These photos, courtesy of Professor Daniel Morse from the University of California, Santa Barbara, show specialized reflective cells in the epithelium of giant clams.
These reflective cells act as a kind of sun-screen; protecting the animal’s tissues from damage from the intense solar irradiation which they are exposed to in the shallow tropical waters of the Pacific Ocean. However, Professor Morse and colleagues have now discovered a second function of these cells – they are also photo-symbiotic.
He comments on the work: “As well as reflective properties, these cells actually redirect solar photons deeper and laterally into the clam tissue, providing gentle, uniform illumination to the millions of symbiotic unicellular algae that provide nutrients to their animal host by photosynthesis.”
The combined effect of the deeper penetration of sunlight (reaching more algae) 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, and so produce more food than would be possible without the reflective cells.
There is a physical analogy between the evolved function of the clam system and an electric transformer, which changes energy flux per area in a system while conserving total energy.
Professor Daniel Morse adds: “This discovery might even provide a blueprint for improving the design of lightweight, flexible, low-cost plastic-based solar cells, in which efficiency can paradoxically be reduced, just as photosynthesis can be inhibited in the algae, by excessive sunlight.”