Cathedral in the Sea

Instructional Objectives
Background Information
Elementary and Secondary Extensions

Topic: The kelp forest community.

Instructional Objectives:

Students will:

  1. Identify the principal parts of a giant kelp plant.
  2. Construct a model giant kelp plant based on the above information and images viewed in the program.
  3. Construct cutouts of kelp forest inhabitants based on field-guide photographs.
  4. Place animal cutouts in their appropriate positions on or near the plant.
  5. Discuss the relationships among kelp forest inhabitants and their relationships to the giant kelp plant.

Background Information:

In the cool, coastal waters of California there are submerged forests of a marine algae known as kelp. Growing as much as 2 feet a day, giant kelp is one of the fastest growing plants in the world. Reaching lengths of more than 100 feet, it is also one of the largest. The giant kelp plant has long, sinuous stipes-stems that are supported by gas-filled bladders located at the base of each leaflike blade. The plant is anchored to rocky bottoms by its holdfast, a rootlike mass of tangled haptera.

The kelp-forest community contains a number of individual habitats varying with depth. From the canopy, where the tangled plants can be seen lying along the water's surface, to the bottom as much as 130 feet below, the kelp forest is home to a surprising variety of creatures. While many fish species can be found swimming among the stipes and blades, many more invertebrates shelter and feed amid the tangles of the kelp's holdfast.

Please refer to the Secrets of the Ocean Realm episode "Cathdral in the Sea" for more information about kelp.

Activity: Construct A Model Kelp Forest

Time Needed For Activity:One 45-minute period to construct giant kelp plant, one 45-minute period to cut out paper animals and one 45-minute period to place all together-while conducting discussion-for an accurate representation of the kelp-forest community.

Target Grade Level: Middle school


  • Two rolls of 30-inch by 15-foot brown parcel paper
  • Tablets of 12-inch by 18-inch colored construction paper
  • Scissors
  • Tape
  • Pencils
  • Photographic references (recommend the National Audubon Society Field Guides to North American Seashore Creatures and Fishes of the Pacific Coast.)
  • Styrofoam blocks
  • Spray paint


  1. Begin by drawing a giant kelp plant on blackboard or another large-format, visual aid surface.
  2. Use drawing to instruct students in the anatomy of a giant kelp plant, labeling the principal parts: holdfast, haptera, stipe, bladders, blades and canopy.
  3. After students are familiar with the giant kelp plant structure (reviewing the program will reinforce this familiarity), have them begin to draw outlines of these structures in pencil on the unrolled brown parcel paper. Students should work in teams, each team assigned a part of the plant. Be sure that they use the full lengths of both rolls to draw the plant's stipe. This will produce a 30-foot plant (the width of the stipe should be a couple of inches). For an accurate depiction of a healthy plant, there should be scores of blades, each with a bladder at its base. Average length of each blade should be about one foot.
  4. Cut the drawn parts out and begin to assemble them by first hanging the stipe on a wall or another tall display surface, then attaching the various parts.
  5. Extend the canopy along the ceiling-representing the water's surface-joining the canopy to the stipe at the point where the wall meets the ceiling.
  6. Carve styrofoam blocks into large rock shapes and paint them accordingly. The rocks should be piled at the plant's base and the holdfast (about 2 feet across) attached to the rockpile.
  7. Using the field guides as references, students should draw and cut out the various kelp-forests' inhabitants using the colored construction paper. As depicted in the program, these animals include: garibaldi, senoritafish, halfmoon perch, octopus, moray eel, sea cucumber and sea urchin. Use average sizes cited in reference guides to determine scale. Draw to full scale.
  8. Attach the animals to the kelp plant in the proper positions, referring to the program. Fishes should "swim" among the blades and beneath the canopy (they can be suspended from the ceiling), while invertebrates should be placed among the rocks and on the holdfast.


As construction proceeds, lead the teams in discussions of one of the program's central themes: the function of the kelp forest as habitat. Encourage students to consider how the plant's structure works to provide shelter and hunting grounds for the resident creatures.

Extension for Elementary:

Have students consider and write a list of similarities between the kelp forest and land forests. Questions to consider: How is a giant kelp plant similar to a tall tree? How do fishes and other animals find food and shelter among the kelp plants in ways similar to birds and other forest animals that inhabit woodlands?

Extension for Secondary:

Like many other seaweed, giant kelp is harvested as a commercial resource. The natural compound algin, extracted from the kelp plant, is used as a thickening, stabilizing and smoothing agent in hundreds of products ranging from salad dressings to cosmetics. Have students identify such products containing algin in their homes or at the supermarket and report on their uses.

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