Six main reef zones can be identified almost in the case of all coral reef formations that can be studied. Although variations in size, shape and ecosystem biodiversity may apply depending on the geographic areas in question and animal, coral and plant life species forming the food web, the existence of these zones is essential to the survival and long term thriving of coral colonies.
As we explore any coral reef, starting from the shoreline and moving out toward the open ocean, each drop or increase in elevation can tell us a great deal about the structure of the reef in question, as well as its development and the species of animals or plants that live in these areas.
The reef zones themselves are as follows:
- The first area that can be explored as soon as we leave the shoreline is the reef flat that stretches out from the shore to the reef crest. It contains two other significant zones – the back reef and lagoons – and its waters are generally shallow, warm and calm.
- The back reef is the area of the reef that extends to the reef crest and, like lagoons, is sheltered by it, so that its shallow, calm waters are ripe for the development of lush seagrass forests that herbivore fish and sea turtles feed on.
- Lagoons make up a body of water between the back reef and the shoreline, that is quite shallow and teeming with plant and animal life. They are sheltered by the forereef and crest, allowing for a wide variety of marine animals to thrive here as well.
- Next, the reef crest is the most barren zone of any coral reef formation, due to its exposure to strong waves, as well as air and sunlight during low tides. It has the main role of protecting the inner reef from stronger currents.
- The fore reef is the outermost layer of the coral reef formation. Here, strong and tall corals thrive, as the slope decreases and the waves are not as intense. Also, large fish and sea mammals are attracted by the rich biosphere of the fore reef, including barracudas and sea turtles.
- Finally, the deep reef features hard corals, an increase in sediments and a decreasing number of marine creatures, as it descends into the depths of the ocean.
Depending on the type of reef we’re looking at, lagoons may not be present – for instance, in the case of fringing reefs – and the reef flat or the forereef can sometimes extend seaward for several miles before the next change in elevation, offering significant information about the age and size of the reef formation.
When studying coral reef zones, one will find that different species of coral and plant life have evolved to survive in some zones, while they can’t be found in others. Many fish that thrive on the calm areas of lagoons and depend on the back reef’s lush seagrass would not be able to survive on the harsher environment of the upper fore reef and deep reef.
At the same time, many unique coral polyps and colonies have been found at depths where sunlight is scarce, and even less hospitable reef zones such as the reef crest house certain types of animals that have found refuge in certain areas below the waves.