The structure and extent of coral reefs can now, for the first time, be monitored globally, thanks to new observations from NASA's Landsat 7 spacecraft. Detailed images of reefs from nearly 900 locations around the world have been collected in the first year of the Landsat 7 mission.
"Landsat 7's ability to see land features as small as 100 feet (30 meters) across and to repeatedly observe coral reefs worldwide makes this archive of images a unique and valuable scientific resource," said Landsat Project Scientist Darrel Williams of NASA's Goddard Space Flight Center in Greenbelt, Md. "No one else has been willing or able to acquire and archive this type of high-resolution global data for use by the scientific community."
Scientists at the University of South Florida, in collaboration with colleagues at the College of Charleston and Dalhousie University (Halifax, Nova Scotia), have completed initial tests of Landsat 7's ability to study coral reefs and are presenting their results at the 9th International Coral Reef Symposium in Bali this week. Nearly 1500 scientists are expected to attend the quadrennial meeting.
Landsat 7 measurements of live coral in the Carysfort Reef, the largest reef in the Florida Keys, matches detailed surveys taken on the ground, according to a joint study by Frank Muller-Karger, Serge Andrefouet, and Dave Palandro of the University of South Florida's College of Marine Science and Phil Dustan of the College of Charleston. The surface area of live coral in this reef has declined from more than 50 percent to less than 5 percent since 1975.
"Reefs around the world are in ecological collapse, especially in the Florida Keys," says Dustan. "We need to use remote sensing to help fight for their conservation."
Andrefouet has also completed a Landsat 7 inventory of the extensive coral atolls in French Polynesia in the South Pacific using 22 separate scenes, each covering about 12,000 square miles. He was able to identify and map many different types of reef formations, from entire atolls covering hundreds of square miles to individual marine habitats. "This study shows coral reef scientists how to do a large-scale reef inventory anywhere around the world," says Andrefouet, a remote-sensing scientist who was raised in French Polynesia.
"With the Landsat 7 data we can rigorously test hypotheses about how entire reef ecosystems form," says coral reef ecologist Bruce Hatcher of Dalhousie University. "We no longer are limited to the observations we can collect by wandering around in small boats and sampling individual reefs to infer large-scale processes from a few samples."
Hatcher and doctoral student Abdulla Naseer from the Maldives Ministry of Fisheries are using Landsat 7 data to understand how wind, waves, and sea level have shaped the coral-reef nation of the Maldives, south of India. By combining weather and tidal records with a catalog of the physical features of the 2800 reefs derived from Landsat 7 images, the scientists can identify patterns of reef growth and erosion caused by monsoons and the ocean's waves and currents. A detailed understanding of how these climate forces shape coral reefs will enable scientists to better predict how reefs will respond to future climate changes.
With the Landsat 7 image archive, physical damage to reefs can now be monitored in near real-time, says Hatcher. "With Landsat 7's repeated coverage of coral reefs throughout the year and its fine-scale imaging capability, we will be able to see damage to reef structure caused by hurricanes."
Over 5,000 coral reef images have been collected to date by the Landsat 7 mission. Many reefs have been imaged several times, providing a glimpse of seasonal changes in reef structure and biology.
Landsat 7 was launched by NASA in April 1999 and began routine science observations in June 1999. Images are archived, processed, and distributed by the U.S. Geological Survey, which also assumed responsibility for day-to-day operations of Landsat 7 this month.
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