Mapping the Decline of Coral Reefs

Anyone who has strapped on diving gear and glided past a healthy coral reef knows that few sights in nature are as breathtaking. From the intricately embroidered patchwork of the corals themselves to the myriad of multicolored creatures that live in the reefs’ crevices to the shimmering schools of fish that seem to move as one, every cubic inch of a thriving coral habitat appears to be alive and teaming with complexity. In truth, coral reef habitats represent some of the densest and most varied ecosystems on Earth. Though they cover only 0.2 percent of the ocean’s floor, scientists estimate that nearly one million species of fish, invertebrates, and algae can be found in and around the world’s reefs.

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While reef habitats appear to be robust enough to withstand almost anything, they are extremely fragile. Not only are most corals brittle, but they usually need pristine, clear, warm, relatively nutrient-free waters to survive. Over the past 50 years, humans have put an enormous amount of pressure on coral reef environments by altering their waters and tearing up their foundations. From dynamite fishing to global warming, we are rapidly sending the world’s reefs into oblivion. The latest reports state that as much as 27 percent of monitored reef formations have been lost and as much as 32 percent are at risk of being lost within the next 32 years.

For marine biologists, the destruction of the reefs has proven to be as frustrating as it is heartbreaking. Because reef habitats are so complex, and because worldwide reef monitoring and mapping efforts only began a little over a decade ago, scientists simply do not have enough information to keep tabs on the destruction of the reefs, let alone come up with an effective solution. At the rate the reefs are disappearing, they may be beyond repair by the time a comprehensive plan to save reefs can be put into place.

  Coral reefs rival the tropical rainforests as the most diverse ecosystems on Earth. With a wide variey of plant, animal, and microbial life, they are not only beautiful destination for divers, but an important indicator of ocean health. (Photograph copyright Corel Corporation)

Tuanake Atoll

Scientists at NASA’s Goddard Space Flight Center and at several universities around the world, however, may have at least a partial solution to this problem. They have been examining detailed images of the ocean collected by the Landsat 7 and other high-resolution remote sensing satellites. While these types of satellites were primarily launched to observe land-based change, they have also been found to produce detailed images of shallow waters around the ocean’s margins. Using these images, the scientists have been able to map reefs in a fraction of the time it takes to map them by boat or airplane. With funding, the researchers believe they could have a comprehensive map of the world’s reefs within three years. This map would not only be useful for identifying large-scale threats to the reefs, but would allow the researchers to locate those reefs that are in the most trouble.

next Corals in Crisis

The data used in this study are available in one or more of NASA's Earth Science Data Centers.


Tuanake Atoll in French Polynesia is one of many of the remote reefs recently mapped with the help of satellite data. This true-color image was acquired by Landsat 7. (Image courtesy Serge Andrefouet, University of South Florida)