Temperatures in the waters off the coast of southern Florida and the Florida Keys this month have been as high as 97 degrees Fahrenheit, according to the National Data Buoy Center.

In the summer, waters in the Keys are normally reminiscent of bath water, but temperatures that high can threaten coral reefs. And it’s still fairly early in the season. Heat stress usually affects corals the most in August and September, reported The New York Times.

“We’re entering uncharted territories,” said Derek Manzello, an ecologist and the coordinator of NOAA’s Coral Reef Watch program, as The New York Times reported.

The longer exceptionally high temperatures last, the more stressed corals can get, reported The Conversation. Part of the reason is that, unlike other marine animals, corals can’t swim in search of a cooler spot.

Coral reefs are so colorful and vibrant because they have the most biodiversity of any marine ecosystem, according to the National Oceanic and Atmospheric Administration (NOAA). Though they only cover 0.2 percent of the seabed, coral reefs support approximately 25 percent of all ocean life.

Coral reefs like those in the Florida Keys support the economy by attracting tourists, and also support the fish and fisheries that feed millions.

Warming waters due to climate change can be so damaging to corals because they are so sensitive to changes of even a degree or two.

The planet’s oceans absorb the excess heat generated by the burning of fossil fuels, and when water temperatures get too high, it causes corals to expel the algae they feed upon, turning them white, The New York Times reported. If the waters stay warm for too long, or bleaching events happen too close together, corals may not recover.

According to one study, the world has lost half its living corals since the 1950s.

Corals “host a microscopic symbiotic algae called zooxanthella that photosynthesizes just like plants, providing food to the coral. When the surrounding waters get too warm for too long, the zooxanthellae leave the coral, and the coral can turn pale or white,” Ian Enochs, a research ecologist with NOAA, wrote in The Conversation. “If corals stay bleached, they can become energetically compromised and ultimately die. When corals die or their growth slows, these beautiful, complex reef habitats start disappearing and can eventually erode to sand.”

About 70 percent of Florida Keys reefs have become “net erosional,” research published in November of last year found, which means more habitat is being lost than built.

“Building these reefs has taken corals tens of thousands of years. Decimating them has taken humans mere decades. Since the late 1970s, healthy coral cover in the Florida Keys has fallen 90 percent,” reported Climate.gov.

Coral bleaching has been seen recently in other parts of the world, including in Costa Rica, El Salvador, Mexico, Columbia, Belize and Panama, The Conversation reported.

The overarching cause of the current marine heat wave is human-caused global warming, which has been exacerbated by El Niño. Thankfully, mass coral death hasn’t been seen with this extreme bout of ocean warming yet.

“Coral bleaching on a large scale has really been documented only since the early 1980s. When I talk to people who have been fishing and diving in the Florida Keys since before I was born, they have amazing stories of how vibrant the reefs used to be. They know firsthand how bad things have become because they have lived it,” Enochs wrote in The Conversation. “There isn’t currently a single silver-bullet solution, but ignoring the harm being done is not an option. There is simply too much at stake.”

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