ORLANDO, Fla. – The Atlantic Ocean and Gulf of Mexico are on fire. When it comes to Florida’s coral reefs, it’s not just that the water temperatures are blazing hot, it’s about how early the heat has come.
“Given that 70% of Florida’s coral reef is already net erosional, I’d say that I’m very concerned about the future of Florida’s corals,” said Dr. Derek Manzello, coordinator of NOAA’s Coral Reef Watch program.
Ocean temperatures off the coast of Southwest Florida and the Florida Keys are the hottest they have ever been in the satellite era this early in the year. The satellite era began in the 1960s.
Water temperatures have surged into the mid-to-upper 90s in the Florida Keys over the past few days.
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The average sea surface temperature has consistently been around 90 degrees, putting that well above the coral bleaching threshold.
The black line in the chart below shows that sea surface temperatures have been among the hottest on record all year.
When sea surface temperatures surpass the blue line, corals start becoming stressed.
Coral bleaching is the breakdown in the symbiotic relationship between the coral animal host and its algal symbionts.
“A bleached coral is essentially starving to death because it has lost its main source of nutrition, the algal symbionts,” said Manzello. “The damage that corals experience from marine heatwaves is a function of the duration, or how long the heat stress occurs, plus the magnitude of the heat stress anomaly.”
Corals can recover from bleaching if the heat stress subsides, but they will have impaired growth, reproduction and will be more susceptible to disease for several years.
If the heat does not subside, the coral will die.
Mortality becomes likely if corals experience sea temperatures 1°Celcius greater than average for two months, or 2° Celsius greater than average for or month.
An anomaly of 3° Celsius or greater would cause the coral to start experiencing mortality in three weeks or less.
The current sea surface temperature anomaly in the Florida Keys is greater than 3° Celsius.
During the previous large-scale bleaching events, most recently that happened in the Florida Keys, bleach-level sea surface temperatures didn’t occur until mid-August.
“Thus, we are a full month ahead of what is the normal ‘bleaching season.’ What this means is, unless significant cooling takes place, such as repeat passage of hurricanes or tropical storms, the corals of the Florida Keys may be looking at upwards of three consecutive months of thermally-stressful conditions, which would be unprecedented,” said Manzello.
Previous bleaching events last about 4-6 weeks.
Many other species such as spiny lobster, stone crabs, and many fishes rely on coral reefs. These species are extremely important to the Florida economy.
“In response to this, the Mission Iconic Reefs program is urgently working to grow corals and outplant them to 7 different ‘iconic’ reefs of the Florida Keys, with a goal of restoring coral cover and ensuring that the ecological services provided by these reefs is maintained. Managers and scientists are currently in a race against time, and a warming ocean, to try and restore Florida’s cherished coral reefs,” said Manzello.
“The fact that temperatures are so hot so early in the year is extremely concerning for coral reef ecosystems in Florida. There have been eight mass bleaching events that have impacted the Florida Keys since 1987. Marine heatwaves are increasing in magnitude, duration, and spatial extent as a result of climate change. This is an existential threat to coral reefs because reef-building corals live very near their upper thermal limits and coral bleaching is a clear sign of ocean warming. Given that 70% of Florida’s coral reef is already net erosional, I’d say that I’m very concerned about the future of Florida’s corals,” said Manzello.
A large Saharan dust plume is crossing the Atlantic. While this won’t cool the atmosphere, this may help to limit solar heating for a short time, potentially putting a pause on the rapid heating. The dust in the upper atmosphere acts to reflect some sunlight.
El Niño a player in warmer oceans
El Niño is the warm phase of the El-Nino Southern Oscillation. It is a naturally occurring climate phenomenon marked by warmer-than-normal sea surface temperatures in the Central and Eastern equatorial Pacific. On average El Niño comes around every 2-7 years. Its impacts extend far beyond the Pacific Ocean.
The National Oceanic and Atmospheric Administration declared the arrival of El Niño in June. The El Niño is forecast to strengthen later in the summer.
According to Manzello, the first mass coral bleaching event from ocean warming occurred 40 years ago in the Eastern Pacific. This was associated with the severe El Niño of 1982/83.
Since then, there have been three global bleaching events, 1998, 2010 and 2014-2017. All of these were El Niño years.
During the most recent severe El Niño, more than 75% of reefs on the planet experienced bleaching-level heat stress.
Climate change’s role
El Niño was around well before climate change. While in an El Niño episode the earth typically warms, heat anomalies associated with the naturally-occurring El Niño are becoming more extreme due to climate change.
According to Climate Central, the oceans have absorbed about 93% of the heat trapped in the atmosphere since 1970. This is because of their vast depth, area and seawaters higher heat capacity compared to the atmosphere.
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