Strange forests lurk beneath the waves of sunny California. These underwater forests have no trees, however. Their canopy is provided by enormous seaweed: kelp.

Kelp forests are dominated by two species of the seaweed: giant kelp and bull kelp. Giant kelp and bull kelp share many features: holdfasts, stipes, pneumatocysts, and blades.

Read the information in the photo gallery to learn more about these unusual features, and answer the following questions.

  1. What is a stipe?

    • Answer

      A stipe is the kelp's thick, hollow stalk or stem.

  2. What is a pneumatocyst?

    • Answer

      A pneumatocyst is an air-filled sac that keeps the kelp buoyant.

  3. What is a blade?

    • Answer

      A blade is the thick, ridged, leaf-like structure where a kelp absorbs sunlight and oxygen for photosynthesis.

  4. What is a holdfast?

    • Answer

      A holdfast is the strong, root-like structure that attaches the kelp to the rocky substrate.

  5. What is a thallus?

    • Answer

      A thallus is the body of a plant-like organism that is not differentiated into roots, stems, or leaves. Algae, fungi, and lichen are composed of thalli.

  6. What are the differences between giant kelp and bull kelp?

    • Answer

      They have different arrangements of pneumatocysts and blades.

      Bull kelp has a single pneumatocyst on its stipe. The pneumatocyst holds many blades.

      Giant kelp has many pneumatocysts on its stipe. Each pneumatocyst holds a single blade.

  7. What species of kelp is more likely to wash up on the beaches of Vancouver Island, British Columbia, Canada? On the beaches of San Diego, California?

    • Answer

      Bull kelp is more common around Vancouver, while giant kelp is more common around San Diego.

blade
Noun

large, flat, leaf-like structure on some seaweeds.

buoyant
Adjective

capable of floating.

canopy
Noun

one of the top layers of a forest, formed by the thick leaves of very tall trees.

corrugated
Adjective

bent into rigid folds.

Noun

steady, predictable flow of fluid within a larger body of that fluid.

Noun

irregular, recurring weather system that features a warm, eastern-flowing ocean current in the eastern Pacific Ocean.

holdfast
Noun

root-like structure that attaches the kelp thallus (body) to the rocky substrate.

Adjective

characteristic to or of a specific place.

kelp
Noun

type of seaweed.

Noun

substance an organism needs for energy, growth, and life.

Noun

process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars.

pneumatocyst
Noun

air-filled sac that makes kelp buoyant.

seaweed
Noun

marine algae. Seaweed can be composed of brown, green, or red algae, as well as "blue-green algae," which is actually bacteria.

stipe
Noun

stem-like stalk that supports vegetative structures such as a mushroom cap.

storm
Noun

severe weather indicating a disturbed state of the atmosphere resulting from uplifted air.

substrate
Noun

base of hard material on which a non-moving organism grows. Also called substratum.

thallus
Noun

body of some plants and plant-like organisms, not differentiated into roots, stems, or leaves.

Noun

rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.