Coral reefs, though covering less than one percent of the ocean floor, support roughly a quarter of marine species. Rising sea temperatures can cause coral to expel the algae living within their tissues. This process, known as bleaching, leaves coral vulnerable to disease and death. Some reefs have shown the ability to recover if conditions improve quickly enough. Scientists are studying heat-resistant coral varieties in hopes of aiding future recovery. According to the passage, what happens to coral during a bleaching event?
