Credit: US National Oceanic and Atmospheric Administration
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While it is thought more than half of the world's coral reefs could disappear in the next 50 years, in large part because of higher ocean temperatures caused by climate change, scientists have found evidence that some reefs are adapting to survive global warming.
"Corals are certainly threatened by environmental change, but this research has really sparked the notion that corals may be tougher than we thought," said biologist and study co-author Stephen Palumbi, from the Woods Institute for the Environment at Stanford University in the US.
Palumbi and colleagues began studying the resiliency of coral reefs in the Pacific Ocean in 2006.
"The most exciting thing was discovering live, healthy corals on reefs already as hot as the ocean is likely to get 100 years from now," Palumbi said. "How do they do that?"
Coral reefs form the basis for thriving, healthy ecosystems throughout the tropics. They provide homes and nourishment for thousands of species, including massive schools of fish, which in turn feed millions of people across the globe.
Corals rely on partnerships with tiny, single-celled algae called zooxanthellae. The corals provide the algae a home, and, in turn, the algae provide nourishment, forming what is called a 'symbiotic' relationship.
But when rising temperatures stress the algae, they stop producing food, and the corals spit them out - and without their algae symbionts, the reefs die and turn stark white, an event referred to as 'coral bleaching'.
During particularly warm years, bleaching has accounted for the deaths of large numbers of corals. In the Caribbean in 2005, for example, a heat surge caused more than 50 percent of corals to bleach, and many still have not recovered, according to the Global Coral Reef Monitoring Network, an international collaboration of government officials, policymakers and marine scientists.
In recent years, scientists discovered that some corals resist bleaching by hosting types of algae that can handle the heat, while others swap out the heat-stressed algae for tougher, heat-resistant strains.
Palumbi's team set out to investigate how widely dispersed these heat-tolerant coral reefs are across the globe, and to learn more about the biological processes that allow them to adapt to higher temperatures.