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Coral reefs are experiencing another global bleaching event. Growing corals on artificial reefs could help save them


By Michelle Cohan, CNN

(CNN) — Miami Beach, Florida is known for its art deco flair and turquoise waters. But just off the coast of this colorful city lies an underwater world in decline.

Florida’s coral reef spans nearly 563 kilometers (350 miles) and is home to some 40 species of corals that not only provide food and shelter for aquatic life, but also help protect coastal communities from storm damage.

Like other coral reefs, over the last few decades, this vibrant ecosystem has been suffering from the effects of climate change, with the National Oceanic and Atmospheric Administration recently reporting a fourth global mass bleaching event – the second in the last decade.

Bleaching happens when the corals become stressed due to changes in their environment and expel the colorful algae living on them. The corals turn white and begin to weaken.

“If the bleaching goes on for an extended amount of time, the corals die,” says Diego Lirman, associate professor of marine biology and ecology at the University of Miami.

Lirman runs the Rescue a Reef lab, which aims to help conserve and restore this valuable yet vulnerable habitat. “Coastal ecosystems protect our shorelines against the impacts of storms and waves,” Lirman says. “They’re the speed bumps of the ocean.”

Off the coast of North Miami Beach, he leads an underwater experiment that combines natural corals with an artificial structure – creating a hybrid reef that he hopes will mimic the effects of a real one.

“Speed bumps of the ocean”

Increasingly, artificial reefs are being implemented all over the world to help restore marine ecosystems – from 3D-printed tiles to sunken ships. Studies suggest that man-made structures can be effective, but factors like location, design and placement can influence the outcome. In 2009, the UN’s International Maritime Organization produced guidelines around the placement of artificial reefs, noting that these reefs can have a negative impact “especially when waste, recycled or unsuitable materials are used.”

Lirman’s hybrid ECoREEF project consists of a concrete foundation covered with corals transplanted from his nurseries.

The experiment was born in the lab, where model versions went through many tests, including extensive simulations in a powerful wave generator capable of recreating category 5 hurricane conditions.

Lirman says the base alone can reduce wave action by 60 to 70%, with corals further reducing it by another 15 to 20%.

“Combined, these two approaches can reduce wave energy and wave height by about 80 to 90%, which is what we want to protect our shorelines,” Lirman tells CNN.

In partnership with the city of Miami Beach, two hybrid reefs were deployed in March 2023. Over the last year, Emily Esplandiu, a research associate in Lirman’s coral restoration lab, says they’ve witnessed different fish species colonize the reef, along with turtles, sharks and rays.

She tells CNN that they’ve seen the corals they planted grow and flourish there, as well. “So now we can look at how different species and genotypes survive in these conditions and how resilient they are through high temperatures,” she says.

Coral gardening

Lirman’s team has been growing and testing coral colonies at the university for more than 15 years.

“We’re trying to understand why some corals survive while others in the same environment die,” Lirman says. “We’re learn[ing] from the survivors, what is it about their physiology, their genetics? And then we’re using that information to create climate-resistant corals.”

The lab is also experimenting with “stress hardening,” where researchers expose corals to sub-lethal temperatures to prime their physiological response, making them less vulnerable to fluctuating ocean temperatures. The corals are then transplanted onto natural reefs or onto the hybrid structures.

Every year, his team plants 10,000 to 15,000 corals onto the reefs of Miami-Dade, Lirman says.

Over the next few years, Lirman and his team plan to expand the scale of the ECoREEF project significantly, deploying bigger structures around the Miami area, thanks to US Department of Defense funding.

“They realized that the health of the coastal ecosystems becomes a national security issue when their coastal bases get impacted by storms, and then they are unable to do their job,” Lirman tells CNN.

A global problem

Ocean ecosystems are declining and suffering around the world, Lirman says.

The number one threat to corals globally is climate change, which is increasing sea temperature and leading to changes in storm patterns and ocean chemistry. Overfishing and dredging also play a role, Lirman says. As a result, coastal areas are becoming more exposed to waves and flooding.

“After every storm, the cost of rebuilding and the loss of property and lives, it is just huge,” Lirman says. “We need to protect our shorelines and nature-based solutions [like] hybrid reefs are one effective, cost efficient way of doing that.”

While Lirman hopes his experiment can serve as an example for other seaboard cities around the world, he says we also need to curb climate-warming carbon emissions – “if we don’t do that, no amount of artificial reefs will save our coastlines.”

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