The Great Barrier Reef follows the shoreline off the northeastern coast of Australia. It stretches for 1,200 miles, most of it below the surface at high tide. Low tide reveals ridges and islands made of hard jagged stone. The whole region is a menace to shipping for most of the treacherous reef is hidden.
The great reef is called a coral reef because most of it was made by tiny corals, and corals are small sea animals. We can say then that the Great Barrier Reef was created partly by animals. However, plants had a share in the great building project also. Some of the stony material came from seaweeds. These seaweeds are crisp and brittle from stony substances they take out of the water. We call them the stony seaweeds.
The corals build themselves apartment houses from stony materials found dissolved in sea water. Each coral is a small, soft bodied animal. To protect himself, he builds a stony house. And he builds his stony house on a pile of such houses built by his ancestors. In time, the coral apartment house becomes a great pile. In the warm seas where corals thrive, countless varieties of coral pile up their dwellings in one place. Stony sea weeds also thrive in these waters. Together, the plants and animals construct a building that rises from the ocean floor. The Great Barrier Reef is such a building, made by both plants and animals.