Meeting Abstract

76.2  Friday, Jan. 6  A monte-carlo model of photon transport in symbiotic giant clams HOLT, A.L.*; GAGNON, Y; SWEENEY, A.M.; MORSE, D.E.; Univ. California, Santa Barbara; Univ. California, Santa Barbara; Duke University; Univ. California, Santa Barbara

Giant clams of the genus Tridacna have a complex photonic system combining photosynthetic and absorbing brown algae with single cell reflectors, the functions of which are currently poorly understood. To explore the functionality of the iridocyte cells in this unique photonic system, we developed a novel, detailed model of light scattering in the tissue using a stochastic Monte Carlo photon transport method. Using optical and transmission micrograph data, we replicated in silico the organization of algae and iridocyte cells in three-dimensions and many levels of spatial hierarchical organization. Monte Carlo ray tracing was then used to explore photon transport in this biologically realistic three-dimensional space. Our model used fixed cell positions and probability-weighted scattering functions for algal cells and iridocytes to then calculate the scattering of thousands of photons based on these probabilities. The computational efficiency of our method is high because the code has been vectorized in Matlab, allowing us errors of <1% of these tracked parameters. We used our model to track the values of total absorption and individual cell absorption by algal cells in the 3D tissue with a high degree of realism and accuracy. By systematically changing the scattering probabilities of the iridocytes and determining which ones most accurately describe reflectance, optical, and transmission micrograph data, we learned that the iridocytes are organized on multiple spatial scales to scatter light into the tissue in a way that optimizes photosynthetically active irradiance in both wavelength and intensity, according to the physiological abilities of the algae.