GAINESVILLE, Fla. — What do St. Augustine’s Castillo de San Marcos and Egmont Key near Tampa have in common? They are two of thousands of Florida’s heritage sites that are vulnerable to rising seas. "Jupiter Lighthouse, Fort Zachary Taylor in Key West, Fort Jefferson and Fort Pickens in Pensacola — all of these places are threatened," said Clay Henderson, executive director of Stetson University’s Institute for Water and Environmental Resilience.The Castillo de San Marcos withstood two sieges in 330 years and changed hands five times, but its latest invader — the rising Atlantic Ocean — threatens to erode the historic St. Augustine fortress.The coquina shell walls of the oldest masonry fort in the United States once absorbed cannonballs but will be susceptible to the buffetings of the sea.On the other side of the state, Egmont Key was named one of the state’s 11 most endangered places this year by the Florida Trust for Historic Preservation because rising seas threaten to submerge the island. Just outside Tampa Bay in the Gulf of Mexico, the island holds sacred significance for the Seminole Tribe of Florida, as well as the ruins of another Spanish-American era fort, but its elevation is just six feet."It’s the first project that we’ve placed on our annual endangered list because it’s endangered by sea level rise," said Clay Henderson, who was president of the trust when the key was added to the list earlier this year.Read more:From 2011 to 2015 the sea level rose faster in Florida and the southeast U.S.Like the St. Augustine fort and Egmont Key, thousands of Florida’s heritage sites are vulnerable to rising seas, said Henderson, executive director of Stetson University’s Institute for Water and Environmental Resilience. "Jupiter Lighthouse, Fort Zachary Taylor in Key West, Fort Jefferson and Fort Pickens in Pensacola — all of these places are threatened.""When you look at St. Augustine, the oldest city in existence in our country, and it’s flooded twice in the last year, these are real threats," he said. "They’re no longer academic and off in the future. They’re in real time."Growing concernsSimilar concerns are growing across the state and country as experts begin to assess what could be damaged or lost and how soon that could happen. In some places, damage already is occurring.Federal scientists say seas in parts of Florida have risen at a rate of about a third of an inch a year over the past decade. Mid-range forecasts from the National Oceanic and Atmospheric Administration indicate seas could rise anywhere from 13 to 39 inches in Florida by 2070 and as much as 72 inches by 2100.Native American burial mounds, antebellum mansions, cemeteries, cracker-era cabins and even examples of more contemporary but unique-to-Florida architecture could be submerged if they are not somehow salvaged.Not everything will be saved, said Lorrie Muldowney, a trust board member and former head of Sarasota County’s Historical Resources Department. "We’re not going to move everything. We’ll have to make choices."Efforts to save heritage sites will compete for attention and money with the scramble to shore up roads, utilities and neighborhoods against the rising water.A team of scientists led by David Anderson with the University of Tennessee recently analyzed an index of thousands of archaeological and historic sites across the Southeastern United States. They concluded roughly 3.3 feet of sea level rise could submerge 19,676 archaeological sites in the region.It would result in the loss of a substantial portion of the "historic period human habitation of the coastal margin in the Southeastern United States," concluded the study, published in late November in the journal PLOS One.The study’s authors, also from Northern Kentucky, Indiana universities, added that many resources, including native American sites, might be missing from the Digital Index of North American Archaeology.If, or when, the higher end predictions for sea level rise materialize, the number of threatened resources and historical sites rises exponentially. Florida — low, flat and surrounded by water — stands to see the biggest losses.Neither the state nor the federal government could provide a specific list of Florida’s most threatened historical resources. But the Trust for Historic Preservation cites a 2013 state study that estimated 16,015 historical resources in Florida could be affected by a 39-inch rise in sea level. That number would rise to nearly 35,000 with a six-foot rise in sea level, the Trust stated.Read more:How rising sea levels will reshape the face of the Tampa Bay areaThe realization of the magnitude of resources at risk has gotten the attention of the archaeological and historic preservation communities. State and national conferences the past three years have compared challenges and strategies, exploring measures such as living shorelines, sea walls, elevation and relocation. Professionals and volunteers interested in archaeology and historic preservation have launched a comprehensive effort to document and monitor the expected impacts to known historic sites in Florida.But while the experts say they’ve seen interest increase exponentially, action plans and solutions aren’t materializing as quickly.The Florida Public Archaeology Network is focusing on building partnerships with land management agencies around the state and hopes to work with cities and counties to document historical resources, said Della Scott-Ireton, associate director of the network. But at this point, she said, "there are a lot of people with their heads in the sand, even as coastal sites already are eroding.""It’s mind-boggling to me," said Scott-Ireton. "It’s not about belief. It’s happening."Coastal and riverfront communities in Jacksonville have seen incremental sea level rise since the 1920s, said Adrienne Burke, executive director of Riverside Avondale, a Jacksonville nonprofit dedicated to preserving one of the state’s largest historic districts. Recent studies have shown sea level has risen faster over the past decade."Any additional sea level rise exacerbates flooding and storm surge," she said. "It’s something we need to be having discussions about and getting people prepared and asking questions about what that means for our neighborhoods."Read more:Poll: Majority of Floridians favor tax earmarked for environmental protectionIt will have economic, environmental and social impacts, she said. "I feel like at this point there are more questions than answers."So far, the chief strategy seems to be "abandonment in place," said Sarah Miller, northeast/east Central Florida regional director for the Archaeology Network. She’s based at Flagler College in St. Augustine, one of the network’s eight locations around the state.Location, location, locationMany of Florida’s resources are vulnerable because the state’s cultural and architectural history is so closely associated with its seas, bays, rivers and other waterways.Prehistoric tribes, European explorers, plantation owners and territory-staking pioneers settled near the shores. They fished the estuaries and traveled by dugout canoes, sailboats or steamships, relying on waterways as their highways long before roads and railways traversed the peninsula."If we think back historically, those waterways would have been routes of communication and resource-rich places that would have made a lot of sense to have population close to them," said Paul Backhouse, tribal historic preservation officer for the Seminole Tribe of Florida and director of its Ah-Tah-Thi-Ki Museum."Even today, our densest populations are close to coastlines and it was no different in the past with Native American society," Backhouse said.Two years ago, in a downtown Pensacola neighborhood, local historians and archaeologists uncovered evidence confirming the remains of the oldest multi-year European settlement in the United States. Don Tristan de Luna founded the Spanish colony in 1559, six years before St. Augustine was established. The ill-fated settlement was hit by a hurricane a month into its existence, sinking its six ships just five weeks after the 1,500 settlers arrived. The settlement survived only two years.Now, as sea levels continue inching higher, historians wonder what damage future hurricanes could wreak on other historical resources. Already the experts say they see increased damage from higher tides with passing storms and seasonal high tides.The projected number of at-risk historic sites mentioned in the various studies doesn’t factor in storm surge, said Sara Ayers-Rigsby, a Florida Public Archaeology Network director at Florida Atlantic University.Surging seasWhen Hurricane Matthew and Hurricane Irma struck within 11 months of each other in 2016 and 2017, seawater surged into St. Augustine, washed up to the lighthouse on Egmont Key, and impacted other historic properties around the state.Matthew was a wake-up call for many Floridians, but especially in St. Augustine, said Leslee Keys, director of historic preservation and special initiatives at Flagler College. Water swirled up through the breezeways in the Hotel Ponce de Leon.When Irma arrived 11 months later, folks in historic downtown St. Augustine were ready, Keys said, rigging handmade door dams to help keep the water out.South of St. Augustine, Fort Matanzas has been closed for much of the past 16 months. The fort itself is undamaged, but storm surge from the two hurricanes, Matthew and Irma, heavily damaged the ferry docks where boats take visitors to the tiny, historic fort on Rattlesnake Island.Surge impacts also have been seen at Fort Pickens on the northern Gulf coast and the nearby Gulf Island National Seashore. The seashore includes remains of a Native American site, a Civil War battlefield and the Persidio Isla De Santa Rosa, a Spanish settlement built in the Pensacola area after the area was recaptured from the French. The settlement existed from about 1722 to 1750.Despite already being submerged, the state’s many shipwrecks also are vulnerable."We think because they are already submerged we don’t have to worry about that," said Miller. But rising water temperatures and increases in salinity caused by rising seas could expedite deterioration of the sunken vessels, she said. For archaeologists checking on wrecks, "no-compression dives will become compression dives."Three shipwrecks identified as belonging to the de Luna party were recovered in 1992, but changes in salinity or turbulence can impact the ships. After Hurricane Matthew, Ayers-Rigsby said archaeologists discovered a shipwreck near St. Augustine shifted about 1,000 feet.Aside from storm surges, nuisance flooding from random higher-than-normal tides or heavy rainfall is occurring more often, Keys said. In St. Augustine, the city is working "very hard to try to repair the storm drains," she said, and talking about adding a resiliency action plan to its historic preservation plan.Cemeteries may prove to be an especially heartbreaking challenge for historians. At least 630 historic cemeteries are in perilous locations, considered threatened by increasing storm surges.Some cemeteries possibly could be salvaged, Keys said. She participated in a Kentucky project to relocate a Revolutionary War-era graveyard and another from the post-Civil War period to make space for new highways. The wooden coffins had deteriorated and could not be moved, she said. "We took the bones out and re-interred them."‘Hard truths’With the encroaching water threatening billions of dollars of infrastructure and thousands of homes, historic preservation experts know challenging decisions will be made in the years to come.It will require facing "some hard truths," said Linda Stevenson of Bradenton, a preservation architect whose projects have included circus magnate John Ringling’s home in Sarasota (Ca’ d’Zan) and the historic train depot in Venice. "We have to figure out how to best invest our resources."Resiliency is an important part of the conversation, said Burke of Riverside Avondale, but the fixes are going to get "really complicated" given the long-held standards and regulations used by the historic preservation community for grant eligibility and historic integrity. For example, elevating a structure to make it more resilient changes its historical integrity and its relationships to the buildings around it, she said. But the alternative might be losing the building entirely."There’s a lot of debate around that in the historic preservation world right now, she said. Some communities have built an entire economy around their historic districts, she said. If those districts start changing, will the tourists still visit?At Canaveral National Seashore, a barrier island along the scenic Mosquito Lagoon, the park is working with Linda Walters of the University of Central Florida on shoreline restoration efforts, said Kristen Kneifl, resource management specialist. The park also works with its Southeast Archaeological Center, she said, to study and document prehistoric Native American middens such as Turtle Mound and Castle Windy, as well as other historic sites, and develop methods of protection.Read more: Tampa Bay among top 10 regions most threatened by climate changeThe Florida Park Service also approaches the issue on a case-by-case basis and does not have a comprehensive list of the resources at risk, said Jason Mahon, a spokesman for the Department of Environmental Protection. In each park’s unit management plan, parks staff identify projects that would help with our coastal resiliency," Mahon said. "That’s one of the ways we would address that growing issue."The Seminole Tribe of Florida is very much involved with the statewide efforts, said Backhouse. The vast majority of archaeological sites across the Southeast are Native American, he said, and the region covers much of the historic homeland of the tribe. "The area we’re concerned about isn’t just Florida, Alabama and Georgia, it’s all the way up to Tennessee," he said. "It’s the entire southeastern United States."The tribe has been very public about its interests at Egmont Key, where hundreds of captured Seminoles were held during the Seminole Indian Wars. The key has been at the forefront of the Tribe’s conversations about sea level rise because of its significance in history, said Backhouse. Tribal members "were kind of dumped on the island and left to fend for themselves."Within the next 50 to 75 years, much of Egmont Key could be submerged, he said, its memories alive only in the stories retold by tribal elders. "We want the next generation of tribal elders to know what happened on this island," he said.Documenting historyAnderson and the scientists who collaborated with him on the new study called for development of a comprehensive database that includes information by state, federal, tribal and local government agencies to identify and create a triage system for the region’s cultural resources.They suggest consideration be given to relocating or building protective barriers for monuments such as the Castillo de San Marcos and Fort Matanzas. "Delay in thinking about these matters and in seeking solutions accomplishes nothing," the authors warn.The Archaeology Network is not waiting. The 20 archaeologists working in the program across the state have launched a massive effort to get the sites that could be in the path of the creeping sea confirmed and documented, training citizen scientists to observe and report their findings. The network is connected through the state university system and tries to work in partnership with public land management agencies, such as the state and federal park service and water management districts.More than 200 volunteers have been trained to assist in the efforts, including a group with the Seminole Tribe. Participants visit known archaeological sites and record what they see. They’re collecting hundreds of reports, building a baseline to be shared with the state, for the Florida Master Site File kept by the state Division of Historical Resources."Literally just having photos is one of the most helpful things," said Ayers-Rigsby. "Are there artifacts washed out? Are there sections that look like they’ve been washed away?"Volunteers also are expected to answer several questions, said Jeff Moates, the network’s west central director at the University of South Florida."Is there anything left?""Are there any human remains visible or present?"In Manatee County, Moates considers Indian middens and burial mounds near De Soto National Memorial, which commemorates the 1539 landing of Hernando de Soto, to be especially endangered. Other endangered sites include Perico Island, Emerson Point, Terra Ceia Island and the runaway slave settlement of Angola on the Manatee River.The effort to document the historic sites also includes checking to see if the site is mapped in the right place. Miller said some sites recorded 50 or more years ago have never been revisited.A site "may be described as being 40 meters from a road that is no longer there," said Ayers-Rigsby.Regardless of its location, after an archaeological site is confirmed and recorded by the network and its volunteers, eventually a decision will have to be made as to whether to excavate it and save its contents, or leave its fate to the rising waters.History goes high-techMorris Hylton III, director of the historic preservation program at the University of Florida’s College of Design, Construction and Planning, is preparing for the day when many of the state’s historic structures could be lost.Hylton is documenting buildings for posterity, using technology from another UF endeavor. The Florida Department of Transportation provided a grant to UF’s GeoPlan Center to create laser-scanned aerials of the state’s coastlines mainly to document roads and bridges, and then to run models indicating how sea level rise could affect that infrastructure. Hylton capitalized on that technology for what is being called the Resilient Communities Initiative.In February 2016, he laser-scanned a five-block area of Cedar Key from ground level, documenting historic structures from as far away as 150 meters with an accuracy of 2 to 4 millimeters. Using the data, he created three-dimensional, model images that he graphically "flooded" to determine the "vulnerability" of those assets. In September 2016, those projections proved to be precisely accurate when Hurricane Hermine submerged the same area.The technology will enable preservationists to create 3-D records of historic buildings that cannot be relocated, Hylton said. He has used it to document temples in Thailand and Myanmar and other historic buildings in the United States such as Steinway Hall in New York City. At a national historic preservation conference in Annapolis in the fall, Hylton showed the effects of flooding on the main street in Annapolis, home of the United States Naval Academy, established in 1845.In South Florida, Hylton recently scanned the stone breakwater barge behind Vizcaya, the historic estate on Biscayne Bay of tycoon James Deering, and the façade of the mansion. Other Florida venues on his to-do list include St. Augustine, Key West and other areas where historic structures may succumb to rising waters.The data could be used to construct exact replicas or, through virtual reality devices, to recreate structures as images so that future generations can "experience them."It won’t be the same as walking through an old fort or other historic building, he said. But it will be preferable to having no record at all.