A mysterious pathogen is wiping out starfish along the Pacific coast, a potential catastrophe that has flummoxed marine biologists who are joining forces to find the culprit.

The uncontested star of tide pools is withering and dying by the thousands, disappearing from large areas along the entire coast. Nobody knows what is causing the die-off, but the killer - most likely some kind of virus, bacteria, or pollutant - is widespread and extremely virulent. It has ravaged a variety of starfish species in tide pools and in deeper water along the coast from Mexico to Alaska.

Pete Raimondi, a marine biologist and lead researcher on a team of scientists, laboratory technicians, and geneticists, said he has seen 90 percent of the sea stars, as the multi-armed marine invertebrates are also known, die within in an infected area in less than two weeks.

"Where it has hit, it has been lethal," said Raimondi, a professor in the Department of Ecology and Evolutionary Biology at the University of California, Santa Cruz. "This is going on up and down the coast. It's going to change what's out there pretty fundamentally."

Syndrome Discovered

The disease, which has been dubbed "sea star wasting disease," was first detected last summer in tide pool areas along the coast of Monterey. Raimondi, who teaches a class in kelp forest ecology, soon began noticing dead and dying starfish further underwater during dives with his students.

Researchers in Sonoma County and in Washington state also detected the syndrome, which causes the starfish to become mushy and deteriorate until body parts begin falling off.

Raimondi said there seems to be a progression, or sequence, of infection in which different starfish species get the disease at different times.

"The Ochre star, the purple or orange starfish most commonly seen in intertidal regions, is typically the first to get hit," he said. "It's dying in huge numbers. We've seen them go from a lot to zero fast."

The disease has spread from the shoreline into deeper water, ravaging the population of sunflower stars, the largest sea stars in the world. Short spined sea stars and giant sea stars have also been hit hard.

"The ones that get it first are all predators," Raimondi said of the starfish, which have very few predators and feed on a variety of invertebrates, including mussels, sea urchins, clams, and snails.

Monterey Aquarium Hit

The disease has even found its way through the filtration system of the Monterey Bay Aquarium, which uses sea water in its tanks. Michael Murray, the director of veterinary services, said the aquarium carefully controls temperatures and other factors like salinity, but cannot keep out natural impurities.

"There is something going on in the water," Murray said. "Unfortunately, we're not really sure what it is, so we really don't have the ability to say what it isn't."

Raimondi said he believes the starfish are succumbing mainly to a secondary bacterial infection caused by the disease, which spreads in the water almost like the common cold among the dense, often interwoven, populations of starfish.

UC Santa Cruz biologists are collecting samples up and down the coast from Washington to California while scientists from Western Washington, Cornell, and Brown universities are trying to isolate the pathogen in the laboratory. They are looking for marine biotoxins and viruses and exploring a variety of possible sources, including radiation from the debris that washed across the Pacific Ocean after the 2011 Fukushima disaster.

"We're not throwing anything out yet," Raimondi said.

Ecological Impact

Although he doubts it will result in extinctions, Raimondi said the loss of so many starfish could have serious consequences as mussels and other starfish prey begin to overpopulate areas where their numbers were once controlled. As a result, he said, fish, invertebrates, crabs, and other species that feed on algae, plants, and other sea life that thrive when starfish are in control will be marginalized and forced to look elsewhere for food.

"It just started, so we don't know yet what it is going to do," Raimondi said. "The theory is that there is going to be a fundamental shift" in the balance of sea life.

Starfish die-offs have occurred in the past, but Raimondi said they have been localized and clearly associated with specific events, like a sewage spill or a sudden influx of warm water. The last substantial sea star die-off occurred during the 1998 El Niño weather pattern, but that was restricted to Southern California.

It isn't the only weird thing to happen of late along the California coast. Marine scientists have been trying to find out why previously unknown blooms of toxic algae are suddenly proliferating along the coast. The mysterious blooms, including deadly red tides, have been bigger, occurred more frequently and killed more wildlife than in the past.

Last year at about this time, legions of big predatory Humboldt squid gathered along the Northern California coast and stranded themselves on Santa Cruz beaches, far north of their normal habitat.

Other Wildlife Healthy

By most accounts, though, the California ocean ecosystem has been healthy. Herring were abundant in San Francisco Bay last year, and there are plenty of salmon off the coast. Harbor porpoises, bottlenose dolphins, and orcas have returned to the region in larger numbers than anyone can remember, while humpback and other whale migrations have been growing.

The strangest thing about the starfish die-off is that it is happening at a time when ocean temperatures along the West Coast are going through an extended cool period, something normally associated with ocean abundance. So far, Raimondi said, there are no signs that the mysterious killer is slowing down.

"Usually it is pretty obvious what is causing it. None of those factors exist," he said. "I don't think it's the end. We see it in more and more sites."