Lab 3: Building a Reef

The lab activity described here was created by Erin Bardar of TERC for the EarthLabs project.

Summary and Learning Objectives

During this lab, students learn about the life cycle of corals, including how they grow and reproduce. Students consider the chemistry of seawater and the importance of the symbiotic relationship between corals and zooxanthellae in the formation of coral reefs. They blow CO2 through calcium hydroxide (limewater) to model how respiration assists coral in precipitating calcium carbonate. Students also build on the coral polyp models they made in Lab 2 to demonstrate coral growth, reproduction, and reef formation.

After completing this investigation, students will be able to:

  • explain the process by which corals extract reef-building material from seawater;
  • describe how corals grow, reproduce, and form reef structures; and
  • build physical models of coral growth, reproduction, and reef formation.

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Context for Use

This activity follows Lab 2: Coral Anatomy, in which students learned about the basic body parts and biological processes of corals. Students will explore additional coral processes to build an understanding of how corals grow, reproduce, and form reef structures. The entire investigation will take approximately two 50-60 minute class periods. Part A is a hands-on wet lab that requires some supplies that should be collected and prepared in advance. Part B includes a few short reading assignments and a modeling exercise using the coral polyp models students made in Lab 2 and additional craft supplies.

Activity Overview and Teaching Materials

Part A helps students understand the roles of photosynthesis and respiration in the formation of skeletal reef material. Students model the precipitation of calcium carbonate from seawater by exhaling carbon dioxide into limewater. The limewater should be prepared at least 24 hours prior to the class meeting (see Teaching Notes and Tips below). Students should work in pairs or small groups for this activity. Each team will need two clear plastic cups (one filled about one third of the way with the limewater and the other empty), two drinking straws, a small (#2) coffee filter, water, white vinegar, and an eyedropper.

The first part of Part B has three short reading assignments that may be assigned for homework. The second half of the activity requires the coral polyp models students made in Lab 2 as well as additional craft supplies for additions and modifications.

Printable Materials

  • Activity Sheet ( and )
  • Reading: How Do Stony Corals Grow?
  • Reading: How Do Corals Reproduce?
  • Reading: How Do Coral Reefs Form?

Teaching Notes and Tips

To prepare the limewater:

  • Place 1 teaspoon of calcium hydroxide in a clean glass jar, up to 1 gallon in size. 1 teaspoon will produce a fully saturated solution whether you use a gallon jar or a smaller one. Since limewater is a saturated solution, there will be some extra chemical that doesn't dissolve.
  • Fill the jar with distilled or tap water and shake vigorously for 1-2 minutes. Let the solution stand for 24 hours.
  • Being careful not to stir up the sediment, pour the clearer solution off the top of the jar through a clean coffee filter or filter paper into another jar.
  • Repeat the filtering step if necessary to obtain a clear limewater solution.
  • Store the final solution in a clean jar or bottle.

Go over all lab safety rules and procedures before beginning this lab. Stress that students should be careful not to ingest anything while breathing through the drinking straws in Part A.


You can assess student understanding of topics addressed in this Investigation by grading their responses to the Stop and Think questions and by evaluating their coral process models.

State and National Science Teaching Standards

Additional Resources

NOAA Facts on Coral Spawning

NOAA info on Coral Skeleton growth and Coral Coring

Types of Hard Coral

Types of Soft Coral