Fringing Reef - Reef Development

Reef Development

The most important determinant of reef growth is available space as determined by sea level changes. Sea level changes are mostly due to glaciation or plate tectonics. There are six different major ways in which fringing reefs grow and develop.

• Reefs can develop vertically as far as the space below the surface allows. The reef generally grows upward from a starting point towards the surface. Once the reef crest reaches sea level the reef may begin growing seaward. Growth begins after flooding, mostly from parts of the reef that have died. Because the reef grows upward, the oldest sediments are found lower in the reef. The reef flat's age indicates when the reef reached sea level. Catch-up reefs have younger surfaces than keep-up reefs of this type.

• Reefs can expand seaward from the shore. This requires a fairly constant sea level. If the sea level drops, the reef flat in more seaward areas slopes downward.

• Reefs can grow atop muddy sediments which can predate the reef or accrete along with the reef's growth. These reefs also grow seaward from the shore. Older sediments are closest to shore and are not buried. Coral, seagrass and algae filter sediment before it is placed on the reef crest.

• Reefs can form in a gradual, sporadic manner, with alternate vertical and horizontal growth episodes. In this type of fringing reef formation there are multiple separate reefs that are found parallel to the shore and the original fringing reef. These reefs become a single, large reef when reef sediments fill in the spaces between the different reefs.

• Reefs can develop when an offshore reef grows to sea level forming a barrier. When the crest grows faster than the flat, a lagoon forms. The lagoon then fills with inshore sediments.

• Offshore reefs can form their barrier using storms to move coral and other debris inwards. The recurring storms continually reshape the seaward side of such reefs.