Kevin Harris, age 11, of Mesa, Ariz., for his question:

WHAT IS A CORAL REEF?

A coral reef is a formation that is made out of the rocklike accumulation of millions of skeletal remains of a type of tiny marine animal. The animals secrete a kind of calcium that forms a hard cup. It offers the animal an anchor and a place to withdraw for protection.

Coral animals form shapes that look like branching trees or building domes. They can be in a wide variety of colors including green, orange, yellow or tan. As these tiny creatures die, they leave their limestone skeletons which become ridges in the sea called coral reefs.

Reef forming corals live only in water that stays above the temperature of 65 degrees Fahrenheit. They are found primarily in the warm and tropical seas of the South Pacific, in the Indian Ocean, the East Indies and around Madagascar on the southeastern coast of Africa. You'll also find some along the Florida coast, near Bermuda, throughout the West Indies and along part of the eastern coast of Brazil.

Although some types of corals can live in deep ocean water, reef building corals are only found in shallow seas. Light must be able to penetrate the water and reach them.

In the same family of animals that form coral are the hydras, jellyfish and sea anemones. Most of the creatures are less than an inch in diameter but some can grow to be as long as a foot in length. A cylinder shaped body has a mouth at one end that is circled by small tentacles which reach out for food. The other end attaches to a hard surtace.

There are three kinds of coral reefs: fringing reefs, barrier reefs and atolls.

Fringing reefs are platforms of living coral animals that extend from the shore to sea.

Barrier reefs follow the shoreline but are separated from land by water.

Atolls are ring shaped islands of coral that are out in the open sea. Often they form on the rim of a sunken volcano's crater. The atoll surrounds a lagoon.

Some of the world's finest specimens of coral can be found in the Coral Sea, a part of the Pacific Ocean that is located between the northeast coast of Australia, the Solomon Islands and the New Hebrides Islands. In this area are a great many coral atolls and fringing reefs.

The Japanese offensive was checked by United States naval forces for the first time in World War II by a key battle that was fought in the Coral Sea.

Coral polyps form their limestone skeletons by absorbing calcium from seawater. The tiny animals deposit calcium carbonate, which is limestone, around the bottoms of their bodies. As new polyps grow, the limestone base grows in size too and becomes larger.

Coral polyps eat tiny swimming animals, such as the young of starfish.  Algae is an important part of coral reefs. A coral polyp must have algae before it can secrete limestone.  Coral polyps reproduce either from eggs or by budding.