Photosynthesis and light utilization in the Caribbean coral Montastraea faveolata recovering from a bleaching event

Coral bleaching - the loss of symbiotic dinoflagellates - is initiated when corals are exposed to sea surface temperatures above the regional summer average and has been responsible for massive coral mortality episodes. The ability of symbionts to recolonize the host after bleaching may be critical in determining if a colony will recover or experience mortality. Here, following the serendipitous bleaching of specimens of Montastraea faveolata of known photosynthetic, spectroscopic, and genetic characteristics, we describe changes in photosynthesis and light utilization during the recovery process. Fully recovered M. faveolata had minimum quantum requirements (l/Φ_max) that are very close to the theoretical minimum, indicating that symbiotic corals are not only one of the most efficient light collectors in nature, but also use this energy with maximum efficiency. Analyses of the photosynthetic responses of M. faveolata throughout the recovery process indicate that during the early stages, the symbiont population exhibited characteristics consistent with acclimation to higher irradiance relative to fully recovered corals. The absorption spectra of bleached samples showed contributions of chlorophyll b (Chl b) associated with a biomass increase of the endolithic algae. The propagation of endolithic algae after bleaching may provide partial protection to the surviving symbionts from excessive radiation by reducing the reflectivity of the skeleton. Changes in the relative abundances of different symbiotic algae between recovered and unbleached colonies did not result in significant variations in photosynthetic and light utilization characteristics.