For 20 years, Ken Nedimyer has been strapping on his diving gear and diving into the waters off the Florida coast in a desperate effort to restore coral reefs destroyed by climate change and pollution. In 2019, he launched his newest venture, Reef Renewal USA. The group's YouTube channel shows Nedimyer and other members carefully attaching nursery-grown coral underwater to structures designed to build healthy reefs.
“We are working under pressure to innovate, speed and efficiency to repopulate our coral reefs,” the narrator says.
Scientists say diving conservationists like Nedimier will lose the race against time unless humans act quickly to halt emissions of climate-warming pollution. According to an article in Nature magazine, extreme temperatures in the Southern Hemisphere's Coral Sea, where Australia's Great Barrier Reef is located, recently reached their highest levels in 400 years.
Ben Henry, a paleoclimatologist at the University of Melbourne, told the New York Times: “If we don’t change our current course, our generation may witness the demise of one of the greatest natural wonders on Earth, the Great Barrier Reef.”
“Invisible”
According to a 2023 Pew Research Center poll, a majority of Americans believe global warming is a major threat. If you dig a little deeper and ask this group which ecosystem they care about most, they're likely to mention tropical rainforests, or alpine regions, or arctic tundra.
They are not wrong to care about these important communities. But our bias toward land blinds us to ecosystems that may be even more endangered beneath the ocean's surface.
“Coral reefs face an out-of-sight, out-of-mind dilemma,” said Jessica Levy, a marine biologist with the Florida Coral Restoration Foundation.
“What we're looking at is the potential loss of entire ecosystems, which we've never experienced in human history,” Levy said. “I don't think anyone wants to know if we had a complete collapse of our coral reef ecosystems. “
The threat of coral bleaching
Marine biologists use the term “bleaching” to describe how corals react when water becomes too hot and the symbiotic algae that live in their transparent tissues are expelled by stress, exposing the coral's white skeleton.
Derek Manzello said bleaching had long been considered a local reaction, but that changed in 1998.
“That summer was the first time on record that we experienced global coral bleaching,” he said.
Manzello coordinates the National Oceanic and Atmospheric Administration's Coral Reef Watch, a federal program that integrates data from satellites and field equipment to monitor ocean and weather conditions to warn of potential bleaching events.
Bleaching is not necessarily fatal. Algae may return to coral tissue, but only if the water cools quickly enough.
“Coral survival depends on the temperature of the water and how long the temperature remains elevated,” Manzello explained.
The summer of 1998 was brutal on both counts. Sea surface temperatures in the Florida Keys have been above normal for the 12th consecutive week. Ten thousand miles away, surface water temperatures in parts of Australia's Great Barrier Reef were even higher, reaching nearly 90 degrees for 12 consecutive days. In the Indian Ocean, water temperatures around the island nation of the Maldives remain well above normal from April to June, with water depths as low as 100 feet. These high temperatures combined with persistent thermal anomalies are lethal for all three ocean basins. During that catastrophic year, the Earth lost 16% of its coral reef cover.
A report released by the Australian Institute of Marine Science in late 1998 acknowledged that the reefs could regrow if “this was just a severe one-off event.” The report concludes with a warning: “However, if recent bleaching events are linked to global climate change and are repeated regularly… then the consequences for many coral reefs will be severe.”
Because the language of science is carefully constructed, it is not stated exactly how serious these consequences are.
Marine scientists later concluded that human-caused climate change was responsible for the 1998 coral reef massacre, and that the disaster was far from a one-off event.
“It's kind of crazy,” Manzello said. “Twenty-six years later, we are facing the fourth global bleaching event on record. The current event, which began in February 2023, is much worse than what occurred in 1998. [2010]appears to be more severe than the third global bleaching event [2014-2017]”.
“Ocean rainforest” in danger
The ocean is on the frontline of the climate crisis. That's because 90% of all human-caused warming since the onset of the Industrial Revolution has been absorbed by the oceans. Without this buffer, average land temperatures would be much higher than existing levels.
“Coral reefs are paying the price for this buffer,” Manzello said.
This most biodiverse marine ecosystem covers less than 1% of the ocean floor but is associated with a quarter of all known marine life, or approximately 1.3 million species.
“Coral reefs are the rainforests of the ocean,” Manzello explains.
Out of sight, out of mind, but that doesn’t shield us from what’s going on beneath the waves. The destruction of coral reefs has significant impacts on humans. Several species of fish that depend on coral reefs are a major source of protein for millions of people and an income for millions more.
Coral reefs also protect coastal communities from hurricanes and cyclones, absorbing 97% of wave energy during storms. But this only happens if the reef is healthy.
“If coral dies, the reef will eventually be flattened by erosion,” Manzello said. “This means greater damage to coastal communities during storms, and rising sea levels will only exacerbate the problem.”
Other dangers to coral reefs
Climate change is not the only threat facing coral reefs.
“Coral reefs have been damaged by so much human activity,” said Jessica Levy, listing the various scourges, including overfishing, destructive fishing practices such as trawling and blast fishing (the use of explosives to stun and killing fish) and pollution flowing from rivers into rivers.
Karen Neely, a coral ecologist at Nova Southeastern University in Florida, focuses her work on another major threat: disease.
“We often talk about coral reefs being cut down 1,000 times and dying,” Neely said. “Climate change and coral disease are two of the biggest threats that have emerged over the past few decades.”
Although disease is a natural phenomenon, Neely noted that climate change is exacerbating the problem.
“When it's very hot, corals get stressed,” she said. “Just like humans, stress weakens their resistance to disease. In fact, many coral pathogens fare better in warmer waters than in colder waters.
An improved environment for pathogenic microorganisms coupled with reduced coral resistance is having a devastating impact.
The race to save corals
Neddy Meyer understood the urgency of the situation very well. In the 1970s, he ran a small business in the Florida Keys collecting and selling tropical reef fish and live rock for the aquarium trade.
“What happened 50 years ago is etched in my mind,” he said. At the time, coral cover on Florida's main reefs was about 45 percent. Today, this proportion has dropped to 2%. “After a while, I was basically just watching the coral reefs die around me and I thought, someone needs to do something. I need to do something.
With extensive coral reef diving experience and a degree in marine biology, Nedimyer became a pioneer in the field of coral propagation and reef restoration, growing corals from small living fragments of healthy corals. When the corals grow large enough, they are removed from their nurseries in 20-30 feet of water and replanted in dead spots on the reef.
His “American Reef Renewal” project has grown from a small-scale experiment into a larger, more technologically advanced project, planting hundreds of thousands of corals in the islands alone.
“Ken Nedimyer is basically the godfather of coral gardening,” says Reef Watch’s Manzello. “His work is the basis for nearly all coral restoration efforts in the Caribbean.”
Initially, when it came time to choose which corals to plant, Nedimyer had to choose between coral species. But advances in genetic testing in recent years have allowed him to focus on breeding subsets of coral species known as genotypes. Because certain genotypes are better able to tolerate warmer water, these become the genotypes Nedimyer seeks to breed.
“We went to areas that used to be very hot,” he explains. “We're looking for the victors, the survivors in these extreme environments.”
But by 2023, ocean temperatures reached record highs, lasting longer than ever before. Reef Watch began issuing warnings in mid-May, three months earlier than was once the norm. Previous bleaching events in the archipelago didn't occur until mid-August, putting Nedimeyer's new technology to the test under extreme conditions.
“I've been diving here for 50 years,” he said, “but I've never seen what I saw last summer. It's crazy.
As summer approaches, coral restorers hope their nurseries can survive the hot weather. Under Nedimyer's guidance, American Reef Renewal worked at breakneck speed to create a nursery at a depth of 70 feet and move 1,200 corals there.
“We have 120 different genotypes of Acropora, and we moved 10 of each genotype to deeper water,” he said.
The nursery remained there until the ocean began to cool in September, and Nedimeier began cultivating corals in the water column, a few feet at a time.
“Most corals in nurseries that haven't been moved don't do very well,” he said. In fact, few of them survive past July, regardless of genotype.
“The water went from hot water to extremely hot water within a week,” Nedimier said. “Most of them don't even have time to bleach. They just cook and die. I don't think anyone has seen this happen before.
But most of the 1,200 coral fragments Nedimyer moved to deeper waters survived, offering a new potential pathway for reef recovery.
Given how dire the situation has become, even with these innovations, the question remains: Can coral reefs be saved?
“That's the question that keeps me up at night,” Levy said. “It all depends on how you define 'reef' and 'saved.'”
She firmly believes that saving coral reefs is still possible, given advances in genetics and the way the entire field is reorganized from a heavy reliance on university research to interdisciplinary efforts and larger-scale projects.
“It's not just your average coral reef biologist studying these questions,” she said. “Now we're seeing people from engineering, materials science and other disciplines coming together for the common good. I think we're going to see some very exciting and positive stories.
Still, she worries that coral reefs, such as those in Florida, may not return to historical baselines of biodiversity and coverage: “I think we're past that point. Restoration needs to consider protecting what we have. In Places like the Islands, where we're thinking about preventing species extinction.
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