Underwater umbrellas could shield coral reefs from heat and reverse bleaching: Study
Florida: Temporary underwater umbrellas placed over vulnerable corals can protect them from marine heatwaves and even partially reverse bleaching, according to a new study by Florida scientists.
The study found that shades placed over particularly vulnerable Caribbean corals can mitigate damage from high sea temperatures driven by global warming, which turns corals ghostly white and eventually kills them.
While restoring dead reefs is possible, the process is difficult and expensive and still leaves them vulnerable to future heatwaves. Scientists now believe they have found a new way to protect them, at least on a small scale.
Study lead author Dr. Karen Neely of Nova Southeastern University explained that shading cannot cool the water, but it prevents ultraviolet and irradiance damage, which worsens 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,” Dr. Neely said. “This study stemmed directly from that event: we wanted to provide proof of concept for tools to save targeted corals in similar future events.”
In the summer of 2024, Dr. Neely and her team set up 20 custom-made shades over 10 different colonies of two species of brain coral, Pseudodiploria clivosa and Colpophyllia natans, along with 20 matching corals to act as controls at Newfound Harbor in the Florida Keys.
The parasol-like shades, made of PVC pipe and nylon fabric, were temporarily fixed to the seabed with cord and floated a foot (30 cm) above each coral. They reduced light by 60 percent, according to the study published in the journal Frontiers in Marine Science.
Divers visited every two weeks to track colour changes and take tissue biopsies to monitor the algae living inside the coral.
Dr. 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. Algae also lend corals their colour, so when corals turn white under heat stress, 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 colour than expected, with the differences greatest during the most intense periods of thermal stress.“Shaded corals even recovered some of their colour, after the shades were installed,” Dr. Neely said.
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,” she added.
The research team found no differences in density of algae occupation or algae species between the control and shaded groups. They believe that if the shades had been installed earlier in the heating event, they might have been more effective.
The study found a significant positive impact, though scaling the method remains a challenge.“We found it was effective on two highly-susceptible coral species, so it is likely to be useful for most others,” Dr. Neely concluded, adding that additional studies are needed to answer more questions.
