In the summer of 2013, the ochre sea stars of the California coast fell victim to a deadly plague.

First they developed ominous white patches. Then, in a touch straight from a horror movie, their rotting arms began to detach from their bodies and crawl away. They didn’t make it far.

“They just kind of dissolve within days,” said Lauren Schiebelhut, a biologist at the University of California, Merced, who studies the creatures.

More than 80 percent of the ochre sea stars on the northern coast died as a result of that outbreak of sea star wasting syndrome, as the disease is called. In the wake of the devastation, Dr. Schiebelhut and her colleagues looked at the survivors and wondered: Did they have something that the dead did not?