Question

what are corals? Briefly explain the different types of coral islands.

Answer 1

A coral island is a type of island formed from coral detritus and associated organic material. They occur in tropical and sub-tropical areas, typically as part of coral reefs which have grown to cover a far larger area under the sea. 
There are two completely different kinds of origin of reef islands: uplift and accretion. In the first, part or all of a reef system may become land as a result of crustal movements raising it above sea level (e.g., the Aldabra Islands in the western Indian Ocean). The previously submarine reef top becomes a low plateaulike feature, and such islands are typically rocky, with cliffs, and with land surfaces pitted and sculptured by solution weathering (karst). They are often still recognizable as atolls with a lagoon, now much shallower or even completely dry, as an interior basin. If present sea levels were to fall again, as they have done in the recent geological past due to an increase in polar ice, most of the world’s coral reefs would, in effect, become raised features. It is only because present sea levels are the highest for many thousands of years that there are no raised reef islands of this kind now.

Answer 2

They are plant -kind things in water