POINTE-AUX-CHENES, La. — On the brackish waters of Louisiana, about 40 miles southwest of New Orleans, residents mark the passage of time by the landmarks that have been lost to the tide. In their 60-plus years, Theresa Dardar and her husband, Donald, two of the 790 tribal members of the French-speaking Pointe-au-Chien tribe, have seen their ancestral land transition from cattle pastures to marshes and then to open water. Traveling in their flat-bottom boat, the Dardars pointed out the canals dug by oil companies to access oil fields and bury pipelines. Those canals are accelerating the erosion that is causing Louisiana to lose an average of a football field of land every 100 minutes. A nearby tribe, the Isle de Jean Charles band of Biloxi-Chitimacha-Choctaw, just four miles away, is planning to retreat inland. “We are trying to save everything we can for the moment,” said Theresa. At stake is a sacred tribal mound, one of a complex of five that dates to 900 A.D. The purpose of the mounds isn’t clear, said Charles “Chip” McGimsey, Louisiana’s state archaeologist, but they were occupied and used, possibly for ceremonial purposes. Theresa said her ancestors carried dirt to build the mounds in baskets woven with palmetto leaves. Now one of mounds is being carried away by 60-foot-wide canal that was once a 3-foot-wide ditch marking a property boundary. The Dardars and their tribe are turning to an unlikely source for the mound’s salvation: 400,000 pounds of oyster shells discarded from New Orleans restaurants.

Emily Kask for HuffPost Theresa and Donald Dardar pose for a portrait in the Pointe-au-Chien community in Lafourche Parish, Louisiana., on May 19, 2019.

With $65,000 in grants from the National Oceanic and Atmospheric Administration and the local government, as well as help and recycled oyster shells from the Coalition to Restore Coastal Louisiana (CRCL), the Pointe-au-Chien tribe is building a 400-foot-long oyster reef along the eroding banks. Oyster reefs are strong and enduring barriers against storm surges and habitat erosion — and more cost-effective than almost any other type of shoreline protection, natural or manmade. They also provide food and healthy habitat for fish and other marine life, and can clean pollution from water. A single oyster filters up to 50 gallons of water a day. Earlier this year, 100 volunteers — from the tribe, New Orleans businesses, and environmental groups — stacked 30-pound nylon string bags of oyster shells next to the shoreline until the columns reached about 6 feet high, just below the water’s surface. (The bags don’t interfere with the oysters or other marine life.) Once in the water, the shells attract oyster larvae that will attach themselves to the old shells and begin to grow their own. This process will continue for the life of the reef, cementing the oyster shells in place and creating a living, continuously growing shoreline. Studies have shown oyster reefs can even adapt to rising seas and sinking land.

Rebuilding The Reefs Around the country and around the world, natural oyster reefs are being lost at an alarming rate. A 2011 study found 85% of all oyster reefs had been lost worldwide, due to factors such as over-harvesting and pollution. Along the Gulf Coast — once home to massive reefs, including one that researchers call the Great Barrier Reef of the Americas — 50 to 85% of reefs have been destroyed by dredging, mining and changes in water composition and quality. The 2010 Deepwater Horizon oil spill resulted in the deaths of between 4 and 8.3 billion sub-tidal oysters along the coast, even in the waters normally harvested by Dardar and other tribe members, according to assessments. Populations have recovered, but not entirely. In Alabama, last year’s oyster season was called off after only 136 sacks of oysters were harvested in 2017, compared to 7,000 sacks in 2013. The National Oceanic and Atmospheric Administration, among others, is trying to stop the trend. NOAA has funded 70 oyster reef restoration projects in 15 states. The U.S. military is building oyster reefs to protect bases in Florida, Virginia and New Jersey. Oyster beds are being replanted in Puget Sound, Washington, as well as New York Harbor to revive dwindling oyster populations and help clean the water. Many of the efforts, such as in Pointe-aux-Chenes, are not intended to produce oysters for harvest. (Indeed, in polluted waters like New York Harbor, the mollusks aren’t safe to eat.) But by building a healthy population of oysters that produce larvae, the reefs can help sustain existing oyster fisheries and provide habitat for other fisheries, explained Earl Melancon, a Louisiana State University biologist and expert in oyster restoration who works with NOAA. Many members of the Pointe-au-Chien tribe count on fishing, shrimping and harvesting oysters for income.

Emily Kask for HuffPost Wood pallets loaded with oyster shells ready to go into the water at the Coalition to Restore Coastal Louisiana oyster shell collection center in Buras, Louisiana., on May 21, 2019.

Rebuilding oyster reefs won’t work everywhere, Melancon said. In some areas, the water is too rough and oyster larvae can’t get to the oyster shells to start growing. In other areas, the water salinity isn’t just right. “It’s kind of an art and a science,” that includes a lot of trial and error, said Seth Blitch, coastal and marine conservation director for The Nature Conservancy in Louisiana. Where it does work, it can work wonders — and fast. CRCL completed its first oyster reef in 2016 in Biloxi Marsh, near the Mississippi border. Last year’s sampling of the half-mile-long reef found it had three different sized classes of oysters and had slowed erosion by half, said Deborah Abibou, restoration programs director with CRCL. Abibou and others are pushing Louisiana to include more oyster reef projects in its $50 billion coastal master plan, an ambitious effort to stem the loss of land in Louisiana by rebuilding barrier islands and building wetlands by diverting sediment from the Mississippi River. “In those areas where we can’t save the marshes, we can still transform it into a productive habitat that provides a lot of risk reduction and other benefits to communities as opposed to just letting it go into the open Gulf of Mexico,” said Natalie Peyronnin Snider, director of science policy for the Environmental Defense Fund’s Mississippi River Delta Restoration program. Paying It Forward While man-made reefs can be built out of limestone or concrete, oyster larvae prefer to latch onto oyster shells, said Melancon. But the shells, which can be used for everything from a road base to a supplement to chicken feed, are in short supply and can be expensive to purchase. So, all along the nation’s coasts, a growing number of programs that recycle shells from restaurants are helping to jumpstart restoration efforts. One of the largest programs in the U.S., the Oyster Recovery Partnership in the Chesapeake Bay, collects 2.3 million pounds of shells a year from 350 restaurants in Virginia, Washington, D.C., and Maryland, which greatly offsets the cost of buying solely from shucking houses, said Stephan Abel, executive director of the partnership. The restaurants get value from the program too, said Karis King, a spokeswoman for the partnership. “They like that sustainable green halo,” she said. “It’s a win-win.” Earlier this year, Mississippi announced it will use $650,000 of BP oil spill money to begin recycling oyster shells to help rebuild the oyster population in the Mississippi Sound. In Louisiana, which produces more oysters than any other state in the nation, there are plenty of shells to recycle. CRCL collects roughly 50 to 60 tons of shells, or 100,000 pounds, each month, Abibou said, and has collected more than 4,115 tons since the recycling program started in 2014.

Emily Kask for HuffPost LEFT: Jose Orlando dumps the shells of eaten oysters into the collection bin in the kitchen at Superior Seafood in New Orleans, Louisiana., on May 16, 2019. RIGHT: Sydney Comeaux of Superior Seafood collects oyster shells into a bag at the Coalition to Restore Coastal Louisiana oyster shell collection center in Buras, Louisiana., on May 21, 2019.