WELLS, Maine — Ridgway’s rail is a rare bird that relies on the salt marshes south of Los Angeles to survive. And that’s why its future is in doubt — the salt marsh is disappearing under rising seas.

Scientists working with the federal government said the rail’s plight at Seal Beach National Wildlife Refuge is indicative of what’s happening to salt marshes around the country.

Their assessment of eight of the country’s coastal salt marshes found that half would be gone in 350 years if they didn’t regain some lost ground. The other four also are backsliding, and coastal communities and wildlife will suffer as the marshes continue to deteriorate.

‘‘That’s something that’s happening right in front of our eyes — an endangered bird that doesn’t have anywhere to nest anymore,’’ said Neil Ganju, the lead author of the study.

Salt marshes are ecosystems along the coast flooded frequently by seawater. They provide vital habitat for animals, such as birds, crustaceans, and shellfish, and are important for their role in protecting coastal areas where people live from flooding and erosion.

The US Geological Survey set about to determine the danger that erosion poses to eight salt marshes on the two coasts. The group, led by Ganju, a Woods Hole, Mass.-based oceanographer, was surprised to find all eight marshes losing ground, some significantly. Their findings were published in January in the journal Nature Communications.

The scientists said salt marshes around the country are falling victim to pressures such as sea-level rise, land development, and damming rivers. Natural erosion also plays a role.

The group found that Blackwater National Wildlife Refuge in Maryland, Schooner Creek in New Jersey, and Reedy Creek and Dinner Creek at New Jersey’s Forsythe National Wildlife Refuge are unlikely to survive beyond 350 years from now. Seal Beach, Point Mugu Naval Air Station in California, Rachel Carson National Wildlife Refuge in Maine, and Fishing Bay Wildlife Management Area in Maryland also are losing ground, albeit more slowly.

The group used aerial photography and other remote sensing techniques to determine how much of each marsh was open water and how much was covered by plants. The team used that data to determine which of the marshes are best equipped for survival.

Ganju said the information will be useful for conservationists and land use managers looking to restore salt marshes.

The report illustrates that salt marshes are not keeping up with the rise of sea levels, said Joe Kelley, a University of Maine professor of marine geology who was not involved in the work.

‘‘Somebody in 50 years who looks at some of the marshes we’ve looked at, they’ll just see lots of open water,’’ Kelley said.

The study has also gotten the attention of environmental groups that have advocated for decades for the health and preservation of salt marshes. The research is a wake-up call to start working to preserve the marshes before it’s too late, said Stephanie Wear, a senior scientist with The Nature Conservancy.

‘‘This is probably a realistic forecast which would not bode well for coastal communities in long term,’’ she said. ‘‘There are many ways to address the potential loss and prevent it — studies like this play an important role in putting a spotlight on a problem so we can give it the attention it deserves.’’