For over a decade, coastal waters from Mexico to Alaska have witnessed a devastating phenomenon that baffled scientists and concerned environmentalists alike. Billions of sea stars—colorful, spiny marine animals critical to ocean ecosystems—have been mysteriously melting away, losing arms, becoming disfigured, and dying in mass numbers. This troubling outbreak, known as sea star wasting disease, is considered the largest marine epidemic ever recorded in the wild.

The puzzle of what caused this “melting” and death remained unsolved for years. But in August 2025, a team of dedicated Canadian researchers from the University of British Columbia (UBC), alongside collaborators from the Hakai Institute and the University of Washington, announced a groundbreaking discovery that finally unlocked this mystery. The cause? A harmful strain of bacteria named Vibrio pectenicida. This discovery marks not just a scientific breakthrough but a hopeful turning point for efforts to save sea stars and protect marine ecosystems.

Understanding Sea Star Wasting Disease and Its Effects

Sea stars—often called starfish—play a vital role in ocean life. Among them, the sunflower sea star is one of the largest and most important. Growing to the size of a bicycle tire and boasting up to 24 arms, these creatures are natural predators of sea urchins. Sea urchins eat kelp, the large underwater seaweed that grows in dense forests along the coastline. Kelp forests provide habitat and food for countless marine species and act as natural barriers protecting the shoreline from erosion and strong waves.

When sea star wasting disease emerged around 2013, the impact was catastrophic. Sea stars would start showing strange symptoms: their arms curling strangely, turning white, degrading, and eventually falling off. The animals would seem to melt into a gooey mess, sometimes within just one or two weeks after infection. The disease spread rapidly, killing over 90% of sunflower sea stars in many areas, along with dozens of other sea star species.

Without these natural predators to keep sea urchins in check, urchin populations exploded, feasting on kelp to the brink of collapse. This created a ripple effect through marine ecosystems—less kelp meant fewer fish and sea creatures found shelter and food. The loss also affected the livelihoods of local fishing and tourism communities and disrupted the cultural heritage of many coastal First Nations peoples who rely on healthy marine ecosystems.

The Search for the Culprit: Years of Science and Dedication

Scientists worldwide had been racing to find the cause of sea star wasting disease for more than a decade. Early theories ranged widely—from viruses to environmental factors like water temperature and pollution. However, no single factor was conclusively identified as the trigger.

The investigative team led by UBC’s Dr. Melanie Prentice and colleagues undertook a thorough and challenging four-year study. They collected samples from sick and healthy sea stars along the west coast—from Alaska down to Mexico. Using DNA sequencing, they looked for differences in the microscopic organisms living in and on the animals.

Their research revealed a striking pattern: a particular strain of bacteria, Vibrio pectenicida, was consistently present in diseased sea stars but absent or rare in healthy ones. This discovery surprised many researchers because earlier, the main suspect was a virus.

To prove V. pectenicida was indeed the cause, the team isolated the bacteria from sick sea stars and cultured it in the laboratory. Then, in a series of controlled experiments, they introduced the cultured bacteria into healthy sea stars. The healthy stars quickly developed symptoms of wasting disease, confirming the bacterium as the cause. This was a crucial step that satisfied what scientists call Koch’s postulates—the gold standard for proving the cause of infectious diseases.

Dr. Alyssa Gehman of UBC described the moment they identified Vibrio as “chilling” yet rewarding. The discovery has been called “the discovery of the decade” by researchers closely following the epidemic.

Why This Bacterium, and What Role Does Climate Change Play?

Vibrio bacteria are known to thrive in warm water. They can cause devastating diseases not only in marine animals but also in humans—Vibrio cholerae, for example, is the bacterium responsible for cholera, a dangerous human illness.

As oceans warm due to climate change, conditions become more favorable for Vibrio bacteria to grow and spread. The sea star wasting disease outbreaks are happening earlier and progressing faster in warmer regions, showing a strong link between climate and disease spread. This dual threat—climate change making the seas warmer and the bacterium growing more rapidly—has made the fight to save sea stars harder.

The discovery of Vibrio pectenicida unlocks new doors for understanding how warming oceans might exacerbate this disease and how marine life might adapt or be supported to resist it.

Impacts on Ocean Ecosystems and Communities

The decline in sea star populations has far-reaching consequences. Kelp forests are some of the planet’s most valuable ecosystems, often called the “rainforests of the sea.” They help in carbon sequestration, absorbing large amounts of carbon dioxide and helping slow climate change. They provide homes for fish, birds, and marine mammals and protect coastal communities against wave damage and erosion.

The loss of sea stars has made some kelp forests vulnerable to being overrun by sea urchin “barrens,” barren areas where kelp has been almost entirely eaten away. This threatens not just marine biodiversity but also the economic and cultural well-being of the region’s coastal peoples.

A Path Forward: Recovery and Protection Efforts

With the cause now confirmed, scientists and conservation groups such as The Nature Conservancy are working on ways to help sea stars recover and protect the marine ecosystems they support.

Research is underway to understand if some sea stars have natural genetic resistance to Vibrio pectenicida. These resistant individuals could be bred in captivity, helping build stronger sea star populations.

Scientists are also trying to develop probiotics—good bacteria that can help sea stars fight off harmful Vibrio. Similar methods have shown promise in protecting corals from diseases.

Efforts are in place to breed sea stars in aquariums and carefully reintroduce them into the wild, monitoring their health and survival to restore balance to coastal ecosystems.

Why This Discovery Matters

This landmark discovery by UBC and collaborators is a critical step in ocean science and marine conservation. It shows how years of dedicated research, advanced technology, and teamwork can solve complex environmental problems.

Moreover, it serves as a reminder of how human actions—especially climate change—can influence natural ecosystems in unexpected ways. Understanding these connections can help people make better decisions to protect our planet.

Finally, this discovery offers hope. Knowing the cause of sea star wasting disease allows targeted actions to be developed, giving these remarkable and vital animals a chance to survive and thrive once again.