When most people think of coral reefs, they think of warm clear tropical or subtropical waters. What many people don’t realize is that warm water can be a threat to coral reef ecosystems. El Niño is a state of the ocean-atmosphere system in the tropical Pacific that brings important consequences for weather around the globe. The El Niño current brings warm waters eastward from the western Pacific and leaves low tides in the western Pacific. Both can cause the bleaching and death of corals, damaging the balance of these ecosystems. Connections of the El Niño to the atmosphere may cause coral bleaching in the Caribbean as well.
Recent observations from the National Oceanic and Atmospheric Administration (NOAA) indicate that strong El Niño conditions are currently developing in the tropical Pacific. NOAA’s Climate Prediction Center forecasts that the warm event will bring weather changes to many areas, including the United States. The El Niño current usually occurs every two to seven years. Relaxation of the trade winds in the central and western Pacific allows warm water to flow east and reduces upwelling in the eastern Pacific. This raises sea surface temperatures and drastically reduces primary productivity in the eastern Pacific, shutting down the upwelling that supports fisheries off Latin America from Mexico to Chile.
Many corals live in water that is already near their upper temperature limit. If water temperatures rise too high, corals expel the symbiotic algae (zooxanthellae) from their tissues and turn white. When bleached, corals lose the food that the algae normally provide. While corals often recover their zooxanthellae and survive through bleaching events, they often die if the stress is too severe or prolonged.
In 1982-83 the largest El Niño on record reached the eastern Pacific. 70-95% of the corals in Costa Rica, Panama, Colombia and the Galapagos Islands died because of bleaching caused by the warm waters brought by El Niño. The damage did not stop with the bleaching. The death of some species of corals removed protection against predators such as the Crown of Thorns starfish. Increased erosion of the coral skeletons by sea urchins resulted in destruction of these reefs that continues today. Erosion of reef frameworks in Panama has exceeded one inch per year. Many of these reefs have still not recovered from the 1982-1983 El Niño.
In 1982-83, low sea levels in the western Pacific resulted in the exposure of reefs to the air during the day. Corals in Guam, Vanuatu, French Polynesia and the Tokelau Islands have reported bleaching and death of corals due to past El Niños. Warm climates over the Caribbean, connected with the unusually warm Pacific waters, spreads this effect even further east. Subsequent El Niños have been associated with bleaching in the Caribbean that occurred in 1987 and in the early 1990s.
In 1983, no one expected to see an entire reef turn white, there were no El Niño forecasts and few tools existed to observe and document the events. Now, satellites and buoys monitor the temperature across the Pacific and El Niño forecasts are provided regularly. New satellite technology provides indications of potential bleaching sites across the world. Scientists and divers are aware of coral bleaching and will be watching for changes in the reef systems. While there may be nothing that we can do about El Niño, at least we will be ready to document its effects.
As the El Niño heats up, many corals may be in hot water. Only
time will tell how this El Niño will affect coral reefs. Some
climate experts predict that this El Niño will match the event of
1972, which bleached and killed extensive shallow reefs in Guam, or the
event of 1987, when corals bleached across the Caribbean. Others
suggest that it may even build to the strength of the 1982-83 event from
which coral reefs in the eastern Pacific have still not recovered. Regardless
of the form this El Niño takes, already threatened coral reefs may
soon be subjected to a straw that may break their backs.
Office of Public and Constituent Affairs
National Oceanic and Atmospheric Administration
14th & Constitution Avenue, NW rm. 6013
Washington, DC 20230
Marine and Coastal Programme
IUCN - The World Conservation Union
Rue Mauvernay 28
CH 1196 Gland
tel: (41 22) 999-0251
For more information on the effects of 1982-83 El Niño in the eastern Pacific, contact:
Peter W. Glynn
University of Miami
tel: (305) 361-4134
For more information on the current El Niño event, see the
June 17 NOAA Press Release at:
For more information on coral bleaching and the impact of warm water
on corals see 52 Stories release #17 at:
For more information on the potential impact of El Niño on
California marine life, see the June 17 NOAA Press Release at:
OR CHECK-OUT THE NOAA CORAL REEF WEBSITES:
NOAA's Coral Reef Home Page at:
Experimental satellite products to locate ocean hot spots with a
high potential for coral bleaching at:
Yesterday's observations of Tropical Pacific temperatures and winds
are available at:
Updates on tropical El Niño developments are available on
the Internet through NOAA's Climate Prediction Center at:
El Niño Advisories showing sea surface temperature effects
along the U.S. West coast are available through the service's Southwest
Fisheries Science Center at: