Kim Cobb, a marine scientist at the Georgia Institute of Technology, expected the coral to be damaged when she plunged into the deep blue waters off Kiritimati Island, a remote atoll near the center of the Pacific Ocean. Still, she was stunned by what she saw as she descended some 30 feet to the rim of a coral outcropping.
“The entire reef is covered with a red-brown fuzz,” Dr. Cobb said when she returned to the surface after her recent dive. “It is otherworldly. It is algae that has grown over dead coral. It was devastating.”
The damage off Kiritimati is part of a mass bleaching of coral reefs around the world, only the third on record and possibly the worst ever. Scientists believe that heat stress from multiple weather events including the latest severe El Niño, compounded by climate change, has threatened more than a third of Earth’s coral reefs. Many may not recover.
Coral reefs are the crucial incubators of the ocean’s ecosystem, providing food and shelter to a quarter of all marine species, and they support fish stocks that feed more than one billion people. They are made up of millions of tiny animals, called polyps, that form symbiotic relationships with algae, which in turn capture sunlight and carbon dioxide to make sugars that feed the polyps.
An estimated 30 million small-scale fishermen and women depend on reefs for their livelihoods, more than one million in the Philippines alone. In Indonesia, fish supported by the reefs provide the primary source of protein.
“This is a huge, looming planetary crisis, and we are sticking our heads in the sand about it,” said Justin Marshall, the director of CoralWatch at Australia’s University of Queensland.
Bleaching occurs when high heat and bright sunshine cause the metabolism of the algae — which give coral reefs their brilliant colors and energy — to speed out of control, and they start creating toxins. The polyps recoil. If temperatures drop, the corals can recover, but denuded ones remain vulnerable to disease. When heat stress continues, they starve to death.
Damaged or dying reefs have been found from Réunion, off the coast of Madagascar, to East Flores, Indonesia, and from Guam and Hawaii in the Pacific to the Florida Keys in the Atlantic.
The largest bleaching, at Australia’s Great Barrier Reef, was confirmed last month. In a survey of 520 individual reefs that make up the Great Barrier Reef’s northern section, scientists from Australia’s National Coral Bleaching Task Force found only four with no signs of bleaching. Some 620 miles of reef, much of it previously in pristine condition, had suffered significant bleaching.
In follow-up surveys, scientists diving on the reef said half the coral they had seen had died. Terry Hughes, the director of the Center of Excellence for Coral Reef Studies at James Cook University in Queensland, who took part in the survey, warned that even more would succumb if the water did not cool soon.
The Latest on: Coral bleaching
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The Latest on: Coral bleaching
- Insuring Nature to Ensure a Resilient Futureon September 7, 2019 at 4:22 pm
But coral reefs can themselves be damaged by severe storms—especially those that have already been weakened by pollution, disease, overfishing and bleaching—which then greatly reduces the protection ...
- Reefs In Hot Water: Keys On High Alert For Coral Bleachingon September 5, 2019 at 6:44 pm
All of the Florida Keys reef is under thermal stress — meaning the water is warm enough that corals may start bleaching. Corals bleach when they expel the algae that feed them and give them color.
- Another Blow for the Future of Coralson September 5, 2019 at 3:07 pm
In some places, these mass-bleaching events are happening too often for the reefs ... “Usually, when we survey a coral reef, we measured things like the percentage of live coral cover, or the ...
- Breakdown in spawning synchrony: A silent threat to coral persistenceon September 5, 2019 at 11:41 am
Our changing climate is a threat to corals, causing disfiguring bleaching and mortality to reefs that once teemed with life. Shlesinger and Loya alert us to an equally dangerous yet nearly invisible ...
- Climate change is knocking coral mating dance out of sync, Israeli study findson September 5, 2019 at 12:47 am
The coral benefits from the sugars, oxygen and waste removal services supplied by the algae. When the seawater warms too much, however, corals will expel their algae lodgers and turn white in an event ...
- Hope for 'coral candy' algae to give Great Barrier Reef a sugar hiton September 2, 2019 at 4:33 am
The research was published as the latest report on the condition of the Great Barrier Reef saw its outlook downgraded from "poor" to "very poor", owing to coral bleaching and deforestation. Loading ...
- Great Barrier Reef: Outlook for Australia's coral network downgraded to 'very poor' due to warming oceanson August 30, 2019 at 12:18 am
The Great Barrier Reef Marine Park Authority's condition report, which is updated every five years, is the latest bad news for the 133,360sq mile colourful coral network off the north-east Australian ...
- Climate change, human activity lead to nearshore coral growth declineon August 28, 2019 at 10:03 am
The research team looked at the relationship between growth rates and specific acute stress events, such as coral bleaching. Coral bleaching happens when corals become stressed by pollution or ...
- Scientists reproduced Atlantic coral in a laboratory for the first time. Aquarium-grown coral could save America's 'Great Barrier Reef.'on August 28, 2019 at 5:58 am
Techniques perfected on Pacific coral could help repopulate Atlantic coral reefs, too. Here's what the successful efforts look like.
- ASU working to save Hawaiian coral reefs during onset of new ocean heatwaveon August 28, 2019 at 12:50 am
If the ocean continues to warm even further as projected, we are likely to witness severe and widespread coral bleaching across the Islands." This event is coming a mere four years after the ...
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