Atoll

When does an atoll take shape?

An atoll or coral reef begins to form when tiny marine animals called coral polyps attach themselves to rocks on the sea bed. The reef, which eventually takes the shape of a ring or horseshoe enclosing a lagoon, is made up of the lime-based skeletons of innumerable polyps.

After building skeletons round themselves, coral polyps produce new polyps, which in turn surround themselves with skeletons. The young polyps remain attached to the parents so that succeeding generations combine to produce a great mass of coral.

Atolls occur only in shallow water where the temperature if over 65° Fahrenheit (18.3° Centigrade). They are found in the West Indies, the Indian Ocean. Along the coast of Brazil and, notably, in the Pacific North-east of Australia huge reefs have formed and some atolls may stretch 40 miles in diameter and more than a thousand feet in depth.