Scientists believe they have uncovered the reason for a massive die-off off of starfish, killing millions of the creatures along the California coast.

The epidemic appears linked to a previously unidentified virus — SSaDV — and it threatens the food chain along the coast and could change the ecosystems of tide pools for many years, based on research from Cornell University, UC Santa Cruz, the Monterey Bay Aquarium, and a few other institutions, according to the San Jose Mercury-News.

The same virus responsible for killing the starfish can be found in starfish in museums dating as far back as 1942, suggesting that the virus is not a new phenomenon. However, none of the past outbreaks have been as big as the most recent one, which killed 95 percent of starfish in some areas and stretched from Mexico to Alaska.

Scientists say something must have happened recently to cause the virus to “go rogue.”

The virus is known as “wasting syndrome,” and it has been found in 20 species of starfish since first detected in June 2013 off the coast of Washington state. It eventually spread to Oregon, Monterey Bay, and as far south as Baja California in Mexico. It found its way into aquariums in Seattle, Vacouver, Monterey, and a few other cities, killing starfish there.

The virus causes starfish to become sluggish and develop white lesions. They then curl up and their arms start to break off. Eventually, the starfish turns to goo and dies.

Scientists have determined that the disease can be classified as a type of densovirus, similar to viruses that affect insect populations and other invertebrates, such as sea urchins. It is a distance relative of the parvovirus, which affect dogs and cats.

Researchers called it a “huge breakthrough” that could help them start addressing the problem. Now, scientists can look into what triggered the epidemic and if there are problems in other species.

They have found that the same virus can be found in sea urchins and sand dollars, but those creatures aren’t dying off like the starfish.

Scientists believe the virus, which is no danger to humans, may be a natural phenomenon that will simply have to run its course, as finding a cure would be impossible.

It’s not easy to find the virus, either, as researchers noted that there are 10 million viruses in a drop of seawater, making such a search nearly impossible.

Scientists were able to learn how the disease spread by taking a small amount of tissue from starfish collected along the West Coast and injecting it into healthy specimens in lab tanks to observe it.

The next step will be to find out the reason for the wide spread. It could be natural, related to overpopulation, or it could be due to pollution or warming waters. If it’s the latter case, humans can take steps to reduce the problem.

However, researchers believe it is “probably” part of their population cycle.