Come Hague or High Seas: China’s Environmental Legacy in the South China Sea

Following the 10th anniversary of the South China Sea tribunal ruling, the United States and several other countries renewed their support for the Philippines and its landmark legal victory against China’s expansive maritime claims. Like much of the past decade’s discussion on the South China Sea, these statements touched upon sovereignty issues and the rejection of China’s nine-dash line. However, another aspect of the ruling deserves attention: By failing to safeguard the marine environment of the South China Sea, China violated its obligations under the United Nations Convention on the Law of the Sea (UNCLOS). This legacy of environmental degradation should inform assessments of whether China is prepared to serve as a responsible leader in similar institutions, as it gradually positions itself at the forefront of another landmark treaty under UNCLOS.

After decades of negotiations, the Agreement on Biodiversity Beyond National Jurisdiction (BBNJ), also known as the High Seas Treaty. entered into force globally on January 17, 2026. This agreement establishes the first legally binding framework for protecting, conserving, and sustainably managing biodiversity in the high seas, which make up roughly two-thirds of the ocean. Just a day before the BBNJ took effect, China submitted an official bid to host the BBNJ permanent secretariat seat in its coastal city of Xiamen, offering a generous funding package and promoting itself as a longtime supporter of the treaty. It is therefore paradoxical that while China continues to reject the South China Sea arbitral award as “null and void,” it has simultaneously taken deliberate steps toward becoming a leader in global ocean governance under the same convention.

A Decade of Environmental Degradation in the South China Sea

In 2016, the tribunal concluded that China had failed “to protect and preserve the marine environment” of the South China Sea by constructing artificial islands and failing to prevent Chinese fishers from harvesting endangered and vulnerable marine species. In doing so, Beijing violated its obligations under Articles 192 and 194 of UNCLOS.

Although the environmental findings represented only one component of the Philippines’ submission, they have gradually become a more prominent feature of the country’s South China Sea policy under President Ferdinand “Bongbong” Marcos Jr. Philippine officials even discussed pursuing a second arbitration case or raising the issue before the UN General Assembly in response to China’s continued environmental negligence and aggressive actions against Philippine vessels in the South China Sea.

Since the ruling, the tribunal’s findings have done little to halt further environmental degradation. A decade later, the marine environment of the South China Sea remains largely unprotected, while state activities that contribute to further damage have continued—and, in some respects, accelerated.

The tribunal’s first major environmental finding centered on China’s island-building activities. Through dredging and land filling, China had irreparably damaged approximately 3,170 acres of coral reefs by 2016. These processes involve cutter suction dredgers slicing through reef structures before pumping accumulated sediment via floating pipelines to create artificial islands. Entire reef ecosystems are effectively buried beneath the reclaimed land, and leftover sediment can float toward surrounding areas, killing other marine life.

Although China’s large-scale island-building campaign appeared to conclude around 2017, satellite imagery revealed dredging at Antelope Reef in the Paracel Islands beginning in October 2025. Measuring roughly 1,500 acres, the project is on pace to become China’s largest artificial island in the South China Sea. As a result, the estimated coral reef destruction caused by China’s island-building activities has now risen to approximately 6,224 acres—about half the size of Manhattan in New York City.

The tribunal’s second environmental finding concerned harmful fishing practices carried out by Chinese fishers. Giant clam harvesting was deemed “especially problematic” because of clams’ vital role in maintaining reef ecosystems and the destructive method used to extract them. Fishers drag specially designed brass propellers across coral reefs in semicircular patterns to expose buried clams, leaving behind distinct arc-shaped scars documented through satellite imagery. Despite supposed protection by the Convention on International Trade in Endangered Species of Wild Fauna and Flora from exploitation and illegal trade, the giant clam’s classification changed from “vulnerable” to “critically endangered” in 2024. And although Chinese authorities cracked down on the sale of giant clams in 2017, evidence indicates that harvesting continued well into 2019, and giant clam products are still being sold on the black market for high prices.

As it stands, China’s island-building and giant clam harvesting activities have destroyed an estimated 22,759 acres of coral reef across the South China Sea. This figure combines overall reef destruction caused by land filling and dredging (6,224 acres) and the damage left behind by giant clam harvesting methods (16,535 acres). Despite this record, Beijing is seeking to position itself as a champion of environmental protection under the BBNJ.

Ocean Governance or Selective Governance?

In recent years, Beijing has sought a larger role in shaping how the world’s oceans are to be managed. China became one of the first countries to ratify the BBNJ in December 2025, signing the agreement on the day it opened for signature. The following month, it submitted its bid to host the secretariat seat, contesting bids already made by Belgium and Chile. This push extends beyond the BBNJ; under its 15th Five-Year Plan, China has elevated global ocean governance as a national priority. And at this year’s Meeting of States Parties to UNCLOS, China’s deputy permanent representative to the United Nations, Sun Lei, emphasized that his country highly values “the conservation and rational use of marine resources,” highlighting how China has designated approximately 37 million acres of marine conservation red lines and established 353 marine protected areas.

China’s ongoing campaign to host the BBNJ secretariat, together with its continued emphasis on marine protection, should not be viewed in isolation from its environmental record. Its actions reflect another example of Beijing’s selective use of UNCLOS to advance its national interests in the maritime domain. In some cases, China embraces aspects of UNCLOS that reinforce its image as a responsible actor and upholder of international law, like pursuing much sought-after seabed mining efforts through the UNCLOS-established International Seabed Authority. At the same time, it continues to reject other aspects that do not support its actions in disputed areas, like disregarding the tribunal’s ruling on the nine-dash line as contrary to international law. This selective approach raises questions about the type of leadership Beijing intends to exercise as BBNJ secretariat, especially as it appears to treat the South China Sea as an exception to its rules. During the final negotiations of the BBNJ, China fought to have the South China Sea explicitly excluded from its scope, despite the presence of a pocket of high seas in the center of the body of water. China’s arguments were ultimately blocked by strong opposition from other countries.

Beijing employed a similar strategy in October 2025, when it unilaterally announced plans to establish a marine nature reserve covering more than 8,600 acres around the disputed Scarborough Shoal. In line with its biodiversity efforts, the National Forestry and Grassland Administration stated that coral reefs were the reserve’s main target of protection. The Philippine government quickly condemned the proposal as “a clear pretext towards eventual occupation” rather than a genuine conservation initiative, amid increasing tensions between the two countries at Scarborough Shoal. Ultimately, the proposal was largely symbolic, as years of China’s giant clam harvesting had already severely damaged the feature’s reef ecosystem, leaving little of the marine habitat left to protect.

While the participation of maritime powers is necessary for the success of international conservation efforts, taking up the mantle carries expectations of credibility. In January 2027, the Conference of Parties (COP), consisting of UNCLOS member states, will make the important decision on who will host the BBNJ’s secretariat seat. Two-thirds majority by secret ballot is needed to elect the new secretariat, which will act as the administrative and logistical support system to the COP. As states consider China’s bid and evaluate its broader role in shaping the future of ocean governance, its environmental record in the South China Sea must not be treated as a separate issue. Giving China a leadership seat now, when it has shown that it does not consistently follow established conventions under international law, ultimately weakens the principles of the BBNJ and global ocean governance as a whole.

Monica Sato is a research associate with the Asia Maritime Transparency Initiative at the Center for Strategic and International Studies in Washington, D.C.