The Beginning

• Coral reefs most often form in the tropics.
  
  Coral reefs form from the growth of coral on underwater surfaces. As living creatures, coral begin as larvae, swimming in the ocean. Several latch onto rocks or other hard surfaces in colonies beneath the water's surface and grow into large groups of coral polyps numbering often in the hundreds of thousands. As they grow, coral reefs form into one of three types. Preferred locations for most coral reef formation include shallow areas of warm tropical waters.
  
  

Fringing Coral Reef Formation

• Coral grows up to the shoreline on this fringing coral reef near Eilat, Israel.
  
  A coral reef can form directly off of the shoreline, just under the water's surface. The coral larvae attach themselves onto an island's continental shelf where they extend the shore of the island far out into the sea.
  
  

Barrier Coral Reefs

• Water separates the Great Barrier Reef from the shore.
  
  Coral prefer shallow waters, often found near islands, but the larvae do not have to grow to extend the surface shoreline of a nearby island. Coral reefs can grow in a line following the shoreline of an island, but a narrow body of water separates the reef from the land. These reefs are known as barrier reefs. One famous example is the Great Barrier Reed near Australia.
  
  

Atolls

• Satellite image of the atoll of Nukuoro, Federated States of Micronesia
  
  Atolls formed once as fringing coral reefs, but the volcanic island in their center sank into the sea following an explosion. The coral reef continued to grow upward around the sunken island, eventually forming a ring shape surrounding a lagoon.