Meeting Abstract
We recently described a “solar transformer” in photosymbiotic tridacnid giant clams, an evolved system that functions to redistribute solar flux incident on the clam’s mantle to spatially patterned Symbiodinium algae within the mantle tissue. Our measurements and models suggest that even at the most extreme solar fluxes experienced in shallow tropical water near the equator, all Symbiodinium cells within the clam system could function at maximum photosythetic efficiency, while all incident solar flux is used for photosynthesis. To gain further insight into the clam system and understand whether a synthetic algal culture system based on clam principles may be industrially useful, we sought to directly measure photosynthetic efficiency of Symbiodinium with single-cell spatial resolution within the clam. Typically, measurements of photosynthesis are made with pulse-amplitude modulated (PAM) fluorimeters that average the efficiency of hundreds or thousands of photosynthesizing cells over a large area on or close to the surface of an organism. To measure efficiency at small spatial scales and depths of millimeters within the highly absorbing and structured clam tissue, we developed a PAM instrument that has micron-scale spatial resolution. We modified our existing optical microprobe technique for measurements of scalar irradiance to mount two pulled optical fibers in the same ~50 µm scattering sphere. One fiber emits pulsed blue light, and the other is coupled to a spectrometer to measure chlorophyll fluorescence response – light both enters and exits the scattering sphere and our probe can “see” 10’s of cells within the clam system. We will present proof-of-concept data from the instrument and initial estimates of photosynthetic efficiency from the interior of the clam system.
