by Florida’s coral reefs are facing what could be an unprecedented threat from a marine heat wave that is warming the Gulf of Mexico and pushing water temperatures into the 90s.
The main concern for coral is not just the current sea temperatures in the Florida Keys, even though they are the hottest on record. The daily average surface temperature of the Keys on Monday was just over 90 degrees Fahrenheit (32.4 degrees Celsius), according to the National Oceanic and Atmospheric Administration.
The real concern, scientists say, is that it’s only July. Corals typically experience the most heat stress in August and September.
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“We’re entering uncharted territory,” said Derek Manzello, an ecologist and the coordinator of NOAA’s Coral Reef Watch program.
Coral reefs are natural wonders that support countless species and blunt damage from storms. According to NOAA, reefs in the United States generate $3.4 billion annually in economic benefits for fishing, tourism and coastal protection.
But oceans have absorbed about 90% of the extra heat humans create when we burn fossil fuels and destroy forests. When the sea temperature rises too high, corals bleach and expel the algae they need for sustenance. If the water doesn’t cool down fast enough, or if bleaching events happen in quick succession, the corals will die. For decades, scientists have been warning that climate change poses an existential threat to coral reefs. The world has already lost much of its coral reefs, perhaps half since 1950.
“To be blunt, it can be very depressing,” Manzello said. “Unfortunately, I’m a scientist who sees it happen.”
The heat at sea is not only affecting the Gulf of Mexico. Globally, about 40% of the planet experiences a marine heat wave, according to Dillon Amaya, a physics scientist at NOAA who studies them.
“Florida is just one patch in a horrible quilt right now,” Amaya said.
In part, that’s because the planet is entering a natural climate phenomenon known as El Niño, which typically results in warmer oceans. But now El Niño comes on top of the long-term warming caused by greenhouse gas emissions.
Although coral is particularly vulnerable, heat waves harm numerous species, and the effects vary around the world as species are adapted to different temperature ranges.
In general, fish need more oxygen when the water is warmer. That is a problem, because warmer water retains less oxygen.
“Large-scale fish kills are becoming more common as our climate changes,” said Martin Grosell, a professor of ichthyology at the University of Miami.
Coral reefs are particularly important because so many species depend on them. According to NOAA, about 25% of all marine life, including more than 4,000 species of fish, depend on reefs at some point in their lives.
While there are no reports of bleaching in Florida yet, it has already begun on reefs to the south, Manzello said, off Belize, Mexico, El Salvador, Costa Rica and Colombia.
Florida’s coral reef system stretches about 350 miles from the mainland St. Lucie Inlet south and west beyond the end of the Keys, and is frequented by sea turtles, manta rays, flounder, and lobster.
What happens in Florida will depend on conditions in the coming weeks. Storms, which stir up deeper, cooler water and reduce sunshine, could bring relief, scientists say. El Niño periods are usually associated with below-average Atlantic hurricane seasons, but that may not be the case this year.
Researchers who care about coral are deeply concerned.
“It keeps me awake,” says Andrew Baker, a professor of marine biology at the University of Miami, where he directs the Coral Reef Futures Lab. “But I don’t want to write the eulogy just yet.”
Scientists like Baker are scrambling to find ways to help corals become more resilient to higher temperatures, such as crossing Florida’s corals with varieties that seem to withstand more heat. But ultimately, the survival of corals and countless other species depends on humans’ ability to curb climate change.
“You have to get to the root causes,” said Lizzie McLeod, the global oceans director at The Nature Conservancy. “We need to reduce emissions, we need to move to clean energy, we need to reduce subsidies to the fossil fuel industry.”
In Key West, beachgoers expressed surprise at the warmth of the ocean, compared to bath water. Lynsi Wavra, a captain and ecotour guide, said her mother had lived there for 20 years and had witnessed the coral decline.
“She came home crying,” Wavra said.
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