Giant clams have vanished from places where they used to thrive

The giant clam – celebrated for its vibrant, mesmerizing mantle and unique, curved shell – now stands on the edge of extinction. Over the past century, its population has plummeted by an astounding 80 percent.

Recently, a team of researchers led by Ruiqi Li from the University of Colorado Boulder sounded the alarm on this critical situation.

Conservation status of the giant clam

The team’s efforts have prompted a critical shift in the International Union for Conservation of Nature’s (IUCN) approach to protecting these animals.

Thanks to this research, the IUCN has reclassified the giant clam, moving its status from “vulnerable” to “critically endangered.”

This red list status indicates that the species is just one step away from completely vanishing the wild. The IUCN also revised the statuses of 11 other species that are part of the giant clam family.

Ecological importance of giant clams

The two primary stressors that are driving the decline of giant clams are overfishing and climate change.

“Along with coral reefs, these clams provide important habitats for other creatures living in the reefs,” noted Li.

“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.”

Halting the sixth mass extinction

The IUCN’s recent announcement coincides with the 2024 United Nations Biodiversity Conference (COP16) in Colombia.

Representatives from 175 nations are gathering to debate measures to halt the “sixth mass extinction,” a severe loss of biodiversity due to human activities.

The World Wildlife Fund’s estimates reveal that global marine wildlife has shrunk by 56% since 1970, highlighting the gravity of the situation.

The ocean’s largest bivalve

The giant clam, Tridacna gigas, is perhaps the most iconic of all clam species. Known as the world’s largest marine bivalve, it can reach an impressive 4.5 feet in length and weigh over 700 pounds.

This remarkable creature thrives in the shallow, tropical waters of the Indo-Pacific, from the coasts of Malaysia to Australia and Fiji.

Lack of research on marine invertebrates

The growth mechanisms of T. gigas remain a puzzle for scientists. Like corals, these clams have a symbiotic relationship with algae living within them. The clams offer the algae a safe habitat, while the algae provide essential nutrients that help the clams survive.

The last time their population came under scientific scrutiny was in 1996 when the IUCN labeled T. gigas as “vulnerable” in its Red List of Threatened Species.

Due to inadequate research efforts, the previous assessment failed to consider several other giant clam species.

According to Li, there’s a persistent issue in the conservation world. Marine invertebrates often get sidelined as the focus tends to gravitate towards mammals and birds due to their appeal and familiarity.

Giant clams becoming locally extinct

In collaboration with experts at the Senckenberg Natural History Museum in Germany, and Neo Mei Lin from the National University of Singapore, Li embarked on a reassessment of all 12 giant clam species.

The team made a sobering discovery indicating that T. gigas has become locally extinct in numerous regions where it used to thrive, such as Taiwan. The overall population of T. gigas has seen a precipitous decline of 84% over the past century.

Unique beauty under threat

Giant clam species are renowned for their stunning mantles – the flesh that lines the shell.

Intriguingly, even among the same species, the mantles’ color patterns display substantial variation, rendering each clam unique. Many parts of the world harvest these clams for their meat or as decorative shells.

Climate change poses another significant threat, causing the clams to expel the beneficial algae in their tissues when the ocean water heats up excessively. Without these algae, the clams risk starvation.

Protections for giant clams

The updated Red List now accommodates some recently discovered species under the “data deficiency” category, opening the doors to future research.

Li emphasized that despite invertebrates like insects and mollusks accounting for over 95% of the world’s total animal biodiversity, they often remain out of attention. There is still a treasure trove of yet-to-be-discovered species.

Efforts to safeguard the giant clams have garnered momentum. The National Oceanic and Atmospheric Administration (NOAA) has proposed that ten giant clam species, including T. gigas, should be listed under the Endangered Species Act.

If approved, this would provide these giant clams with legal protection in the U.S., prohibiting the harvesting and trade of wild specimens. Li has backed this move by submitting his assessment to NOAA.

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

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