After a decade of death, Canadian scientists say they've found the sea star killer

Scientists say they have found the cause behind the disease that turns vibrant, 24-armed sea stars into puddles of goo.

Melanie Prentice, a research scientist at the Hakai Institute, is part of a team that has spent years investigating the cause of this disease. Their research was published on Monday in the journal Nature Ecology and Evolution.

"The agent is a bacteria. It's called Vibrio pectinicida," Prentice told CBC News.

After a decade of these creatures being pushed to the brink of extinction, experts say this is the first step in a road to recovery, not just for this species, but for a critical support in humanity's defence against climate change. 

Twisted arms that walk away 

The most affected species are sunflower sea stars, which once boasted a range along the west coast of North America, from Baja California to Alaska.

Then, in 2013, a mass die-off occurred from sea star wasting disease.

And it's a gruesome end.

"Their arms kind of twist back on themselves, so they get kind of into puzzle pieces," said Alyssa Gehman, a marine disease ecologist who is also part of the Hakai Institute research team.

They then tend to lose their arms, and then, "their arms will sort of walk away from their bodies." 

Soon after, Gehman says that lesions form and the sea stars dissolve and die.

The paper estimates that more than 87 per cent of sunflower sea stars in northern parts of the west coast have been killed. In the southern habitat ranges, the species is considered functionally extinct.

"When it first happened, it was just fields and fields of puddles of dying sea star goo," said Sara Hamilton, science co-ordinator for the Oregon Kelp Alliance. Hamilton was not involved in the research.

"It was like something out of a horror movie." 

The hunt for the star killer 

Multiple theories identifying the cause either didn't pan out or were disproven.

What the team did in this case was take healthy sea stars into the lab and expose them to infection. They did this over several years to try and isolate the cause.

Gehman explained the process: "We take body fluid or tissue from a sick star and then we put that experimentally into other sea stars that we know are healthy."

The paper's result was that 92 per cent of these exposures worked in transmitting the disease to the healthy star — killing it within 20 days.

These experiments also revealed that Vibrio pectinicida was the most likely culprit.

Experts are impressed with the paper's diligence and effort.

"They didn't just stop when they found one level of evidence — they went and found a second level of evidence and a third level of evidence," said Hamilton, from Oregon Kelp Alliance.

Amanda Bates, ocean conservation professor at the University of Victoria, also said "there's a pathway — essentially that you isolate disease agents and link them to being a cause of an outbreak — and this research team followed those processes perfectly."

Hope for recovery

Knowing the cause provides hope for restoration efforts, experts say.

"Now we can go out and actually do tests and see the actual prevalence of this pathogen in the field," said Gehman.

Furthermore, any captive breeding programs that are trying to restore sea star populations can now screen and test those populations before putting them back into a risky environment. 

Hamilton agrees.

"That's one of the things we're most worried about with some of these recovery efforts," she said.

"If we do captive breeding and outplant, we certainly don't want to introduce … a new outbreak of the disease."

The lost decade 

Bates, who has seen this disease as far back as 2009, is cautious about the rush to recovery.

"While we know disease impacts us as humans, I think we often forget that it impacts wildlife," she told CBC News.

"We're a decade on since that really big mass mortality event, and we still don't have pycnopodia [sunflower sea stars] recovering in many places." 

Hamilton said the reintroduction of sunflower sea stars will be valuable because of what their absence has meant for ecosystems. Sea urchin populations have gone up — which also means kelp forests have been decimated.

"Urchins are kind of like the goats of the ocean," she said. "They'll eat anything, they just mow things down." 

Restoring the sea star means kelp forests might once again thrive. This will likely mean improvements to biodiversity, food, tourism as well as serve as coastline defences against erosion and storms supercharged by climate change. 

"It's definitely our ally in the climate crisis," Prentice said.

"I think when we're talking about sea star wasting disease, we're not just talking about the sea star species — which we love in their own right — but entire marine ecosystems that have collapsed because of this epidemic."