Underwater umbrellas could protect coral reefs from heat—and even partly reverse the bleaching, according to a new study by Florida scientists.
Temporary shades placed over particularly vulnerable Caribbean corals can mitigate damage from high sea temperatures driven by global warming, which turns them ghostly white—and eventually kills them.
Restoring dead reefs is possible, but the process is difficult and expensive, and still leaves them vulnerable to future heatwaves. Now, scientists believe they’ve found a new way to protect them—at least, on a small scale.
Study lead author Dr. Karen Neely explained that shading can’t cool the water, but it prevents ultraviolet (UV) and irradiance damage, which worsens the heat damage.
“The 2023 coral bleaching event in Florida essentially wiped out branching corals, and at some inshore sites had a devastating impact on brain corals.
“This study stemmed directly from that event: we wanted to provide proof of concept for tools to save targeted corals in similar future events.”
So, in the summer of 2024, Dr. Neely and her team from the Nova Southeastern University in Florida set up twenty custom-made shades overtop 10 different colonies of two species of brain coral, Pseudodiploria clivosa and Colpophyllia natans—along with 20 matching corals to act as controls.
The parasol-like shades, made of pvc pipe and nylon fabric, were temporarily fixed to the seabed with cord and floated a foot above each coral (30cm).
They reduced light by 60%, according to the study published in the journal Frontiers in Marine Science.
Divers visited every two weeks to track color changes and take tissue biopsies at Newfound Harbor in the Florida Keys, to monitor the algae living inside the coral.
Neely explained that corals have a “symbiotic” relationship with the algae: the coral provides the algae with a home and the algae provides the coral with most of its nutritional needs.
She said algae also lend corals their color, so when corals turn white under heat stress, scientists know that the relationship has broken down and the coral is starving.
Although the heat stress measured at Newfound Harbor that summer was the second-highest on record, the corals shaded by fabric lost less color than expected.
And the differences were greatest during the most intense periods of thermal stress.
Not only that, Dr. Neely found another salient benefit.
“Shaded corals even recovered some of their color, after the shades were installed.”
They also saw less bleaching than expected overall, and no dead coral.
“Shades reversed the observed bleaching, but the event wasn’t severe enough to cause mortality on control or shaded corals.
“However, we know that even bleaching that doesn’t cause mortality can impact corals’ future disease susceptibility and reproductive capacity.
The research team found no differences in density of algae occupation or algae species between the control and shaded groups. They believe that if they’d been installed earlier in the heating event, the shades might have been more effective.
The study found a “significant” positive impact, except for the method’s limitation of scaling it.
“We found it was effective on two highly-susceptible coral species, so it is likely to be useful for most others,” she concluded—but additional studies are needed to answer more questions.
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