Article révisé par les pairs
Résumé : Marine heatwaves trigger severe coral bleaching events that result in dramatic coral loss worldwide. An increasingly common method used to mitigate coral bleaching is to shade portions of reefs. However, shading may lower the thermal tolerance of corals, which would be detrimental to their survival. Here, we investigated how long-term shading modifies the response of Montipora capitata to both light and temperature stress. After 2 years of growth, we used the Coral Bleaching Automated Stress System (CBASS) to compare responses of 73%-shaded and unshaded corals during 1) temperature stress under ambient light, 2) temperature stress under low light, and 3) light stress under ambient temperature. Results show that shaded corals are less resistant to light stress and to heat stress under ambient light, but not to heat stress under low light. We further demonstrate that low light intensity reduces the decline of photosynthetic efficiency associated with increasing temperature, regardless of the light history of the coral colonies. Our data show that light-mediated stress is both independent of, and synergistic with, heat-induced stress, and suggest that light and heat stresses trigger different molecular and cellular pathways. We hereby confirm the benefits of coral shading under short-term temperature stress, and show that long-term shading does not lower coral heat tolerance, despite its negative impact on tolerance to light stress and on coral growth.

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