Bill Precht is a forty-five-year veteran of coral research based in Miami. He has signaled that the coral reefs are at a turning point as ocean temperatures for July have reached temperatures as high as 97F off Florida’s Atlantic coast due to the unprecedented heat wave. In an interview with Jeff Beradelli, chief meteorologist at WFLA, which serves the Tampa Bay region, Precht said that the extraordinary marine heatwave would be the “death knell” for Florida’s corals.
Everything colored red in the above graphic from NOAA’s Coral Reef Watch has a 100% chance of bleaching. Corals only have a chance of survival if the extreme temperatures last only a few weeks. But that won’t happen in 2023 unless the reef gets hammered by multiple hurricanes that mix the water to a more survivable temperature.
Coral Bleaching happens during severe temperatures in their habitat, the temperatures can be cold from winter intrusions, but primarily they are hot and brought about by marine heatwaves.
Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.
In 2005, the U.S. lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. The warm waters centered around the northern Antilles near the Virgin Islands and Puerto Rico expanded southward. Comparison of satellite data from the previous 20 years confirmed that thermal stress from the 2005 event was greater than the previous 20 years combined.
Florida Coral Reef Tract
Healthy Coral: Coral and algae depend on each other to survive. Corals have a symbiotic relationship with microscopic algae called zooxanthellae that live in their tissues. These algae are the coral’s primary food source and give them their color Stressed Coral: If stressed, algae leaves the coral. When the symbiotic relationship becomes stressed due to increased ocean temperature or pollution, the algae leave the coral's tissue. Bleached Coral: Coral is left bleached and vulnerable. Without the algae, the coral loses its major source of food, turns white or very pale, and is more susceptible to disease.
WHAT CAUSES BLEACHING? Change in ocean temperature Increased ocean temperature caused by climate change is the leading cause of coral bleaching. Runoff and pollution Storm generated precipitation can rapidly dilute ocean water and runoff can carry pollutants — these can bleach near-shore corals. Overexposure to sunlight When temperatures are high, high solar irradiance contributes to bleaching in shallow-water corals. Extreme low tides Exposure to the air during extreme low tides can cause bleaching in shallow corals. NOAA’s Coral Reef Conservation Program.
The atmosphere is a fluid and it's all connected. Waves of energy ripple through the upper levels as the jet stream with ridges (heat domes) and troughs (cool pools). We see TransAtlantic ridging and then most prominent is the giant heat dome that builds across the US next week. pic.twitter.com/FjkC10cdbt
Average coral cover on most Florida Keys reefs has dropped from between 30-50% before 1975, to less than 3% now. Precht says this is due to coral disease, coral bleaching events, hurricanes and cold water impacts during the winter. What’s left has been significantly weakened.
“Right now, I’d say the corals in the Florida Keys are as vulnerable as they have ever been to catastrophic levels of bleaching and bleaching-related mortality,” Precht warns.
Coral thrives in a fairly narrow range of water temperatures which, Precht says, rarely exceeded 84 degrees a century ago. Now, due to man-made climate heating, regularly rise into the upper 80s.
Water temperatures in South Florida have been recorded as high as 97 degrees shattering the already warm temperature records of the high 80s.
Images of devastated coral reefs, a common reminder of climate change, can give the impression of a static landscape. But time-lapse footage of coral bleaching as it happens shows a surprisingly active process. This video, taken by scientists in a laboratory at Queensland University of Technology in Brisbane, Australia, captures a coral ejecting its resident population of algae. The behavior helps corals survive warmer water in the short term, but extended periods of bleaching can be lethal to corals and the ecosystems they support. NG
“We are a full month ahead of what is the normal ‘bleaching season’, Manzello explains. “What this means is, unless significant cooling takes place (e.g., repeat passage of hurricanes or tropical storms), the corals of the Florida Keys may be looking at upwards of 3 consecutive months of thermally-stressful conditions, which would be unprecedented. Most previous bleaching events lasted about 4-6 weeks.”
And that’s the problem. It’s not just the heat, it is the ‘relentless’ heat that can take a deadly toll – the accumulated heat stress. When corals get stressed by warm water, they turn white (bleach) as they expel the colorful algae living in their tissues. If the heat lasts long enough the coral can die. That’s why Precht says this summer may be the “death knell” for South Florida coral.
Jeff Beradelli has emerged as a climate hero and is not afraid of the climate trolls on Twitter. You can follow him here.
