Coral reefs are made of living creatures and their bony skeletons. Scalefin anthias swim in a coral reef off the coast of Egypt.

A giant green turtle rests on a reef near the island of Sipadan, in the Celebes Sea.

Purple fairy anthias and orange anthias pass through a reef off the coast of Fiji, in the South Pacific Ocean.

Surprise! A ribbon eel pops out of a hiding place in the Great Barrier Reef, off the northwestern coast of Australia. The Great Barrier Reef is the world’s largest coral-reef system. The reef stretches for more than 1,600 miles. About 1,500 species of fish live there.

Starfish rest on a reef where a diversity of fish, coral and other animals thrive.

A colorful coral reef teems with life off Miyako Island, Japan.

Divers swim above a bed of dead corals off Malaysia’s Tioman Island, in the South China Sea. Overfishing is a big killer of corals. Other culprits are pollution and rising global temperatures.

Coral lies dead on the reefs near the Maldive Islands, in the Indian Ocean.