DAMARISCOTTA, Me. — Alice Kelley stood on the bank of a tidal river, next to a grassy bluff dotted with apple trees. This is not just a scenic spot: Hidden beneath the grass is a massive pile of oyster shells left by Native Americans. And hidden among those shells are rich, detailed stories thousands of years old.

Middens like this one line Maine’s tortured shoreline. “We know that there are over 2,000 shell heaps on the coast of Maine,” said Dr. Kelley, an associate research professor at the University of Maine Climate Change Institute. “In virtually every case here in southern Maine, they are disappearing or they are gone.”

Dr. Kelley was speaking at Maine’s best-known site, the Whaleback Shell Midden State Historic Site, during a recent conference she organized to discuss the vulnerable shell heaps.