Mike Beach, age 13, of Louisville, Ky., for his question:

WHAT IS A CORAL REEF?

Coral reefs are found mostly in tropical and warm seas because reef forming corals live only in water that is 65 degrees Fahrenheit or warmer. Coral is a limestone formation formed in the sea by millions of tiny animals.

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

Fringing reefs are submerged platforms of living coral animals that extend from the shore out into the sea. Barrier reefs follow the shoreline, but are separated from it by water. The Great Harrier Reef of Australia is more than 1,250 miles long.

An atoll is a ring shaped coral island in the open sea. It forms when coral builds up on a submerged mud bank or on the rim of the crater of a sunken volcano. The atoll surrounds a body of water called a lagoon. Many coral islands of the South Pacific Ocean are atolls.