The marine creature ancient Americans ate billions of that's now a delicacy

Empty oyster shells are shown on the Damariscotta River in Maine. This site and others contain massive quantities of oysters harvested more than 1,300 years ago.

(CNN)Ancient humans ate copious quantities of oysters -- shucking billions of shells over thousands of years in a way that did not appear to cause oyster populations to collapse as they have in many places today.

New research, based on an analysis of dozens of archaeological sites in the United States and Australia, suggested that oysters were sustainably farmed on a massive scale by Indigenous groups. The mollusks were an abundant source of food despite being harvested intensively.
    The authors of the study, which published Tuesday in the scientific journal Nature Communications, said these sites were a "forgotten resource" that could inform the future management of oyster beds.
      "The fact that there are so many oysters at archaeological sites in so many different regions is an important lesson," said study author Leslie Reeder-Myers, an assistant professor of anthropology at Temple University in Philadelphia, in a statement.
      "These systems have a ton of potential and huge quantities of oysters can be sustainably harvested over long time periods if the ecosystem is healthy," said Reeder-Myers, who is also director of Temple's anthropology laboratory.
      The amount of oysters consumed in some places was staggering, the study found.
        A massive shell mound at the Crystal River site in Florida is shown.
        The researchers documented middens -- essentially trash piles -- that contained billions of shells. The largest total for a single site was an island called Mound Key in Estero Bay on Florida's Gulf Coast.
        Mound Key contained the shells of some 18.6 billion oysters harvested by the region's Calusa tribe, the study estimated. About 200 miles (322 kilometers) north in Cedar Key, Florida, a site known as Shell Mound features the remains of an estimated 2.1 billion oysters.
        Oyster shells discarded more than 1,000 years ago have been found at this eroding archaeological site on Maryland's Eastern Shore.
        The biggest shell middens towered up to 30 feet (9 meters) and were important ceremonial, sacred and symbolic structures. Others were much smaller, perhaps suggesting the camps were only used seasonally.
        The oldest oyster middens were found in California and Massachusetts and date back more than 6,000 years, the study said. The sites used over the longest periods span some 5,000 years.
        Today, places that were once rich in oyster beds like the Chesapeake Bay on the US East Coast, San Francisco Bay, and Botany Bay near Sydney, populations of the bivalve have be