Two of Four Parts
At the heart of each individual coral is a polyp, a clear, tube-shaped animal with a ring of tentacles that it uses to catch prey. Some corals surround themselves with a limestone skeleton forged from calcium absorbed from sea water.
Corals get their color from thousands of plant-like organisms known as zooxanthellae, which live inside the corals and provide them with food. It is a symbiotic relationship that is fundamental to the health of reef ecosystems around the world.
Despite their tough exterior, warm water corals are sensitive creatures. When water temperatures rise, they become stressed and expel their zooxanthellae, leaving them prone to disease and starvation.
That is why researchers are so worried about a heat wave sweeping across the ocean. Since early 2023, water temperatures have risen by as much as 5°C in some places. In February 2024, the average global sea surface temperature had passed 21°C, a record high. Just a few weeks later, perhaps the world’s most-famous collection of corals, the Great Barrier Reef, was baking under unprecedented heat.
Researchers say a combination of climate change and the El Niño weather event are driving the record sea surface temperatures.
Like a wildfire moving through brush, the ocean heat wave has ravaged corals. Scientists recorded bleaching in 53 countries from February 2023 to April 2024, according to the United States’ National Oceanic and Atmospheric Administration and the International Coral Reef Initiative, which is supported by UNEP. That number, American data suggests, has since climbed to 62 nations.
Among the hardest hit areas is the Great Barrier Reef, where nearly 80 percent of coral outcrops had bleached, according to a report from the Australian government.
The Great Barrier Reef has captured the most attention but researchers say similar situations are playing out in the Caribbean Sea, the South Atlantic, the Red Sea, the Gulf of Mexico, the Western Indian Ocean and the waters of East Asia.
Reefs that were once brimming with life have been reduced to what Carvalho from UNEP called “graveyards,” filled with the grey and white carcasses of dead and dying corals.
Researchers believe the bleaching event is continuing to gain steam and could soon become the most-widespread on record.
“This crisis isn’t over,” says Carvalho. “We could be going from bad to worse if we don’t act now to reduce the greenhouse gas emissions driving climate change.” (To be continued)
