproven. To solve the mystery, the research team conducted a series of painstaking lab experiments. "We take body fluid or tissue from a sick star and then we put that experimentally into other sea stars that we know are healthy," explained a researcher.
This method proved highly effective, transmitting the disease to healthy stars with 92% efficiency and causing death within 20 days. By carefully isolating variables through these repeated exposures, the scientists were able to pinpoint Vib-rio pecti-nicida as the most likely causative agent.
The disappearance of the sunflower sea star has had a devastating ripple effect on the marine environment. As a primary predator of sea urchins, their absence caused urchin populations to explode. These unchecked urchins, which are described as "the goats of the ocean," have since mowed down vast underwater kelp forests.
The loss of kelp forests has far-reaching implications. These critical habitats support biodiversity, provide nursery grounds for fish, drive tourism, and act as natural defenses that protect coastlines from erosion and storm surges intensified by climate change.
For researchers, saving the sea star is about more than a single species. when we're talking about sea star wasting disease, we're not just talking about the sea star species... but entire marine ecosystems that have collapsed because of this epidemic. With the killer now identified, the path toward reintroducing sunflower sea stars and rebuilding these resilient ecosystems is finally in sight. As Prentice puts it, a healthy kelp forest is "definitely our ally in the climate crisis."