From the plane flying over the Gulf Islands National Seashore, scientists from the U.S. Geological Survey were scanning the ocean, trying to find Ship Island. Their maps and GPS system told them they were over its eastern end, but there was no sign of it.

"I don't see Ship anywhere," said Asbury H. Sallenger, a oceanographer at the Geological Survey who was sitting in the co-pilot's seat and had the best view. "On the map we see it, but all I see is breakers. There is just zip left of this thing."

Eventually, the scientists spotted the western part of Ship, but its eastern half had all but disappeared. A small patch of land and whitecaps breaking on underwater shoals were all that remained.

The damage was considerable, but it was the kind of land loss they would see often on their flight, which they made about 48 hours after Hurricane Ike struck the Gulf Coast, as part of the survey's long-standing effort to track storm damage on the coast.

The geologists should not have been surprised. Scientists studying the way stormy weather erodes the coast have long been able to identify regions at risk for inundation if sea-level rise continues, an inevitability in a warming world.

For example, researchers have estimated that large stretches of another barrier chain, the Outer Banks of North Carolina, will vanish if seas rise more than 2 feet, which many scientists consider quite likely by 2100.

But on the Gulf Coast, "we are not talking 100 years," Sallenger said, "we are talking three years," the time since Hurricane Katrina and a parade of other storms, including Hurricanes Gustav and Ike this year, virtually destroyed several islands running west into Louisiana. Among them are the Chandeleur Islands, a barrier chain formed thousands of years ago in a now-defunct delta of the Mississippi River, and other islands in the Breton National Wildlife Refuge.

Storms and climate change are partly to blame. But the region as a whole is subsiding. And in some areas, some critics contend, federal dredging projects are robbing islands of sand.

The result is a chain of feeble island remnants. In many places, as Sallenger observed at one point, "there ain't nothing here but white water."

So Karen Morgan, a geologist at the Geological Survey making photos of the landscape, at times found herself instructing the pilot, Rob Kent, to navigate not by a shoreline but by a line of white water breaking over the submerged shoals that are the islands' remains. In some places, there were not even breakers to show where dry land had been.

These islands are uninhabited, but they are valuable nonetheless, and not just for storm protection. With their extensive dunes and vegetation, the islands were once an important nesting place for brown pelicans and a variety of other birds. In the last few years, Sallenger said, the Chandeleurs have lost about 85 percent of their land mass, and with this loss "the habitat for birds on the flyway has decreased by an enormous percentage."

Of course, the islands have not vanished altogether. And the scientists, who fly this coast regularly, have many times seen islands in these chains erode in storms and then recover -- at least somewhat. But that can happen only as long as their underlying platforms of marsh remain intact, providing a place for sand to collect. In many places today, those platforms are "frail and really beaten down," Sallenger said.

Sallenger said the Geological Survey scientists would try to advise officials at the Fish and Wildlife Service, which administers the refuge, what they could expect in the next five to 10 years. The outlook is grim.

Will the islands bounce back? "We are going to look at the data again," Sallenger said. "It looks very tenuous."