Ways that Fringing Reefs Develop

A Fringing reef, named for the visual fringe around the shoreline, may be the closest look many who visit the tropics will get to a coral reef. This most common and first stage of reef formation grows best on the hard rocky surface along the shore where the reef-building coral animal is one of the rare marine life species to survive in the clearer waters closer to the warm surface.

The water in a Fringing reef is less than thirty feet deep and hugs the fringe of the land where the growing corals settle in and form around the island’s underwater ledge. The eventual outcome over millions of years would see the corals raise and the land mass subside eventually showing a ring of coral with an open lagoon centre. Such reefs are visible on the ocean surface.

As the coral grows the sea level rises and in turn as the sea level raises the coral grows. This cycle ebbs and flows at different rates over time based on many outward conditions. The sea varies continually due to many factors such as melting glaciers and shifting sea floors and shelves. The Fringing Reef grows vertically in the water rise but on cresting the surface then grows horizontally again until the water level rises and then it once again goes vertical.

Another way for the Fringe to grow when the sea level is constant is in a seaward horizontal direction outwards, where the oldest growth is found closest to the shore and the new growth dropping below the water levels. Alternatively a Fringing Reef may form from the shore but instead of reaching below the sea it will grow above on top of the muddy sediment and grasses.

Separate Fringing reefs may also form around the island parallel to the shore and to each other eventually joining to a larger circling mass. Another common fringe starts deep off shore growing vertically but as the innermost closest to the shore edge in the shallow water reaches the sea level it forms its own lagoon trapping sediment in the uneven growth. A variation on this type occurs when storms move debris into the uneven fringe growth lagoon and coral drug in with the wash then continues to grow on the surface and the seaward side erodes in the waves of the open sea.

Fringing reefs are the first stage in reef development initiating close to the land, followed by the Barrier Reef forming a well defined zone separated from the land surface by a lagoon, and eventually a ring like formation of reefs encircling an entire lagoon create what is called an Atoll.