Optics and Ecophysiology of Coral Reef Organisms

This research topic focuses on the optical properties of coral species and their effects on coral bleaching, photoprotection, and photophysiology. Studies have demonstrated that differences in light scattering from the top ~200 μm of the skeleton are related to bleaching susceptibility, and that faster-growing corals typically have lower mass-fractal dimension, denser skeletons, and lower light availability. Corals produce GFP-like proteins to screen the symbiotic algae from excess sunlight, and these proteins can influence the growth rates of corals in different light intensities. Additionally, active chlorophyll a fluorescence is an important tool for understanding photosynthetic activity in cnidarian/dinoflagellate symbioses.

Red coralline algae have adapted to different light environments in coral reefs by using their ability to precipitate CaCO3 and their thallus optical properties. Fluorescence Imaging Systems (FluorIS) have been developed to acquire daytime fluorescent photographs and identify coral recruits. Visual signals under environmental illumination conditions can be determined by examining the fluorescence of marine organisms. Non-intrusive measurement methods have been developed to examine photochemistry of intact corals, based on redox kinetics of the primary electron donor in Photosystem I and chlorophyll fluorescence kinetics.

The type of symbiont associated with Stylophora pistillata affects the coral's ability to acquire carbon and nitrogen, and Symbiodinium clade C is more efficient at fixing carbon at low light levels. In bleached corals, Symbiodinium light exposure was up to fivefold enhanced relative to healthy corals, and Symbiodinium spp. in corals from the mesophotic environment had adapted to lower light conditions by shifting their light harvesting to a PSII based system.