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Guam, a volcanic island completely surrounded by a coralline limestone plateau, is a U.S. territory located in the southernmost part of the Mariana Archipelago. It is the largest island in Micronesia and lies relatively close to the Indo-Pacific center of coral reefs. A variety of reef types are represented on Guam, including fringing reefs, patch reefs, submerged reefs, offshore banks, and barrier reefs. Fringing reefs are the predominant reef type, extending around much of the island. Guam possesses one of the most species-rich marine ecosystems among U.S. jurisdictions. More than 5,100 marine species have been identified from Guam’s coastal waters, including over 1,000 nearshore fish species and 300 species of stony corals.
The health of Guam’s coral reefs varies considerably around the island and depends upon a variety of factors including geology, human population density, level of coastal development, level and types of marine resource usage, oceanic circulation patterns, coral predator outbreaks, and natural stressors such as cyclonic storms and earthquakes. Similar to the decline in health of reefs across the Indo-Pacific, the vitality of many of Guam’s reefs has declined over the past 40 years.