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Place 01 · The Great Barrier Reef · Chapter 1 of 7
An Animal Built This
It is 1,400 miles long, it is alive, and it was made by something the size of a pinhead.
About 15 minutes · 1 video · 1 3D model · 3 quick activities
Start here
A soft animal with no brain and no bones built this
You can see it from the International Space Station. It was not built by machines, or by people, or by anything you would call geology. It was built by a soft animal with no brain and no bones, one microscopic layer at a time, for about eight thousand years.
Watch this
See it move
Khaled bin Sultan Living Oceans Foundation — How Corals Eat. Two minutes. These look like plants right up until the moment they start eating.
While you watch, look for
- Where the food goes once a tentacle catches it
- How many polyps share one colony
- Something you did not expect. Hold onto it.
The short version
Three things going on here
The animal
A polyp in a stone cup
Each polyp is a soft sac with a ring of tentacles, like a tiny sea anemone that built itself a limestone house and never leaves.
The structure
Mostly a graveyard
The reef is a limestone apartment block. Only the outer skin is alive. Everything underneath is the skeletons of the generations before.
The clock
8,000 years of work
The living reef started growing about 8,000 years ago, when the sea rose at the end of the last ice age and flooded the shelf it sits on.
Photos: laylia, Liisa Tervinen, Leonardo Lamas / Pexels
Play with it
Hold a real coral skeleton
This is a 3D scan of a real coral skeleton from the Smithsonian’s collection. This kind, bird’s-nest coral, grows on the Great Barrier Reef. Drag to spin it, scroll to zoom in, and look for the tiny cups where each polyp lived.
3D model: Seriatopora hystrix, Smithsonian Institution, on Sketchfab (CC0 public domain).
Two questions to answer while you are in there
- Zoom all the way in. How many tiny cups can you count on one branch?
- Each cup held one polyp. Roughly how many animals built this one skeleton?
Try it yourself
Check yourself
Try it
How Big Is Big?
Eight flip cards. Guess the answer before you flip: how long, how old, how many, and how small.
Try it · interactive
Reef Scale Slider
Slide through trips you already know and see how they stack up against the reef.
Open the Reef Scale Slider in its own window (opens in a new tab).
Words you will hear
Four terms, that is all
Polyp
The individual coral animal
Colony
Many polyps sharing one skeleton
Calcium carbonate
The limestone corals build with
Barrier reef
A reef separated from shore by a lagoon
Check your understanding
Practice the whole chapter
Everything in this chapter, in eight quick questions. Retry as often as you like. Read the feedback on every answer, right or wrong, because that is where the learning is.
Practice
Practice: An Animal Built This
Eight questions covering the video, the three cards, the four terms and the interactive above.
If you want more
Go deeper
- Webb 4.10 — Coral Reefs — LibreTexts · 6 minutes · the assigned reading
- Tropical Marine Biology 1.2–1.4 — Coral Reefs: An Introduction — LibreTexts · optional
Photo credits (Pexels): SlimMars 13, Jiří Mikoláš, laylia, Liisa Tervinen, Leonardo Lamas.
Hop to:
← The Great Barrier Reef — place overview
All Places
- The Great Barrier Reef
- Monterey Bay
- The Galápagos
- The Ridge and the Trench — in development
- The Southern Ocean — in development
- The North Pacific Garbage Patch — in development