FIGURE 6.

Schematic diagram illustrating different optical strategies of corals. (A) The diffuse backscattering properties of skeletons from the coral Porites branneri have been measured and it was shown that the skeleton was highly reflective with an almost isotropic distribution of the backscattered light. Such scattering can lead to a diffusely enhanced light field for Symbiodinium (based on Enriquez et al., 2005). (B) Low-coherence enhanced backscattering spectroscopy has been used to identify that the optical properties of coral skeletons show a great variability in the microscopic reduced scattering coefficient μ_s’ (for short photon pathlengths). It is shown that a continuum of skeletal scattering properties exist, which are affected by the fractal dimensions of the skeleton (based on Marcelino et al., 2013). (C) Monte Carlo simulations are used to identify the optical properties of live faviid corals including intact coral tissue. A combination of light transport is identified where the tissue strongly scatters and enhances irradiance locally, while the skeleton homogenizes and distributes light to otherwise shaded areas. These two optical strategies are used to counteract the light gradient present in coral tissues. Symbiodinium cells (yellow dots) in oral tissue layers receive high amounts of light while in aboral tissue layers irradiance is reduced and Symbiodinium (dark orange) uses the remaining low light efficiently (based on this study and Wangpraseurt et al., 2012, 2014a, 2016).