Giant clams, carbon, microplastics, and coral recovery: Jordan Flagel on Marine Conservation Happy Hour
IMARCS Vice President and Lead Environmental Scientist Jordan Flagel joined Dr Scarlett Smash and Dr Craken MacCraic on Marine Conservation Happy Hour to talk about giant clams: what makes them different from every other clam, and why IMARCS thinks they may matter for carbon, microplastics, and bleached coral.
A small team, built on partnerships
Jordan described IMARCS as a distributed team of about eight people across Spain, Japan, Canada, and Micronesia, operating as a US-based nonprofit. The research associates are based at the University of Barcelona, and the tanks are at IMARCS's own facility in Shiga, Japan. "We can only do so much with a small team," he said, which is why most of the work runs through partnerships.
What makes a giant clam giant
Giant clams are filter feeders like any other clam. The difference is the zooxanthellae living in their mantles, the same algae found in corals. Photosynthesis gives the clams extra energy, which is how the largest species, Tridacna gigas, can reach over 250 kilos. The same algae produce the colors. Jordan noted that the photos and videos on the IMARCS website are not altered.
He walked through the species: gigas, maxima, noae, the fluted giant clam, and the Hippopus clams. Hippopus is one of the species IMARCS is focusing on for its coral bleaching work.
The carbon question
Dr Craken asked the obvious question: if a clam builds a heavy calcium carbonate shell, why isn't it a carbon sink? Jordan's answer is that in regular ambient seawater, giant clams are not necessarily net negative, because building the shell releases carbon into the water. The published literature is not settled either way.
That is where the IMARCS approach comes in. IMARCS scientists are testing whether raising the pH in tanks can hold more carbon as carbonate ions that the clams can reuse. That work is under way at the Shiga facility.
Microplastics
Giant clams clear turbidity, and published research shows they filter microplastics. Jordan was clear that IMARCS has not yet started its own microplastics trials. He sees it as one of the areas with the most potential, especially paired with hatchery-based reseeding in places where giant clams have become locally extinct.
How the coral recovery idea started
The bleaching work began with an observation at the Kosrae giant clam hatchery in Micronesia. The hatchery's director saw bleached coral recover after ground-up giant clam mantle was introduced to it. "Our hypothesis is that the bleached coral took up the zooxanthellae," Jordan said. Genetic material is preserved on cards and shipped to the University of Barcelona, where Dr Vanessa Arranz and Dr Juan Moles lead the genomic analysis. There are no live clams in Spain.
The clams in Japan come from hatcheries in southern Japan and from Kosrae, which is where IMARCS's Tridacna gigas came from. Giant clams are also typically more tolerant of warm water than many corals. That tolerance is why IMARCS is asking whether zooxanthellae from giant clams can help the most sensitive corals recover. The full set of programs is on the current research page.
Myth check
Can a giant clam trap a diver? "A giant clam could never eat a human being," Jordan said. The shell folds shut slowly rather than snapping, and a trapped arm or leg could be pulled out. On pearls, he believes the legends of giant pearls came from giant clams.
What comes next
"All the work we're doing is meant to be a kind of proof of concept that can be taken up by other larger organizations and actually deployed and implemented," Jordan said. His personal hope is to see the work used at scale, in places like Australia and Indonesia.
Listen and follow
The full episode is on the Marine Conservation Happy Hour website and Spotify. Jordan returned for a second episode on mangroves: Why mangroves store so much carbon.
Want to support the clams directly? Adopt a giant clam.