A Disease Turning Sea Stars to Goo Will Ruin Your Tide Pool Visit—and the Ecosystem

Scientists have pinpointed the cause of a syndrome wiping out whole populations of the saltwater creature.

(Photo: Alison Leigh Lilly/Flickr)

Nov 19, 2014· 1 MIN READ
Katharine Gammon has written for Nature, Wired, Discover, and Popular Science. A new mom, she lives in Santa Monica.

For the past 18 months, more than 20 species of sea stars (also known as starfish) have been hit by a mysterious disease that causes them to lose their limbs and slowly decompose—as if they were melting.

But scientists announced this week that they have found the probable cause of the weird, pervasive illness: a sea star virus.

It didn’t come as a surprise to Cornell biological oceanographer Ian Hewson, who wrote the paper on sea star disease, which was published in the journal Proceedings of the National Academy of Sciences.

He and a group of scientists had been working to unlock the mystery die-offs that started sweeping the West Coast in 2012.

“We had an idea that it was a virus because of some preliminary work that showed there were no cellular pathogens involved,” he said.

Called a densovirus, it has been found in sea urchins. Densoviruses are also responsible for parvo, a condition that affects dogs, and are used in pest control to kill cockroaches.

Hewson and colleagues around the country looked at 465 samples of sea stars—a relative of urchins and sand dollars—collected from current coastal populations as well as from museums.

They discovered the disease in specimens dating back to 1942 and found that healthy stars turned sick if they were put near sick stars, concluding that the disease could be transmitted through seawater. To find sea star patient zero, the researchers plan to conduct more molecular analyses to determine how the disease became so virulent so quickly. In some areas, 98 percent of sea stars have died from the virus.

A disease that wipes out a keystone predator such as the sea star can have ripple effects throughout the ecosystem.

Hewson pointed out that the populations of prey that sea stars used to eat may explode in the absence of a key predator.

“It will be a pulse of change in the short-term,” said Hewson. “But when the bivalves run out of food, their numbers will be brought into check and eventually reach an equilibrium—something that might continue for decades.”

Meanwhile, the bodies of all those oozing sea stars will likely fuel bacterial blooms in the affected coastal areas.

But it’s not all bad news.

“There are 10 million viruses in every drop of seawater,” said Hewson. Since viruses tend to affect animals that are most abundant, knocking them out can actually create an increase in biodiversity.

“Viruses can give a little breathing room to other things that aren’t as good at competing for food and space,” he noted.

Even though fewer sea stars could create space for other organisms to flourish, Hewson said that some people are thinking up ways to create virus-resistant creatures.

“Some juveniles can bear a large amount of virus in their bodies but remain asymptomatic—so that’s something to investigate in the future,” he said. Sick juveniles could be used to restock the species. The researchers also hope to understand the impact of warmer and more acidic waters on the disease’s spread.