Despite a prediction in 2016 that it might take a decade for sea stars to recover after a mysterious wasting disease struck the colorful animals along the West Coast, they’re already making a rebound, researchers reported this week.
One species, the purple and orange ochre sea stars often seen at low tide, seem to be stabilizing around the San Juan Islands in Washington, according to Drew Harvell, an ecology professor at Cornell University and an affiliate professor at the University of Washington.
“And virtually all of the stars, except for maybe one or two, were healthy,” she said. “So that was really good news,” she said.
Harvell said ochre stars around the San Juan Islands are still about 70 percent below their pre-outbreak numbers.
The occurrence was first documented in 2014 when beachgoers and researchers noted that colorful seastars’ arms were dissolving and crawling away — right before their eyes.
Scientists were baffled as they tried to figure out what was causing the sea stars to melt in what they called the largest known marine wildlife viral outbreak to date. It was first observed in the Seattle and Vancouver waters in June 2013, and then widely seen along the coast of Oregon in 2014 and 2015, including in some tidal zones in Curry County. Other outbreaks of the disease were seen in Central California, Santa Barbara and Los Angeles.
“There were very, very large-scale losses in the intertidal zone,” said shellfish researcher Steve Rumrill, of the Oregon Department of Fish and Wildlife. “Eighty percent — that’s big.”
Scientists dubbed what they were seeing “sea star wasting disease” and eventually blamed it on a pathogen and warming ocean tidal waters that are most affected by climate change.
The intertidal zone is the tidepool area where people traipse in search of critters stranded in pools by the outgoing tide; the allure of the colorful sea stars is a big draw to the Oregon Coast. The subtidal zone is that area only seen at extremely low tides, and features large, multi-legged sea stars, mussels and urchins.
Tests showed the most likely culprit was the sea star associated densovirus. A Proceedings of the National Academy of Sciences (PNAS) paper indicated the die-off was not caused by ocean pollutants, but might have been in the sand or water columns emitted by other infected sea stars.
And increasingly, scientists feel warming waters are affecting a myriad of ocean species.
“The heat wave in the oceans — a product of increasing atmospheric temperatures — is exacerbating the sea star wasting disease,” said Harvell in a January University of California-Davis paper. “It’s a lethal disease, and when you add a higher temperature to that, it kills faster, causing a bigger impact.”
The sea star wasting disease epidemic has hit an alarming number of (sea star) species in all shallow water habitats,” PNAS paper said in 2016. “Eight of 11 species sampled contained the virus.
And the virus that mystified scientists throughout the summer of 2014 is not a new one.
“There is genetic evidence of it from sea stars in museums from 40 years ago,” Rumrill said. “The curious thing is, why did it blossom and outbreak?”
It also appears the virus might have been present in the water for decades before it took hold.
“It only became an epidemic recently due to unmeasured environmental factors not present in previous years that affect animal susceptibility or enhance transmission,” the PNAS paper reads.
To a lesser degree, Rumrill said, those larger, predatory stars in the subtidal zone also succumbed to the virus.
“We’re starting to see a recovery on a small scale of the ochre stars (in the tidepools); the juveniles are coming back,” he said three years ago. “But by and large, we have not seen the recovery of the big predatory stars.”
Other species, like the giant sunflower sea star, have not rebounded and are imperiled in the San Juan Islands, Harvell said.
The Reef Environmental Education Foundation (REEF) conducted thousands of surveys from Southern California to Alaska. Before 2013, divers reported an abundance of sea stars, and recorded increased temperatures of up to 4 degrees Celsius.
Scientists from the National Oceanic and Atmospheric Administration surveyed sunflower sea stars in thousands of deep trawls from Mexico to the Canadian border, as well, and recorded 100 percent decline in water down to 1,000 meters.
Harvell said different colored stars died more rapidly than others during the epidemic, and at many sites, only the orange stars seemed to be affected.
“At most of our sites we only have the purple ones left,” Harvell said. “But at this one site there were just so many of the orange ones that we were happy to see them and happy to see that they had obviously survived or re-migrated back following the epidemic.”
It’s possible the creatures are evolving to be resistant to the pathogen that attacked them, and researchers are investigating that possibility, as well.
Tide-pool visitors are asked to not touch the sea stars they see along the coast to better increase their chances of survival.
“We know the agent is still out there, we’re still seeing losses of stars in some places and times and for some species,” Harvell said. “The fact that the ochre star is looking pretty good is a great sign.”