Coral reefs are often called the rainforests of the sea, and the comparison is apt. Though they cover less than one percent of the ocean floor, reefs support roughly twenty-five percent of all marine species. The structures themselves are built by tiny animals called coral polyps, which secrete calcium carbonate skeletons and live in close partnership with photosynthetic algae. This relationship is exquisitely sensitive to temperature: when water warms beyond a narrow range, the algae are expelled and the coral bleaches, losing both its color and its primary food source. Prolonged bleaching leads to death. Climate change has caused mass bleaching events of increasing frequency and severity across the world's major reef systems. The Great Barrier Reef, the largest coral structure on Earth, has experienced multiple bleaching events in the past decade. Scientists are experimenting with heat-tolerant coral strains and assisted evolution as potential tools for helping reefs adapt, but the window for meaningful intervention is narrowing.