Geographic distribution of coral reefs in shallow marine waters

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            Coral reefs have been in existence for many years and are the most biologically diverse marine ecosystems on the planet. They range in different lengths and sizes and are considered to be the largest geological features that are built by organism. Nevertheless, some of them take years to grow by an inch. They can be divided into two stationary types namely the hard corals and the soft corals. These two can be differentiated by the fact that soft coral lack an exoskeleton which is present in the hard corals. This exoskeleton gives protection to the delicate bodies of the coral reefs. Examples of hard corals include the star, Elkhorn and pillar collars. On the other hand, also known as gorgonians, the soft corals comprise of sea fans, sea whips and sea rods (Reef Relief All about the coral reef).

            Being soft and lacking the rigid exoskeleton, they are easily influenced by the currents and waves of the sea but are static on the ocean bottom. Both the soft and hard coral reefs play a major role in the prevention of soil erosion on the shorelines. Their survival also encourages the existence of other sea life which acts as a source of food for many and also act as a source of medication. Consequently, the healthy coral reefs have natural values since their ecosystem in many tropical areas of the earth hugely benefit economically through their reacreational resources that include tourism and fishing. This growth is favoured by the fact that many tropical regions on earth are not too developed (Reef Relief All about the coral reef).

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            Living things often deposit limestone in water and together with calcium carbonate, these components make up reefs. Only a small number of the corals in the coral reefs family produce limestone that makes up the reefs but they are still considered to be essential components that make up the reefs. However, these corals also need to combine with other organisms in order to make up coral reefs. One of the most important organisms necessary for the formation of coral reefs is the algae. The algae make up coral reefs when they deposit significant amounts of calcium carbonate which are necessary in the building up of corals. These coral reef forming algae are referred to as coralline algae which are mostly essential in the growing of the pacific coral reefs than the Atlantic ones and they usually grow on hard sheets. Algae may at times deposit larger amounts of calcium carbonate than corals (Coral reefs 4).

            The importance of these algae not only lies in the formation of coral reefs. They also serve as protection for the coral reefs since they offer the support that keeps the coral reefs from being washed away in the shallow marine waters. This is because the algae can form a stony pavement that is usually strong enough to endure the tidal waves that are likely destroy the coral reefs within the shallow marine waters. Apart from that, the algae also form a distinctive rim on the reefs which helps to resist the force that comes from the waves thereby protecting the coral reefs from the destruction that may occur as a result of erosion (Coral reefs 4).

            Coral reefs are generally limited in geographic distribution to shallow waters since their existence heavily depends on a balanced marine environment in the sea life which consists of snails, sponges, rays and turtles among others. Coral reefs are made of thin layers of calcium carbonate secreted by coral polyps. These polyps are tiny and soft bodied animals and give the coral reefs its colour. They mostly grow in the warm tropical waters and mostly on top of the remains of limestone thus creating coral reefs. They live in symbiotic relationship where its algae host zooxanthellae takes in carbon dioxide and gives off oxygen which is used by the polyp (Reef Relief All about the coral reef).

            Further still, the geographic distribution of coral reefs is essentially limited to the shallow waters because of the particular requirement they need in order for them to grow. Because of these specific growth requirements it is not common to see reefs growing on soft bottoms since the larvae of the corals need a hard surface for them to settle on. Therefore it is only possible for the larvae to get a convenient place to nature in the shallow marine waters. This extensively shows why their geographic distribution is limited to this area which is the only conducive place for the coral reefs to grow from the larvae to the actual coral reefs (Coral reefs 6).

Furthermore coral reefs also require light for them to grow as their growth largely depends on zooxanthellae which also needs light. What is more the cancerous algae which are also essential for the growth of coral reefs also need light which thus grow in shallow marine water. This is why the coral reefs are also geographically distributed in this as the requirement necessary for them to grow are also available in the shallow marine water. However, some coral reefs can live in deeper water than others since different species have specific depth limits even though most of them grow well in shallow water on the continental shelves of water bodies and most of them can be found around islands or at the top of seamounts. However, the corals that thrive well in deep water bodies usually do not require light for their growth since they do not contain zooxanthellae which use light for photosynthesis. Besides, such corals do not make up reefs (Coral reefs 6).

The distribution of coral reefs in shallow marine waters can also be attributed to the fact that their growth is usually activated by clear waters which is characteristic of the shallow marine waters. Unclear water that is usually clouded with sediments and other deposits such as plankton will not support the growth of coral reefs since they hinder light penetration. As aforementioned, light is an essential requirement for the proper growth of coral reefs (Coral reefs 6).

            Further still, the corals that help in the building of reefs usually require warm water in order for them to grow and reproduce. This therefore means that they can only thrive well in water temperatures that are about 20°C and such water temperatures are mostly favoured by shallow marine waters. The deep water bodies mostly have lower temperatures since they can not maintain the warm temperatures. For that reason, coral reefs are not likely to develop in the deep water bodies since they do not contain favourable temperatures that they require in order to sustain their growth and reproduction. Consequently, it is evident that the geographical distribution of coral reefs is limited to shallow marine waters because this is where they can get light and warm water temperatures essential for their sustenance (Coral reefs 6).

            Since it has been established that coral reefs require warm water temperatures in order to grow, it is important to examine the issues that may arise in case the temperature levels change. First, when the temperature levels rise above the normal 20°C, the coral reefs tend to react to the excessive heat by bleaching. While bleaching, the reefs usually unleash the zooxanthellae which help in photosynthesis. As a result, the reefs then turn to a whitish colour since they have expelled the zooxanthallae that gives them the golden brown or greenish colour (Coral reefs 7).

            Extreme temperatures may also cause reefs to expel large quantities of slimy mucus. The reefs can however regain their growth through the development of the few that survive the extreme temperatures. Nevertheless, if the temperatures still remain harsh for a long time, the coral reefs will ultimately die. This is the reason why they grow well in shallow marine waters as the temperatures can regulate and remain conducive for the development of coral reefs (Coral reefs 7).

            Corals usually react to reduced levels of salinity in water since they can not thrive well in places that have large volumes of fresh water. This is the reason why they can not grow well in river mouths since such areas usually have low salinity and what is more, they usually bring in large deposits of silty sediments which hinder the development of coral reefs. It is obvious that when the silty sediments are deposited in the river, they tend to cloud the water and this prevents light from reaching the zooxanthellae. Besides, these silty sediments may also stifle the coral or even cause disease (Coral reefs 8).

            Nevertheless, corals react differently to different levels of sediment and silty environments. Some corals are able to thrive in environments that have large amounts of sediments and even build reefs in silty water while others may even feed on the organic particles within the sediments that are deposited in water.  On the other hand, some corals will only develop in clear water with very minimal levels of sediments. This is because they are susceptible to large amounts of sediments and if the wave or current action is not strong enough to wash the sediments from the water body, the coral reefs may end up getting destroyed. This is why such coral reefs can not grow in rivers since rivers are usually prone to the deposition of sediments that come from human activities such as mining, logging, construction as well as dredging (Coral reefs 8).

            Corals can also get damaged by pollution of water bodies which is usually common in rivers. The presence of chemicals such as pesticides and industrial wastes in water can cause harm to coral reefs and especially the larvae can get destroyed even by low concentrations of such chemicals. On the other hand, high concentrations of such chemicals also may cause harm to the growth of reefs because of the excess nutrients which may hinder their development. Other human deposits such as sewage and fertilizers that are washed into the sea may also destroy corals. This is because such human deposits contain nutrients that may impede the development of the coral skeletons that act as protective mechanisms. Apart from that increased levels of nutrients in the water body may also interfere with the ecological balance of the coral reef community (Coral reefs 9).

             Further still, corals thrive well in water bodies that naturally contain low levels of nutrients. This is because environments that have low levels of nutrients are not conducive for the growth of sea weeds and therefore their growth can be controlled by grazers. This is important in the growth and reproduction of coral reefs since in such cases they will be able to compete for space and light unlike when the sea weeds grow within the same environment. High levels of nutrients promote the growth of sea weeds and this may affect the development of coral reefs. This is because sea weeds grow faster and this may lead to them shading and chocking coral reefs thereby hindering their growth and ultimately destroying them (Coral reefs 8).

            It is also important to examine the structure of the shallow marine waters so as to establish why it is conducive for the growth and development of the coral reefs. The shallow marine waters usually contain low levels of nutrients and as mentioned above; coral reefs mostly grow properly in water bodies that contain low levels of nutrients.  Besides, the low levels of nutrients in these water bodies also imply that phytoplankton or primary production is very little therefore the growth of coral reefs is enabled (Coral reefs 16).

            Furthermore the environment in the shallow marine waters is unproductive and the coral reef communities grow well in unproductive environments. This is essentially linked to the relationship that lies between the corals and the zooxanthallae. The corals usually provide food and help in the formation of calcium carbonate skeleton that is necessary for the reefs. The zooxanthallae therefore is protected and is able to get appropriate supply of carbon dioxide together with essential nutrients such as nitrogen and phosphorus (Coral reefs 16).

            The wastes that come from the use of nitrogen and phosphorus by the corals are used up by zooxanthallae as nutrients. The zooxanthallae in turn use sunlight to turn the nutrients into organic compounds that will be used up by the corals. The nutrients are usually recycled in the entire cycle such that the reefs require low levels of nutrients and this is only heightened by the low productivity of the shallow marine waters (Coral reefs 16).

            What is more, the low productivity of the shallow marine waters is conducive for the development of coral reefs because they are highly productive. Apart from recycling the nutrients that they use in their growth development, coral reefs can also provide their own nutrients since they contain nitrogen fixers such as cyanobacteria and symbionts that help in nitrogen fixation. Such nitrogen fixers also help in the provision of nutrients for zooxanthallae. Therefore, since the shallow marine waters lack nutrients, the coral reefs are still able to survive as they will produce their own nutrients and what is more, this helps to regulate the amount of nutrients in the water. Excessive nutrients in the water may lead to bleaching or even total destruction of the coral reefs (Coral reefs 16).

            The shallow marine waters are also known to have few numbers of sea weeds. This is advantageous to the coral reefs since they have to compete for space on the hard places of the water bed so as to affix themselves. Coral reefs also compete with sea weeds for light. Therefore it is clear that they will most likely grow on shallow marine waters because these areas have fewer amounts of sea weeds and this therefore means that the competition for light and space is reduced and the environment can remain conducive for the growth and development of the coral reefs (Coral Reefs 18).

Since limestone is necessary for the formation of coral reefs, their geographical distribution is highly limited to areas that encourage their formation. Secretion of limestone enables the formation of coral reefs. In other words, algal-cnidarian symbiotic machineries require specific types of marine environment which is likely to encourage the productions of limestone. Thus, coral reef formation will only occur in areas where temperatures do not fall below 18 degrees and where the temperatures will last for a considerable period. However, this does not apply to all coral species since others may grow in water temperatures ranging from 11 degrees to 25 degrees (Reef Relief All about the coral reef).

            The growing climate change is likely to result to death of coral reefs by 2080 especially in the deep waters like the Persian Gulf, Pacific and Indian Ocean. Coral reefs geographical distribution to shallow waters can also be accounted for by their tendency to flourish in geographical areas consisting of clear, saline and warm waters. Their concentration also highly depends on the depth of water and the balance of the water to light. Moreover, the coral reefs limited survival cannot exist in areas where they will have limited or no access to light. In other words, light penetration also euphotic zone acts as an important factor that helps its host the zooxanthellae to photosynthesize thus proving crucial in supporting the health and reproduction of coral reefs (UNEP GRID Rapid response assessment).

            According to UNEP, all the living resources and the marine life are not evenly distributed in the waters and is associated with the sea bed. As aforementioned, many environmental factors contribute to the limited geographic distribution to shallow waters. Whether these shallow waters will provide the essential factors in supporting the life and population of coral reefs hugely depends on a number of environmental policies that the coral reefs have adopted for their survival in the shallow waters (UNEP GRID Rapid response assessment).

            Concentration of carbon dioxide in the atmosphere contributes to the its absorption in the deep waters which subsequently results to the waters becoming more acidic. As a result, such an environment discourages the growth of coral reefs more so in the higher latitudes. In addition, acidification of the deep waters reduces the formation of of calcareous phytoplankton which significantly interferes with food distribution for the marine life (UNEP GRID Rapid response assessment).

            Environmental locations also restrict the existence of coral reefs.  For instance, their growth is highly favoured in the tropical and semi tropical waters. In areas with higher attitudes of approximately 30 degrees, the growth of a number of species is highly discouraged. Additionally, these reefs heavily depend upon the mangrove and sea grasses. The mangroves trees which are mostly submerged in water act as breeding grounds for most of the marine life which enhance the existence of coral reefs. Being salt tolerant, they produce nutrients by producing foods to support the habitat foods. As well, they filter pollutants coming from the land to the marine life which may also block the necessary light (UNEP GRID Rapid response assessment).

            Coastal development is projected to significantly impact on approximately 80% of all marine pollution including coral reefs. This occurs when there is a rise in the coastal population, increased sewage pollution and increased sediments among other factors. Rapid destruction of mangroves further enhances the pollution of many waters. UNEP projects that an estimated 91% of all tropical coasts will enormously be impacted on by 2050 due to rapid development among the coast lines (UNEP GRID Rapid response assessment).

            Thy growth of coral reef species significantly declines in deep water areas. Mostly, this may be attributed to the fact that very deep waters may increase high levels of sediments which discourage the growth of coral reefs. High levels of sediments in the deep waters tend to block the mouths of the most habitants in the sea life thus restricting feeding. As well, these sediments decrease the level through which light penetrates in the waters (UNEP GRID Rapid response assessment).

            On the other hand, sea grasses provide environment with foods for sea life survival. As flowering marine plants, they also act as a nursery for the sea life by filtering the feeding organisms and providing food to the sea life which includes sea cucumbers and urchins. The sea grass also contributes by filtering the water from deposits and remains, stabilizing the bottom and through releasing oxygen.  In turn, the coral reefs need these balanced environments for their existence which also benefits its hosts (Reef Relief All about the coral reef).

            Climate changes significantly interfere with the quality and nutrient cleaning thus accounting to the limited geographic distribution to shallow marine waters.  Currents in large scale deep waters also assist in the ‘flushing and cleaning’ of nutrients.  However, climate changes tend to significantly reduce the frequency and strength of the coastal cleaning mechanisms. Over the next 100 years, UNEP projects that this will be more concentrated in areas of lower and medium latitudes thus increasing the level of pollution in deep waters (UNEP GRID Rapid response assessment).

            Factors like climate change and increased development which in turn triggers pollution and also leads to dead zones. Also, these changes in climate tend to disrupt the productivity in deep waters. These are mainly observed in the coastal waters most of which are deep. As a result, the geographic distribution of coral reefs in marine waters becomes limited. These dead zones comprises of areas with inadequate oxygen. However, only a few of these are as a result of natural occurrences. Also, the rate of these factors which accelerates the spread of dead zone in marine waters is likely to increase. By 2006, the number of dead zones significantly increased by 51 from the year 2003 (UNEP GRID Rapid response assessment).

            Other factors like over harvesting in deep waters degrade the marine life and its habitants subjecting them to be more vulnerable to climate change. Studies show that the capacity of fishing is almost 2.5 times more than the number needed in harvesting and maintaining from the world’s fisheries. As a result, this practice has largely damaged the sea beds thus affecting marine life in the deep water (UNEP GRID Rapid response assessment).

            This can further be enhanced by use of uncontrolled large vessels in bottom fishing which causes 95% damage through its use of trawls and traps. Studies show that use of trawls in fishing have severe and long term damages in the marine life which includes coral reefs. More so, contrary to the shallow waters, these impacts slowly recover in deep waters. Some deep waters never recover from the damaging impacts as a result of mismanaging of deep water fishing (UNEP GRID Rapid response assessment).

            Contrary to shallow waters and its favour on the growth of coral reefs, deep waters are more vulnerable to invasive species. Their vulnerability results due to many infestations brought about by ships. Thus other geographical areas tend to encourage coral reefs as the shallow waters as not as disturbed as the deep waters which easily become polluted. Many of these invasive species are brought about especially in the shipping routes and areas that are polluted. Moreover, climate change also leads to such invasions (UNEP GRID Rapid response assessment).

            It could therefore be concluded that the geographical distribution of coral reefs is limited to shallow marine waters because of the specific requirements necessary for the growth and development of coral reefs. Coral reefs require space, light, warm water temperature, clear water as well as an environment that has fewer nutrients. Shallow marine waters on the other hand have some o these requirements since they are usually less productive, have less sea weeds, and the waves also sweep away sediments and silty deposits thereby leaving the water clear. Other water bodies such as the seas and rivers are usually susceptible to human deposits thereby making hindering the environmental requirements necessary for the growth and development of the coral reefs. Therefore these are the factors that contribute to the limited distribution of coral reefs in shallow water marines (UNEP GRID Rapid response assessment).

Works Cited

“Coral reefs.” 2008. “Marine Biology.” 30 October 2008 <>

Reef Relief. Protect Living Coral. 2008. “All about the coral reef.” 30 October 2008 <>

UNEP GRID. 2008. “Rapid response Assessments” 30 October 2008


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Geographic distribution of coral reefs in shallow marine waters. (2016, Aug 18). Retrieved from

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