Question

What are atolls?
A) They are rectangular coral reefs
B) They are circular or horse-shoe shaped coral reefs
C) These are triangular coral reefs
D) None of the above

Answer 1

Hint:
India has a vast mainland. Besides this, the country also has two groups of islands which are the Lakshadweep Islands group lying close to the Malabar coast and the Andaman and Nicobar Islands located in the Bay of Bengal extending from north to south.

Complete Answer:
Short-lived microscopic organisms that live in colonies are called Coral polyps. They thrive in warm, shallow, and mud-free water. They also secrete calcium carbonate. Their skeletons and coral secretion form coral deposits in the form of reefs. Majorly these reefs are of three kinds: Atolls, Barrier reefs, and fringing reefs. The Great Barrier Reef in Australia is a great example of the first kind of coral reefs. New Hebrides Society Islands off Australia and off the southern coast of Florida.
The Atoll reefs are circular, horse-shoe shaped, or ring-shaped coral reefs, including a coral rim that encircles a lagoon partially or completely. On the rim, coral islands or cays may be there. Originally, the typical atoll was formed as an oceanic volcano. As a result, a coral reef formed around the shore of the volcano, and then over several million years, the volcano subsequently eroded and subsided completely beneath the surface of the Ocean. A lagoon has formed over the place of the former volcano and the reef and the small islets on top of it are all that is left of the original island. The coral reef must be maintained at the sea surface, with coral growth matching any relative change in the sea level for the atoll to persist.

Thus, option (B) is correct.

Note:
Most atoll reefs can be found in the Pacific Ocean where the waters are warm and salty. More animals are found in an atoll reef than in the other types of coral reefs.