For several years now, the starfish of America's Pacific coast have been dying by the millions, victims to a common virus that appears to have mutated over time.
Called sea star wasting disease, the effects of the virus (related to the parvovirus that affects dogs) are disturbing. The starfish's limbs will separate from its body, and lesions will form on the remaining limbs. The starfish eventually disintegrates into a pile of white goop.
In this National Geographic video, professor Ben Miner and his colleagues explore an area that was covered with starfish just a few years ago. The results of their dive are depressing—the disease has done its work, and the team found fewer than 20 live sea stars. Miner says there used to be thousands. "It's one of the largest mortality events associated with a disease that we've ever observed in the ocean," he says.
The loss of the starfish population has already begun to ripple through the ecosystem. Mussels, a common prey of the starfish, are experiencing a population boom and dominating formerly diverse areas. Sea urchins are also on the rise (which scientists suspect is linked to the starfish decline, but they cannot yet be sure). The urchins are depleting coastal kelp forests, which are home to many other species.
The hope is that some of the surviving starfish will remain unaffected by the disease, and be able to repopulate the area with offspring with a stronger immunity. Researchers remain hopeful.