Nate Fletcher / Pacific Rocky Intertidal Monitoring Lab, University of California at Santa Cruz A sea star affected by "wasting syndrome," photographed by researchers on the West Coast, has lost two arms and part of a third.

When marine researchers from the University of California at Santa Cruz traveled to Alaska this summer, they noticed something unsettling in the waters near Sitka: populations of starfish were losing their arms. Then other reports started pouring in to their laboratory: from Southern California to British Columbia, uncounted numbers of one of America’s best known sea species appeared to be disintegrating.

It’s normal for a tiny portion of starfish populations to suffer from so-called “wasting syndrome.” If the creatures’ skin is wounded or becomes too dry, little lesions can become infected and lead to the loss of arms. But the disease is typically isolated to one or two starfish among hundreds in a rocky tide pool. And even in bad cases, it rarely stretches beyond a single population. “The spatial extent is unprecedented,” says Pete Raimondi, chair of the ecology and evolutionary biology department at UC Santa Cruz, which monitors starfish populations on the West Coast. “If it’s as extensive as it looks like it is, then we’re talking about a loss of millions and millions.”

While starfish—which scientists call sea stars to avoid the misconception that they are actually fish—often recover from the lesions, infections on the West Coast are proving lethal. Populations of starfish monitored by Raimondi have essentially disappeared over a period of months. “They will start losing arms or bits of arms and in the end, they kind of disintegrate … into a gooey mess,” he says. An individual sea star may go from whole to remains in a period of days. Though starfish generally have the ability to grow new arms, in these cases wounds don’t heal and innards become exposed as the animal falls apart.

So what gives? It could be environmental factors, a virus, bacteria or some combination. Wasting syndrome actually describes a whole set of symptoms without a universal cause. When other outbreaks struck the West Coast in recent decades, scientists identified warm water as the likely culprit. Starfish are primarily cooler water species, so when the water heats up, it compromises their health, making them more susceptible to infected wounds, Raimondi says. Bacteria also divide faster in warmer temperatures, meaning disease can spread more quickly. But the West Coast has been in a cold-water period. “Right now, we don’t really have a culprit,” Raimondi says.

Scientists on the East Coast have observed similarly mysterious starfish deaths in recent years. Researchers at universities like Cornell and Brown are working to figure out why. The state of California recently dedicated $50,000 to starfish experts at their state universities, who are sending a specialized team to sweep the coast for evidence of wasting in coming months. UC Santa Cruz is also running a website on which ordinary beach-goers can learn how to report sightings. It may yet turn out that the disease isn’t as widespread as reports suggest; concerns now are based on a small sample of the starfish living along the Western seaboard.

So far, the species that seems to be taking the biggest hit is pisaster ochraceus, a starfish that can be reddish, orange or purple and up to 18-in. (46 cm) from arm to arm. It’s also one of the most common species in Pacific tide pools. Researchers in Washington are investigating reports that another species, a 24-armed giant known as the sunflower starfish, is falling prey to the disease. Raimondi says about 10 other species have shown symptoms.

Identifying the root cause of the problem isn’t going to be quick or easy. And discovering what’s happening on one coast doesn’t necessarily explain what’s happening on the other. Ben Miner, a biology professor at Western Washington University, says he expects to have a clearer picture in a couple months. He cautions that if this does turn out to be a worst case scenario, other animals will feel the impact, as the lack of starfish ripples through the ecosystem. “We just started looking,” Miner says. “If this is affecting sea stars up and down the coast, we’ve never seen anything like that before.”