Yubudo, South KoreaAs Byeongwoo Lee slowly walks across a sandy tidal flat on Yubudo, a small island off the west coast of South Korea, the birding guide does so quietly.
“You can’t see the birds right now,” Lee said. “You can feel them.”
Through the scope, it was just possible to make out their blurry shapes in the dark, and to hear the gentle but powerful “whhhrrr-reet-reet-reet” of tens of thousands of birds as they fed at the shoreline and in the shallow water.
As the sun rose, the tide retreated until it revealed six miles of the muddy sea floor. Channels of water like tree branches crisscrossed mud teeming with crabs, clams, snails, and sea worms.
Tidal flats like these are a type of wetland found on coastlines around the world. Korea’s Yellow Sea tidal flats, like those found on Yubudo Island, form the heart of an 18,000-mile route traveled by 50 million shorebirds as they migrate from eastern Russia and Alaska in the summer to Australia and New Zealand in the winter.
Many of them only stop once on their marathon journeys, and the tidal flats of South Korea provide them with essential food and shelter.
Yet despite their critical importance to the environment, many are at risk of disappearing. Some of the most important, and most endangered, are found surrounding the Yellow Sea along the shores of China and the western side of the Korean peninsula.
For decades, people have been transforming them into industrial sites and farms, squeezing them into smaller areas and pushing some species to the brink of extinction. But as science increasingly shows how wetlands like these benefit wildlife and help fight climate change, South Korean scientists and conservationists are gaining momentum in their effort to save and restore what’s left.
Why tidal flats are an environmental powerhouse
“The tidal flats made the relationship between humans and the sea possible,” said Joon Kim, a senior researcher at the Jeonnam Research Institute who studies the culture around Korean tidal flats.
Since prehistory, South Korea’s coastal communities relied on tidal flats for harvesting clams, crabs, octopus, and seaweed, adjusting their way of life to the tide’s schedule. Their biodiversity and abundance inspired many beloved local cuisines, unique coastal culture, and a fishing economy worth over $330 million U.S. dollars a year.
These same ecosystems are now helping fight climate change.
South Korean universities are partnering with the government to study tidal flats and their ability to clean polluted water, protect shoreline communities from storms, and mitigate climate change by absorbing carbon dioxide.
Korean tidal flats are full of tiny one-celled organisms called benthic diatoms that sink through the mud as they complete their life cycle, burying carbon dioxide in the deep sediment, says Jong Seong Khim, a marine scientist and professor at Seoul National University.
The diversity and number of benthic diatoms make South Korean tidal flats unique, as does its thick mud—over 80 feet deep in some tidal flats.
In 2021, Khim and his fellow researchers published a study showing South Korea’s tidal flats and salt marshes absorb 260,000 tons of carbon dioxide annually, equivalent to taking about 110,000 cars off the road every year.
The same year, the South Korean government announced a four-year project to bring back tidal flats and salt marshes to help fight climate change.
Kim hopes that by showing how effectively tidal flats store carbon, governments and conservation groups will recognize them as valuable and save them from being destroyed.
Why tidal flats are in danger
In the past 70 years, South Korea has transformed from a country devastated by war into a highly developed, industrial nation. During this rapid change, two-thirds of its tidal flats subsequently disappeared.
In a country surrounded by the ocean on three sides, like South Korea, engineering solid, dry land over water-logged terrain, a process referred to as land reclamation, can expand territory or create more farmland.
Of all the threats to tidal flats—such as sea level rise and pollution—land reclamation has led to the most loss.
Scientists are only beginning to understand the true extent of this loss globally, but one recent study suggests 16 percent of the world’s tidal flats have disappeared in the past few decades.
“We are at a point where we should consider what we can do to give back to tidal flats,” said Kim.
One of the most controversial shoreline developments is Saemangeum, a 100,000-acre reclamation project seven times the size of Manhattan.
Developers first envisioned Saemangeum as a vast agricultural area for rice cultivation, then as the economy changed, they promised to turn it into an industrial corridor.
In 2006, despite lawsuits and protests, a 21-mile-long wall in Saemangeum deprived the ecosystem of the water it needed to exist. Just one part of the region’s transformation, it set the Guinness World Record for the world’s longest sea dam.
Millions of shellfish died when the wall severed the ecosystem from the tide.
Finding no food and no place to land, tens of thousands of migratory birds disappeared. About 90,000 now-endangered great knot birds died, driving their total population numbers down by at least 24 percent.
It wasn’t only wildlife that suffered. Before the wall, the area was known for the nation’s best clams, with a fishing industry supporting around 20,000 people. Nearly all of that disappeared.
And yet despite promises of jobs made to the community, developers have completed less than half of the reclamation, and much of what has been reclaimed are undeveloped empty lots.
Saemangeum developers now plan to build an airport over the last remaining tidal flat, Sura, with construction scheduled to begin in 2024. Activists are suing to stop it, pointing out that the site still provides habitat for endangered species like black-faced spoonbills and Far Eastern curlews.
“It’s painful to remember how much it’s changed. Sometimes you forget how beautiful it was in the past because your eyes adjust to what it looks like now,” said Dongpil Oh, one of the activists involved and leader of the Saemangeum Citizen Ecological Investigation Team.
A new era of conservation
After 30 years of construction, Saemangeum has become synonymous with ecological collapse, but it also sparked an environmental movement in South Korea after people witnessed what happens when tidal flats are lost.
Two years after the Saemangeum seawall was finished, in 2008, the South Korean government banned new large-scale reclamation projects—though developments already in progress, like Saemangeum, are still permitted.
And in 2019, reclamation of tidal flats finally plateaued in South Korea, when the net gain from restoration barely surpassed the loss, according to a 2023 report from the International Union for Conservation of Nature.
One of the best places to see the benefit of this kind of conservation is South Korea’s Suncheon Bay Wetland Reserve, on the peninsula's southern edge. The wetland was spared from the threat of development in the ‘90s, when residents and activists protested the government’s plan to mine the land.
Suncheon Bay became the country’s first internationally protected coastal wetland, and its tidal flats were designated a UNESCO World Heritage site in 2021, along with four other tidal flats in South Korea. Every year, over six million tourists visit the wetland and the nearby National Garden to see wildlife like hooded cranes and blue-spotted mud skippers.
With municipal and national funds, the Suncheon Bay Wetland Reserve bought nearby farmland by the coast, restoring the connection with the sea.
Their holistic approach to restoration has introduced organic rice farming to reduce pollution from runoff and educational opportunities for ecotourists, residents, and children in local schools. Suncheon’s success is a blueprint for tidal flat conservation around the world.
“Our focus is on letting the tide flow again, like it always did,” said Sunmi Hwang, a conservationist with the wetland reserve. “And then nature heals itself.”