USGS Pacific Coral Reefs Website

Mapping Coral Reefs

Many of the world's coral reefs already have been severely damaged by human activities. In order to protect and preserve the health of these treasured and important ecosystems, it is essential to monitor our Nation's coral reefs. Mapping and understanding the history of coral reefs is a large first step toward this goal.

At the U.S. Geological Survey, we are applying a mixture of new and old technology to map coral reefs. The objectives are to: 1) determine the best methods and combinations of data needed to characterize this coral reef system; 2) establish baseline thematic maps; and 3) provide a GIS-referenced database for future scientific studies. These baseline digital maps and databases are needed to detect and understand changes in the reef environment over time.

Remotely sensed data from different sources are being analyzed to determine their capacity for detecting and mapping the location of live and dead reef areas, density of coral cover, algae, silt, sand, and possibly the type of coral present.

Remote sensing by itself, however, is found to be only partially capable of accurate mapping. Interpretation of the remotely sensed data is corroborated by field mapping and in situ measurements of coral cover.

Aerial photography gives us an idea of areas that have shown change on shallow parts of the coral reef over the past few decades.

Lidar (light detection and ranging) technology uses lasers to produce high resolution sea-floor bathymetry maps. These new sea-floor maps show remarkable details of coral reef structure.

Multispectral and hyperspectral imagery have been used on a limited basis to map coral reefs in Hawai‘i, Datasets are currently being processed to evaluate their applicability for coral reef monitoring.

While various remote sensing techniques provide an overview of coral reefs, snorkel and scuba dives allow scientists to directly identify coral species and make estimates of living coral coverage and biodiversity. In-the-water observations, including underwater photography, and georeferenced videography provide records that can be incorporated into maps and used to understand subtle changes in the reef ecosystem.

Mapping of coral reefs provides important information about a number of reef characteristics, but no single approach is effective for evaluating the overall health of a reef. It is only through combining techniques that scientists can establish the most complete view of a reef, one that can be used for evaluating reef health and for future monitoring of Hawai‘i's coral reefs. One example of our efforts may be seen in the U.S. Geological Survey Open File Report 2005-1070 entitled "Moloka‘i Benthic Habitat Mapping".

Example of map from USGS Open File Report 2005-1070 "Moloka‘i Benthic Habitat Mapping". Landsat satellite image overlaid with the benthic habitat classification map of Moloka‘i showing the Dominant Structure/Substrate layer and the percentage of each class. The benthic habitats were mapped using a combination of methods described above. Click on link to visit website for full version of report and maps.

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