A natural reef is a bar of rock, sand, coral or similar material, lying at or near the surface of the ocean. Natural reefs result from biotic or abiotic (physical, chemical) processes. Artificial reefs are man-made structures, intentionally or unintentionally (e.g. shipwrecks).
Examples of biogenic reef: coral reef, oyster reef, reefs built of worm tubes (Sabellaria alveolata)
Examples of abiotic reef: beach rock, moraine ridge
Reefs have a number of ecological functions:
- feeding grounds for birds and marine mammals;
- habitat and retreat;
- habitat and nursery area with high species diversity;
- spawning grounds and feeding ground for fish;
- stepping-stone and regeneration reservoir for the expansion of benthic organisms.
Reefs can also be created artificially for several reasons:
- Protect coastlines from erosion;
- Promote sea life for recreation and aquaculture;
- Create a wave pattern that promotes the sport of surfing.