The world’s coral reefs are dying faster and cover an area smaller than researchers previously thought, according to a study released yesterday by the U.N. Environment Programme. The UNEP report estimates that almost 60 percent of the reefs are under threat from human activities. For example, some Asian fishers use dynamite or cyanide to catch fish that live in the reefs; nutrient-rich runoff breeds algae, which smothers coral; and rising ocean temperatures from global warming cause bleaching, which can kill coral. In the first worldwide mapping of the reefs, UNEP found that the reefs cover between one-tenth and half of the area previously thought. The agency said 97 percent of reefs were threatened in Thailand and the Philippines, while in Indonesia, 82 percent were at risk.