After a decade of death, why are sea stars having a baby boom?
The deadly sea star wasting disease caused a mass die-off of sea stars along the West Coast. But recent signs of a resurgence make experts cautiously optimistic.
Once thought to be on the brink of extinction, sea stars along Oregon’s coast are having a baby boom. Tide pools are clogged with juvenile sea stars that stretch the size of a few pennies, chowing down on the mussels and urchins that had overtaken these environments during their absence.
It’s a promising sign. Starting in 2013, sea stars on the West Coast began dying from what came to be known as sea star wasting disease. The illness caused sea stars to curl up, lose limbs and even melt into a pile of goo.
Within a decade, sea star wasting disease had decimated 90% of the West Coast’s sea star population, crippling marine ecosystems that depend on the voracious predators to keep certain other species in check. But after a decade of death, scientists have started to notice that the marine creatures are making a comeback.
“It’s still a really good sign that there’s a recovery,” Angela Jones, a researcher at Northeastern University’s Marine Science Center who has studied sea stars on both the West and East coasts said. “That gives us a lot of hope.”
Jones witnessed something similar on the East Coast, in Rockland, Maine, where there is far less known about the extent of the devastation caused by wasting disease.
“I’ve been here for five years, and this summer was the first time I’ve ever seen that in our stars,” Jones said.
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As for why, after a decade-long mass extinction, sea stars are returning, scientists have a few ideas.
One potential reason for the recent comeback could be that sea stars, stressed from warming waters and wasting disease, could be releasing all of their eggs at once in a last ditch effort at survival, Jones said.
“Even if you get 1% or 0.1% survival of one individual’s offspring, we’re looking at 300 to 3,000 [sea stars] minimum for some of these species,” she said.
Sea stars are broadcast spawners that release millions of eggs with a low chance of survival and recruitments typically occur when sea star eggs and larvae get carried to potential spawning locations by water currents.
“They’ll just go where the water takes them,” said Mica Weld, a researcher working with Jones, about sea stars’ behavior. “If a spot has favorable conditions, they’ll stay, finish their transformation and actually settle as juvenile stars and then you see them in the thousands.”
According to Jones, sea star resurgences — or “recruitments” — are a somewhat regular occurrence on the West Coast, even with sea star wasting disease lingering.But the scale of what’s been measured on the West Coast recently is notable: In some areas, scientists have recorded a more than 8,000% increase in juvenile sea stars, which are anywhere between two months to two years old, she said.
The true test of how well sea stars are recovering, however, will be the amount that make it to adulthood. Sea star larvae are unaffected by sea star wasting disease, and juveniles are somewhat less susceptible, which explains the abundance of younger stars in Oregon right now, Jones noted.
The sea stars that are making it to adulthood without dying of wasting disease appear to be much smaller than those found prior to the mass die-off. It could be years before we see the return of the three-foot wide “monsters” that once occupied West Coast waters, Jones said.
But even small sea stars can make a difference.
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That’s because sea stars are vital to maintaining the delicate balance of marine ecosystems. Without these voracious predators, West Coast marine ecosystems have been overrun by mussels and urchins that have choked out algae and kelp forests that harbor sea life and help reduce the amount of carbon in the atmosphere by absorbing and keeping it in the deep ocean, Weld said.
The recent baby boom brings hope, but it is also tenuous. Sea star wasting disease is still present, and the warm ocean temperatures brought on by this year’s El Niño could stress the surging sea star population once again. A large “blob” of warm water, which was also associated with the worst of the die-off, has returned to the West Coast, so the “recipe is there for sea star wasting 2.0,” Jones said.
Meanwhile, on the East Coast little is known about how much the disease has spread, Jones explained. The recent recruitment in Maine is promising, but the amount of data collected on West Coast sea stars doesn’t yet exist on the East Coast. “It’s hard to tell how our stars are doing and if they’re in a recovery,” Jones said.
To help fill in that information gap, scientists are turning to the public to step in as citizen scientists, cataloging through platforms like iNaturalist any sea stars they find, alive or dead, along the coast.
“We heavily encourage people to go out … at low tides when it’s safe and take pictures of the stars so that we can make sure they’re staying healthy,” Jones said. “If there is a big die off event, we can capture it again.”
