Oregon Ochre Sea Stars Bounce Back After Near-Extinction — Baby Boom Fuels Recovery

Ochre sea stars recover after decade-long collapse

Ochre sea stars, once common along the Oregon Coast, are showing a surprising recovery after a devastating wasting disease wiped out large numbers of starfish beginning in 2013. A new study by researchers from Oregon State University and Cal Poly San Luis Obispo finds that a dramatic influx of juveniles has driven populations at many sites back to levels at or above those seen before the die-off.

What happened

The wasting disease, first noted in 2013, affected more than 20 sea star species along the Pacific Coast and is estimated to have killed billions of individuals. Infected sea stars developed lesions and experienced arm twisting, disintegration and loss. Scientists have recently linked the syndrome to a strain of bacteria, though many ecological questions remain.

Study findings

The study examined ochre star populations at eight locations along the Oregon Coast over a 23-year period. After declines as steep as 84% in 2014, researchers observed an approximately 8,000% surge in young ochre sea stars washing ashore. Many of those juveniles have now matured, and populations at several sites are back to or above pre-epidemic counts.

"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 lead author Sarah Gravem, an assistant professor at Cal Poly and former OSU postdoctoral researcher.

According to co-author Bruce Menge, populations at roughly three-quarters of the study sites have resumed pre-epidemic feeding on California mussels. Ochre stars are once again functioning as a keystone predator in the intertidal zone, helping prevent dense mussel beds from dominating rocky shores and displacing other invertebrates and seaweeds.

Remaining concerns

Despite the encouraging rebound in numbers, scientists warn the recovery is not yet a full return to the previous, stable state. At all but one study site, average body sizes remain about 25%–65% smaller than historical levels, and coastwide populations fluctuate more year to year, likely because the wasting pathogen continues to circulate.

Not all species have recovered. Sunflower sea stars — the largest and fastest sea star species — have not rebounded and their decline has been linked to the loss of kelp forests along Oregon's 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," said Menge.

Why the rebound might have occurred

Researchers are still investigating drivers of the rebound. One hypothesis is ecological release: when wasting dramatically reduced adult ochre stars, food resources (mussels and other prey) became more abundant for larvae and juveniles that survived, enabling higher recruitment and growth — a process Massey compares to how a wildfire can open space for new forest growth. However, scientists caution the timing could be coincidental or influenced by other environmental factors.

Implications: The ochre star’s partial recovery demonstrates resilience in intertidal ecosystems but also underscores ongoing vulnerability — continued monitoring is needed to understand long-term stability, the role of the pathogen, and the prospects for other species that have not recovered.

Study scope: Eight Oregon Coast sites, 23 years of data; lead researchers Sarah Gravem (Cal Poly) and Bruce Menge (Oregon State University).

Read the original reporting on oregonlive.com.