The Beautiful Coral Reefs

Corals belong to the phylum Cnidaria, a group that include gelatinous stinging marine invertebrates like jellyfish and sea anemones.

Coral reefs are composed of the skeletons of marine invertebrates called corals and the each tiny individual coral is polyp. The coral species build reefs by extracting calcium carbonate from seawater to create a hard, durable exoskeleton that protects their soft, sac-like bodies. These are called hard corals. Other species of corals that are not involved in reef building are known as soft corals such as sea fans and sea whips.

Coral polyps live on the calcium carbonate exoskeletons of their ancestors, adding their own exoskeleton to the existing coral structure. As the centuries pass, the coral reef gradually grows, one tiny exoskeleton at a time, until they become massive features of the marine environment. Coral have an array of shapes and colors, from round, brain like to tall with intricate and vibrant colors.

Corals of different shapes, size and colors

Corals are found all over the world’s oceans, from the Alaska to Caribbean sea. However, the biggest coral reefs are found in the clear, shallow waters of the tropics and subtropics. The largest coral reef system is the Great Barrier Reef in Australia which is more than 2,400 kilometers in size.

Corals feed by one of two ways.

Most corals depend on zooxanthellae, a photosynthetic algae which lives inside the coral polyp’s body where they produce food – carbohydrates to corals and for themselves. The coral reefs inturn provides a protected environment and the components to the algae. The corals and the algae share a symbiotic relationship wher both the organisms are benefited by each other.

In addition, zooxanthellae also provide the corals with their lively colors as most coral polyps are colorless without zooxanthellae.

However, some species of corals, mostly the deep corals in the lower, colder zones of the ocean directly catch small marine life, like fish and plankton, by using the stinging tentacles on the outer edges of their bodies.

About the reproduction of the coral species, they reproduce both sexually and asexually. Asexual reproduction happens through budding when new clonal polyps bud off from the parent polyp and grow and form their own colonies. Sexual reproduction occurs during a mass coral spawning. Coral spawning is an annual event when the corals release both eggs and sperms to fertilize. Later, the fertilized eggs develop into coral larvae, which grow further and form their own colonies or reef.

Coral spawning at Great Barrier Reef

Coral reefs are divided into four categories and they are:

  • Fringing reefs – grow near the coastlines around islands. They are most commonly found in the Phillipines, Thailand, Timor-Leste, off the western coast of Australia. Ningaloo reef is the largest fringing reef along the western coast of Australia. In India, the fringing reefs are found in the Gulf of Mannar and Palk Bay.
  • Barrier reefs – similar to fringing reefs, formed when fringing reefs combine with each other and border the coast. They are separated from shores by deeper and wider lagoons.

Example: Great Barrier reef, off the northeastern coast of Australia in the Pacific Ocean.

In India, Barrier reefs can be found in Andaman and Nicobar Islands.

  • Patch reefs – small, isolated reef growing from the bottom of the continental shelf. Patch reefs are present in Ratnagiri, Malvan and Kerala coasts of India.
  • Atoll – is a ring shaped coral reef island in the middle of oceans. Kiribati atoll in the west-central Pacific Ocean is the world’s largest atoll.

The union territory of India, Lakshadweep is also an archipelago consisting of 12 atolls.

Coral reefs are mostly found in warm, clear, shallow water with plenty of sunlight to nurture the algae that the coral rely on for food. Coral reefs covering less than 1 percent of the ocean floor are the most productive and diverse ecosystems on the earth. Hence are called “rainforests of the sea”. Coral reefs are critical marine habitat as they provide home and nursing to around 25 percent of marine life including 4,000 species of fish.

Importance of Coral reefs

  • Coral reefs benefit around 1 billion people with an estimated $30 billion annually in direct economic benefit to people worldwide from the various ecosystem services it  provide including food, coastal protection, and income from tourism and fisheries.
  • They act as wave barriers protecting the coast from erosion and the costal communities of adverse climate events.
  • Attracts millions of tourists every year, adding to the country GDP.  

Threats to coral reefs

Increasing temperatures of the world’s oceans due to global warming is causing coral reefs to expel zooxanthellae. Post which the coral reefs loses their color and are deprived of food eventually leading to their death. Coral reefs losing their color is termed as Coral Bleaching which is an increasing cause of concern.

Also, ocean absorbs immense amounts of carbon dioxide released into the atmosphere through fossil fuel burning which is causing high acidification of the ocean which in turn is inhibiting coral’s ability to produce calcium carbonate exoskeletons, the shelter base of corals.

Agricultural pesticides, chemical fertilizers, sewage discharge, oil, gasoline and sediment from eroded landscapes is polluting the ocean waters, making it difficult for coral to thrive and therefore damages the complex relationships that exist among the marine life and corals.

Unsustainable fishing practices such as cyanide fishing, blast fishing  with explosives and fishing using trawlers is destroying a thousand-year-old complex coral reef system.

The destruction of coral reef around the world, can lead to the extinction of thousands of species of marine life and make coastline communities and infrastructure susceptible to havoc causing storms and cyclones. Some islands and low-lying countries would vanish under the water due to it. Also damaging the economy of various coastal countries.

Healthy corals are the foundation of the Ocean’s food chain contributing immensely to our economy. It has geographical, economical and cultural importance.

Healthy corals lead to healthy oceans, and healthy oceans are vital to all life on Earth. Hence, protecting coral reefs is of utmost importance.


Published by LakesOfIndia

Lakes of India is an E.F.I initiative aimed at sensitizing the larger public on freshwater habitats across the country. A blog platform where one can read about lakes across India. You can become a guest blogger to write about a lake in your hometown and initiate an action to protect that lake.

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