Along the wave-swept rocks of Makah Bay, Washington, a researcher once spent hours prying purple sea stars from their holds and tossing them into deeper water. The tide pools he left behind told a story no one had expected. Within months the familiar mix of barnacles, snails, algae and mussels gave way to a single dominant carpet of mussels. Space that once supported a dozen species became the property of one.
The experiment that redefined how we see shorelines
Robert Paine’s work in the 1960s showed what happens when a top predator disappears from an intertidal community. He kept one stretch of shoreline free of the ochre sea star, Pisaster ochraceus, while leaving a nearby section untouched. In the absence of the sea star, acorn barnacles first crowded the rocks, then California mussels overran everything else. Only a thin layer of algae survived on the mussel shells. Diversity collapsed.
The same shoreline with its sea stars intact stayed crowded with life. Barnacles, mussels, snails, chitons and several kinds of algae all found room because the predator kept any one species from claiming the entire surface. Paine later gave the pattern a name: keystone species. Remove the keystone and the arch of the community falls.
That single finding shifted ecology from lists of who eats whom to questions about which species exert outsized control. The ochre sea star became the textbook example. Its appetite for mussels and barnacles prevents those filter feeders from monopolizing space that other organisms need to settle and grow.
Photo by Clara Cordero on Unsplash
A modern echo on a much larger scale
Beginning in 2013, another kind of removal swept the Pacific coast. Sea star wasting disease struck more than twenty species from Mexico to Alaska. Sunflower sea stars, Pycnopodia helianthoides, suffered the heaviest losses—more than 90 percent in many areas. These large, multi-armed predators normally keep sea urchin numbers in check. Without them, urchins multiplied and grazed kelp forests down to bare rock.
Kelp forests that once swayed in the current became urchin barrens. The change ripples outward. Fish that shelter among the kelp decline. Crabs and snails that live on the kelp lose habitat. Carbon that the kelp once pulled from the atmosphere and stored in deep water stays in circulation instead. Coastal communities that rely on healthy kelp for fisheries and storm protection feel the difference directly.
Scientists have now identified the cause. In August 2025 a team led by researchers at the Hakai Institute and the University of British Columbia published evidence that a specific strain of the bacterium Vibrio pectenicida triggers the wasting symptoms. They isolated the bacterium from sick sea stars, grew it in pure culture, and showed that injecting it into healthy sunflower stars reproduced the disease exactly. The work fulfilled the classic tests for proving a pathogen’s role.
The loss of sunflower sea stars and the earlier Paine experiments both demonstrate the same principle. A predator that seems rare by biomass can still shape an entire ecosystem through what it eats and what it prevents from overrunning the habitat.
Photo by Fiona Dodd on Unsplash
Recovery signals and remaining questions
By 2026, small signs of rebound have appeared. Juvenile ochre and sunflower sea stars are turning up in tide pools that had been empty for years. In some places the young stars are already feeding on the mussels and urchins that expanded during the adults’ absence. Whether these juveniles will survive long enough to restore the former balance depends on water temperatures, the continued presence of the bacterium, and other stressors that remain under study.
Marine monitoring programs along the West Coast continue to track both the disease and the community-level changes that follow sea star declines. The data help managers decide where restoration efforts, such as captive breeding and outplanting of sunflower sea stars, are most likely to succeed.
The story that began with one scientist clearing tide pools now stretches across an entire coastline. What changes when starfish disappear is not simply the number of starfish. It is the architecture of the shore itself—the mosaic of species, the forests of kelp, the carbon stored beneath the waves, and the livelihoods tied to all of them.
