With ocean temperatures that never dip below 20 degrees Celsius (68 degrees F) and only reach up to 30 degrees Celsius (86 degrees F) on hot summer days, the South Pacific Ocean above the Fiji Plateau is the perfect location for coral reefs. Reefs ring nearly all of the country’s approximately 840 islands, and Matangi Island is no exception. In this Ikonos image, underwater reefs form a hazy blue-green halo around the island.
Coral reefs are delicate ecosystems that host an estimated one million species of fish, invertebrates, and algae. In addition to being diverse, the reef ecosystem is also extremely sensitive to climate change and pollution to the extent that scientists often use reefs as a yardstick to determine what ocean conditions were in the past. Today, many reefs are threatened by warming ocean waters, overfishing, and ocean pollution. To prevent and reverse damage where possible, scientists are striving to monitor the health of remote reefs across the globe. The first step is charting reef ecosystems, and the quickest way to do that is through remote sensing.
With the ability to see through as much as 30 meters (98 feet) of clear water, the Ikonos satellite can give scientists a picture of reefs that grow in shallow ocean waters. In this image, acquired on November 21, 2004, reefs are tan clumps in a field of pale green around the island. Getting a clear view of coastal reefs can be a challenge when sediment and algae cloud the waters above the reef. That may be the case in the upper right corner of the image where tan sediment billows out from the island. Algae typically form green and blue swirls of color in ocean water, and may be present in the bay formed by the crescent-shaped island.
For more information, please see “Mapping the Decline of Coral Reefs.”