Reef
 |
A reef surrounding an islet. |
In nautical terminology, a
reef is a
rock,
sandbar, or other feature lying beneath the surface of the water yet shallow enough to be a hazard to
ships. Many reefs result from
abiotic processes—deposition of sand, wave erosion planning down rock outcrops, and other natural processes— but the best-known reefs are those of
tropical waters developed through
biotic processes dominated by
corals and
calcareous algae.
Reefs can be created artificially either by special construction or through deliberately sinking ships, but one can argue that these "reefs" are not real ones, as it is seldom the case that an artificial obstruction would be created that is a hazard to shipping. These structures are usually created to enhance physical complexity on generally featureless sand bottoms in order to attract a diverse assemblage of organisms, especially
fishes. Thus, "
artificial reef" is a misnomer, though firmly established as the term used for man-made underwater habitat structures.
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
coralline algae.
Ancient reefs buried within
stratigraphic sections are of considerable interest to
geologists because they provide paleo-environmental information about the location in
Earth's history. In addition, reef structures within a sequence of
sedimentary rocks provide a discontinuity which may serve as a trap or conduit for
fossil fuels or mineralizing fluids to form
petroleum or
ore deposits.
*
Coral Reefs of the Tropics: facts, photos and movies from
The Nature Conservancy*
NOAA Photo Library*
Reef Environmental Education Foundation
