In just 100 years, the emblematic stone sculptures that guard the coastline of Easter Island could be little more than simple rectangular blocks, conservation experts are warning.

Carved centuries ago, the heads represent the ancestors of Easter Island’s Polynesian people, the Rapa Nui, and have brought it UNESCO World Heritage site status.

Dozens of giant Moai statues dominate the hillsides surrounding the island’s Rano Raraku wetland, but they are facing the threat of what locals describe as a kind of leprosy: white spots that are appearing on their iconic facades.

Caused by lichens, a marriage of fungi and algae, the patches eat away at the sculptures, softening them to a clay-like consistency and deforming their features.

The statues must also contend with coastal erosion, rising sea levels, high winds and damage from freely roaming livestock.

“I imagine that in a century more, these Moai will basically be rectangular figures,” said Tahira Edmunds, adviser to Chile’s National Forestry Corp., who has worked on cleaning the sculptures to remove the lichen.

Archaeologist Sonia Haoa, an Easter Island native, is compiling an inventory of its heritage, including the Moai. She estimates that about 70 percent of the more than 1,000 statues are affected by lichens.

Although the deterioration can appear shocking to visitors who flock to the volcanic island 3,500 kilometers (2,200 miles) from mainland Chile, Haoa said it is still possible to save them through laborious cleaning and coating with sealant chemicals to curb moisture and prevent the porous volcanic rock from collapsing.

The most famous Moai groupings — such as the Ahu Tongariki, 15 statues arranged along a platform by the sea, and those scattered around the source of the stone, the Ranu Raraku quarry — are already being cared for by heritage experts and the indigenous community’s administrators of the Easter Island tourism park.

But the island has at least 30,000 archaeological sites spread across its 166 square kilometers (64 square miles), most of which are exposed to the environment.

Protecting all the statues could cost as much as $500 million, and international help will be needed, according to local authorities and experts.

“You will never be able to entirely prevent the impact of time or the weather, but you can hold it back so that more people can see them first,” Haoa said.

With no government fund specifically dedicated to preserving the island’s heritage, the community allocates a large part of its income from tourism to repair and protection. They say resources are scarce.

The mayor of Easter Island has come up with an innovative solution: seeking royalty payments from nations whose explorers took some of Easter Island’s statues into their possession centuries ago.

Among them is the Hoa Hakananai’a, a 7-foot-tall (2.1-meter) basalt statue that has become one of the British Museum’s most popular exhibits since it was removed from the island by British sailors more than 150 years ago.

The Easter Island authorities and the Chilean government sent a delegation to London in November to request the return of the 4-ton statue. The museum responded that it was happy to consider a long-term loan of the Moai.

Mayor Pedro Edmunds Paoa instead suggested the Hoa Hakananai’a could act as an “ambassador” for Easter Island, and Britain could keep it in return for regular payments to ensure the upkeep of its Easter Island counterparts. “We would win much more,” he said.

Although Easter Island’s heritage is more than just statues, their celebrity could be the key to sustaining it all.

“What do you leave to a 10-year-old boy, what will there be in Easter Island for the European or Chilean tourist to come see if we don’t save them?” Paoa asked. “It’s the only oil well we have.”