Billions of Starfish Have Died in a Decade-Long Epidemic. Scientists Finally Know Why

A mysterious disease has killed billions of sea stars along the Pacific coast of North America over the past decade. Now, scientists have identified the cause — a previously unknown bacterium that has wreaked havoc on marine ecosystems. The discovery comes after more than ten years of research, with many dead ends and false leads along the way.

Baby sunflower sea stars on display at Shedd Aquarium

A Gruesome Disease

Starting in 2013, a mysterious illness known as sea star wasting disease began spreading rapidly from Mexico to Alaska. The disease is characterized by lesions, disintegration of the body, and the loss of arms, often leading to the death of the affected sea star within days or weeks. The most severely impacted species was the sunflower sea star, which experienced a 90% population decline in the first five years of the outbreak.

"It's really quite gruesome," said Alyssa Gehman, a marine disease ecologist at the Hakai Institute in British Columbia, Canada, who helped identify the cause. Healthy sea stars have "puffy arms sticking straight out," she said, but the disease causes them to grow lesions and "then their arms actually fall off."

The Culprit: A Previously Unknown Bacterium

The study, published in the journal Nature Ecology and Evolution, found that the real culprit behind the disease is a bacterium called Vibrio pectenicida. This bacterium has also infected shellfish, indicating a broader environmental impact.

"It's incredibly difficult to trace the source of so many environmental diseases, especially underwater," said Blake Ushijima, a microbiologist at the University of North Carolina, Wilmington, who was not involved in the study. He praised the research team's "really smart and significant" detective work.

The Impact on Ecosystems

Sea stars play a critical role in marine ecosystems. They are voracious eaters and help control the populations of sea urchins, which, in turn, feed on kelp forests. With the decline of sea stars, sea urchin populations have exploded, leading to the destruction of nearly 95% of kelp forests in Northern California within a decade.

"They're voracious eaters," said Gehman. "They look sort of innocent when you see them, but they eat almost everything that lives on the bottom of the ocean."

A New Path Forward

Now that scientists have identified the cause of the disease, they can take steps to help sea star populations recover. The International Union for Conservation of Nature has listed the sunflower sea star as critically endangered. Scientists are now considering strategies such as relocating healthy sea stars, breeding them in captivity, and transplanting them to areas that have lost most of their population.

The study also highlights the link between rising seawater temperatures and the spread of Vibrio bacteria. Researchers are now looking into whether some populations have natural immunity and whether probiotics or other treatments could help boost immunity to the disease.

The Road Ahead

Restoring sea star populations is not only important for these creatures but for the entire Pacific ecosystem. Kelp forests, which are often referred to as the "rainforests of the ocean," provide food and habitat for a wide variety of marine life, including fish, sea otters, and seals.

Scientists hope the new findings will allow them to restore sea star populations and regrow the kelp forests that are vital to the health of the ocean. As Rebecca Vega Thurber, a marine microbiologist at the University of California, Santa Barbara, said, "The findings solve a long-standing question about a very serious disease in the ocean."