In Southern California, sea stars may be staging a comeback after a mysterious disease devastated populations and species across the West Coast, per the Orange County Register. Scientists in southern California report seeing adult stars in tide pools for the first time in years.

Why it matters: Sea Star Wasting Syndrome causes the animals to melt and dissolve in just a matter of days before they die, limbless. Sea stars are considered a 'keystone species', which means they play a bigger role in supporting their ecosystem that other species. When they're removed from their environment, biodiversity drops rapidly.

Yes, but: This is just one area, and this doesn't mean the disease is gone. A major outbreak is happening in the Salish Sea in Washington, and the disease appears to be persisting at low levels from North/Central California up through British Columbia.

Some good news: Across the coast, there's been an abundance of baby sea stars. This 'pulse', first identified a few years ago, appears to be growing, per a September report by UC Santa Cruz researchers. Although some juveniles show signs of the disease, researchers hope they'll prevent the populations from collapsing.

The history: Sea Star Wasting Syndrome first appeared in ochre stars off the coast of Washington in 2013, and spread to several species up and down the West Coast by 2015. Die-offs like this have happened in past decades, but only in isolated areas. There's never been a coast-wide die-off before.

What's happening: So far, scientists don't know if the disease is caused by a virus, a bacteria, or a combination thereof. Anecdotally, some sea stars seem to do better when treated with antibiotics, but that could be because virus-caused lesions are prone to infection. A USGS study found the illness was caused by something virus-sized, and other research has implicated densovirus.

Go deeper: The University of California, Santa Cruz maintains a database of sea star die-offs and issues reports several times a year.