Northern Guam geospatial information server

Reefs in northern Guam

Reefs almost completely surround Guam. They are extremely diverse environments and consist of many distinct habitats.

Reef flat is the relatively flat platforms that extends from the shoreline to the wave-washed reef margin. Reef flats can be from just a few meters to over a kilometer wide. Some reef flats are intertidal and nearly completely exposed during low tides. Others have deeper areas known as "moats", which retain water at all times. The reef flat zone can be covered by algal pavement, sea grass beds, staghorn (Acropora) thickets, Porites microatolls, fields of sand and rubble, and macroalgae.

Reef margin is the edge of a fringing reef, where the waves crash against the reef. They are almost always washed with surf and support encrusting algae and other tough organisms that can resist constant wave action.

Reef front is the area extending seaward from the reef margin. Coral communities in this zone are directly related to the level and frequency of wave action. Areas protected from severe waves usually have gentle slopes with tabular or branching corals. Areas with more wave action are steeper and dominated by lower, stout branched corals. The most typical feature of this zone are alternative ridges and vertical sides channels known as "spur and grooove" formations.

Reef slope includes the reef front and the lower reef slope. The lower reef slope has two ecologically distinct zones. Its shallower zone descends from the base of the reef front to about 50 meters deep. These areas lit by sunlight and generally dominated by reef-building corals. Deeper parts of the lower reef slope are reached by very little light and represent the transition between the sun-drenched upper reaches of the reef and the perpetually dark deep ocean floor. They are dominated by ahermatypic (non-reef-building) corals and organisms that are not directly dependent on light.

Text above is modified from "Environments of Guam" by Danko Taborosi, David R. Burdick, Claudine M. Camacho, Frank Camacho, published by BessPress, 2013.


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