A sperm bank for corals, gathered from reefs in Hawaii, the Caribbean and Australia, could someday restore and rebuild damaged reefs, researchers say. Mary Hagedorn at the Hawaii Institute of Marine Biology has a one-of-a-kind collection of 1 trillion frozen coral sperm, enough to fertilize 500 million to 1 billion eggs, The New York Times reported. Corals can reproduce asexually, as fragments of coral can grow into clones of their parents, but Hagedorn emphasized only sexual reproduction can protect genetic diversity within populations, vital for a coral species\' capacity to survive and adapt to changes in the marine environment. Warming seas are making corals more prone to disease and to a condition known as bleaching, where stressed corals are forced to expel the colorful algae that is their main food supply. If warming, bleaching and the acidifying of ocean from rising carbon dioxide levels continue to increase, a majority of the world\'s reefs will be at risk of dying off by 2050, researchers say. That makes Hegedorn\'s collection of sperm important, coral researchers said. \"Mary is my insurance policy,\" said Greta Aeby, a biologist who studies coral disease throughout the Pacific. \"We\'re working as quickly as we can,\" she said, \"but it\'s not enough. I keep telling my students, \'Study faster!\'\"