Darwin sure was a productive guy. When he wasn't busy developing the most important theory in biology, he apparently found time to map the world's coral reefs. And it's a good thing he did, because until recently, they were still the best reef maps available.
Darwin based his maps on observations from his global expeditions in the first half of the 19th century, but scientists can now monitor the state of the world's coral reefs with satellites. After more than a century, technology from NASA has at last made it possible to produce maps with new details, such as the quality and temperature of the water surrounding coral reefs.
"Until we made the map of coral reefs with Landsat 7, global maps of reefs had not improved a lot since the amazing maps that Darwin drafted," said Frank Muller-Karger, professor of oceanography at the University of South Florida, in a release from NASA's Goddard Space Flight Center.
The launch of Landsat 7 about 15 years ago also helped launch coral reef maps into the the 21st century. The satellite, a collaborative effort from NASA and the U.S. Geological Survey, was the first Landsat to return data on coral reefs — previous Landsat missions were "turned off" over large oceans to conserve power.
Over the last couple of years, Landsat 8 has provided scientists with unprecedented details about coral reefs. Equipped with a sensor called the Operational Land Imager (OLI), Landsat 8 allows scientists "to outline the reefs around the world and measure area and estimate depth in ways never possible before," Muller-Karger said in the release.
Sensors aboard NASA's Terra and Aqua satellites also keep scientists updated on the cumulative heat buildup around coral reefs worldwide. This information is critical because if the water around reefs gets too warm, a phenomenon known as coral bleaching kicks in.
Coral is not a plant, but a marine animal that depends on algae not only for its color, but for its survival. In extremely warm waters, this symbiotic relationship doesn't work out so well and the coral is left algae-less, colorless, and eventually lifeless, if it stays in this condition for too long.
Scientists at the National Oceanic and Atmospheric Administration currently monitor data from these satellites and others through Coral Reef Watch — an online tool that provides close to real-time monitoring and long-term forecasting of tropical coral reefs.
Researchers are now working on further improving the quality of coral reef images from satellites. Monitoring reef color to help curtail coral bleaching and obtaining higher-resolution images are priorities. NASA is currently testing to see whether its Hyperion sensor could help on both of these accounts.
