JEJU ISLAND, South Korea—Seventy-year-old Hwang Gyesook has been diving into the chilly waters of the Korea Strait off Jeju Island for more than 45 years. Generations of female divers called Haenyeo have learned to hold their breath for long periods underwater to catch the delicacies beneath the sea.

For as long as seven hours a day, without oxygen tanks, they dive as deep as 30 feet for several minutes before coming up for air and then quickly return underwater to fish for abalone and sea urchin. Theirs is one of the distinctive practices of Jeju Island, attributed to its geographic isolation, 60 miles from the Korean Peninsula.

The divers and other island natives also developed a unique dialect of the Korean language as a result of their isolation that preserves several words and grammatical styles from the Middle Ages.

While much about their culture remains unchanged, Hwang has noticed changes in the sea over the past few years. 

The number of abalones—a prized catch—has decreased noticeably, she said. In addition, South Korea’s only soft coral habitat is near the Haenyeo diving area, and she worries that it may be getting smaller. 

In October, the Global Coral Reef Monitoring Network released a report collating global statistics on corals. The document surveyed the status of  12,000 reefs in 73 countries over 40 years. The researchers found that the world has lost 14 percent of its corals from 2009 to 2018.  

Corals are animals related to jellyfish and anemones. Hard corals form calcium-based skeletons and build large reefs like Australia’s Great Barrier Reef. Soft corals secrete structures within their tissues to support their bodies, and while they do not produce rigid calcium skeletons and do not form reefs, they are present in reef ecosystems. The Great Barrier Reef is made up of more than 600 hard and soft coral species.

Soft corals are found in tropical or semi-tropical waters. Jeju’s southern sea is one of the most northerly points in the world with the right conditions for these sea flowers to bloom, according to Kaoru Sugihara of Japan’s National Institute for Environmental Studies.

Marine biologists say climate change represents the greatest threat to coral reef ecosystems. The oceans are warming dramatically, and as the water temperatures rise, infectious diseases are becoming more lethal, as are bleaching events, which occur when warm ocean waters cause coral to eject the algae it relies on for nutrients. 

The South Korean government classified 22,000 acres of water—nearly half the size of Washington, D.C.—off the southern coast of Jeju as a legally protected natural monument for housing soft corals. A significant portion of the same area was also designated by UNESCO in 2002 as a Biosphere Reserve, and Jeju Island became, by 2010, the only place in the world to receive all three UNESCO natural science designations. It was also named a World Heritage Site in 2007 and a Global Geopark in 2010. 

While UNESCO does not necessarily protect the Biosphere Reserve, 16 species of soft corals inside the area are protected by South Korean law as marine organisms under protection.

In 2012, South Korea decided to build a naval base on the island, the Jeju Civilian-Military Complex Port, similar to the U.S. base at Pearl Harbor. The military said the base protects trade routes and allows rapid response to possible conflicts over Socotra Rock, a submerged rock topped with a South Korean research station that China claims lies within its waters.

The base has been operational since 2016, housing more than 3,000 servicemembers and a submarine squadron. The U.S. Navy does not have a permanent presence but occasionally docks there.

Around $7 million was contributed to the village’s fishing cooperative, of which the Haenyeos are members, to compensate for possible impacts on local fisheries. 

“The naval base creates jobs, and our future generations, including my daughter, want to pursue a career other than diving into the sea without oxygen tanks,” said Hwang. “But recently I am seeing fewer marine life than before, although I am not sure I can simply point at the Navy as the root cause.”

During the construction period in 2013, the contractor Samsung C&T Corporation was accused of polluting the water off the coast by dumping cement dust into the sea. The South Korean Navy said there were silt protectors to prevent the spread of environmental contaminants, but Jang Hana, an elected member of the National Assembly, and two civic groups, Gangjeong Village Association and Hot Pink Dolphins, have claimed that the protectors were largely damaged and provided insufficient protection.

Soft corals were damaged during construction of the base. The South Korean Navy confirmed the damage in its October 2015 report on soft corals near the Jeju naval base site. According to the report, more than half of the types of soft corals diminished in number between November 2014 and October 2015.

Red soft coral, the dominant species in the habitat, saw a significant decrease. The average percentage living coverage of red soft coral on the reef ranged between 9 percent and 17 percent in 2009. In 2015, two years after the naval base construction, the range dropped to 0 and 11 percent, the report said.

Sixteen types of soft corals were observed near the lighthouse located .2 miles away from the naval base site in 2009, years before construction. In 2015, the number of species at the same location had dropped to 10, according to the report.

The decline in Jeju’s soft corals is one example of human causes that threaten global coral reefs, at a time when soft coral forests were already being replaced by other organisms due to the impact of climate change. The U.N.’s Intergovernmental Panel on Climate Change projects that 70 to 90 percent of the world’s coral will die if the Earth’s atmosphere warms 1.5 degrees Celsius above pre-industrial levels. 

South Korea’s Cultural Heritage Administration, the authority that oversees natural monuments like Jeju’s soft corals, plans to launch an island-wide investigation of soft corals. Using the results of the survey, the heritage agency hopes to establish plans to protect and enhance the conditions of the island’s soft coral forests in the waters off Jeju.

Vianney Denis of National Taiwan University visited Jeju several times to research corals around the island. “Additional stressors such as the construction of this naval base may jeopardize the persistence of these soft coral forests as well as the functions and diversity relying on them,” said Denis.

An environmental activist, Choi Hyea-young, has been regularly monitoring the soft corals since 2014, diving into the waters near the Jeju Naval Base to record their status.

“There is a freshwater cave 50 feet below the lighthouse near the naval base that housed red soft corals and Dendronephthya, known for its vibrant pink color,” said Choi. “When I dived the same spot in 2015, the cave was noticeably grey with many soft corals no longer alive.”

Choi said that the more she dives underwater, the more leftovers of what used to be soft corals she inevitably sees. “I cannot say with full certainty that the damage was solely caused by naval activities as scientific research has not been conducted to empirically prove with numbers,” Choi said. “But I can say for sure that monitoring soft corals near the base has prevented the Navy from recklessly causing damage to marine life.”

Local environmental activists have been waging campaigns to protect the soft corals.

“We tried several times to bring the ongoing soft coral destruction to UNESCO’s attention since the corals are at the Biosphere Reserve that they designated,” said Kim Jeongdo, director for the Korean Federation Environmental Movement of Jeju, the largest coalition of environmental activists on the island. “Their response was always the same, that UNESCO does not interfere in domestic politics. I ask, how can this be political?”