Coral Reefs

A coral reef is an underwater ecosystem characterized by reef-building corals.

Reefs are formed of colonies of coral polyps held together by calcium carbonate.Most coral reefs are built from stony corals, whose polyps cluster in groups.

Unlike sea anemones, corals secrete hard carbonate exoskeletons that support and protect the coral.

Most reefs grow best in warm, shallow, clear, sunny and agitated water.

Factors Affecting Coral Reefs

Overfishing and Destructive Fishing Methods

Overfishing by commercial producers in shallow waters depletes species of fish which are vital to the health of the reef ecosystem. This can lead to rapid changes in the health and viability of other species in the food chain and is one of the leading causes of destructive algae growth in coral reefs. Unsustainable and destructive fishing methods such as dynamite fishing causes irreparable harm not just to the balance of the ecosystem but also to the physical structure of the reef.

Climate Change

Global warming, the cause of so many ills in our natural environment, has had a terrible impact on coral reefs. Because reefs are essentially hidden under water this impact may be less evident, but that doesn’t make it any less important. The rise in the world’s ocean temperatures can lead to coral bleaching (which is the result of a stress reaction by the reef) and the death of the millions of species which depend on the reef for sustenance and safety.


Unsustainable and irresponsible tourism directly contributes to the destruction of the world’s coral reefs. Careless tourists, eager for a fun experience and not educated on how to safely interact with the reefs, can cause great harm to the structures by touching it or otherwise upsetting the system. The hotels which cater to the influx of tourists in tropical beach areas, not to mention the constant construction done in order to keep up with their numbers, add to the problem through the dumping of waste or other materials into the water.


Urban and industrial waste, oil pollution and trash take a huge toll on coral reefs. This can happen when sewage and runoff from farming increases the level of nitrogen in the water, which leads to the growth of algae. This algae can then suffocate the coral reef.

What do Coral Reefs need to Survive?

Sunlight: Corals need to grow in shallow water where sunlight can reach them. Corals depend on the zooxanthellae (algae) that grow inside of them for oxygen and other things, and since these algae needs sunlight to survive, corals also need sunlight to survive. Corals rarely develop in water deeper than 165 feet (50 meters).

Clear water: Corals need clear water that lets sunlight through; they don’t thrive well when the water is opaque. Sediment and plankton can cloud water, which decreases the amount of sunlight that reaches the zooxanthellae.

Warm water temperature: Reef-building corals require warm water conditions to survive. Different corals living in different regions can withstand various temperature fluctuations. However, corals generally live in water temperatures of 68–90° F or 20–32° C.

Clean water: Corals are sensitive to pollution and sediments. Sediment can create cloudy water and be deposited on corals, blocking out the sun and harming the polyps. Wastewater discharged into the ocean near the reef can contain too many nutrients that cause seaweeds to overgrow the reef.

Saltwater: Corals need saltwater to survive and require a certain balance in the ratio of salt to water. This is why corals don’t live in areas where rivers drain fresh water into the ocean (“estuaries”).

Coral Reefs Found in India

Andaman and Nicobar -Situated in the Bay of Bengal, exclusively fringing reefs of about 572 islands, most of these islands have a healthy biodiversity.•

Gulf of Kutch – Exclusively consists of fringing reefs. The reefs are relatively less developed due to large range of temperature and high salinity. The harbours have less biodiversity. The entire Gulf of Kutch is also known as a marine national park•

Gulf of Mannar- Fringing reefs with a chain of 21 islands from Rameswaram in the north to Thoothukudi (Tuticorin) in the south. This part of the gulf forms part of the Gulf of Mannar biosphere reserve.•

Lakshadweep-Exclusively coral atolls with 36 islands, of which 10 are inhabited. The islands range from less than 1 km (0.62 mi) to about 9 km (5.6 mi) in length, and do not exceed 2 km (1.2 mi) in width.•

Other places- Tarkarli in Malwan, Maharashtra is a smaller reef. There are some coral reefs around small inlets in the western part of the Gulf of Khambat. Angria Bank is a coral reef off Vijaydurg in Maharashtra. There is a coral reef in Netrani Island in Karnataka.

Shell reef in Gulf of Kutch is a shell shaped reef made from bio rock and decorated with coral in the deep waters of Gulf of Kutch, off the coast of Gujarat. It helps Coral Polyps to get healed 20% faster than usual.

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