Natural selection in an extreme environment has gradually sculpted the giant clam into an exceedingly efficient farmer; it turns the fierce sunlight in its equatorial ocean home into algae, and those single-celled plants into food.

Two Penn researchers are teaming up to unlock the secrets of this living greenhouse and use it as a blueprint for new materials that harvest solar energy or convert it to biofuel.

Alison Sweeney, an assistant professor in the Department of Physics & Astronomy in the School of Arts & Sciences, and Shu Yang, a professor in the Department of Materials Science and Engineering in the School of Engineering and Applied Science, are the recipients of a National Science Foundation INSPIRE grant. Designed to fund bold, creative, and highly interdisciplinary research, the grant will provide the team with $3 million over the next five years.

Sweeney and Yang will use the funds to study the microscopic structures in the clam’s body that direct sunlight to its internal algae farms, and to develop new synthetic materials based on what they find.

“Sunlight at the equator is so intense that most plants can’t make use of it without being destroyed,” Sweeney says, “But giant clams have structures called iridocytes that scatter the light such that it hits the sides of pillars of algae they grow inside their bodies. And evolution has made it so that the iridocytes and pillars are perfectly matched for maximizing the efficiency of the light they receive.” 

While Sweeney works to understand the underlying physics that enable this phenomenon in clams, Yang will attempt to replicate it in the lab.

Unlike attempts to maximize solar efficiency in synthetic materials, which rely upon precisely manipulating their structure on the atomic scale, the giant clam’s approach is more disordered—an intriguing prospect for an engineer.     

“If the algae pillars in the clam were perfectly ordered like a crystal, they’d block each other’s light, and if the iridocytes were perfectly structured, they wouldn’t scatter as wide a range of wavelengths to be absorbed,” Yang says. “This means being less precise is actually an advantage in this case. We can work on the micro scale, which is much easier and less expensive than working on the nano scale.”   

Beyond the research aims, the NSF grant will support the team’s educational outreach efforts, both in Philadelphia and in Palau, an island country in the south Pacific Ocean where local aquaculture provides a sustainable source of the endangered clams. The grant will support a Palauan graduate student, who will travel to Penn to work with Sweeney and Yang, as well as several local interns.   

“You’d be hard-pressed to find two more different places on the planet than Philadelphia and Palau, but students in both places face similar challenges in being very talented but lacking access to scientific infrastructure,” Sweeney says. “Palau also has some of the last best coral reefs on earth. If we want to preserve coral reefs for the next generation, we need to invest in that infrastructure and in the students there.”