Despite being only one-tenth of 1 percent of Earth’s oceans by area, coral reefs are home to about a quarter of all marine species. They are biodiversity hotspots, providing food and shelter to marine creatures and countless benefits to the people who live nearby.

But coral reefs have been under tremendous pressure from threats like overfishing, pollution and climate change. Warmer temperatures cause coral bleaching. (NOAA offers a great explanation of what coral bleaching is and why it matters.) Carbon dioxide in the atmosphere gets absorbed by the ocean, making it more acidic, which is also detrimental to corals. If current trends continue, scientists predict that up to 70 percent of coral reefs could be lost by mid-century.

This is what a mostly lifeless, bleached coral reef looks like. A sad sight.This is what a mostly lifeless, bleached coral reef looks like. (Photo: Acropora/Wikipedia)

Thankfully, it’s not all bad news

If you find most of the recent news on coral reefs depressing, you’re not the only one. But not all of the headlines are bad.

In 2018, researchers discovered "oases" where coral reefs were thriving. They looked at 38 oases in the Pacific Ocean and the Caribbean and categorized them as escape, rebound or resist oases. "Escape oases are coral communities that have been able to avoid disasters such as bleaching, invasions by coral-eating sea stars, and the wrath of hurricanes. Resist oases are corals that appear hardy and able to resist environmental challenges. Rebound oases are coral reefs that have suffered damage but have rebounded," explained The National Science Foundation (NSF).

"There's hope in the form of coral reef oases," said NSF-supported marine biologist Peter Edmunds. "That doesn't contradict reports of coral reefs suffering huge losses. However, there are kernels of hope where corals are doing better."

One promising area is The Island of Hawaii.

In 2015, Hawaii suffered its first statewide coral bleaching event, with the worst of it occurring in western Hawaii. That area experienced an average of 60 percent of reefs bleached, with some reefs having 90 percent mortality. But in the years since, scientists discovered that some of the reefs have stabilized.

"Bleaching events like what occurred in 2015 can overstress a coral reef to the point where it may never recover," Eric Conklin, director of marine science for The Nature Conservancy’s Hawaii program, told West Hawaii Today. "We surveyed over 14,000 coral colonies at 20 sites along the West Hawaii coast from Kawaihae to Keauhou and were thrilled to see that many of the area’s reefs have stabilized, which is the first step toward recovery."

Russell Reardon dives in the waters of Midway Atoll on March 31, 2013, to remove a fishing net from a coral reef Russell Reardon dives in the waters of Midway Atoll on March 31, 2013 to remove a fishing net from a coral reef. (Photo: NOAA/NMFS/Pacific Islands Fisheries Science Center Blog/Flickr)

Not surprising, the most-resilient reefs are located in areas with limited human exposure and shoreline access. The least-resilient ones are also in areas with land pollutants, runoff and heavy fishing.

"Interestingly, the number of stressors affecting an area, not the severity of a single one, was the most important factor," said Kim Hum, the Conservancy’s marine program director. "Reefs that are fighting the impacts of several stressors are more susceptible to temperature stress, making them more likely to bleach and less able to recover if they do."

The state government is also stepping up its efforts to help the coral reefs. It's committed to managing 30 percent of the marine environment near the shores by 2030.

Editor's note: This article has been updated since it was originally published in March 2016.

Michael Graham Richard ( @Michael_GR ) Michael writes for MNN and TreeHugger about science, space and technology and more.

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