Scientists puzzled by massive North American starfish deaths
Starfish on a sandy ocean floor (Shutterstock)

Scientists are struggling to find the cause of a disease that is killing off numerous species of starfish on both the Pacific and Atlantic coasts of North America, dispatching the five-armed creatures in a particularly gruesome way.

Researchers said on Thursday they have ruled out some possible culprits including fungi, some parasites and certain other microorganisms and are taking a hard look at whether viruses or bacteria may be to blame.

The starfish, also called sea stars, are being obliterated by an unexplained wasting disease that causes white lesions to appear before the animal's body sags and ruptures and it spills out its internal organs.

"The magnitude of it is very concerning. There's the potential that some of these species could actually go extinct," said Cornell University ecologist Drew Harvell, one of the scientists involved in the loosely organized search for a cause.

Harvell said she is concerned because the mysterious pathogen is affecting 18 different West Coast species along their entire range. Pathogens that affect an animal's range in such a way like a fungus that has targeted frogs can be particularly damaging, she said.

The disease appeared last year and is showing no indication of abating. "I wish we had a sign that it was petering out, but believe me it definitely is not," Harvell said.

The scientists seem to have more questions than answers.

"What is it that has caused this? Where did it come from? If it's exotic, how did it get here? Is it something that's likely to be repeated?" asked Pete Raimondi, chairman of the Department of Ecology and Evolutionary Biology at the University of California, Santa Cruz.

Raimondi expressed concern that the disease that is killing the starfish could be a harbinger of bad things to come for other marine species. "This is a really difficult disease in lots of ways because it's very virulent," Raimondi said.

The researchers noted that starfish were the victims of previous diseases in past decades that reduced their numbers, but the current one is more serious.

The scientists are wondering whether the starfish have been infected by a virus, bacterium or something else unwittingly imported to the region or whether a pathogen already present somehow became more dangerous, Raimondi added.

Scientists prefer to call the animal a sea star rather than a starfish because these marine creatures are not fish but rather echinoderms, cousins of sand dollars, sea cucumbers and sea urchins. Most have five arms, although some have many more.

They are remarkably durable creatures, and when healthy are able to regenerate lost limbs. They are predators and use suction to pull shells apart to get at the soft body inside. When the shells are pried opened, the starfish pushes its stomach out of its body and into the prey, secreting enzymes that digest the victim's soft body parts.

They are significant predators in their ecosystems, the scientists said.

"These animals are really important ecologically. If they do go extinct, or at least ecologically extinct for some period of time, there undoubtedly would be some really huge impacts on the ecosystems that they live in," said Bruce Menge, a marine community ecologist at Oregon State University.

(Reporting by Will Dunham; editing by Andrew Hay)