Coral reefs have been called the rain forests of the ocean because of their vast biodiversity and genetic wealth. And over the last few years we have seen a massive die-off of these ecosystems, with a quarter of the world's reefs already gone. Surveying the destruction, the marine biology community has launched an all-out effort to restore the reefs to health. But first biologists must understand the sources of destruction, from global warming to overfishing and attacks by predators and diseases. The man-made part of the disaster, caused by burning fossil fuels, has increased ocean temperature an average of 1.33 degrees Fahrenheit since the start of the Industrial Revolution, according to a study in Science. That slight warming is enough to kill some microalgae needed to help the reefs calcify and stay strong. What's more, the study, led by a team at the University of Queensland in Australia, says that CO_2 released in the course of coral death not only raises temperatures but also makes the water acidic, leaving the reefs brittle and vulnerable to predator attack. Marine biologists point to the example of Carysfort Reef off the coast of Florida: In 1975 it was healthy.
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