Scientists In Kiribati Islands Observe 50% - 90% Of Corals Bleached; 30% Already Dead

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A team of researchers from the Georgia Institute of Technology, led by professor Kim Cobb, spent two weeks on Christmas Island in early November conducting photographic surveys of the corals there and installing devices to capture data on environmental conditions, such as temperature. While there, they discovered that 50 to 90 percent of the corals they observed had bleached, thanks to the warm-water effects of El Niño. Even more concerning, up to 30 percent were already dead at some sites.

This response was likely caused by the extreme increases in water temperature observed with this El Niño event, Cobb said. While water temperatures normally hover around 81 degrees Fahrenheit, she and her team measured temperatures up to 88 degrees during their expedition. Corals are living animals themselves, but they thrive by maintaining a symbiotic relationship with certain species of algae, who live inside the corals (incidentally giving them their brilliant colors) and provide them with energy and nutrients. But under certain types of environmental stress, including extreme water temperatures, corals will expel their algae, turning white, or “bleaching,” in the process.

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Christmas Island may be one of the best places in the world for this kind of research, thanks to several key characteristics. First, it’s home to a diverse collection of coral species, which are already showing differing responses to the El Niño event. Second, corals in different areas of the atoll are subject to differing levels of human pressures, such as heavy fishing and pollution, making it convenient to study the ways different stressors compound each other and affect a coral’s ability to stand up to heat stress.

“We have 40 different sites around the entire atoll that basically span an unparalleled gradient in human disturbance, from the most degraded to most pristine,” Baum said. “You can go from site to site and basically see how coral reefs fall apart.”

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https://www.washingtonpost.com/news/energy-environment/wp/2015/12/14/el-ninos-extreme-effects-corals-around-this-island-arent-just-bleaching-theyre-dying/