WELLS, Maine -- Scientists working on an assessment of salt marshes along the U.S. coast say half of those they studied will be gone in 350 years if lost ground isn't regained.

Salt marshes provide vital habitat for animals and are important for their role in coastal protection. But the ecosystems along the coasts are falling victim to pressures such as sea-level rise and changing land uses, and are flooded frequently by seawater.

The U.S. Geological Survey set about to determine the danger erosion poses to eight salt marshes on the two coasts. The agency says it was surprised to find all eight of the marshes losing ground, some severely.

The study involved marshes in California, Maine, Maryland and New Jersey.

"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 U.S. 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, Massachusetts-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 and including 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."

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