The Great Sea Star Mystery

Crabs, kelp, and sea stars live in the waters outside Jason Hodin’s laboratory. They’re like his co-workers. Hodin studies these species. He’s a marine biologist. He works at the University of Washington in Washington State. But one kind of sea star started disappearing. Hodin took the loss of his co-worker personally.

Sunflower sea stars once lived all along the Pacific coast (see Sunflower Sea Star Range). But they began to get sick starting in 2013. They died in large numbers. People along the coast stopped seeing them on beaches.

“They were everywhere, and then suddenly they were nowhere,” says Hodin. Scientists were puzzled. What could be killing sunflower stars so quickly? Could it be stopped? If not, what would happen to the rest of the ecosystem?

Sunflower sea stars are star shaped. They move over the seafloor like vacuums. Their many arms help them move quickly. They catch sea urchins, small crabs, snails, and other prey.

“They’re pretty much the top dog on the seafloor,” says Hodin. These hunters live in kelp forests. They’re an important part of a forest’s food web (see Kelp Forest Food Web).

Kelp forests provide food and homes to many creatures. One example is sea urchins. They eat kelp. And sunflower stars eat the urchins. This keeps the kelp forest in balance.

“When we lost all of these sunflower stars, we ended up with huge populations of urchins,” says Alyssa Gehman. She studies ocean ecosystems. She works at the Hakai Institute. It’s in British Columbia, Canada. The growing numbers of urchins quickly ate the remaining kelp forests. “We knew sunflower sea stars ate urchins,” says Gehman. “We didn’t know how much sea stars mattered until they nearly all died.”

No one knew what was making the sea stars sick, but two things were clear. The illness easily spread from critter to critter. And it was deadly. The muscles of infected sea stars waste away, leaving them gooey and deflated. “They essentially melt,” says Hodin.

Scientists named the mystery illness “sea star wasting disease.” It affected many different types of sea stars, but sunflower stars have been hit the worst. Scientists estimate that more than 5 billion of the animals have died. With so few sea stars remaining, the species has nearly died out.

No one knew what was making the sea stars sick. But two things were clear. The illness easily spread from animal to animal. And it was deadly. The muscles of infected sea stars wasted away. That left them gooey and deflated. “They essentially melt,” says Hodin.

Scientists named the mystery illness “sea star wasting disease.” It harmed many types of sea stars. But sunflower stars have been hit the worst. Scientists think more than 5 billion of the animals have died. The species has nearly vanished.

Scientists raced to identify what caused the disease. When they examined the bodies of dead sea stars, they couldn’t find the culprit. They would need to study living sea stars in the lab. But there was another problem: No one knew how to raise the sea stars in captivity.

Hodin knew that to solve the mystery, he had to find a way to raise sunflower sea stars. In 2019, he and his team dove into the waters around their lab. They found 35 adult sea stars that had survived the outbreak. They brought them back to the lab and tried to breed them.

Scientists raced to find what caused the disease. They looked at the bodies of dead sea stars. But they couldn’t find the problem. They would need to study living sea stars in the lab. But no one knew how to raise the sea stars in tanks.

Hodin knew there was only one way to solve the mystery. He had to find a way to raise sunflower sea stars. He and his team dove into the waters around their lab in 2019. They found 35 adult sea stars. They’d survived the disease. The scientists brought them back to the lab. They tried to breed the animals.

The sea stars had poppy seed-sized babies. Most of them died at first. Hodin and his team didn’t give up. They spent months experimenting. They used different tank setups and foods with each new batch of babies. Finally, they found a system that worked! They raised more than 200 sunflower sea stars over the next few years.

Meanwhile, Gehman had been hunting for the cause of the wasting disease. Then some of the sunflower stars in Hodin’s lab got sick. Gehman’s team rushed to study them. The scientists collected samples. They compared the sick and healthy sea stars. They found a type of bacteria in the sick sea stars. It wasn’t found in healthy stars. They exposed healthy stars to the bacteria. Those stars got sick. “We all had chills,” says Gehman. “We thought, ‘That’s it. That’s what causes wasting.’”

Gehman’s team announced they’d found the killer this past August. Hodin and other scientists are still raising healthy sunflower sea stars. They’re releasing some back into the wild. Now scientists know what causes the wasting disease. They can work on finding ways to stop or treat it. “It makes me more hopeful that we might actually be able to do something for sunflower sea stars,” says Gehman.