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


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.


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.


Barrier reefs


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.


Patch reefs
Patch reefs, are isolated reef platforms of various shapes and sizes.