### formation | ridge | reef | coral reef:

Atoll
* Most atolls are in the warm parts of the Pacific Ocean or the Indian Ocean.
* are a little ring of living coral reef built on a kilometers high pile of dead coral
  - all low islands, barely breaking the ocean's surface
  - also rings of coral, often incomplete, but no island is present
  - areas of shallow water carbonate deposition in the open ocean
  - circular shaped reef crests surrounding a central lagoon
* are coral islands consisting of a reef surrounding a lagoon
  - islands, made entirely of coral that occur in deep water
  - generally remote from other land masses
  - horseshoe or ring-shaped, open sea reefs that surround a lagoon
  - islands that have long since sunk below the ocean surface, leaving only the barrier reef
  - large coral reefs found in the sea around the Solomon Islands
  - large, ring-shaped reefs lying off the coast, with a lagoon in their middle
  - low-lying and formed mostly from dead coral
  - potentially suitable sites because of their profile, however atolls are coral outgrowths
  - rare in the Caribbean and the rest of the tropical Atlantic Ocean
* are reefs surrounding a lagoon
  - that surround a central lagoon
* are rings of coral reef usually with a large and quite calm lagoon in the middle
  - reef, with steep outer slopes, that enclose a shallow lagoon
  - small ring-shaped reefs, which occur in the middle of the ocean
  - the coral islands that romantic dreams are made of
* are, in fact, some of the most complex and vibrant structures on the planet.
* develop near the sea surface on underwater islands or on islands that sink, or subside.
* enclose shallow pools or lagoons.
* form far from land typically.
* generally rise up out of very deep water.
* grow in the shape of a circle.
* owe their existence to the growth of coral reefs.
* separate a central lagoon and are circular or sub-circular.
* usually form on top of submerged volcanoes.

### formation | ridge | reef | coral reef | atoll:

Coral atoll
* are the most widespread type of reef in the South Pacific.
* form around the edge of an old volcano.

### formation | ridge | reef | coral reef:

Barrier reef
* are broader and lie farther away from the coast
  - platforms separated from the adjacent land by a bay or lagoon
  - reefs that are separated from land by a lagoon
* can be enormous
  - extend all along a coast if the water is warm enough to support coral growth
* consist of a line of single reefs running parallel to a coastline.
* follow the shoreline, but are separated from it by water.
* form a little way offshore.
* grow further away from the beach shoreline.
* occur farther offshore
  - in association with continental land masses
  - on a variety of scales
* tend to develop along the edge of the continental shelf.

### formation | ridge | reef:

Oyster reef
* Most oyster reefs provide habitats
  - shelter
* Some oyster reefs are so large they are included on topographic maps.
* are bottom communities and constitute an important commercial fishery in Mobile Bay
  - more diverse than surrounding, unstructured areas
  - most successful where the bottom currents carry sediments away from the reef
  - prolific within the estuaries of Southwest Florida
* benefit humans, as well.
* locate themselves where freshwater and saltwater meet.
* provide habitat for rockfish and many other species