During the 2024 marine heat wave in the Florida Keys, researchers deployed 20 makeshift shades—PVC pipe, foam, and agricultural cloth—over colonies of two brain coral species at Newfound Harbor. The shades stayed in place from August to November, while sea temperatures exceeded the local bleaching threshold for at least 61 days.
Corals under the shades bleached less than nearby unshaded ones, and some that had already started paling recovered once shaded. "As soon as those shades went on, those corals all recovered," said Karen Neely, a marine biologist at Nova Southeastern University and co-author of the study, which appeared in Frontiers in Marine Science.
The team expected shading to shift the mix of symbiotic algae inside the corals, but species composition and density were roughly the same in shaded and unshaded corals. Neely suggested the 2023 heat wave may have already eliminated heat-sensitive symbionts. Mark Warner of the University of Delaware, who was not involved, noted the unshaded corals may have been acclimating to bright light by reducing chlorophyll rather than losing algae.
The authors say the results give Caribbean managers local evidence that shading works, and the approach proved cheaper than restoration—about one-tenth the cost of replacing a dead coral. The shades also required little upkeep.