How do corals grow into reefs?

In constant evolution…

Like every living species on Earth, coral reefs have to go through different stages regarding their growth. They start as a fringing reef, change slowly into barrier reef, and may even turn into atolls (if the circumstances are right).

Fringing reefs

Fringing coral reef near Eilat (Israel).
Photo: Wikimedia Commons.

Fringing reefs are relatively young. They can develop in shallow waters along the coast of tropical islands or continents. The corals grow upwards to sea level or just below and outwards towards the open ocean. Fringing reefs are generally narrow platforms a short distance from shore and don't contain a substantial lagoon.

Fringing reef. Source: NOAA.

With time, however, the narrow platform of the fringing reef may become hollowed out to form a shallow, lagoon-like channel and slightly transform into a barrier reef.

Fringing reef transforming into barrier reef. Source: NOAA.

Barrier reefs

Australia's Great Barrier Reef as seen by the Terra satellite (26/08/00).
Source: NASA.

Barrier reefs are similar to fringing reefs as they border the shoreline, however they occur at much greater distances from the land and a deep and wide channel or lagoon forms between both.