Tales of the Coast
America's Coasts


Coral Coast Formation

Reef-building corals require clear water. The corals need to be free of sediments in order to trap food particles, and their algae require sufficient light for photosynthesis. The upper limit of reef growth is controlled by the level of low tide. Corals cannot stand more than brief exposures out of the water (for example, during the passage of a steep wave trough).

While coral reefs produce rock structure, they also produce calcareous sediments. Waves and currents pulverize coral skeletons into sand-sized particles. However, on many reefs, calcareous algae (Hallemeda sp.) produce a majority of the sediments. The crushed calcareous cells of other animals, such as mollusks, sea urchins and sand dollars, also provide sediment.


Coral Reefs

One of the critical ecological issues of our times is the rapid degradation of coral reefs around the world by various natural and human activities. The most widespread impacts are water pollution, dredge and fill operations, over-harvesting of fish and shellfish, and the harvesting of some corals for jewelry. Even far from the coast, deforestation, urban sprawl and sloppy agriculture produce vast quantities of sediment and pollution that enter the sea and degrade reefs in the vicinity of river mouths.