Coral reef how is it made

How did this vast natural wonder come to be? Coral reefs form under a rather specific set of circumstances—the temperature, water chemistry and range of water depths must be just right.

Although deep water corals do exist, most reef builders like to be in shallow waters, where sufficient sunlight can penetrate to fuel the photosynthesis of the tiny algae that live inside the coral animals and provide them with essential food.

As sea levels rise and slowly flood coastal plains, coral reefs follow. Over time, the skeletons of dead corals and shells become cemented together, trapping sand and coral rubble, to form massive deposits of the rock limestone. There are three types of coral reef structures: fringing reefs, which form close to shore; barrier reefs, which are more substantial reef structures located further offshore; and atolls, which are essentially oceanic reefs that form around an island or volcano.

Atolls can remain as a ring of coral if the island becomes submerged. The present form is the result of millennia of sea level changes, continental shifts and layer upon layer of coral growth. The reef in its present gigantic form is fairly young in geological terms. At the end of the most recent ice age—about 14, years ago—sea level on the coast of Queensland was around metres lower than today. Depending on their size, barrier reefs and atolls can take from , to 30,, years to fully form.

All three reef types — fringing, barrier and atoll — share similarities in their biogeographic profiles. Bottom topography, depth, wave and current strength, light, temperature, and suspended sediments all act to create characteristic horizontal and vertical zones of corals, algae and other species. These zones vary according to the location and type of reef. The major divisions common to most reefs, as they move seaward from the shore, are the reef flat, reef crest or algal ridge, buttress zone, and seaward slope.

Corals usually develop into one of three characteristic structures: fringing reefs, barrier reefs or atolls. Learn more and view a larger image. As coral reefs grow, they establish characteristic biogeographic patterns. We use them to help improve our content, personalise it for you and tailor our digital advertising on third-party platforms.

Coral reefs are made up of colonies of hundreds to thousands of tiny individual corals, called polyps. These marine invertebrate animals have hard exoskeletons made of calcium carbonate, and are sessile, meaning permanently fixed in one place. Polyps grow slowly, forming different shapes and sizes depending on their species.

Assisted by other animals with calcium carbonate skeletons and also coralline algae, corals form complex, three-dimensional reefs.