ocean

A colorful coral reef looks like an underwater rock garden full of fish, but it is actually built bit by bit by millions of tiny living animals over a very long time.

What builds a coral reef?

Q: What builds a coral reef?

Tiny animals called coral polyps. Each coral polyp is a soft, tiny animal smaller than your fingernail that builds a hard little cup of stone around itself. Millions of polyps living together, generation after generation, slowly build the giant, colorful reefs that fish and turtles call home.

Tiny animals called coral polyps ✓
Fish stacking up pebbles
Sand blown in by ocean waves

Tiny animals called coral polyps
Each coral polyp is a soft, tiny animal smaller than your fingernail that builds a hard little cup of stone around itself. Millions of polyps living together, generation after generation, slowly build the giant, colorful reefs that fish and turtles call home.

A coral reef is built by tiny animals called coral polyps, each a soft creature smaller than your fingernail that builds a hard stony cup around its body. Millions of polyps together grow the reef into a colorful home for fish.

Fish do not stack up pebbles to build reefs, and reefs are not made by sand blown in from waves, since neither describes how polyps construct their stony skeletons.

Building a large reef can take hundreds or thousands of years, since each polyp adds just a tiny bit, part of why damaged reefs are slow to recover.

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