Coral bleaching, caused by the loss of brownish-colored dinoflagellate photosymbionts from the host tissue of reef-building corals, is a major threat to reef survival. Occasionally, bleached corals become exceptionally colorful rather than white. These colors derive from photoprotective green fluorescent protein (GFP)-like pigments produced by the coral host. There is currently no consensus regarding what causes colorful bleaching events and what the consequences for the corals are. Here, we document that colorful bleaching events are a recurring phenomenon in reef regions around the globe. Our analysis of temperature conditions associated with colorful bleaching events suggests that corals develop extreme coloration within 2 to 3 weeks after exposure to mild or temporary heat stress. We demonstrate that the increase of light fluxes in symbiont-depleted tissue promoted by reflection of the incident light from the coral skeleton induces strong expression of the photoprotective coral host pigments. We describe an optical feedback loop involving both partners of the association, discussing that the mitigation of light stress offered by host pigments could facilitate recolonization of bleached tissue by symbionts. Our data indicate that colorful bleaching has the potential to identify local environmental factors, such as nutrient stress, that can exacerbate the impact of elevated temperatures on corals, to indicate the severity of heat stress experienced by corals and to gauge their post-stress recovery potential. VIDEO ABSTRACT.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors thank Alex Thomson (Scottish Association for Marine Science) for collecting the P. lichen high light acclimation data and Ryan Goehrung (University of Washington), Courtney Couch (NOAA), Richard Vevers (The Ocean Agency), Martin Savers (Reefscapers at http://reefscapers.com), Shreya Yadav (Hawaiʻi Institute of Marine Biology), Ed Roberts (Tethys Images), Michael Fox (Woods Hole Oceanographic Institution), Bill McGraw (https://www.newaquatechpanama.com), Tess Moriarty (University of Newcastle), Fanny Houlbreque (Institute de la Recherce pour le Développement), Andy Bruckner (Coral Reef CPR), Chris Jones (Great Barrier Reef Marine Park Authority), Brian Zgliczynski (Scripps Institution of Oceanography), Louise Laing (People4Ocean), and Darren Coker (JCU Townsville) for providing photographs and background information on colorful bleaching events. The authors acknowledge funding from Natural Environmental Research Council (http://www.nerc.ac.uk/; PhD studentship under NE/L002531/1 to E.B.; NE/I01683X/1, NE/K00641X/1, and NE/I012648/1 to J.W. and C.D.), Deutsche Forschungsgemeinschaft (http://www.dfg.de; Wi1990/2-1 to J.W.), ASSEMBLE (to J.W. and C.D.), the European Research Council (http://erc.europa.eu/) under the European Union’s Seventh Framework Programme (ERC grant agreement no. 311179 to J.W.), Tropical Marine Centre London, and Tropic Marin, Wartenberg (NERC CASE studentship to E.B.; sponsorship to the Coral Reef Laboratory).