A mysterious disease is turning sea stars to goo and leading to huge die-offs across the North Pacific. The disease, known as Sea Star Wasting Syndrome (SSWS), warps their limbs and causes their bodies to deflate and even disintegrate entirely.
Early accounts of the disease were published by researchers studying common starfish, who reported massive mortalities off the east coast of the United States in the 1970s.
Since then, SSWS epidemics have become even more severe. An outbreak in the Pacific northwest between 2013 and 2016 caused numbers of sea stars across 20 different species to plummet. On the Oregon coast alone, ochre sea star populations declined between 50 and 94 percent.
In a study published in the journal Molecular Ecology, scientists examined that outbreak in detail, focusing on the genes of a key species—ochre sea stars— that was impacted. Researchers wanted to work out why some sea stars died from the disease while others escaped unscathed. That way, they could determine whether the sea stars could adapt to the disease and uncover ways of helping protect them from future outbreaks.
The researchers found healthy ochre sea stars that survived displayed no genetic difference from those that were affected. They said this raises concerns all ochre sea stars could be threatened by the syndrome because the species does not seem to have any genetic defenses against SSWS.
"We were looking for whether or not existing individuals have genes that make them more likely to avoid getting SSWS or if they did have SSWS, don't exhibit the symptoms that lead to death," lead author Andrea Burton of Oregon State University told Newsweek. "If the sea stars did have these genes, then survivors would be able to pass on these genes to future generations, resulting in populations adapted to future SSWS outbreaks. The issue was, in our study we didn't see much evidence for these genes."
The study suggested that sea star populations that did survive the outbreak may not be better protected than their less fortunate counterparts next time around.
The 2013 outbreak in the Pacific northwest was the largest marine wildlife disease outbreak on record. Other less severe outbreaks have also been recorded in British Columbia, Australia and the Yellow Sea between China and Korea.
Future epidemics are expected, Burton said, but much still remains a mystery: "We do not know at this time the origin of the Sea Star Wasting Syndrome. It is still debated as to whether SSWS is caused by a pathogen or not as no one has been able to isolate a causative agent yet."
Scientists may not know where it came from but they do know that warmer ocean temperatures occurring amid climate change make SSWS worse.
"The one thing that studies have repeatedly shown is [that] SSWS correlates with elevated sea water temperatures," Burton said. "Something about warmer temperatures exacerbates the syndrome ... Climate change has resulted in multiple shifts in the ocean that have shown to stress out marine life.
"It's like sticking a person in a really hot room, the body now needs to increase sweat production to stay cool, which can require more energy than the body is typically used to using. As a result, disease outbreaks in marine organisms have been increasing, with temperature often being the primary driver. Which is the case for SSWS."
