CHAPTER ONE WHAT IS A CORAL REEF Life surrounds a bright colorful reef in shallow waters off the coast of Australia Fish of all sizes swim in and around the seafloor structures Plantlike organisms stretch upward from what look like giant rocks But the structures are not rocks They too are living organisms They are called corals Corals do not have noticeable body parts such as Corals can come in many shapes colors and sizes 5
Coral polyps use tentacles to catch tiny floating organisms faces or stems But a single piece of coral is made of thousands of creatures called polyps A Closer Look Coral polyps have soft bodies that measure from 0 04 to 0 1 inches 0 1 0 3 cm across Tentacles around their mouths sting and grab tiny organisms that drift past 6
Each polyp protects itself by sitting in a shell-like cup called a calyx The polyp stretches the top of its body out of the calyx This is how it feeds The creature goes into the cup for protection if danger approaches The polyp builds its cup from calcium carbonate This is also known as limestone Limestone makes coral reefs look and feel stony It also gives reef-building corals their name hard corals How Coral Grows As old polyps die in a coral reef their soft bodies go away But their cups remain Over time new polyps grow over the empty calyxes This is how a coral reef grows Over thousands of years layers of new polyps settle on top of layers of old calyxes This means only the outer layer of a coral reef is alive The rest is made of empty cups Corals grow at different speeds The rate depends on the type of coral and the conditions Different types of reef-building corals grow into a 7
