More than a decade ago, a mysterious illness killed billions of sea stars, particularly along the North American Pacific coast. The sea star wasting disease caused the stars to develop lesions, their arms to fall off and their bodies to disintegrate. Now, researchers in a recent study say they have zeroed in on the cause: a bacterium called Vibrio pectenicida.
The 2013-2014 outbreak caused mass die-offs of more than 20 species of sea stars. The illness still lingers at low levels today. Over the years, researchers have proposed several possible causes, including a virus, but none were proven to be definitive.
To find definitive proof, scientists conducted experiments between 2021 and 2024 on the sunflower sea star (Pycnopodia helianthoides), a species that’s particularly vulnerable to the wasting disease. Once ranging widely from Baja California in Mexico to Alaska in the U.S., the disease wiped it out from much of its southern range in the continental U.S. It’s now listed as critically endangered on the IUCN Red List.
For the experiments, the researchers housed both healthy looking and diseased sunflower sea stars separately in quarantined laboratory conditions. They found that even immersing the healthy sea stars in water from a diseased star’s tank made the former ill.
The researchers also created slurries of both the diseased stars’ tissues, and their coelomic fluid, essentially their “blood.” When they injected either of those into healthy stars, the latter became sick. As a control, when they heated up the slurries to kill any potential microbes in them and injected those, the healthy stars remained healthy. This confirmed there was something in the coelomic fluid of the diseased stars that was making them sick.
The researchers cultured the microbes growing in fluid and found that the diseased stars had high levels of the bacterium V. pectenicida. Exposing healthy stars to the bacterium made them ill.
“When we looked at the coelomic fluid between exposed and healthy sea stars, there was basically one thing different: Vibrio,” Alyssa Gehman, the study’s co-author and a marine disease ecologist at the Hakai Institute and the University of British Columbia (UBC) in Canada, said in a statement. “We all had chills. We thought, That’s it. We have it. That’s what causes wasting.”
Identifying the agent causing sea star deaths is important because sea stars are critical predators in their habitats. Sunflower sea stars, for example, keep kelp-eating sea urchins in check. After the stars’ demise along the Pacific Northeast coast, sea urchin populations boomed, which then overgrazed and led to a loss of kelp forests.
“Understanding what led to the loss of the sunflower sea star is a key step in recovering this species and all the benefits that kelp forest ecosystems provide,” Jono Wilson, research collaborator from The Nature Conservancy’s California chapter, said in the statement.
Banner image: Sunflower sea star in Knight Inlet, Canada. Image courtesy of Grant Callegari/Hakai Institute.
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