A mysterious marine epidemic has erased billions of sea stars from North America’s Pacific coast. After more than a decade of unanswered questions, scientists have traced the disaster to a single bacterial species – an invisible predator reshaping entire shorelines. In its wake, sea stars erupt in lesions, shed their arms and melt away into ghostly remnants of their former selves.
A new study published in Nature Ecology & Evolution has confirmed that Vibrio pectenicida (strain FHCF-3) is the long-suspected culprit behind sea star wasting disease; a fast-moving marine plague capable of wiping out entire populations in a matter of days. Since 2013, the outbreak has killed an estimated five billion sea stars from the coasts of Baja California to Alaska, collapsing populations and sending shockwaves through the ecosystem.
For years, the cause remained maddeningly elusive. Early investigations focused heavily on a densovirus, but it turned out to be a normal resident of healthy sea stars. The breakthrough came when researchers began analyzing coelomic fluid – the internal “blood” of sea stars – rather than just dead tissue. That’s where they detected Vibrio pectenicida, a pathogen previously overlooked because it doesn’t persist well in deceased specimens.
The next step was to test the bacteria on healthy sea stars. Within days, once-vibrant animals displayed the same rapid tissue loss and eventual death seen in the wild; definitive proof that this was the killer.
Identifying the cause finally gives scientists a tangible target to fight against. As marine invertebrate curator Dr. Hugh Carter put it, “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. It's a massive step forward, but we're still a long way from a solution.”
Part of that challenge lies in the nature of the culprit itself. Vibrio bacteria are not outsiders crashing the ecosystem but long-time residents of the sea, woven into the fabric of marine life; cycling nutrients, breaking down organic matter, even sustaining health in the right balance. Yet under the wrong conditions – warmer waters, nutrient surges, or stressed hosts – they can tip from benign to opportunistic, overwhelming defenses and sweeping through communities with lethal efficiency.
The death of a few starfish may seem insignificant until you see the coastline change. Without its keystone predators, the balance of the coastal ecosystem can shift to damage control: urchins strip kelp forests, waves hit harder, and the quiet rhythm of life shifts. The loss may have began underwater, but its echo reaches far wider.
This kind of environmental tipping point is nothing new. For example, when wolves were eradicated from Yellowstone National Park in the early 1900s, their absence set off a chain reaction: elk populations exploded stripping vegetation bare; riverbanks eroded, and waterways shifted. Even beavers vanished as their habitats collapsed. Remove a keystone species, and the ecosystem structure tilts, sometimes beyond recognition.
What’s now unfolding in the Pacific is a similar story, only this time the drama plays out along hundreds of miles of coastline. Here, the keystone is the sunflower sea star (Pycnopodia helianthoides); once one of the most common predators in the intertidal zone. Since the outbreak began, populations have crashed by more than 90%, with some regions seeing near-total collapse. Without these top predators, purple sea urchins have multiplied unchecked, stripping kelp forests down to bare rock.
The result is an underwater deforestation unlike anything seen before in this region. Kelp forests aren’t just scenic backdrops, they are nurseries for fish, feeding grounds for marine mammals, and the scaffolding that holds coastal ecosystems together. They also stabilize the climate by pulling carbon from the atmosphere, buffer shorelines against storms, and slow the erosion that eats away at coastlines. In Northern California alone, more than 90% of these vital forests have vanished, setting off ripples that threaten fisheries, seabird colonies, and the very balance of the nearshore ocean.
Now that scientists have identified the culprit, the path forward is starting to take shape. Though far from easy, captive breeding programs at institutions like the Seattle Aquarium are working around the clock to raise healthy sunflower sea stars for eventual reintroduction, each new generation a small step toward restoring balance in the intertidal zone.
It’s a stark reminder that marine diseases can hollow out ecosystems as surely as a wildfire strips a forest or a blight wipes out crops. But with the cause finally identified, scientists can now work to protect what remains and begin the long process of restoring balance to the Pacific coast’s living infrastructure.
The new study was published in the journal Nature Ecology and Evolution.
Source: Natural History Museum
