For More Information

NOAA Coral Reef Watch

NOAA Coral Reef Conservation Program


NOAA Scientists Predict Coral Bleaching Events

Scientists from NOAA’s Coral Reef Watch Program say conditions are favorable for significant coral bleaching and infectious coral disease outbreaks in the Caribbean, especially in the Lesser Antilles. The forecast is based on the July NOAA Coral Reef Watch outlook, which expects continued high water temperatures through October 2009.

Coral bleaching is associated with a variety of stresses, especially increased ocean temperatures. This causes the coral to expel symbiotic micro-algae living in their tissues – algae that provide corals with food. Losing their algae leaves coral tissues devoid of color, and thus they appear bleached. Prolonged coral bleaching of over a week can lead to coral death and the loss of coral reef habitats for a range of marine life. The bleaching season in the Caribbean is August to October.

Bleached coral

Millions of people and thousands of communities all over the world depend on coral reefs for food, protection, and jobs. The ability to predict coral bleaching events and provide advance warning is critically important to sustaining healthy reefs.

In 2008, scientists with NOAA’s Coral Reef Watch Program developed a new system to predict coral bleaching events. This system uses NOAA experimental sea surface temperature forecasts to develop maps of anticipated coral bleaching severity during the upcoming bleaching season. While NOAA’s Coral Reef Watch Program uses satellite sea surface temperature data to alert managers and scientists around the world of the risk of coral bleaching, the prediction system uses forecast models to develop bleaching outlooks up to three months in advance. The new system successfully identified that there would be a relatively low risk for bleaching in the Caribbean in 2008.

Based on current data, the seasonal outlook for 2009 indicates the potential for a more severe bleaching year in much of the Caribbean than normal and than what was observed in 2008. The NOAA Coral Reef Watch Coral Bleaching Thermal Stress Outlook indicates that there is a potential for high levels of thermal stress in the Caribbean in 2009, especially in Puerto Rico, the U.S. Virgin Islands, and other parts of the Lesser Antilles.

Also of concern between August and November is a region of the central Pacific along the equator from the Kiribati to the Marshall Islands. Some thermal stress may also develop between the Northern Marianas Islands and Japan. However, temperatures are expected to peak soon in both of these Pacific regions, so temperatures are unlikely to rise high enough for a long enough period to cause major bleaching.

Underwater surveys

NOAA scientists conduct underwater bleaching surveys.

An important caveat is that the model used for this outlook is not yet calling for El Niño development. If El Niño conditions continue to strengthen, this could increase the bleaching risk in the central to eastern Pacific and Caribbean, especially in 2010.

A major coral bleaching event occurred in the Caribbean in 2005, resulting in significant coral death in much of the region. Reef managers and scientists had little warning of this event. This new Seasonal Bleaching Outlook system provides greater warning time so that scientists can prepare for better monitoring of impacts and to reduce other stressors to reefs that reduce the survival of corals during bleaching.  In the future, NOAA hopes to have a wider suite of management actions that can be used to combat the impacts of thermal stress.