Supplementary file 1_Casting a shadow: in situ shading of corals reduces hyperthermal paling.docx

One potential mitigation effort is the installation of shade structures that can minimize the synergistic UV stressor contributing to bleaching-related tissue loss. We tested the effect of temporarily installed in situ shade structures over wild colonies of two Caribbean species (Pseudodiploria clivosa and Colpophyllia natans) to determine whether they could mitigate bleaching, affect symbiont to host ratios, and alter symbiont community structure.

Despite 2024 having the second highest cumulative heat stress on record at the study site, corals exhibited only moderate paling/bleaching. This is likely due to symbiont communities consisting almost exclusively of the heat-tolerant Durusdinium, a probable result of the unprecedented thermal stress the prior summer. However, even the moderate loss of color was remedied by the shade structures, preventing further paling/bleaching of experimental colonies after installation.