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15.06.2021 23:24:19
A healthy, resilient reef can either resist a stressful event, like bleaching, or recover from it. When a coral bleaches, it is not dead. Corals can survive if water temperatures return to normal quickly.
See full version: What is coral bleaching
A healthy, resilient reef can either resist a stressful event, like bleaching, or recover from it. When a coral bleaches, it is not dead. Corals can survive if water temperatures return to normal quickly.
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. here
Not all bleaching events are due to warm water.
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.
Can coral survive a bleaching event? If the stress-caused bleaching is not severe, coral have been known to recover. If the algae loss is prolonged and the stress continues, coral eventually dies. Download this infographic: In English | In Spanish
Last updated: 02/26/21
Author: NOAA
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A diver prepares to change out a datasonde at East Flower Garden Bank. (Image: FGBNMS) [links]
This happens when coral polyps expel their symbiotic algae (zooxanthellae) as the result of some kind of stress event. Without the algae, the coral polyps are mostly clear, allowing you to see through to their white skeletons beneath. This results in a bleached appearance.
Through this system, scientists monitor SST at over 30 sites in the Caribbean and Gulf of Mexico, including Flower Garden Banks National Marine Sanctuary. They then compare that data to historic temperature averages to determine the likelihood of coral bleaching at each location.
Most coral bleaching is the result of water temperatures that go beyond the corals' level of tolerance for too long. This usually means temperatures that are too high, but can also mean temperatures that are too low. more
For a better understanding of how corals and zooxanthellae interact, please visit our Coral Basics page.
Bleaching progresses at different rates across the reef. (Image: FGBNMS/Schmahl) more
But scientists say that warmer sea temperatures in February this year may have caused huge damage to the reef.
Coral reefs also help to protect against coastal erosion which can damage cliffs and beaches. [links]
One of the world's most famous reefs, the Great Barrier Reef in Australia, has been hit by its third mass coral bleaching event in the last five years.
And, of course, corals could yet surprise us and find a way of adapting. They could develop abilities to better cope with warming events when they do occur. Just last week scientists announced the discovery of a previously unknown 600 mile-long coral reef system in the Atlantic Ocean at the mouth of the Amazon River. It’s remained hidden thanks to murky water, challenging the commonly held belief that corals require clear water to get enough sunlight to photosynthesize. What other secrets are tropical corals hiding from us?
But what is the specific problem with the coral, and is there any hope of reversing this terrible trend? We’ve got you covered with the science behind the issue.
[quote position="full" is_quote="true"]Many open ocean fish—big fish that are fundamental to the food supply of many, many nations—[have] larvae that hang out on coral reefs. Once that habitat is gone, those fish are not going to make it.[/quote] here
Last week, scientists delivered the news that more than 90% of Australia's Great Barrier Reef is suffering from bleaching. Researchers flew in helicopters and small planes over 911 of the individual reefs that comprise the Great Barrier Reef and found that only 68 of them had escaped bleaching entirely. Many of the rest have turned a ghostly white. "It's like 10 cyclones have come ashore all at once," said Terry Hughes, a researcher at the ARC Centre of Excellence for Coral Reef Studies at James Cook University and head of Australia's National Coral Bleaching Task Force.
So here’s where the bleaching comes in. If the surrounding seawater becomes too hot or if there's too much sunlight, the algae start producing harmful toxins rather than tasty sugars. That triggers the coral's immune system, and the once beneficial partnership breaks down. The corals give their algal partners the metaphorical boot, and the bright white exoskeleton is what remains. Regardless of the term, "There is no bleach involved," says Scott Heron, a physicist with NOAA's Coral Reef Watch.
This should worry you. "The benefits of coral reef ecosystems for people are dramatic, and it's not just people who live in coastal locations," says Heron. here