Oregon sea stars bounce back from near extinction after years of decline

Ochre sea stars, an iconic species once common along the Oregon Coast, are making a recovery after years of decline due to a mysterious wasting disease.

That’s according to a study published earlier this month by scientists at Oregon State University and Cal Poly San Luis Obispo. Their research shows that a significant “baby boom” of new sea stars has helped the species rebound to levels at or above their population numbers before the crisis.

The species’ decline goes back to 2013 when an illness began to decimate sea stars on the Pacific Coast, including in Oregon. It has devastated more than 20 sea star species, killing off billions of starfish over the past decade. The disease leads sea stars to develop lesions and makes their arms twist, melt and fall off. Its cause was only recently traced to a strain of bacteria.

The new study’s findings reveal a dramatic turnaround for the ochre sea stars, which are typically purple or orange and like to suction onto rocks in the surf. Once common at Haystack Rock on Cannon Beach and at many other oceanfront locations, they were almost entirely wiped out.

But now they’re back.

It’s still unclear what led to the recovery. All scientists know is that a large number of baby sea stars ended up onshore in the wake of the wasting disease epidemic.

Many of those sea star baby boomers have now reached adulthood and population numbers are now at or exceeding pre-wasting disease levels, they found.

“After declines in sea star numbers of up to 84% in 2014, we quickly saw an 8,000% increase in young sea stars landing on shore,” said the study’s lead author, Sarah Gravem, an assistant professor at Cal Poly who was an OSU postdoctoral researcher when the project launched.

The research, which analyzed ochre sea star populations at eight locations along the Oregon Coast over a 23-year period, shows the populations are now large enough that the starfish are once again resuming their role as a keystone predator in the intertidal zone, Gravem said. At three-quarters of the study sites, the stars have resumed chomping on their favorite prey, California mussels, she said.

What’s more, the starfish have now grown abundant and large enough that they are eating mussels at similar rates to before the wasting epidemic at most of the sites in Oregon, said Bruce Menge, a professor of integrative biology in the OSU College of Science and Gravem’s research partner.

That means the mussels are no longer able to form mussel beds that in recent years have blanketed intertidal rocks and which made life difficult for other invertebrates and seaweeds.

Gravem and Menge are still working to figure out what caused the stars’ recovery. One hypothesis is that the wasting disease itself set the stage, or triggered, the sea stars’ resurgence, said Menge, much like a wildfire would lead to new forest regrowth.

Both baby and adult sea stars eat the same prey species, so when the wasting disease killed off most of the adults, food was plentiful for the sea star larvae who could survive and grow, Menge said.

But it’s also possible the timing was simply a coincidence, he said.

Despite the good news, scientists said the ochre sea star populations have not yet returned to their previously stable state. At all but one research site, their average body sizes are still about 25% to 65% smaller than they once were. And the sea star populations coast-wide are generally less steady from year to year than before the epidemic, likely because wasting disease remains in circulation.

A similar recovery also has not been observed among sunflower sea stars – the largest and fastest of the starfish species. Their die-off is linked to the disappearance of underwater kelp forests along the Oregon coast.

“The sunflower star was extremely susceptible to wasting, more than any other species including the ochre star, and the disease is still present, so it might be that disease is still suppressing sunflower star recovery,” Menge said.