Reef - Definition and Overview

A reef surrounding an islet.

A reef is a nautical term for a chain of rocks or coral, or ridges of sand, at or just beneath the surface of the water. Such formations can be a hazard to ships.

The best-known reefs are those of tropical waters, developed through biotic processes dominated by corals and calcareous algae. Others result from abiotic processes such as sand deposits and erosion of rock outcrops by waves.

Biotic reef types

There are a number of biotic reef types, including oyster reefs, but the most massive and widely distributed are tropical coral reefs. Although corals are major contributors to the framework and bulk material comprising a coral reef, the organisms most responsible for reef growth against the constant assault from ocean waves are calcarous algae, especially, although not entirely, species of red algae.

See also

• Shoal