A severe marine heat wave off the coast of Florida has brought a burst of abnormally high ocean temperatures, prompting alarms from marine scientists that the unprecedented heat could further stress an already vulnerable coral reef system.
Water temperatures offshore of Everglades National Park this week spiked to roughly 10 degrees higher than the average summer peak, with some locations approaching a blistering 97 degrees Monday afternoon.
Coral scientists worry if the heat were to stick around even a few weeks, corals could begin bleaching, or weakening, as they expel the tiny algae species living in their tissues. Even if corals don’t bleach, scientists fear, the conditions are already ripe for further stress ahead of pivotal coral spawning expected in August.
“These conditions that we’re seeing are totally extreme and not ordinary at all,” said Liv Williamson, an assistant scientist of marine biology and ecology at the University of Miami. Temperatures offshore of the Florida Keys typically peak around late August or early September, not the second week in July, she said.
That could mean corals face upward of three straight months of harmful water temperatures, a threat to the overall health of an ecosystem that harbors more than a quarter of the world’s marine life.
“It’s not looking good,” Williamson said. “We’re all pretty worried.”
The Keys is already under a bleaching alert level one, which brings “significant potential” for coral bleaching over the coming months, according to the National Oceanic and Atmospheric Administration.
At Murray Key, an island about 2 miles south of Flamingo Campground in the Everglades, water temperatures measured a balmy 96.8 degrees Monday. Big Sable Creek, farther up the Gulf of Mexico, logged a 95.7-degree measurement the same day. Across the region, temperatures were well above their averages this week as heat records were shattered across the globe.
“It definitely is anomalously warm,” said Brian McNoldy, a senior research associate at the University of Miami. Wind and wave conditions have been pretty calm off of southern Florida lately, making warm, shallow water move slower with more time to bask under the overhead sun. It’s hot enough for humans to be uncomfortable standing or swimming in the water.
Federal ocean scientists are predicting a 60% to 90% chance that the rest of Southwest Florida will fall under a bleaching alert level one over the next two months. Tampa Bay is under a bleaching warning, meaning there is cause for concern but conditions aren’t bad enough to kill corals yet.
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“Even if the things that are creating these anomalies switched off instantly right now, it would take a long time — weeks — for the ocean to relax to its normal state,” McNoldy said in an interview. “Which is still hot.”
It’s all in the timing
When scientists want to determine the long-term impacts on coral health, it’s not just temperature they need to monitor. It’s also duration. The longer corals are superheated, the worse off they’ll be.
“I’m most worried that this level of heat will persist — that the corals that are experiencing these warm waters will continue to experience these warm waters for the coming weeks,” said Ian Enochs, who leads the Coral Program at the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Lab.
“Because if they are stressed out for a long period of time, it is highly likely that they will bleach.”
Enochs studies how corals handle hotter temperatures to better understand the impact of climate change on reefs. He said some species can handle high marine temperatures better than previously thought, but this abnormal ocean heat wave could be “devastating.”
Researchers are worried heat stress could weaken reefs, leaving them vulnerable to diseases and reproductive issues. Williamson said warm waters could throw off coral spawning season, which usually takes place in August. This year, there is a chance some iconic coral species, like the orange tree-like elkhorn and staghorn corals, will spawn inconsistently or even not at all.
”We’re really worried about that because that has huge implications for the survival of these populations,” she said.
Even if corals are able to spawn, Williamson said there is a risk these new offspring won’t be strong enough to survive. Corals are what scientists call a “keystone species,” meaning they act as a crucial piece in the chain of life. These reefs are some of the most biodiverse systems in nature, but make up only 1% of the ocean.
“It’s like the trees that build a forest — corals build the entire ecosystem,” Enochs said. “When corals bleach and die, what happens is just like a forest where a tree falls.”
Could coral restoration be impacted?
Corals are extremely delicate — and creating more is tricky work.
Heat complicates that work.
This current heat wave could have an impact on coral restoration efforts, which typically begins in the summertime, according to Jacqueline De La Cour, the operations manager for the National Oceanic and Atmospheric Administration’s Coral Reef Watch.
“If the waters are 97 degrees already, you can’t help plant corals,” she said. “You’ll kill them or they’ll have a lesser chance of survival.”
As global temperatures rise from human-emitted greenhouse gasses, scientists are devising creative ways to save the world’s corals. De La Cour said reef management agencies will sometimes resort to shading or pumping cool waters over reefs when extreme heat arises, but it isn’t practical on a large scale.
“It usually is not very effective, especially when you’re talking something the size of Florida’s coral reefs and entire barrier system,” she said. “We are kind of moving into unprecedented territory.”
Researchers say climate change is playing a role in this heat wave. This year’s El Niño — a warm climate pattern in the Pacific Ocean that can help weaken larger hurricanes but has global weather implications — created an expected rise in temperatures.
But while an El Niño is naturally occurring, the extreme fluctuations in temperatures measured by climatologists are not.
”What we’re seeing is definitely driven by climate change, and it is definitely really dangerous,” Williamson said.
Coral reefs support about 4,000 species of fish and hundreds of other marine life species, according to the National Oceanic and Atmospheric Administration. They lead to millions of dollars in tourism revenue, especially in Florida, and buffer shorelines from hurricanes, storm surge and flooding. Enochs said coral reefs have vanished in the Florida Keys; reef systems that were historically made up of 40% coral cover have plummeted to just 4%.
“These are huge die-offs that have occurred in living memory,” Enochs said. “In terms of new normal, I don’t know what is normal right now because these are crazy events.
“These are organisms that live hundreds of years, if not more,” Enochs added. “If the summer kills them, it’s not like they’re going to grow back overnight or in the next season.”