Counting tidepool inhabitants requires specialized equipment: clipboards, flashlights, cloth tape for marking plots and waders. From left, Melissa Redfield, Maya George, Rani Gaddam. (J.D. Hillard/KQED )
In 2013, millions of sea stars on the West Coast began breaking out in lesions, turning to mush, and dying. Scientists recently identified a virus they think causes this “sea star wasting syndrome.” Now they're trying to figure out why this happened.
One place the science of sea star wasting happens is a fenced-off area of seaweed-clad rocks on the coast of the Monterey Peninsula. On a visit during low tide, Rani Gaddam stands with a clipboard. As breakers throw head-high whitewater nearby, her fellow researchers from UC Santa Cruz’s Long Marine Laboratory wade into the tide pools.
“Healthy pateria,” Melissa Redfield calls.
“Healthy pateria,” Gaddam repeats, and makes a note on a clipboard.
“I have a healthy pisaster 30,” Maya George repeats.
“Under the 30-size bin I write ‘one.’ Under the healthy bin, I write ‘one,’ ” Gaddam explains.
Actually, these researchers finished their counts a few minutes ago. This is a demonstration so I can see how they track the ongoing die-off of sea stars.
George says that in the 13 years since they started counting at this site, they’ve seen plenty of gradual fluctuation.
“When the disease came through, it was a lot more striking. We lost a lot of those large individuals,” she says. “And populations or plots that we had been counting for many years went from having hundreds to just a few.”
Today they find eight adults; one may be coming down with the disease. Cornell University Professor Ian Hewson studies viruses in the ocean. When West Coast aquariums began losing their sea stars in late 2013, he began comparing the DNA from viruses in healthy stars with sick ones.
“We had to start without a focal point by a sort of shotgun sequencing, if you will -- everything that was there. We were able to identify this unique densovirus that’s associated with the disease.”
The densovirus he found is related to the parvovirus that causes serious digestive illness in puppies. When Hewson gave this virus to healthy sea stars, they got sick. This disease isn’t new; it likely caused smaller die-offs in recent decades.
“You know it’s been around for 70 years. … it hasn’t cause mass mortality. And then suddenly, it’s just taken off like a bonfire.”
Pressing the investigation
Hewson hopes to get enough funding to find out if the densovirus mutated to become more dangerous. It’s also possible that an environmental change made the stars vulnerable or contributed in some other way to the outbreak. That’s what grad student Monica Moritch is trying to find out in her office at the Long Marine Lab.
In a mapping program on her laptop, Moritch loads data from the sea star counts that her colleagues gathered at the beginning of this story. On her screen, an outline of the West Coast appears. It’s dotted with red and blue triangles.
“The red means sea star wasting is present at a site and blue means that it is not,” she says.
She has been working for months, comparing this map with maps of data on water temperature, pollution, sites and sewage outfalls.
“I want to see if there is something that all the sites with sea star wasting have in common compared to ones that don’t have any sea star wasting present.”
She says there’s plenty more to investigate before she can say whether any of these environmental factors appears to contribute to the disease.
Biology Professor Pete Raimondi leads UC Santa Cruz's research into sea star wasting. In case you’re wondering: “There is no cure, so I want to get that off the table right away,” he says.
“And even if there is a cure, it would be impossible to apply it to sea stars up and down the coast.”
Also, this isn’t the end of the sea stars. Raimondi expects that populations will regrow from individuals that have immunity, or that they will become so sparse the disease can’t spread.
“Once it rips through a population, in many pathogens there’s nothing left for it to be infesting,” he says.
Then the population grows back from individuals that never got sick. Scientists are paying close attention to sea star wasting to see whether the creatures return to their former numbers or remain fewer.
Past experiments predict that if there are fewer stars, there will be many more of their favorite food – mussels. A new phase of observation has begun studying how the ecosystems change.
Meanwhile, the stars may resume their former role in the tidepools pretty quickly. In summer 2014, tidepool surveys identified an unprecedented crop of baby sea stars, with counts as high as the past 15 years combined. But babies are tiny. They’re like smudges of color on the rocks, and right now they’re too small to tell if they’re getting sick.