Ruiqi Li on the Rapid Decline of Giant Clams and Why We Should Be Concerned

According to leading scientists and experts, Earth is entering its 6th Mass Extinction Event — and it’s our fault. Humans have proliferated across the planet, polluting and radically altering the environment. In the process, we’ve set off a chain of events that could lead to a massive, if not catastrophic, decrease in biodiversity.

The 6th features an extinction rate between 500 and 1,000 times higher than previous extinction events. Estimates suggest that three out of four species may be gone within the next several decades. One of those species is the giant clam, a beautiful mollusk species prized for its wavy shell structure and vibrantly colored mantle.

What is a Giant Clam?

The “giant” part of its name is not a misnomer. They are the largest bivalve mollusks in the world. Typically, giant clams weigh more than 440 pounds and span up to 47 inches wide. The largest specimen ever found weighed over a quarter ton and measured nearly five feet in width. They surprisingly outlast most animals, with an average lifespan of over a century. The giant clam’s unique role in the marine ecosystem contributes to its hefty size and weight.

As filter feeders, these mollusks acquire most of their nutrition from single-celled dinoflagellate algae (also known as zooxanthellae). There’s a give and take, however. The mantle of giant clams serves as a habitat for this algae upon which they feed. During daylight, the clams open their shells and extend their mantle tissue. This provides the sunlight needed by the algae to photosynthesize. In turn, the algae grow and the clams grow giant with a constant food source available. This has the added benefit of providing nutrients for other marine life in typically food-deprived areas of tropical oceans. This symbiotic relationship allowed giant clams to once flourish in flat coral sand and broken coral as far down as 66 feet.

Dwindling Numbers

For centuries, giant clams could be found across the Indo-Pacific, especially in shallow coral regions. They can also be found off the coast of the Phillippines and in the coral reefs of Malaysia. Populations, however, are diminishing quickly. An assessment study published last month showed that giant clam populations are falling at an alarming rate. The study made instant waves, prompting the International Union for Conservation of Nature (IUCN) to change the conservation status of giant clams from “vulnerable” to “critically endangered.” The stakes are high, as “critically endangered” is the last stop before a species is declared extinct in the wild.

The study was produced in collaboration between the Senckenberg Natural History Museum in Germany, Dr. Mei Lin Neo from the National University of Singapore, and Ruiqi Li, a postdoctoral researcher at the Colorado University Museum of Natural History. They collected data from previous research and databases on all animals that fall under the giant clam genus. The researchers found that Tridacna gigas (the best-known giant clam species) had become locally extinct in many areas. To make matters worse, “We found that over 80% of the locations where the species occurred in the past are now extinct,” says Ruiqi Li in an interview with A-Z-Animals.com.

About Ruiqi Li

A native of China, Li graduated with his bachelor’s degree in marine biology before entering the Ph.D. program at the University of Colorado, Boulder. He just completed his degree, with his dissertation focused on photosymbiosis in marine environments. Li’s main research focus is not conservation but genomics, evolution, and molecular systems, especially concerning photosymbiosis. The assessment study that spurned the IUCN to change the conservation status of giant clams is a side project of Li’s. As an expert in photosymbiotic clams, he was invited to help assess the status of these animals. “As a scientist, I feel like we study the genomics, transcriptomics, and evolution of species,” Li explains. “On the other hand, we are seeing a lot of species going extinct. I wanted to apply my research results, skills, and understanding of the species to some practical work.”

Counting mammals may be quick work, but that’s not the case for giant clams. Not only do giant clams contain several sub-species, but they live in various regions with heavy overlap. This makes classification difficult. “In terms of species’ endangered status assessment, it’s not very direct,” Li says. “For example, if you’re working on the status of endangered elephants, you can probably count every elephant in a particular area. Giant clams are invisible until you get under the water.”

Reasons for Decline

To solve the tricky task of counting giant clam populations and their diversity, Li used data science. He combined information from biodiversity databases and data from his colleagues like Dr. Mei Lin Neo from the National University of Singapore. The team found that giant clam numbers entered a sharp decline since the previous assessment in 1996. The assessment came to no conclusions about the reason for this falling population, but Li points to several plausible reasons.

For one, climate change is rapidly changing environments and, in turn, changing the conditions to which living things are adapted. Giant clams need clear water for their algae photosynthesis. They are also highly prized for their effervescent, colored shells. In China, the shells are often sold as decorations. This puts tremendous stress on local populations and has undoubtedly led to overfishing. “We cannot say for sure [what’s causing the decline], but it’s likely due to overfishing, habitat laws, and climate change,” Li adds.

The loss of so many diverse species is a tragedy, but declining giant clam populations spells serious consequences. Giants clams are considered a keystone species. This means they serve as a lynchpin of their ecosystem, providing the necessary ingredients for the area to flourish. In terms of coral reefs, giant clams keep them thriving. They act as builders of the reef, food factories, shelters for other animals, and water filters. Without giant clams maintaining the integrity of coral reefs, these ecosystems would quickly perish.

What Can You Do?

As a scientist, Li doesn’t want to get involved in policy but hopes his team’s work will motivate policymakers to enact necessary changes to protect species like the giant clam.

“I want to translate my knowledge to conservation policy, and this assessment is a reference for policymakers,”

Dr. Mei Lin Neo

he says, adding. “Like, ‘Hey, this species is assessed as critically endangered, can you do something about that?'”

With problems that seem systemic, a lot of responsibility falls on policymakers to enact the right changes. There are, however, more economical solutions. For one, the demand for this species has encouraged the spread of giant clam farms. Li thinks these farms could provide a solution to pumping population numbers, even if it doesn’t do much for biodiversity. “I think that they can use the resources from these giant clam farms to reintroduce them to their natural habitat,” he explains.

A glance at the numbers suggests there’s not much any one person can do to preserve the giant clam. That said, there are some steps you can take to stop the extinction of this beautiful species. “I would say don’t buy any giant clam shells. If you’re in Malaysia or a nearby island don’t buy their meat to eat,” Li suggests. “If we don’t buy them, they won’t be fished.”

Things look grim for the giant clam, but there’s still light at the end of the tunnel. Factory farming and drops in demand have successfully elevated other species out of their endangered status. With the right steps and the right policy, the giant clam has a chance to regain its former numbers.