Island-building and overfishing wreak destruction of South China Sea reefs

  • The offshore islets and reefs of the South China Sea have been the stage of intense geopolitical standoffs for decades, as the region’s coastal states compete for territorial control of the productive maritime area that includes oil and gas fields and reef and oceanic fisheries.
  • A new investigation based on satellite monitoring and fisheries data reveals that overfishing, giant clam harvesting and island-building have devasted significant portions of the region’s shallow coral reefs.
  • Experts say the direct loss of some of the world’s most diverse marine ecosystems is not the only cost, citing likely consequences for distant fisheries that depend on spawning grounds on some of the now-obliterated reefs.
  • Actions by China and Vietnam were found to be by far the most egregious; however, experts say the onus lies on all South China Sea coastal states to work together toward solutions that will ensure the long-term protection and health of remaining reefs.

States jostling for territorial dominance in the South China Sea have inflicted untold damage on the marine environment, according to a new investigation by the Asia Maritime Transparency Initiative (AMTI) and China Ocean Institute, both based in the U.S. The findings, presented in a recent report, are the “most complete picture to date” of the devastation wreaked by industrial overfishing, rampant island-building and reckless giant clam harvesting by bordering states, the authors say.

The low-lying but resource-rich features of the South China Sea have been fiercely contested among bordering states for decades. The Philippines, Malaysia, Brunei, Taiwan, Vietnam and China vie for control of the islets and reefs, some of which only breach the ocean surface at extreme low tide. But amid the struggle, the marine environment is being ravaged.

The scale of the damage inflicted by competing states on the region’s coral reefs, which represent the foundations of the South China Sea’s marine food webs, can’t be overstated, according to report co-author Gregory Poling, director of the Southeast Asia program at the AMTI.

“It’s the largest active man-made reef destruction in human history,” Poling said at a press briefing in Bangkok on Feb. 20.

The AMTI is part of the Washington, D.C.-based Center for Strategic and International Studies (CSIS), which is funded in part by the governments of the U.S. and Taiwan; the latter is among the claimants to a disputed part of the South China Sea. The CSIS has also long advocated for a stronger U.S. military presence in the region to counter what it calls “China’s efforts to control the South China Sea.”

As such, the new report identifies China as being by far the most egregious actor in the region, blaming it for destroying not only the most extensive area of coral reefs among the coastal states, but also employing the most reckless methods of fishing, building artificial islands, and harvesting giant clams.

Giant clam
A giant clam photographed in the Indian Ocean, showing the thick shell that is so highly sought after for carving trinkets and ornaments that look like ivory. Image by Rainer Voegeli via Flickr (CC BY-NC-ND 2.0)

The outsize environmental destruction by China is emblematic of its wider strategy for claiming sovereignty of waters and resources in the South China Sea, the report says. Competing states have frequently denounced China’s operations in the South China Sea, citing instances of China using vessels in aggressive and reckless ways, and its ongoing fortification and militarization of the reefs and islands it occupies in the region.

The year-long investigation by the AMTI and the China Ocean Institute, a Seattle-based fisheries research consultancy, was based on evidence from commercially available satellite imagery and fisheries activity statistics. In total, the team assessed the integrity of 181 occupied and unoccupied features in the South China Sea.

Island-building and harvesting of giant clams by China alone have destroyed at least 8,572 hectares (21,183 acres) of coral reef, according to the findings, an area roughly one-third the area of Malaysia’s capital city, Kuala Lumpur. Vietnam is the second most environmentally destructive state, according to the report, gouging 567 hectares (1,402 acres) of reef, mostly through island-building.

Meanwhile, damage wreaked by the other coastal actors is less extensive, with Malaysia, the Philippines and Taiwan accounting for the loss of 34 hectares (83 acres), 16 hectares (40 acres) and 13 hectares (32 acres) of coral reef respectively, the report says. While Brunei and Indonesia have coastlines on the South China Sea, neither have ever occupied any of the sea’s reefs, and so have never dredged or built on any, nor do they engage in giant clam harvesting, according to Poling.

In addition to quantifying the direct destruction of coral reef ecosystems, the investigation also highlights the relentless and intensifying use of industrial bottom trawling by China and Vietnam in the South China Sea. Despite regional fisheries already suffering stagnant yields as a consequence of historical overfishing, the persistent use of such indiscriminate and destructive fishing methods is overtly unsustainable, the authors say.

The report calls on China, Vietnam and the other South China Sea parties to view their territorial and maritime disputes through an ecological, as well as a geopolitical, lens. To do this, the authors say, each party must prioritize taking stock of damage to marine biodiversity and halt their destructive practices in the region.

Reef fish
Coral reefs are vital nursery grounds for many fish species. Image by Michael Aw / Ocean Image Bank.

One-fifth of Spratly reefs already gone

The South China Sea, extending over an area of 360 million hectares (890 million acres) and semi-enclosed by the coastlines of seven countries, is one of the world’s busiest shipping routes. Although its marine biodiversity typically receives less attention than the nearby “Coral Triangle” hotspot, the South China Sea hosts a staggering diversity of marine species. In 2015, for instance, scientists documented 571 species of reef-building coral in its waters, representing almost one-third of the world’s known species and placing it on a par with the Coral Triangle.

This coral diversity supports an array of associated reef wildlife and serves as spawning grounds for fish populations that underpin vital regional fisheries. And like other offshore coral reef systems, it could prove a crucial genetic resource to help the region’s marine ecosystems adapt to the ocean-warming effects of climate change.

But efforts to responsibly manage the South China Sea’s bounty of marine life have been thwarted by geopolitical tensions and competing maritime claims for years. To date, more than one-fifth of the reefs in the Spratly Islands — an archipelago claimed to varying degrees by China, Vietnam, the Philippines, Taiwan, Brunei and Malaysia — and the surrounding offshore unoccupied features have so far been destroyed, according to Monica Sato, a research associate at the AMTI and a co-author of the report.

Satellite image of dredging in South China Sea
Satellite image of dredging at Tennent Reef in 2022. Image courtesy of CSIS Asia Maritime Transparency Initiative / © 2022 by Planet Labs

Most of the reef damage has been due to states’ island-building activities, a pursuit motivated by the quest for territorial control of offshore waters, fisheries and airspace.

The island construction process takes a colossal toll on seafloor habitats. Gouging and dredging of reefs and lagoons obliterates some reefs and irreversibly degrades others, impacting thousands of species on which the region’s marine food webs depend. The landfill process to fortify the islands up to above high-tide level then creates sediment plumes that “float to other parts of the ocean, [where it] coats wildlife, animals and plants, damaging their health,” Sato said.

These island-building schemes, particularly those operated by China, are often extensive, essentially repurposing the surrounding living system of marine creatures as inert foundations for massive infrastructure projects, including complex military installations and radar surveillance facilities that enable the country to further its sovereignty claims.

The AMTI investigation revealed that between 2013 and 2017, China’s onslaught of dredging and landfill to construct infrastructure on the seven Spratly reefs it occupies and on many unoccupied offshore features throughout the wider South China Sea wiped out roughly 1,881 hectares (4,648 acres) of reef ecosystem.

While the report identifies China as the most destructive coastal state by far, it says satellite data indicate that Vietnam has recently begun using cutter suction dredgers, the most environmentally harmful dredging technique, pioneered in the area by China. It’s a move the authors say will amplify the ecological damage Vietnam exerts as it continues to expand its suite of regional at-sea outposts.

Mongabay reached out to the state communications departments of China and Vietnam for comment on the findings of the investigation, but received no response before publication of this story.

Many ecologically and commercially valuable fish species congregate around offshore sea mounts during crucial life stages. Image by Jayne Jenkins / Ocean Image Bank.

Demand for clams

Besides the coral diversity, some 80% of the world’s giant clam species (Tridacna spp.) live in the South China Sea. But rampant harvesting by mostly Chinese fishers, and also historically by fishers from the Philippines and Vietnamfor their shells that are similar in quality to elephant ivory, has decimated their populations. Ivory bans that came into force in China in 2017 led to a surge in demand for giant clam shells, from which artisans make carvings, trinkets and ornaments.

Despite a 2017 crackdown on overharvesting of the marine animal by Chinese authorities in Hainan Island at the northern extremity of the South China Sea, the AMTI investigation found satellite evidence of giant clam harvesting occurring at offshore features from 2019 onward. The arc-shaped scars were characteristic of giant clam extraction methods uniquely used by Chinese fishers, whose implication is further supported by the fact that the giant clam trade is flourishing in China’s black markets, Sato said.

To extract the giant clams, the harvesters essentially deploy a weighted propeller that scours the ocean bottom. “It doesn’t discriminate between live and dead clams, it just kind of gets everything in its way,” Sato said. “This type of destruction is sort of a double-whammy,” she added. “Not only do you see scarring on the reef, but giant clams are already vulnerable [to extinction].”

Satellite image of South China Sea reef
Satellite imagery of dredging of Subi Reef in March 2015. Image courtesy of CSIS Asia Maritime Transparency Initiative / © Maxar 2024.

What’s more, it appears giant clam fishers from China have diversified their methods of extraction in deeper lagoon areas that are beyond the scope of satellite observation. In 2019, on-site evidence gathered by Philippines-based media at Scarborough Shoal off the Philippines coast, and subsequently by the Philippine navy at nearby Iroquios Reef and Sabina Shoal, revealed lagoon reef damage consistent with high-pressure removal of the reef substrate in search of giant clams.

“They found no live coral, almost no marine life of any kind,” Poling said. “The entire Scarborough Shoal had been turned into a boneyard.” The only thing to be seen on video taken at the scene were dozens of eerily neat piles of giant clams awaiting collection among the rubble, he added.

Based on satellite imagery observations alone, giant clam harvesting by Chinese fishers has damaged 6,618 hectares (16,353 acres) of coral reef in the South China Sea, the report says, contributing to China’s total quantified reef destruction of more than 8,572 hectares (21,183 acres).

Crucially, the actual scale of the destruction — from both clam harvesting and island-building — is likely much higher, the authors noted, when damage to deeper-water reefs beyond the scope of satellite data, which can only penetrate surface waters, is taken into account. “The real number could be double, triple, quintuple — who knows how much acreage of coral reef has actually been severely damaged by clam harvesting,” Poling said.

A Vietnamese fishing boat on the South China Sea. Photo by Jean-Pierre Bluteau via Flickr (CC BY-NC 2.0).
A Vietnamese fishing boat on the South China Sea. Photo by Jean-Pierre Bluteau via Flickr (CC BY-NC 2.0).

Contrasting drivers of overfishing

The unprecedented levels of coral reef destruction will have inevitable secondary effects on the regional marine food web, Poling said. These risk contributing to the decline of the South China Sea’s fisheries, which account for roughly 12% of global fish catch, he added.

“This is a single ecosystem,” Poling said. “Fish larvae that are spawned on one reef move to another, and it doesn’t just affect the health of fisheries in the Spratly Islands, it affects the health of fisheries throughout the South China Sea, also in Thailand and all of the internal waters of Indonesia, the Philippines and Malaysia. Knock-on effects are going to be a lot less mature fish and a lot less large species like sharks throughout the region.”

Fish stocks in the South China Sea are already overexploited. A 2020 analysis of fishing trends in the sea since the 1950s showed that yields have plateaued over the past three decades, despite considerable increases in fishing activity. This phenomenon indicates the industry is “fishing down” the food chain, the study authors suggest, a situation they say can only be rectified through coordinated mitigation efforts among the bordering countries.

“Anyone who has gone around to a coastal community in Palawan or central Luzon [in the Philippines] or central Vietnam knows that markets are now full of what used to be bait fish,” Poling said. “Nobody would think of selling this stuff 30 years ago, but that’s the only thing you can get out of the South China Sea now, because all of the large species and all of the mature fish have already been caught.”

Based on each country’s self-reported catch statistics and reconstructed models of likely unreported catches, the investigation found that Vietnam’s industrial fishing intensity now matches and, in the case of bottom trawling, surpasses China’s efforts in the South China Sea. However, there’s an important distinction between what China and Vietnam are doing, according to Poling.

“Vietnam’s problem is a lack of state capacity — an inability to monitor and effectively enforce fishery regulations against its fleet — but it is trying to fix [this],” Poling said. In 2017, Vietnam was issued a yellow card from the EU for illegal fishing and is currently improving its vessel monitoring systems and stepping up port inspections, Poling said: “Vietnam is at least making an effort.”

Map of fishing in South China Seas
Map displaying the intensive fishing effort and trawling activity in the South China Sea during 2023 (Left); and a closeup of fishing + trawling in proximity to the Spratly Islands, indicating intense activity at Scarborough Reef in the upper center of map (Right)

In contrast, Poling said that China’s overfishing is driven by state policy. Chinese fishing bases in the South China Sea are too far offshore for China’s small-scale fishers to productively fish, and too close for the country’s distant-water fleet. So the state subsidizes fishers to station themselves in the South China Sea, he said, thereby asserting the country’s sovereignty in the region. “Almost all Chinese fishing in the South China Sea happens only because the state pays for it to happen.”

The presence such Chinese fishing fleets, which are often militarized, in the South China Sea has raised tensions with coastal states in the past. More than 200 vessels stationed at Whitsun Reef in early 2021, for instance, sparked concerns with maritime authorities in the Philippines, which lays claim to the area. Satellite data subsequently confirmed the fleet were not fishing, with analysts linking their presence to political posturing and intimidation tactics.

Carl Thayer, an emeritus political scientist at the University of New South Wales in Australia, has observed the decline of natural resources in the South China Sea and the tussles over them for decades. He said China’s overtly destructive harvesting of giant clams is most likely down to the “avarice and greed” of commercial interests, rather than politically motivated natural resource depletion. Yet he said the historical island-building is purely a sovereignty issue.

Thayer told Mongabay countries must seriously consider what will happen as a result of the depletion of reef resources. “In 20 years’ time, what are you going to have [in the South China Sea]? They might have artificial bases, but they’re killing off the ecosystem and biodiversity. And as environmental issues rise up over the next several decades, that will come home to roost,” he said. “China is all over the world with its deep-water fishing, so they can just move on. But all the people in Southeast Asia who are living [nearby], they’re going to be sitting there with the South China Sea ruined, devastated.”

Green turtle
A green turtle, one of many large marine herbivores that depend on offshore coral atolls for vital stages of their lifecycle. Image by Gabriel Barathieu / Ocean Image Bank.

Long-running geopolitical standoffs

The disproportionate effects on natural resources are the latest in the decades-long territorial disputes among the South China Sea coastal states. Many such disputes have centered on environmental damage. Following increasing aggression from China’s fishing fleets in proximity to the Philippines, for instance, Manila appealed to the International Tribunal for the Law of the Sea, which ruled in 2016 that China’s territorial claim to the South China Sea was incompatible with international law, and that the actions of its fishing fleet flouted injunctions to cooperate with neighbors in managing fragile ecosystems and fisheries.

The heated jurisdictional complexities and outright hostilities from occupying states typically hamper access for independent research to quantify environmental damage, limiting the extent to which science can inform the management of the South China Sea. The lack of agreement and coordination among the coastal states also stymies efforts to manage fisheries or delineate marine conservation areas. Marine biologists have long proposed protecting the region’s remaining coral reefs through the development of an international peace park agreement between nations, but the reality remains far from such measures.

China, which dismissed the 2016 tribunal ruling against it, is particularly averse to cooperation. Thayer said that “beautiful” plans for marine parks and methods of joint resource management exist on paper, but China “will not come to the table” since it would necessitate negotiating with countries it is in dispute with. Instead, China acts unilaterally in the South China Sea to assert its sovereignty, he added.

There are some signs of progress, though, according to Poling. Recent years have seen a greater degree of political coordination between some coastal states, with the Philippines and Vietnam signing an agreement in January 2024 to improve coast guard operations and incident reporting in the South China Sea.

In late 2023, the Philippines announced its intention to gather evidence to file a second arbitration case against China under the United Nations Convention on the Law of the Sea, focused on environmental issues. Poling said he anticipates giant clam harvesting damage will be central to that case if it comes to fruition.

While most of the destruction documented in the investigation has been at the hands of China and to a lesser extent Vietnam, the report calls on all coastal states to center the preservation of marine ecosystems in their South China Sea policies. It also calls for greater cooperation among regional governments and improved access for researchers and environmental organizations to take stock of the health of the marine ecosystems.

Ultimately, what might bring about real change is when the most egregious actors recognize their reputational damage. “The only way to get China to dial this back is going to be the imposition of diplomatic costs,” Poling said, “if there’s a large-enough coalition of international partners putting enough pressure on China so that it feels that this behavior undermines its global interests.”

Carolyn Cowan is a staff writer for Mongabay. Follow her on 𝕏, @CarolynCowan11.

Banner image: Satellite imagery of dredging at Tennent Reef in 2022. Image courtesy of CSIS Asia Maritime Transparency Initiative / © 2022 by Planet Labs


Huang, D., Licuanan, W. Y., Hoeksema, B. W., Chen, C. A., Ang, P. O., Huang, H., … Chou, L. M. (2015). Extraordinary diversity of reef corals in the South China Sea. Marine Biodiversity, 45(2), 157-168. doi:10.1007/s12526-014-0236-1

Pauly, D., & Liang, C. (2020). The fisheries of the South China Sea: Major trends since 1950. Marine Policy, 121, 103584. doi:10.1016/j.marpol.2019.103584

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