Research from Penn and UCSB shows how giant clams harness the sun

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PUBLIC RELEASE DATE: 2-Oct-2014

Contact: Evan Lerner
University of Pennsylvania
Research from Penn and UCSB shows how giant clams harness the sun

Evolution in extreme environments has produced life forms with amazing abilities and traits. Beneath the waves, many creatures sport iridescent structures that rival what materials scientists can make in the laboratory.

A team of researchers from the University of Pennsylvania and the University of California, Santa Barbara, has now shown how giant clams use these structures to thrive, operating as exceedingly efficient, living greenhouses that grow symbiotic algae as a source of food.

This understanding could have implications for alternative energy research, paving the way for new types of solar panels or improved reactors for growing biofuel.

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"Many mollusks, like squid, octopuses, snails and cuttlefish," Sweeney said, "have iridescent structures, but almost all use them for camouflage or for signaling to mates. We knew giant clams weren't doing either of those things, so we wanted to know what they were using them for."

While the true purpose of these iridescent structures, cells known as iridocytes, was not known, the team had a strong hypothesis. Like neighboring coral, giant clams are home to symbiotic algae that grow within their flesh. These algae convert the abundant sunlight of the clams' equatorial home into a source of nutrition but are not particularly efficient in the intense sunlight found on tropical reefs; sunlight at the latitude where these clams live is so intense that it can disrupt the algae's photosynthesis, paradoxically reducing their ability to generate energy.

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"We see that, at any vertical position within the clam tissue, the light comes in at just about the highest rate at which these algae can make use of photons most efficiently," Sweeney said. "The entire system is scaled so the algae absorb light exactly at the rate where they are happiest."

"This provides a gentle, uniform illumination to the vertical pillars consisting of the millions of symbiotic algae that provide nutrients to their animal host by photosynthesis," said Morse. "The combined effect of the deeper penetration of sunlight — reaching more algae that grow densely in the 3-dimensional volume of tissue — and the "step-down" reduction in light intensity — preventing the inhibition of photosynthesis from excessive irradiation — enables the host to support a much larger population of active algae producing food than possible without the reflective cells."

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