As coral reefs go through their various stages of development, they form three kinds of reefs. The first of these to develop are the fringing reefs, which are directly offshore in tropical waters. As the first stage of growth, this type of reef develops quite close to land. It does need a hard surface on which to form and therefore the most likely place is an area where the bottom of the sea is rocky, rather than sandy. They can, though, develop in areas where the bottom is soft as long as there are a few hard spots in it to which the coral can latch on.
At first, a fringing reef manifests itself as a narrow strip extending out from the shoreline. It grows very slowly at the rate of 2 to 7 meters per year. It is sometimes hard to tell the difference between a fringing reef and a barrier reef in the size and shape. The main difference lies in the depth of the water because fringing reefs are found in waters that are less than 10 meters deep.
A fringing reef consists of two main structures. The broadest part of this type of reef is flat, which is why it is called the reef flat. The depth of the water is really shallow and at low tide the top part of the reef may be above the surface of the water. Because of its close proximity to the shore and the damage it can sustain from waves, there is usually very little life on a fringing reef. The main living formations are those of sea grass, seaweeds and a few soft corals.
The other part of a fringing reef is called the reef slope, which is found at the outer edge of the reef closest to the ocean. It doesn’t have to be a slope because in many cases this drop off at the edge of the reef is very steep and is almost like a cliff. Here you will find abundant life and growth of coral and many more species than can be found on the reef flat. This area is under less stress from the effects of the rocks and the waves and the waves that do roll over the slope carry in the nutrients required to sustain the coral life, while carrying away the sediment.
Fringing reefs can grow at the same rate as the rises in sea level. These are called keep up reefs because they can keep up a steady rate of growth. There are others that do not grow as the sea level rises, but when it reaches a certain height then they grow rapidly to catch up. Some reefs are unable to grow at the right pace and therefore die before they fully develop.
The amount of space a fringing reef has around the shoreline and extending out into the ocean will determine its pace of growth and eventual size. The reef initially starts growing under the water and will extend from the bottom to the surface of the water at a height equal to the depth of the water. Where the sea level remains constant, once the reef develops vertically, then it begins to expand horizontally outwards from the shore. The growth can be rapid, sporadic or very slow depending on the conditions of the water and the amount of stress there is for the reef.
The backreef will have the least amount of living organisms and become more numerous and diverse the farther out they are on the reef. This is usually the area with the most plankton on which the corals feed and their density also makes the water dark protecting it from UV radiation which is harmful to the coral.
Like all other life forms, the development of a fringing reef is a complex process that only Mother Nature can truly understand.