Underwater shades reduced color loss in Florida Keys corals
Temporary underwater shades helped two brain coral species retain color during heat stress in the Florida Keys. The field experiment cut incoming light by 60 per cent without cooling seawater. Shaded colonies stopped losing color and some regained it, while no colony died in either group. The findings concern selected colonies, with survival and longer-term outcomes still outside the experiment’s demonstrated benefit.
Science··Evening
Shade stopped color loss during a hot summer
Temporary underwater shades reduced color loss in two brain coral species at Newfound Harbor in the Florida Keys, the island chain off the southern United States. The field experiment followed selected colonies through the summer of 2024. After the structures were installed, shaded colonies stopped losing color and some regained it.[1], [2]
The team selected 20 colonies each of Pseudodiploria clivosa and Colpophyllia natans, dividing them between shaded and unshaded groups. Floating frames held cloth about 30 centimetres above the coral surface. The cloth cut incoming light by 60 per cent; water temperature stayed unchanged.[1]
Algal partners faced heat and light together
Corals receive much of their nutrition from symbiotic algae living in their tissue. Heat can disrupt that partnership, bringing paling or bleaching. The shades tested whether reducing the added light stress would help. Researchers tracked coral color and algae, but found no shade-linked difference in algal density or community composition. They suggested that exceptional heat in the previous year may have left heat-tolerant Durusdinium algae dominant.[1]
Permits and storms interrupted the intervention
Permit delays pushed installation until after heat stress had risen, and storms forced temporary removal of the shades. Tissue samples came from relatively shaded colony edges. The summer’s cumulative heat stress was the second highest measured at the site, yet controls bleached less than expected and no colony died. That leaves a survival benefit unestablished.[1]
The experiment covered selected colonies rather than an entire reef. It did not measure long-term disease or reproductive outcomes after shade removal, and its results cannot be directly extended to other species or more severe marine heatwaves.[1]
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