National Marine Sanctuary of American Samoa
About Fagatele Bay National Marine Sanctuary

Coral Reefs

CoralThe coral reef is a vibrant marine ecosystem. It provides shelter and habitat for tropical fish of all shapes, sizes and colors, as well as other sea life such as crustaceans, squid, sharks, and sea turtles. Coral reefs are the oldest and most diverse assemblage of life on earth. Even though they cover less than two-tenths of one percent of the earth, it is estimated that they contain approximately 25 percent of the ocean's species.

Coral may look plant-like, but it is actually an animal. The Fagatele Bay coral reef contains more than 140 species of coral. Corals are cnidarians, a class of animals which also includes sea anemones and jellyfish. There are two groups of corals: hard corals and soft corals.

Hard corals are the true reef-building corals and are distinguished by their white limestone skeletons. It is this relatively indestructible skeleton that actually forms the coral reef, as new coral continually builds on old dead coral and the reef gradually grows.

Coral colonies grow very slowly. Under optimum conditions, massive corals may grow up to two centimeters a year and branching corals may grow up to 10 cm a year. Scientists can determine the age of a coral the same way as a tree, by counting annual growth rings. Some of the corals along the Great Barrier Reef in Australia are estimated to be over 800-1000 years old.

Did You Know?


  • All corals have polyps: tiny fleshy tubes, ringed at the top by even smaller stinging tentacles. These sting the passing prey, usually plant or animal plankton, and pull it inside the tube, to the polyp's stomach. Polyps are no bigger than the size of a pencil eraser.
  • Each polyp is an individual creature, but they live in colonies. Each polyp catches its own dinner and digests it, but the nutrients are passed along to the whole colony.
  • Corals feed during the night, and this is the best time to see them in their full splendor. Often during the day the polyps withdraw into their hard skeletons for protection.
  • Corals live in a symbiotic (mutually beneficial) relationship with microscopic plant cells, or algae. Coral polyps give the tiny plant cells nutrients, protection, housing, and carbon dioxide.
  • The algae uses this carbon dioxide and sunlight to make oxygen and carbohydrates, through a process called photosynthesis. The corals use the oxygen to breathe and the carbohydrates to supplement their plankton diets.
  • Coral by itself is actually white. The bright yellow, red, green, blue, and purple colors you see in the coral are actually the microscopic plants living in the polyps.
  • Different types of coral serve as a source of medicine for a variety of diseases. Some scientists think that within the coral reef lie the cures for AIDS and cancer.

Cycles of Destruction and Regrowth

The Fagatele Bay coral reef has faced many obstacles to its growth. In the late 1970s, the reef was infested by the crown-of-thorns starfish. This attack on the reef destroyed over 90 percent of the coral in the bay. This near-destruction of the reef emphasized the need to protect it and led to the sanctuary designation in 1986.

Since then, as the coral was slowly being replenished, two hurricanes and several major storms have hit Fagatele Bay, continually battering the new coral. These are natural disasters that have always faced coral reefs, and the coral in the bay will survive this cycle of destruction and continue to rebuild.

Recently, there has been some bleaching of the coral, which occurs when coral expel the algae they depend on, losing their color in the process. Prolonged periods of bleaching without recovery eventually lead to the death of the coral. No one knows for sure what causes this bleaching, but marine biologists have blamed salt level and water temperature changes and pollution. Researchers study the reef in the Fagatele Bay to learn more about this phenomenon that is affecting corals around the globe.

Revised July 19, 2017 by National Marine Sanctuary of American Samoa | Contact Us
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