Coasts: Coral Reefs

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Coral Reefs

Click here to see National Geographic coverage on Great Barrier Reef

Coral reefsare some of the most diverse ecosystems in the world. They are home to about 25% of all marine life. Living ridge of biochemically deposited magnesium and calcium carbonate structure in the sea formed by the growth and deposit of coral.

A coral reef represents community of living organisms. It is made up of plants, fish, and many other creatures. These reefs are generally built from a unique type of coral called a hermatypic coral and can only exist in warm ocean water. Hermatypic corals are symbiotic animal.

Only 0.1% of the world’s ocean floor is covered by coral reefs. The reefs grow best in warm, shallow, clear, sunny and moving water.However, they grow very slowly. On an average from 0.3 cm to 10 cm per year.

Location of the warm water coral reefs

The largest coral reef is the Great Barrier Reef in Australia. The second largest coral reef is found off the coast of Belize, in Central America. Other reefs are found in Hawaii, the Red Sea, and other areas in tropical oceans as reef-building tropical corals require warm water and sunlight found in clear, shallow ocean.

Major regions of warm water coral reef

The Coral Triangle (Indo-pacific reef)
The Mesoamerican reef (the Caribbean region)
The East African coast (The red sea region)
South West Pacific reef (Hawaii, Borabora)

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Warm water corals are symbiotic animals, at the risk of coral bleaching

Most reef-building corals have a mutually beneficial symbiotic relationship with a microscopic unicellular algae called zooxanthellae that lives inside the sac of each coral polyp. The algae gives off oxygen and other nutrients that the coral polyp needs to live and in return the polyp gives the algae carbon dioxide and other substances the algae needs. That is why coral reefs grow so near the surface of the water where there is enough sunlight as the algae need sunshine for photosynthesis.

Another byproduct of the symbiotic relationship with zooxanthellaeis color. Several million zooxanthellaelive and produce pigmentsin just one square inch of coral. These pigments are visible through the clear body of the polyp and are what gives many reef-building coral their beautiful color. The greatest threats to reefs are rising water temperatures and ocean acidification linked to rising carbon dioxide levels. High water temperatures cause corals to lose the microscopic algae that produce the food corals need—a condition known as coral bleaching.

The Great Barrier Reef is the largest coral reef. It is made up of over 2 900 individual reefs and 900 islands stretching for over 2 600 kilometers off the northeast coast of Australia. With 76% of the world’s coral species, the Coral Triangle is the planet’s richest centre of marine life and coral diversity.

Cold water coral reefs

Classwork and Article review

Click here to draw the distribution of the Coral Reefs on the given map

Unlike tropical corals, cold-water corals don’t have symbiotic algae living in their polyps so they don’t need sunlight to survive. Click here to read WWF article on cold water deep sea corals.

About half the world’s shallow warm water coral reefs are already gone, and without urgent action to address climate change, pollution, overfishing and destructive coastal development, these natural wonder will disappear in near future. Read WWF article on the threats to the coral reefs.