Bacteria that’s melting starfish alive has finally been identified

For more than a decade, sea star wasting disease (SSWD) has ravaged starfish along North America’s Pacific coast. It shreds arms, melts bodies, and pushes iconic species like the sunflower sea star to the brink of extinction.

Now there’s a turning point: researchers have identified a single bacterial species – Vibrio pectenicida – that can trigger the full suite of wasting symptoms.

This breakthrough offers a path toward earlier detection and, eventually, smarter response strategies, even as the ocean’s “three-dimensional dynamic environment” makes intervention challenging.

Pacific starfish face collapse

The scale and speed of SSWD are unprecedented. Since 2013, outbreaks have swept from Alaska to Mexico, striking more than 20 sea star species.

Early signs include loss of appetite and small white lesions. Then the animals go limp as the disease hits the water vascular system. Arms detach and sometimes wriggle independently, and the entire body disintegrates into mush within days.

“Sea star wasting disease is pretty horrid,” said Hugh Carter, a marine invertebrate curator at the Natural History Museum in London and a starfish expert. “It causes the starfish to stop feeding and forms white lesions across the body as the soft tissue starts breaking down.”

The ecological shock is profound. Sunflower sea stars – important predators of sea urchins – have lost more than 90 percent of their population, and the cascade is visible on the seafloor.

“When we lose billions of sea stars, that really shifts the ecological dynamics,” said lead author Melanie Prentice from the University of British Columbia (UBC). “In the absence of sunflower stars, sea urchin populations increase.”

“This means the loss of kelp forests, which has broad implications for all the other marine species and humans that rely on them. So, losing a sea star goes far beyond the loss of that single species.”

Solving a marine mystery

For years, scientists pursued competing hypotheses, with a virus suspected early on but later ruled out. One reason the search took so long is that sea stars deteriorate rapidly – often within a week of exposure.

By the time researchers collect samples, secondary infections and generalized stress responses may obscure the primary trigger.

The new study overcomes those obstacles. In controlled laboratory experiments, the team raised sunflower sea stars and exposed them to diseased tissue in different ways.

Simply touching infected parts or being injected with tissue homogenates proved deadly: 92 percent of exposed sea stars died.

Scientists name the starfish killer

Critically, when the homogenates were filtered or heat-treated first, the starfish did not develop the disease. This was strong evidence that a living microbe was the cause.

The researchers then compared coelomic fluid – the sea stars’ blood-like internal fluid – from healthy and exposed animals. One signal dominated.

“When we compared the coelomic fluid of exposed and healthy sea stars, there was basically one thing different: Vibrio,” said senior author Alyssa Gehman from UBC. “We all had chills, we thought that’s it. We have it, that’s what causes wasting.’”

To satisfy the gold standard of causation, they isolated Vibrio pectenicida from diseased sea stars, cultured it to a pure strain, and injected it into healthy animals. The recipients rapidly developed classic wasting symptoms.

Field data reinforced the lab results: in British Columbia, V. pectenicida appeared in sea star samples only after an outbreak had begun.

Progress with no easy fix

The identification of V. pectenicida marks the first time researchers have reproduced the full disease by introducing a single pathogen.

“There have been lots of competing theories over what causes sea star wasting disease, so it’s great that we know what is actually causing it,” Carter said. “It’s a massive step forward, but we’re still a long way from a solution.”

Pinpointing the bacterium could improve surveillance, allowing diagnostics to target V. pectenicida during early flare-ups. But practical control is far tougher offshore.

“While knowing the bacteria that cause it might allow us to detect new outbreaks earlier, it’s still hard to quarantine or treat the disease in the 3D dynamic environment of the sea. It’ll take a great deal more research until sea star wasting disease can be managed effectively.”

Warming seas fuel starfish disease

Like many vibrios, V. pectenicida appears to thrive in warmer conditions, which aligns with observations that wasting spreads faster during marine heatwaves.

The bacterium is already infamous in aquaculture as a scallop pathogen that secretes toxins. Those same virulence factors may damage sea star tissues and water vascular systems, accelerating the grisly progression.

Unpacking that mechanism – what toxins are produced, how they interact with sea star immunity – will be crucial for forecasting risk and testing interventions.

With oceans warming due to climate change, the stakes are rising. Hotter waters can both boost bacterial growth and stress sea stars, potentially lowering their defenses.

Understanding that one-two punch could help managers anticipate where and when disease pressure will spike, enabling them to prioritize monitoring or protective measures for the most vulnerable populations.

Fighting future outbreaks

The immediate priorities are clear. Researchers need to map the distribution of V. pectenicida across species and coastlines and refine rapid tests for early detection. They also need to investigate how environmental variables – temperature, salinity, organic matter – modulate bacterial bloom-and-bust cycles.

Hatchery and aquarium settings may serve as testbeds for mitigation strategies, from biosecurity protocols to microbiome-based approaches that bolster sea stars’ defenses.

But translating lab breakthroughs into ocean-scale solutions will take time. In the near term, the best defense for kelp forests and the myriad species that depend on them may be vigilant disease surveillance.

Ecosystem management that reduces compounding stressors, such as overgrazing by urchins, is also crucial.

Even so, science has turned a corner. Identifying the culprit shifts the field from guesswork to targeted investigation and from helpless witness to informed action.

The study is published in the journal Nature Ecology & Evolution.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–