Initial Publication Date: August 12, 2008

Building a Reef

Part B: Coral Reproduction and Reef Formation

A coral reef is formed by the skeletons of many coral polyps joining together. Fossil records suggest that some of these structures have been around for hundreds of millions of years. In order to understand how reefs are formed, you need to know how coral polyps grow and reproduce.

  1. Read the short NOAA article How Do Stony Corals Grow? to learn more about how individual coral polyps grow, secrete skeletal material, and what forms they take when they join together. Click on the images in the article for additional information and images.

    Checking In

    Answer the following questions to check your understanding of coral growth.

    • Describe the process by which coral polyps grow upward.
    • Besides contributing to the growth of the polyp, what other purpose does the coral skeleton serve?
  2. Read the short NOAA article How Do Corals Reproduce? to learn more about coral reproduction. When you've finished the reading, watch the short video below of a broadcast spawning event.
    NOAA NOS - If the video doesn't play, click the video link that follows the second paragraph in the reading.

    Checking In

    Answer the following questions to check your understanding of coral reproduction.

    • Do corals reproduce sexually or asexually?
    • What are the advantages of mass spawning events in which many corals release their gametes at the same time?
  3. Read the short NOAA article How Do Coral Reefs Form? to learn more about the process by which reefs form and about the different shapes they take.

    Checking In

    Answer the following questions to check your understanding of coral reef formation.

    • What are the three major reef structures?
    • How quickly do coral reefs grow and how long might it take for a reef to form?
  4. Working with a partner or in a small group, come up with a creative way to demonstrate the following coral processes. Use available craft materials to modify, reinvent, or extend the coral polyp model you made in Lab 2. Include as many details as you can to fully describe each process.
    • Demonstrate how a coral polyp grows upward by depositing calcium carbonate.
    • Demonstrate how a single polyp can become a coral colony through asexual reproduction.
    • Put some polyps together and model a coral spawning event. Compare the results of spawning to the results of asexual reproduction.
    • Come up with a way to illustrate the actual size of coral polyps and the number of polyps in a reef. For instance, if a single polyp were as large as your initial model, how large would its coral reef be?
    • Connect multiple polyps together to create a model of a coral head in one of the eight shapes that are characteristic of stony corals.
  5. Paired with another group, or in front of the class, use your models to demonstrate and explain coral reef processes. 

    Stop and Think

    2: Discuss the strengths and weaknesses of each model as well as further ideas for improving them.

Optional Extensions

How Do Corals Build Their Skeletons? - Read about a graduate student studying corals.

Cores From Coral Reefs Hold Secrets of the Seas' Past and Future - Read more about coral cores and the environmental data they hold.

Coral Cores - windows into past climates. Watch this video from the Australian Institute of Marine Science to learn about coring coral and climate.

Coral for Studying Past Climate Video Learn more about proxy data and corals.

Birth of an Atoll - video about how coral reefs form.

Coral Reef Zones - video