In the previous section it was determined that coral reefs are divided into four main types of reefs: fringing, barrier, atoll, and patch. Each reef can then be further divided into zones. The zones are depth, wave energy, light intensity, temperature, and water chemistry. It is important to note the parameters that surround each zone, these factors influence the distribution of particular organisms, especially corals. The reef zones that will be explored in this section are reef flats, reef crests, fore reef or reef fronts, and back reefs.

The lagoon is not technically considered a zone but can help indicate and describe some of the zones. Lagoons are classified as shallow bodies of water that are separated by coral reefs, sandbars, barrier reefs, or other natural barriers. Typically Lagoons are located throughout the Indian and Pacific oceans however, smaller lagoons typically exist in the Atlantic Ocean. Characteristics in lagoons vary dependent on abiotic factors. Shallow lagoons with little wave actions may get very hot. In addition, lagoons that are near mangroves and experience high levels of human activity typically contains water with high nutrients and low visibility. This makes it seemingly difficult for certain species of coral to survive in this environment. Lastly, it is important to note that there are typically two types of lagoons: atoll and costal. Atoll lagoons typically, form when an island subsides beneath the water, whereas coastal lagoons are formed along sloping coasts, and tend to be separated from the ocean by an island, reef, or sand bank. Atoll lagoons are typically deeper and are not connected to ocean by an inlet like coastal lagoons.

Now that there is a basis for the zones, the first zone “Reef Flats” can be discussed. Reef flats are a zone protected from wave action, meaning this zone experiences little to no waves. The size, shape and depth of reef flats vary. The length of reef flats can vary from feet to miles while the depth can vary from centimeters to a meter. Due to the wide range of temperatures, light intensity, and salinity found in reef flats, corals have learned to adapt in order to survive in this zone. In addition, this zone experiences less dissolved oxygen in seawater, and extremely low tides exposing corals to air. Due to the difficult living conditions found in this zone, it often experiences a lot less diversity opposed to other zones. However, it is important to lastly note that several species have acclimated to the life in this zone, and many are only found exclusively within this zone.

Reef crest are the next zone to be discussed, and are known as the “highest” point of the reef. This zone unlike the reef flat zone experiences the fullest impact of wave energy due to the reef crest breaking the waves. Reef crests also experience the greatest amount of light energy due to its location being closest to the water’s surface, or even right above it. Corals found within this zone must have sturdy and strong structures, to be able to withstand the intense wave action, high light intensity, and aerial exposure. Due to the rigorous living conditions found within this zone it only experiences a small amount of diversity, as several species would not be able to thrive in this zones conditions.

Reef front or Fore reef zones are furthest from the shore. The shape typically slopes downwards and reaches great depths. However, in some cases the reef front extends almost straight down forming a vertical wall known as a “drop-off.” In this zone, the most coral diversity is present, this is because most corals thrive in the intermediate reef front between 15-65 feet deep. In the intermediate part of this zone, corals are exposed to relatively low wave action and light making it extremely suitable to live in. However, in deeper and shallower portions of this zone coral diversity declines, as most corals acclimate and adapt to living in specific depths.

The last zone is known as the “Back Reef.” The Back Reef is the zone that slopes into a lagoon. This zone is often more protected from wave action, but can be exposed to air during low tide. Diversity in this zone remains low due to the possible air exposure. Typically, patch reefs and coral rubble exist in this zone.