The carnage began in 2013. The victims were the multi-armed, jewel-bright sea stars that glisten along the West Coast of North America. They suffered a gruesome decline: oozing lesions, arms twisting into odd shapes and often breaking away, bodies dissolving into a mucus-like white goo.
As vast colonies vanished, ocean floors resembled macabre battlegrounds, strewn with detached limbs and pulpy flesh. Not even those in captivity were safe. Sea stars died in public aquariums, visitors’ centers, university laboratories. By 2017, Sea Star Wasting Syndrome had spread from Alaska to Mexico, with the toll soaring from millions to more than five billion.
Among the twenty-plus species affected, the magnificent sunflower star–with twenty or more long, supple arms—was hit hardest. Fast-moving and voracious, these “lions of the sea” devour purple sea urchins — and nearly anything else in their path. Yet even they could not escape. In some areas, fewer than 10 percent survived.
Scientists scrambled to identify the cause of the epidemic. Early suspicions fell on a densovirus, but it was never conclusively proven to be the sole culprit. Some hypothesized that environmental stressors, such as warming waters or harmful algal blooms, might be accomplices. But the mystery of the fallen stars remained unsolved—until now.
After a four-year investigation, researchers from the Hakai Institute, the University of British Columbia and the University of Washington have identified the elusive assassin: strain FHCF-3 of the bacterium Vibrio pectenicida. In humans, a relative of this lethal menace causes cholera, the deadly diarrheal disease that infects thousands globally every year.
To pinpoint the serial killer, scientists injected healthy sunflower stars with contaminated water, infected tissue or coelomic fluid (sea star “blood”). Over 90 percent of exposed stars developed wasting symptoms and died within a week.
The only consistent difference between sick stars and healthy controls was the presence of Vibrio bacteria in their coelomic fluid. “When we saw the microscopic evidence,” one researcher told reporters, “we all had chills. We thought, ‘That’s it. That’s what causes wasting.’” Since Vibrio bacteria proliferate at higher temperatures, wasting may be more likely and deadlier in warmer waters.
The massive sea star die-off reshaped marine ecosystems. Without predators to keep them in check, purple sea urchins exploded in number, devastating the kelp forests that shelter countless species. But in recent years, we’ve seen a rebound of ochre sea stars, the glamorous intertidal beauties of the northern California coast. Their recovery may be due to genetic adaptations that bolster resistance to wasting syndrome. As one ecologist put it, “We’re seeing evolution happen right before our eyes.”
Evolution may not occur quickly enough to save the sunflower stars, which are “locally extinct” in some regions. With the identification of Vibrio pectenicida, scientists may be able to develop potential probiotic treatments to curb future outbreaks. As discussed in a previous post, they’ve already made progress on an alternative route to recovery.
Cutting-edge breeding programs, initiated in 2019 at the University of Washington Friday Harbor Marine Laboratories with support from the Nature Conservancy, have succeeded in spawning and raising sunflower stars in settings that mimic the natural environment. Last year the Friday Harbor team released pioneer sunflower stars into local waters, where scientists are monitoring their growth and survival rates.
These advances, the result of years of rigorous research, are giving rise to a new hope: Under a canopy of starry skies, galaxies of sea stars may once again shimmer beneath the waves.
