Giant Clam Extinction Could Undermine Climate Stability

The giant clam, with its vibrant, cape-like mantle and large, wavy shell, faces a dire future with its population plunging by over 80% in the past century, according to a new assessment led by Dr. Ruiqi Li, a postdoctoral researcher at the University of Colorado, Boulder.

This dramatic decline raises urgent questions about the ripple effects on coral reefs and ocean ecosystems – and, ultimately, what this means for climate change.

Ecological contributions of giant clams

The giant clam, or Tridacna gigas (T. gigas), is the most well-known species of giant clam. Often admired for their striking colors and impressive size, they are the largest marine bivalve mollusks in the world, capable of growing up to 4 feet in length and weighing more than 700 pounds. Found in the shallow, sunlit waters of the Indo-Pacific, these clams are essential for the health of coral reef ecosystems.

T. gigas hold an important symbiotic relationship with algae. The clams provide a safe habitat and sunlight access for the algae, and in return, the algae use sunlight to produce nutrients through photosynthesis, sharing these nutrients with the clam. This relationship allows giant clams to thrive in nutrient-poor tropical waters and helps sustain their significant size.

Giant clams also play a broader ecological role in supporting coral reefs. They act as natural nutrient recyclers, releasing beneficial compounds back into the water that support other marine organisms.

“Along with coral reefs, these clams provide important habitats for other creatures living in the reefs. They are also important nutrient producers in shallow ocean water, which is generally deprived of food. If the giant clam becomes extinct, it will have significant ecological impacts on tropical oceans,” said Li.

Together, these functions help coral reefs flourish, enhancing biodiversity and stabilizing these ecosystems.

Coral reefs as carbon sinks

Coral reefs are not only biodiverse ecosystems but also serve as essential carbon sinks. They absorb dissolved carbon dioxide to build their calcium carbonate skeletons, helping to remove and store carbon from the atmosphere, through a natural process called calcification.

Giant clams also play a vital role in supporting this carbon-capturing environment. By housing algae that photosynthesize, giant clams contribute to nutrient cycling in these ecosystems. The clams release nutrients like nitrogen and phosphorus into the water, which promotes the growth of coral and other marine organisms that further support reef health. This nutrient cycling is crucial in waters that are often low in resources, helping coral reefs remain resilient and productive carbon sinks.

Threats to giant clams and implications for climate change

The potential extinction of giant clams threatens this delicate balance. Without these nutrient providers, coral reefs could face significant declines in health, limiting their ability to capture carbon and support marine life. This disruption would not only impact biodiversity but could also weaken the reef’s role in carbon sequestration, reducing the ocean's ability to buffer against climate change.

Giant clam populations are under severe threat from overfishing and habitat destruction, with human activities driving these declines as clams are harvested for food, decorative shells and traditional medicine. 

“As a biologist, I'm working on translating findings from my research into policy changes, but not enough biologists are doing this. I hope to encourage more biologists to devote time into population assessment and conservation,” said Li.

Reference: Li R, Neo M.L. IUCN red list of threatened species: Tridacna gigas. IUCN Red List of Threatened Species. Published online May 23, 2024. Accessed October 29, 2024. https://www.iucnredlist.org/en