This writeup is intended to provide an intuitive definition of what a coral reef system is. It begins by providing a brief description of what a coral reef is along with a few examples. It then describes what a coral reef system is and provides an example.

Coral reefs

A coral reef is a single, mostly connected reef of coral (there may be gaps of a few dozens of meters). Coral reefs can be right next to a shoreline or they can be many kilometers away from the nearest land. When next to a shoreline, they can run for tens or even hundreds of kilometers and can completely surround modest to large islands. When away from land, they appear in a wide range of sizes although sizes of a few kilometers across are probably typical.

Three examples:

  • I once flew in a commercial airliner over a quite large tropical island (probably New Caledonia but I'm not really sure). I happened to look out at just the right moment and saw a truly spectacular coral reef which was a couple of kilometers wide and ran for many kilometers along one side of the island.
  • Davies Reef is a coral reef in the Australian Great Barrier Reef (often abbreviated GBR). It's kidney shaped and about five kilometers across. There is no land anywhere near the reef although it does have a lagoon.
  • Myrmidon Reef is another coral reef about fourty or so kilometers from Davies Reef. It has no lagoon and is about twenty kilometers away from the nearest other reef or land.

Coral reef systems

A coral reef system is a collection of individual coral reefs which are close enough together to interact in some way. For example, some species of fish might swim between them and currents might carry silt and plankton from one reef to another.

The Great Barrier Reef off the northeast coast of Queensland, Australia is a coral reef system. It is over 2,000 km long and consists of about 3,000 individual coral reefs and another 900 islands. Many of the reefs are vaguely similar to Davies Reef although the sizes, shapes and styles vary quite widely.

Davies Reef is located within the main body of the GBR roughly fifty kilometers east of Townsville, Queensland. Myrmidon Reef is located about twenty kilometers out to the east of the main body of the GBR (i.e. further out to sea). Davies Reef is clearly part of the Great Barrier Reef "system" whereas Myrmidon almost certainly isn't.

Sources: personal knowledge and experiences