Coral Bleaching

Coral reefs grow in shallow waters, where zooxanthellae are getting the most sunlight. When a coral bleaches, it loses its zooxanthellae, and can die within a matter of weeks unless the zooxanthellae can be replaced. The term bleaching is used because the dazzling colors of living corals are due to the colors of zooxanthellae in coral tissue, and when zooxanthellae are lost, corals appear white, or “bleached.” Bleaching is caused by many factors that might stress the coral, such as rising water, temperatures, pollution, solar radiation, changing salinity, and bacterial infections –which are all becoming greater threats to reefs worldwide.

Images of bleached coral and same coral recovering from bleaching event
Image source:Andy Bruckner, NOAA's National Marine Fisheries Service.

The death of corals and the resulting disappearance of reefs would result in the loss of an uncountable number of marine invertebrates and fishes that rely on the physical structure of the reef for survival. Coral reefs sustain large numbers of people that rely on fishing for daily food and income. They also protect coastlines by absorbing constant wave energy from the ocean, thereby protecting people living near the coast from increased storm damage, erosion and flooding. 

While free from the local stresses that degrade reefs or might cause coral bleaching, the Phoenix Islands have not been spared the threat of global warming. In late 2002 one of the hottest ever-recorded warming events that has affected any reef around the world hit the Phoenix Islands. Because of their remote and pristine nature, high levels of damage were restricted to small areas within the Phoenix Islands, with many reef areas showing greater resistance and resilience to bleaching than have been documented elsewhere in the world. Their remoteness and the guaranteed protection by the Phoenix Islands Protected Area will help the Phoenix Islands to remain as one of the least-impacted reef systems to climate change and serve as a model target for protecting and rehabilitating other reefs heavily degraded by humans.