Five years ago, millions of sea stars off the west coast of North America were killed by a mysterious virus that caused the animals to lose limbs and liquefy, with several species under serious threat of extinction. Following the peak of the epidemic, described as “one of the largest marine mass mortality events on record,” scientists noticed that young ochre stars, among the species most impacted by the virus, were surviving at much higher rates. Today, the starfish have seemed to miraculously recover, and researchers may have the explanation for their salvation. A new study suggests that the animals possibly developed a genetic resistance to the still-puzzling densovirus, a threat that had been lurking in the region for decades but could have been fully activated by climate change.

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Purple ochre sea star with one arm partially dissolved and disintegrating in the water

About 80 percent of ochre sea stars died as a result of the mysterious virus, which was disturbing for its ecological consequences and the manner with which it killed. “The sick ones tend to just fall apart in front of your eyes,” biologist Jeff Marliave told KUOW in 2013. “An arm will actually break off and crawl away.” Scientists now believe that the massive die-off accelerated the process of natural selection. “When you’ve removed a whole bunch of them, you’ve shifted the whole genetic diversity of that population,” researcher Chris Mah told the Guardian. “In other words, to put it in human terms, if you wiped out a huge chunk of the human species, you would change the genetic makeup of humans.”

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Those that survived the wasting syndrome had the resistant gene, which they then passed onto their offspring. While the sea stars may have avoided a terminal fate this time, such epidemics are expected to occur with greater frequency in the future. “The concern is that marine disease, extreme environmental events and the frequency of those are on the rise,” study lead author Lauren Schiebelhut told the Guardian. “If we have too many extreme events in a row, maybe that becomes more challenging for species to respond to.”

Via The Guardian

Images via Jerry Kirkhart, Oregon State University and David O.