Physics Under the Sea

In a world searching for efficient, inexpensive energy sources, Alison Sweeney’s research suggests that we examine the giant clam.

Sweeney, who joined the faculty this year as an assistant professor of physics and astronomy, was trained as a biologist. She realized early on, though, that she was most interested in explaining the physical underpinnings of what evolution acts on. “To satisfy my own curiosity, I ended up having to learn more and more physics,” she says.

Her curiosity ultimately brought her to the biophysics of organisms, specifically bio-optics. She’s currently focusing on mollusks, which share a class of proteins called reflectins, with which they build what Sweeney calls “remarkable little optical apparatuses.” Her most recent work, begun as a postdoc with Dan Morse at the University of California, Santa Barbara, has been on giant clams, to learn what they were doing with their reflectins. “It seemed completely bizarre that these clams that just sit there and filter feed, basically, have these remarkable, beautiful, sparkly shells,” Sweeney says.

“You could use the same strategy the clams use as a mechanism for shrinking the size of big solar cells.”

What she discovered may have big implications for biofuels, which involve growing algae and extracting lipids for fuel. When algae are grown in vats, however, they shade each other, and the energy used to stir them for light exposure negates the energy they produce. “It turns out clams have this beautiful solution to this problem,” says Sweeney. “Those little cells that appear sparkly at the top are actually there to exactly spread the light out so that the algae are perfectly evenly illuminated.” Beyond biofuels, there’s also a promise of improved solar cells: “You could use the same strategy the clams use as a mechanism for shrinking the size of big solar cells,” she says. She’s already started talking with professors in the School of Engineering and Applied Science about working together.

Her work on another mollusk, squid, examines how they use their reflectins for camouflage. Squid must hide from predators—including whales, sharks, and other squid—in the open space of the ocean, against the complexity of light through the water. Sweeney has found evidence indicating that the structures in squid skin are evolved to provide very good cloaking against the radiance in the ocean. “When the only thing you have to hide you is this complex light field, it takes a complex reflector to do the hiding,” she says. She and her graduate students are also studying the other end of this optical system:  the squid eye. “Camouflage has to evolve in response to a viewer, right?” says Sweeney. “You only have to be as good as the visual system that wants to eat you.”

Like the clams, this may someday have implications for human engineering. Sweeney’s own work is only possible because of recent technology like miniaturized fiber optic spectrometers, sophisticated optical modeling software, and computers big enough to handle the sort of simulations she needs. “It’s allowed people like me to open up this question of what nifty optical adaptations and strategies and solutions life has come up with to solve problems.”