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Coral reefs are limestone sediments in the ocean zone, which are made of living corals and dead corals that attach to each other. Meanwhile, coral is a type of coral which is a collection of animals from the Order Scleractinia that produce calcium carbonate as the main reef forming.

So, coral reefs are lime sediments formed by calcium carbonate produced by calcium carbonate-producing marine biota which is then going through a process of sedimentation. Sedimentation that occurs in corals can come from corals or from algae.

Coral reef ecosystems are ecosystems located in the tropical ocean floor formed by calcium carbonate-producing marine biota, such as calcareous coral and algae, and also other biota that live on the seabed, such as the types of molusca, crustacea, echinodermata, porifera, and other biota that live freely on ships, including plankton and nekton.

Location and Density

Coral reef ecosystems are generally found in shallow, warm and clean seas so that this ecosystem has a lot of high biodiversity. This coral reef ecosystem also grows in areas near the coast that have tropical ecosystems such as in Indonesia with temperatures around 210 to 300˚C. For example on the east coast of Africa, the south coast of India, the Red Sea, off the northeast and northwestern coast of Australia to Polynesia , the beaches of Florida, the Caribbean and Brazil. The largest coral reef in the world is the Great Barrier Reef which is located off the east coast of Australia with a length of about 2,000 km.

Types of Coral Reefs

Based on the type, coral reefs are divided into two, namely:

1. Hard Coral

Hard coral reefs are also called hard corals. This coral reef is formed of hard limestone corals. Although it looks very strong and sturdy, corals are actually very fragile, easily broken and very vulnerable to environmental changes. Examples of hard coral reefs are brain coral and Elkhorn coral.

2. Soft Coral Reefs

This soft coral reef does not form corals. Examples of soft coral reefs are like sea fingers and sea whips. Soft coral reefs consist of three types. The first is fringing reef, which is the type of reef that grows along the coast, on the continental shelf.

The second type is the coral atoll, which is a type of soft coral that resembles a ring that grows around volcanic islands. And finally, the third type of soft coral reef is the barrier reef which is a type of coral reef that grows along the coast but rather farther out which is usually separated by a lagoon.

Coral reef ecosystems have a very important function for life on the sea floor and also human life. The functions of the coral reef ecosystem include:

1. As a Food Source

In living coral reefs there are various types of small biota and plankton which are food from larger fish that live around reefs and seabirds whose food sources are around coral reef ecosystems.

2. As a Protector

Coral reefs provide protection for animals that live in it such as sponges, small fish, jellyfish, starfish, shrimp, sea horses, and others. In addition, coral reefs can also protect coastal benefits from abrasion and erosion due to ocean waves.

3. As a Natural Habitat for Marine Biota

Coral reefs are habitat and shelter that are good for 25% of the biota in the sea. Because in it, there are food sources and provide protection for the biota that live in them.

4. As a Big Wave Barrier

Coral reefs can be a big wave barrier that comes to coastal areas. With the presence of coral reefs, large waves become smaller or completely blocked so that people can settle in the area around the coast.

5. As a Tourist Attraction

The beauty that exists in this coral reef ecosystem coupled with beautiful biota around it can be used as a marine tourism object which is currently quite admired by local and foreign tourists. And this of course will increase the regional economic value.

6. As a Source of Medicine

In the coral reef, there are many chemicals that can be used as medicine for humans.

7. As an Industrial Raw Material and Jewelry

On corals that are quite hard like rock corals, they can be used as industrial raw materials and can also be used as jewelry or high-value accessories.

Damage to Coral Reefs and Its Factors

In recent years, many coral reefs have been damaged not only in Indonesia, but also in 93 other countries. Until now there have been around 35 million hectares of damaged coral reefs. This damage generally occurs because of rising sea water temperatures, ultraviolet light that irradiates coral reefs excessively and changes in environmental functions for other humans, causing the loss of symbiotic algae cells, namely zooxanthella which is a tissue dye and provider of basic nutrients on coral reefs. If zooxanthella does not exist, then the coral reef will die.

Factors that Damage Coral Reefs

Factors that can damage coral reefs include:

• Sedimentation of lime, which is caused by soil erosion from the felling of trees carried by the sea and covering the reef so that corals cannot grow because sunlight is covered by sediment.
• Freshwater flow. This flow usually comes from exhaust pipes, rainwater pipes or factory wastes which are disposed of at sea. This flow will be able to kill the coral if it occurs continuously.
• Various types of waste and garbage, such as agricultural, urban, factory, mining, and petroleum waste can pollute coral reef ecosystems which over time will damage coral reefs and then die.
• The danger of global warming caused by high levels of CO² released into the atmosphere is causing the sea water temperature to rise and corals to turn white and zooxanthella disappears from coral skin tissue because it does not match the environment with high temperatures. The disappearance of zooxanthella causes the growth of coral reefs to be hampered and over time it dies.
• Trial of explosives and nuclear materials at sea can cause radiation as a result of leakage and disposal of nuclear reactors. Leakage or discharge of nuclear reactors can last up to thousands of years which has the potential to increase the amount of damage and genetic changes in marine life.
• Catching the fish using muro-ami, poisons, and explosives, can cause damage to coral reefs.
• Excessive mining and extraction of coral can potentially destroy thousands of square meters of reefs and turn reefs into underwater deserts.
• Spiny starfish attack. This type of sea star is a coral-eating biota whose body surface is filled with thorns.
• Natural disasters. Natural disasters that occur such as hurricanes, tsunamis and earthquakes in the sea can damage coral reefs.

Factors Affecting the Development of Coral Reef Ecosystems

• Coral reefs can grow and develop well in waters that have an average temperature of 230 to 25°C.
• A good percentage of water salinity for coral reef life is 30% to 35%.
• Light and Depth. Light and Depth play an important role for the continuity of zooxantella photosynthesis processes found in coral tissue which is the main formation of the coral reef itself. Generally coral reefs develop at a depth of 25 meters with a light intensity of 15% to 20% of the intensity on the surface.
• Water brightness is related to the level of penetration which triggers ecosystem productivity.
• Waves or tidal benefits can provide a supply of fresh water, oxygen, plankton, and help block the deposition of coral colonies or polyps. But if the waves are too large, it will damage the structure of the coral reef.
• Flow has a good effect on reef ecosystems because currents carry nutrients and organic materials needed by corals and zooxanthella. But currents also have a negative impact because currents can cause sedimentation in the waters of coral reefs and cover the surface of the reef resulting in coral death.
• Sediment is a potential limiting factor for the distribution of coral reef ecosystems.

Coral Reef Conservation Efforts

Efforts that can be made in the preservation of coral reefs include:

• Develop marine conservation areas, such as establishing marine nature reserves and marine wildlife sanctuaries and establishing natural conservation areas such as marine national parks and marine nature tourism parks.
• Strive to manage the conservation of coral reef ecosystems so that they can be used optimally and efficiently for the community.
• Instilling education in the wider community, especially for those who live along the coastline about the benefits and impacts of damage to coral reefs.
• Strive for legislation for the protection of coral reefs, so that there is no legal vacuum in the context of law enforcement for the preservation and protection of coral reefs.

Those are the beneficial functions of coral reef for us and marine biota as well. Besides coral reef makes the marine world becomes aesthetic, it’s better if human could care more about marine life.