Global Warming and Coral Reefs

A Healthy Coral Reef

Photo: © Florida Keys National Marine Sanctuary

Coral reefs are colorful underwater forests which teem with life and act as a natural protective barrier for coastal regions. The fishes and plants which call them home belong to some of the most diverse--and fragile--ecosystems on the planet.

In one year alone, 16 percent of the world's coral reefs were wiped out. A sea temperature change of a mere one degree Celsius would yield similar losses. Increasing levels of carbon dioxide in the water cause additional damage to corals, leaving them defenseless against storm damage and erosion.

Map of coral reef locations in the US

Coral Reef Habitat

The spectacular and delicate coral reefs of Florida, Hawaii and Puerto Rico are ecological gems and important economic resources. Often called "rainforests of the sea" for their rich biodiversity, the coral on which these diverse ecosystems are based are actually living organisms themselves. They form when polyps--the living portion of stony corals--extract calcium from seawater and combine it with carbon dioxide to construct the elaborate limestone skeletons that form the reef.

Between just Key Biscayne and Dry Tortugas, the Florida Keys contain about 6,000 coral reefs. This reef system--third largest in the world--contains more than 100 species of soft and stony corals and hundreds of fish species, from tiny sergeant majors to giant barracudas.

Benefits for Humans and Wildlife

In coral reefs around the world thousands of marine species find food and shelter, which in turn support economically valuable recreational and commercial fishing. Coral reefs also form a breakwater for adjacent coasts, providing natural protection from storm surges.

Coral reefs are hotspots for the tourism industry, which thrive on providing visitors with unforgettable scuba diving and snorkeling experiences. The coral reefs off the Florida Keys help generate more than $1.6 billion in revenues annually.


Bleached Brain Coral


Threats from Global Warming

Higher sea temperatures from global warming have already caused major coral bleaching events. Bleaching occurs when corals respond to the stress of warmer temperatures by expelling the colorful algae that live within them. Some coral are able to recover, but too often the coral dies, and the entire ecosystem for which it forms the base, virtually disappears.

Longer-lasting and more extensive bleaching events are already on the rise, with further increases expected in the decades ahead as ocean temperatures continue to rise. Warmer waters are also expected to increase the incidence of other coral diseases such as black band disease, white band disease, white plague, and white pox, all of which can lead to mass mortality of coral, and subsequently the entire ecosystem it supports.

Ocean acidification--which occurs when oceans absorb carbon dioxide from the atmosphere--is also a threat to coral. As the oceans become more acidic, the corals' ability to form skeletons through calcification is inhibited, causing their growth to slow. A doubling of atmospheric carbon dioxide will reduce calcification in some corals by as much as 50 percent.

Sea level rise caused by melting sea ice and thermal expansion of the oceans could also cause problems for some reefs by making them too deep to receive adequate sunlight, another factor important for survival.

Conservation Investments to Minimize Global Warming Impacts

Reducing overall global warming pollution is essential to minimize ocean temperature increases causing coral bleaching. However, minimizing other impacts not directly related to global warming can improve the ability of these sensitive ecosystems to withstand the duress of global warming.

Managers will need to improve water quality by reducing water pollution from ocean sources (e.g. ocean dumping) and improving watershed management of nearby lands. Other management options could include local restrictions on ocean dredging and large boat traffic, as well as appropriate modifications of regulations relating to tourism, and commercial and recreational fisheries.

Coral monitoring must be expanded to include ocean acidification, calcification rates, water temperatures, and coral bleaching rates if managers expect to be able to effectively conserve these reefs as the climate warms. Research is needed to develop and implement new methods of restoring damaged or destroyed coral reefs.

What You Can Do

To help draw attention to the problem, NWF has launched a public awareness campaign targeted at divers and snorkelers to arm them with information about how they can help protect coral and minimize global warming's impact. Some of the most important actions recommended by NWF include:

  • Never anchor on a reef.
  • Volunteer with organizations working to clean up local waterways. The health of all waterways--rivers, lakes and bays--ultimately affects the ocean.
  • Slow global warming by conserving energy, which includes using energy-efficient lighting and appliances and using mass transportation whenever possible.


Related Resources:

  • Coral Reefs and Climate Change (PDF/2 Mb) - Report by the NWF
  • To Save a Reef - For everyone from tourists to fishermen, understanding the coral necklace off of Florida's southern tip is the first step to conserving it.

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