Scientists claim to have finally solved the mystery behind the death of over 5 billion sea stars on the Pacific coast of North America, a phenomenon triggered by an epidemic that has been ongoing for over a decade.
The sea stars, commonly possessing five arms although some species can have up to 24, display a wide variety of colors, from a solid orange to tapestries of orange, purple, brown, and green.
Since 2013, a mysterious wasting disease in the sea stars caused the massive death of these animals along the coast, from Mexico to Alaska.
The epidemic has devastated over 20 species and unfortunately continues to this day. The most affected species has been the sunflower sea star, which lost approximately 90% of its population in the first five years of the outbreak.
“It’s truly quite horrifying,” stated Alyssa Gehman, a marine disease ecologist at the Hakai Institute in British Columbia, Canada, who helped identify the cause. She described that healthy sea stars have “swollen arms that extend straight out,” but the wasting disease causes them lesions and “then their arms really just fall off.”
Identifying the Culprit and Research Challenges
The culprit behind this mortality are bacteria that have also infected shellfish, according to a study recently published in the journal Nature Ecology and Evolution.
Rebecca Vega Thurber, a marine microbiologist at the University of California-Santa Barbara, who did not participate in the study, pointed out that the findings “address a long-standing question about a very serious disease in the ocean.”
Identifying the cause of the disease was a process that took over a decade and was filled with false leads and setbacks.
Initial investigations suggested a virus could be responsible. However, Melanie Prentice, co-author of the new study and a member of the Hakai Institute, explained that the densovirus that the scientists initially focused on turned out to be a normal resident in healthy sea stars and was unrelated to the disease.
Furthermore, other attempts to find the true culprit failed because the researchers studied tissues of already dead sea stars, which no longer contained the bodily fluid surrounding the organs. However, the latest study included a detailed analysis of this fluid, called coelomic fluid, where the bacteria Vibrio pectenicida were finally discovered.
Blake Ushijima, a microbiologist at the University of North Carolina, Wilmington, who was not part of the research, commented: “It’s incredibly challenging to trace the source of so many environmental diseases, especially underwater.” He said that this team’s detective work was “truly clever and meaningful.”
A Future of Hope for Sea Stars
Now that scientists know the cause, they have a better chance to intervene and help the sea stars.
Prentice stated that scientists could now assess which of the remaining sea stars are healthy and consider whether to relocate or breed them in captivity to then transplant them to areas that have lost almost their entire sunflower sea star population.
Researchers can also investigate whether some populations have developed natural immunity and if treatments like probiotics can help boost immunity to the disease.
This recovery work is not only crucial for the sea stars but for the entirety of the Pacific ecosystems. The researchers explain that healthy sea stars act as predators of sea urchins, keeping their population in check.
Gehman explained that sunflower sea stars “look somewhat innocuous when you see them, but they eat just about everything living on the ocean floor.” She described them as “voracious eaters.”
With a significantly reduced sea star population, sea urchins—their main food source—experienced explosive population growth. In turn, these urchins devoured about 95% of kelp forests in northern California in just a decade.
These kelp forests are vital as they provide food and habitat for a wide variety of animals, including fish, sea otters, and seals.
The researchers hope that these new findings will allow them to restore sea star populations and, in turn, enable the kelp forests, which Thurber calls “the tropical rainforests of the ocean,” to regrow.
