‘Disease detectives’ discover cause of sea star wasting disease that wiped out billions of sea stars

Researchers have identified the cause of the wasting disease that has killed billions of sea stars from Mexico to Alaska since 2013: a strain of the Vibrio pectenicida bacteria.

The strain, named FHCF-3, is detailed in a new paper published today in Nature Ecology & Evolution by scientists from UBC, the Hakai Institute and the University of Washington.

“Wasting disease is considered the largest ever marine epidemic in the wild, but the definitive cause has remained elusive – until now. Now that we’ve identified the disease-causing agent, we can start looking at how to mitigate the impacts of this epidemic,” said first author Dr. Melanie Prentice, a research associate at UBC’s department of earth, ocean and atmospheric sciences (EOAS) and the Hakai Institute.

The Vibrio genus of bacteria has infected coral and shellfish as well as humans—Vibrio cholerae is the pathogen that causes cholera.

With other Vibrio species known to proliferate in warm water, the race is on to understand the link between the disease and warming ocean temperatures due to climate change, Dr. Prentice added. “We see the disease occurring earlier and more rapidly in warmer waters. Sea stars may already be impacted by climate change, so introducing a pathogen that does well in the same circumstances could be a double whammy for some species.”

The disease begins with lesions and ultimately kills sea stars by “melting” their tissues, a process that takes about two weeks after exposure. Afflicted animals become contorted and lose their arms. But identifying the disease in afflicted sea stars was difficult, as sea stars can respond to other stressors, such as changes in temperature, with similar visual signals of contortion and loss of arms.

Over four years, the international research team investigated sunflower sea stars, which have lost over 90 per cent of their population due to wasting disease. The team compared healthy sea stars with those exposed to the disease through contaminated water, infected tissue or coelomic fluid—sea star “blood.”

“When we looked at the coelomic fluid of exposed and healthy sea stars, there was just one thing different: Vibrio,” said senior author Dr. Alyssa Gehman, an adjunct professor at UBC’s Institute for the Oceans and Fisheries and a marine disease ecologist at the Hakai Institute. “We all had chills. We thought, ‘That’s it. We have it. That’s what causes wasting.’”

All three methods succeeded in transmitting the disease, with more than 90 per cent of healthy sea stars dying within a week of showing symptoms.

Co-author Amy M. Chan, research scientist at the EOAS marine microbiology and virology laboratory, created pure cultures of V. pectenicida strains including FHCF-3 from the coelomic fluid of sick sea stars. When these FHCF-3 cultures were injected into healthy sea stars, they all died within a few days of showing symptoms, confirming this strain was the cause of the disease.

“Using DNA sequencing, we saw there was a huge signal of a particular bacteria. This was our prime suspect to isolate. When I did, I saw basically only one kind of bacteria growing on the plates and thought, ‘This has got to be it’.”

The loss of billions of sunflower sea stars—a natural predator of sea urchins—has driven widespread, lasting effects on marine ecosystems. “Without sunflower stars, sea urchin populations have increased, devouring the kelp forests that provide habitat for thousands of marine creatures. These forests also contribute millions of dollars through fisheries and tourism, sequester carbon dioxide, protect coastlines and are culturally significant for coastal First Nations,” said Dr. Prentice.

Researchers and project partners hope the discovery will help guide management and recovery efforts for sea stars and impacted ecosystems.

“This finding opens up exciting avenues to expand the network of researchers able to develop solutions for recovery of the species,” said Jono Wilson, the director of ocean science for The Nature Conservancy’s California chapter, which helped support the research. “We are actively pursuing studies looking at genetic associations with disease resistance, captive breeding and experimental introduction of captively-raised stars back into the wild to understand the most effective strategies and locations to reintroduce sunflower sea stars into the wild.”

Tags: Alyssa Gehman, Hakai Institute, marine diseases, Pacific Ocean, sea stars, sea urchins, UBC EOAS