Editor's Note: Call to Earth is a CNN editorial series reporting on the environmental challenges facing our planet, along with the solutions. Rolex's Perpetual Planet initiative partners with CNN to raise awareness and education around important sustainability issues and inspire positive action.
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, this vibrant ecosystem has suffered the effects of climate change in recent decades, with the National Oceanic and Atmospheric Administration recently reporting a fourth global mass bleaching event - the second in the past decade.
Bleaching occurs when the corals become stressed due to changes in their environment and expel the colorful algae that live on them. The corals turn white and begin to weaken.
"If the bleaching continues for an extended period of time, the corals die," said Diego Lirman, an associate professor of marine biology and ecology at the University of Miami.
Lirman leads the Rescue a Reef laboratory, which aims to help conserve and restore this valuable but fragile habitat. "Coastal ecosystems protect our coastlines from the effects of storms and waves," says Lirman. "They are the speed bumps of the ocean."
Off the coast of North Miami Beach, he is leading 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 reef.
"Speed Bumps of the Ocean"
Artificial reefs are increasingly being implemented around 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 such as location, design and placement can influence the outcome. In 2009, the UN International Maritime Organization issued guidelines around the placement of artificial reefs, noting that these reefs can have a negative impact "particularly 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 originated in the laboratory, where model versions have undergone many tests, including extensive simulations in a powerful wave generator that can simulate Category 5 hurricane conditions.
Lirman says the base alone can reduce wave action by 60 to 70%, while corals can reduce 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 coastlines," Lirman told CNN.
In collaboration with the City of Miami Beach, two hybrid reefs were deployed in March 2023. Over the past year, Emily Esplandiu, a research associate in Lirman's coral restoration laboratory, says she has witnessed several fish species colonizing the reef, along with turtles. , sharks and rays.
She tells CNN that they have also seen the corals they planted grow and flourish there. "So now we can look at how different species and genotypes survive under these conditions and how resilient they are to 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 are trying to understand why some corals survive while others die in the same environment," says Lirman. "We are learning[ing] of the survivors: what about their physiology, their genetics? And then we use that information to create climate-resilient corals."
The lab is also experimenting with "stress hardening," in which researchers expose corals to sublethal temperatures to stimulate their physiological response, making them less vulnerable to fluctuating ocean temperatures. The corals are then transplanted onto natural reefs or onto the hybrid structures.
Each year, his team plants 10,000 to 15,000 corals on Miami-Dade reefs, Lirman says.
In the coming years, Lirman and his team plan to significantly expand the scope of the ECoREEF project, deploying larger structures in the Miami area, thanks to funding from the U.S. Department of Defense.
"They realized that the health of coastal ecosystems becomes a national security issue when their coastal bases are hit by storms and they can no longer do their jobs," Lirman told CNN.
A global problem
Ocean ecosystems are declining and suffering around the world, Lirman says.
The biggest threat to corals worldwide is climate change, which is raising sea temperatures and leading to changes in storm patterns and ocean chemistry. Overfishing and dredging also play a role, says Lirman. As a result, coastal areas are increasingly exposed to waves and flooding.
"After every storm, the costs of rebuilding and loss of property and lives are enormous," Lirman said. "We must protect our coastlines and nature-based solutions [like] hybrid reefs are an effective, cost-efficient way to do that."
While Lirman hopes his experiment can serve as an example for other coastal cities around the world, he says we also need to reduce climate-warming carbon emissions - "if we don't, no amount of artificial reefs will save our coastlines. "
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