Coral reefs cover a very small portion of the ocean floor, yet they support a remarkable variety of marine life. They also protect coastlines by reducing the force of waves, and they provide income for many coastal communities through fishing and tourism. Rising sea temperatures pose a serious threat. When the water becomes too warm, corals expel the tiny algae that live inside their tissues and provide them with much of their food. Without these algae, corals turn white, a process known as bleaching. Bleached corals are not immediately dead, and they can recover if temperatures return to normal fairly quickly. If the heat continues, however, they are likely to die. Scientists are exploring several ways to help reefs survive. Some are growing young corals in underwater nurseries and transplanting them onto damaged reefs. Others are studying corals that seem naturally more tolerant of heat, hoping to breed them. These efforts, however, can only cover small areas. Researchers stress that reducing greenhouse gas emissions remains essential for the long-term survival of reefs.

Corals grown in underwater nurseries are more tolerant of heat than wild corals.