High ocean temperatures are harming the Florida coral reef. Rescue crews are racing to help

Layton, Florida: Steps away from the warming waters of Florida Bay, marine biologist Emily Becker removed covers from the dozens of water-filled tanks under her watchful eye. Nestled in seawater carefully maintained at about 85 degrees Fahrenheit (29 degrees Celsius) lay hundreds of pieces of coral — some a sickly white from the bleaching that threatens to kill them, others recovered to healthy bright iodine in colour.

As Becker looked over the coral, crews of reef rescue groups arrived in trucks carrying more — brought up by divers in a massive effort aimed at saving the coral from an ocean that is cooking it alive. "People jumped into action really quickly, as best as they could," Becker said, wiping sweat from her brow.

Up and down the chain of islands that form the Florida Keys, coral rescue groups and government and academic institutions have mobilized to save the coral from a historic bleaching event that experts say threatens the viability of the third-largest reef tract in the world. They've been working long days and weekends in blistering heat for weeks to get as many specimens as they can onto land amid reports of some reef tracts experiencing near-total mortality.

In mid-July, water surface temperatures averaged about 91 degrees (33 Celsius) off the lower Florida Keys, well above the average of 85 degrees (29.5 Celsius), according to National Oceanic and Atmospheric Administration reports. The hot water resulted in nearly 100% bleaching along portions of the reef, causing the corals to lose their zooxanthellae, the algae that give them colour and nourishment. If they don't recover their zooxanthellae, they will ultimately die.

"We're already seeing not just bleaching but actual coral death out on the reef because the temperatures were so hot," said Cynthia Lewis, director of the Keys Marine Lab, a research institute on the island of Long Key, some 1160 kilometers south of Miami, where rescue groups have already brought more than 1,500 pieces of coral. "And we can't afford to lose more of our reef."

Coral bleaching occurs naturally when waters warm significantly, including in 2016 in the Keys. But Lewis said the current situation is urgent for coral, vital to Florida's economy, coastal protection and marine life. The corals "don't have a lot of time," she said. "They're literally sitting, stewing in the water out there in these hot, hot temperatures." A string of recent overcast and rainy days helped drop water temperatures slightly. But it will likely be late October or November before the coral samples can be returned to the reef, Lewis said.

What's at stake? The Florida Coral Reef is the world's third-largest, extending about 563 kilometres from the Dry Tortugas in the Gulf of Mexico to St. Lucie Inlet, some 115 miles (185 kilometres) north of Miami. The reef is a first line of defence against erosion and flooding from hurricanes and tropical storms, Lewis said. It helps support commercial fishing and a thriving tourism industry, from snorkelling and scuba diving to recreational fishing.

And they nurture "such an amazing amount of diversity and life" in the ocean around them, she said. "In a normal situation, they're like the rainforests of the ocean," Lewis said. "They're incredibly important." The world's oceans have been record-setting hot since April, with scientists citing climate change from the burning of coal, oil and natural gas along with a boost from El Nino, a natural warming of parts of the Pacific that changes weather worldwide and generally heats the planet.

The bleaching occurred rapidly as the water temperature rose in July. "We got kicked in the teeth because it happened so fast in the Lower Keys. I mean, within a week," said Michael Echevarria, president of the nonprofit Reef Renewal USA. Reef Renewal was among those who initially worked to move endangered coral into land-based facilities. More recently, they've worked to save coral in several of their own underwater nurseries in shallower water by moving them to deeper, cooler water, where they hang pieces of coral from tree-like structures.

Reef Renewal founder Ken Nedimyer called the coral bleaching "hard to watch and hard to experience" and said his group knew that coral stress would increase under climate change but didn't think it would come so soon. "There's a lot of people that think this isn't real, that climate change is not real, and that the world is not warming up. And I don't care what they say; it's real. I'm living it right now, and I've lived down here and done this for a long time," he said. "And I've never seen this."

Back at the Keys Marine Lab in Layton, the collected pieces of coral are placed in cooling trays set up on tables that hold between 40 and 400 gallons of seawater. The 85-degree water (29 degrees Celsius) makes for "much happier coral," Becker said. "We've seen some coral that have been really stressed offshore come back into our tables and recover already," she said. "They're already getting colour back. So that's really encouraging to see that."

The work goes beyond saving the coral. Becker and others are studying different types of coral to see which ones survive temperature stress and disease better, hoping to "build a better reef with more resilient corals," she said. Scientists from the University of Miami have established a restoration research site off Key Biscayne to do such work.

Jamison Gove, co-author of a new article in Nature about how Hawaii coral reefs weathered a 2015 marine heat wave that pushed ocean temperatures to their highest levels in 120 years of record-keeping, said his research suggests some corals off Florida may survive better than others depending on the health of local fish populations and runoff from land.

The Honolulu-based research oceanographer with NOAA said reefs that rebounded best after Hawaii's heat wave were those that had both the most fish and the least exposure to sewage from cesspools and septic systems. But he said local management measures won't save reefs if people don't cut greenhouse gas emissions.

The effort to save Florida's coral is appreciated by Jennifer Cullen, manager of Rain Barrel Village, a souvenir shop in nearby Islamorada. "I'm worried about the coral. I'm worried about tourism, worried about stronger hurricanes, because we've already had Hurricane Irma, which was devastating for the Keys and tourism," Cullen said. "It was a very long recovery, and I don't know how much more of that we can take."