DEEP BLUE SCARS

Environmental Threats
to the South China Sea

By Monica Sato, Harrison Prétat, Tabitha Mallory, Hao Chen, and Gregory Poling | December 18th, 2023

A collage of satellite imagery showing the environmental degradation of the South China Sea.

A hidden crisis is unfolding across the South China Sea. While regional powers work to strengthen their claims to disputed waters and territories there, the marine environment in which they maneuver has been declining to critical levels.

Numerous fishing boats swirl around an island in China.

Aerial view of fishing boats in Yangjiang, China. | Chen Jimin/China News Service/VCG via Getty Images

Aerial view of fishing boats in Yangjiang, China. | Chen Jimin/China News Service/VCG via Getty Images

An underwater view of marine life in the Philippines, including coral and a giant clam

A giant clam pictured on a reef at a marine sanctuary in the Philippines on April 11, 2023. | Dante Diosina Jr/Anadolu Agency via Getty Images

A giant clam pictured on a reef at a marine sanctuary in the Philippines on April 11, 2023. | Dante Diosina Jr/Anadolu Agency via Getty Images

Human activity is causing severe ecological damage in the South China Sea.

In recent decades, increased fishing, dredging, and land fill, along with giant clam harvesting, have taken a devastating toll on thousands of species found nowhere else on earth.

To ensure the security and longevity of the plants, animals, and people that call the South China Sea home, this critical environment must be understood through an ecological, rather than merely geopolitical, lens.

I. Understanding Life in the South China Sea

The South China Sea has one of the highest levels of marine biodiversity in the world.

It boasts over 6,500 marine species, each of which has a role to play in the success of this enormous, interconnected ecosystem.

Heatmap of hard coral species count in the South China Sea, with highest count of 540.

This map of the biodiversity of hard coral shows the density of species scattered throughout the South China Sea.

This map of the biodiversity of hard coral shows the density of species scattered throughout the South China Sea.

Empty seafloor
Empty seafloor
Seafloor populated by coral
Seafloor populated by coral and fish
Seafloor populated by coral, fish, and bivalve
Manta rays, whales, dolphins, and shark swim in the sea.
A mollusk and sword tip squid float above the seafloor.
A fishing boat casts its net into the sea.
All life fades out to show an empty seafloor in black and white.
Coral fades into the empty seafloor, in black and white.

Coral

Coral reefs support nearly 25 percent of global marine life. Of the world’s 1,683 reef-forming coral species, 571 are found in the South China Sea.

Coral reefs are considered one of the most vital ecosystems in the South China Sea, providing food and shelter to thousands of species in their surrounding environment. 

They are also one of the most threatened ecosystems in the region, with coral cover declining 16 percent per decade.

Fish

About 22 percent of the world’s fish species are found in the South China Sea, with coral reefs supporting a total of 3,790 species of fish. Pelagic fish such as tuna, also traverse the area. The exceptional variety of fish in the South China Sea make it a central hub for commercial fishing in the broader Indo-Pacific region. It ranks as one of the world’s top five fishing areas.

This map of the biodiversity of fish shows the density of species scattered throughout the South China Sea.

Biodiversity of Fish in the South China Sea

Biodiversity of Fish in the South China Sea

Bivalves

The South China Sea is also home to eight of the ten global species of giant clam. This includes the Tridacna gigas, the world’s largest shellfish. Giant clams are vital to the health of reef ecosystems. They serve as food and shelter for other animals, and act reef builders and shapers. They also counter eutrophication through water-filtering. 

This map of the biodiversity of bivalves shows the density of species scattered throughout the South China Sea.

Biodiversity of Bivalves in the South China Sea

Biodiversity of Bivalves in the South China Sea

Sharks & Mammals

The South China Sea boasts a wide variety of larger species like sharks, rays, and marine mammals like dolphins and whales.

Other Species

It is also home to a myriad of other organisms that live in the water and along the ocean floor. Even species that have no commercial value play crucial ecological roles in maintaining the marine habitat that allows all species to thrive. 

Humans

The South China Sea is a vital source of food and livelihoods for the countries surrounding it, which are home to around 1.87 billion people.

While some communities practice more sustainable fishing methods, the rise of large-scale industrial fishing has endangered large areas of the food web.

Geopolitical competition and poor resource management have put this vibrant ecosystem under threat, starting with its very foundation: the coral reefs themselves

II. Reef Destruction in the South China Sea

Part 1: Dredging & Land Fill

To build outposts that support their competing claims in the South China Sea, claimants have engaged in dredging and land fill across the region. This has destroyed vast areas of the South China Sea’s coral reef ecosystems over the last 10 years.

Dredging: The removing of silt, sediments, and other materials from the seabed, often done in the South China Sea for the purpose of creating channels, harbors, or to gather material for landfill.

Land Fill: The creation of new artificial land with dredged seabed material.

Dredging can entirely remove essential reef substructures, causing irreparable and long-term changes to the overall structure and health of the reef.

A large machine covered in sediment digs in the ocean.

Asia's largest heavy-duty self-propelled cutter and suction vessel in Lianyungang, China. | CFOTO/Future Publishing via Getty Images

Asia's largest heavy-duty self-propelled cutter and suction vessel in Lianyungang, China. | CFOTO/Future Publishing via Getty Images

satellite image of cutter suction dredging at Subi/Mischief Reef

Satellite imagery of China's dredging of Subi Reef on March 5, 2015. | © 2015 by Maxar Technologies

Satellite imagery of China's dredging of Subi Reef on March 5, 2015. | © 2015 by Maxar Technologies

Satellite imagery of clamshell dredging at Tennent Reef on November 11, 2022

Satellite imagery of clamshell dredging at Tennent Reef on November 11, 2022. | © 2022 by Planet Labs

Satellite imagery of clamshell dredging at Tennent Reef on November 11, 2022. | © 2022 by Planet Labs

Satellite imagery of Vietnam's cutter suction dredging at Pearson Reef on September 16, 2023.

Cutter suction dredging at Pearson Reef on September 16, 2023. | © 2023 by Maxar Technologies

Cutter suction dredging at Pearson Reef on September 16, 2023. | © 2023 by Maxar Technologies

Satellite imagery of Vietnam's cutter suction dredging at Pearson Reef on September 16, 2023.

Cutter suction dredging at Pearson Reef on September 16, 2023. | © 2023 by Maxar Technologies

Cutter suction dredging at Pearson Reef on September 16, 2023. | © 2023 by Maxar Technologies

From late 2013 to 2017, China used dredging to build out its artificial islands. Its cutter suction dredgers would slice into the reef and pump sediment through floating pipelines to shallow areas to deposit it as landfill. This process disturbed the seafloor, creating clouds of abrasive sediment that killed nearby marine life and overwhelmed the coral reef’s capacity to repair itself.

Dredging always damages the surrounding environment, but other claimants have a history of using less destructive dredging methods. Until recently, Vietnam had primarily used clamshell dredgers and construction equipment to scoop up sections of shallow reef and deposit the sediment on the area targeted for landfill.

This method is slower and causes less collateral damage to surrounding areas. However, it still destroys the coral reef where the sediment is extracted and deposited.

More recently, however, Vietnam has turned to cutter suction dredgers like China’s. This large-scale expansion of Vietnam’s South China Sea outposts remains ongoing and will have major consequences for the surrounding marine environment.

Commercial satellite imagery analysis undertaken by the CSIS Asia Maritime Transparency Initiative (AMTI) has revealed the approximate total area of coral reefs destroyed by China, Vietnam, and other claimants in the region.

The results show that China has caused the most reef destruction through dredging and land fill, burying roughly 4,648 acres of reefs.

satellite image of cutter suction dredging at Subi/Mischief Reef

Satellite imagery of China's dredging of Subi Reef on March 5, 2015. | © 2015 by Maxar Technologies

Satellite imagery of China's dredging of Subi Reef on March 5, 2015. | © 2015 by Maxar Technologies

Satellite imagery of clamshell dredging at Tennent Reef on November 11, 2022

Satellite imagery of clamshell dredging at Tennent Reef on November 11, 2022. | © 2022 by Planet Labs

Satellite imagery of clamshell dredging at Tennent Reef on November 11, 2022. | © 2022 by Planet Labs

Satellite imagery of Vietnam's cutter suction dredging at Pearson Reef on September 16, 2023.

Cutter suction dredging at Pearson Reef on September 16, 2023. | © 2023 by Maxar Technologies

Cutter suction dredging at Pearson Reef on September 16, 2023. | © 2023 by Maxar Technologies

Satellite imagery of Vietnam's cutter suction dredging at Pearson Reef on September 16, 2023.

Cutter suction dredging at Pearson Reef on September 16, 2023. | © 2023 by Maxar Technologies

Cutter suction dredging at Pearson Reef on September 16, 2023. | © 2023 by Maxar Technologies

From late 2013 to 2017, China used dredging to build out its artificial islands. Its cutter suction dredgers would slice into the reef and pump sediment through floating pipelines to shallow areas to deposit it as landfill. This process disturbed the seafloor, creating clouds of abrasive sediment that killed nearby marine life and overwhelmed the coral reef’s capacity to repair itself.

Dredging always damages the surrounding environment, but other claimants have a history of using less destructive dredging methods. Until recently, Vietnam had primarily used clamshell dredgers and construction equipment to scoop up sections of shallow reef and deposit the sediment on the area targeted for landfill.

This method is slower and causes less collateral damage to surrounding areas. However, it still destroys the coral reef where the sediment is extracted and deposited.

More recently, however, Vietnam has turned to cutter suction dredgers like China’s. This large-scale expansion of Vietnam’s South China Sea outposts remains ongoing and will have major consequences for the surrounding marine environment.

Commercial satellite imagery analysis undertaken by the CSIS Asia Maritime Transparency Initiative (AMTI) has revealed the approximate total area of coral reefs destroyed by China, Vietnam, and other claimants in the region.

The results show that China has caused the most reef destruction through dredging and land fill, burying roughly 4,648 acres of reefs.

A long pipe connected to a blue and yellow boat with heavy machinery sits in the middle of the ocean

Dredging construction at China's Lianyungang Port on October 13, 2022. | CFOTO/Future Publishing via Getty Images

Dredging construction at China's Lianyungang Port on October 13, 2022. | CFOTO/Future Publishing via Getty Images

The actual amount of reef destroyed by these practices is almost certainly greater than these estimates, which cannot account for damage in deeper areas.

Unfortunately, dredging and land fill are only half of the story of reef destruction in the South China Sea.

II. Reef Destruction in the South China Sea

Part 2: Giant Clam Harvesting

Scholars studying the environmental effects of dredging and land fill on coral reefs also discovered another destructive phenomenon: vast areas of coral reef damaged by giant clam harvesting.

The harvesting of giant clams for their remarkable shells has become popular in recent decades because of their resemblance to elephant ivory, which is now extremely difficult or illegal to obtain. The shells are typically worked into jewelry and statues and sold for high prices in China—as much as $106,000 per carved shell.

Giant clam harvesting was especially prevalent between 2012 and 2015 among fishers from the port of Tanmen on China’s Hainan Island. The surge coincided with government efforts to promote maritime activity in the South China Sea. President Xi Jinping visited Tanmen in 2013 and pledged support for fishers while urging them to “catch more big fish.”

Giant clams sit submerged or halfway submerged near the shore.

Giant clams in Bolinao, Philippines. | David Greedy via Getty Images.

Giant clams in Bolinao, Philippines. | David Greedy via Getty Images.

A satellite image of clam harvesting at Scarborough Shoal. Boats are shown in deep blue and green water.

Satellite image of clam harvesting at Scarborough Shoal on December 19, 2015. | © 2015 by Maxar Technologies

Satellite image of clam harvesting at Scarborough Shoal on December 19, 2015. | © 2015 by Maxar Technologies