Seaweed Lesson and Use in the Garden

The following is a synopsis of seaweed lessons and materials used for YMCA classes (mixed ages).

Goal: Give students a understanding of the value of seaweed and it’s importance in our Hawaiian economy and culture.
Time: 30 minutes

Basic Plan:

1) Gather students in circle.  Ask them to share what they know about seaweed or ask them to describe seaweed.  Describe/ask about the 3 words: Seaweed,  Limu (Hawaiian name for seaweed) and Algae (botanical name for seaweed).

2) Ask them when they last used a seaweed product? What if I told you that I bet that all of you put seaweed in your mouth this morning?   Seaweed is a key ingredient in toothpaste!

3) Go over the 3 names that you’ll find in common products  that are actually seaweed.   See this lesson for more information.   Kids will try to tell you that seaweed is not in their chocolate or Strawberry Ice Cream! Seaweeds are high in nutrients and minerals. They are used as a biofuel and have some amazing properties that are used in medicines and vitamins.

4) Talk about how seaweed is different from other plants.   What does it need to grow (sunlight, nutrients, water)?  Talk about how it doesn’t get nutrients from the rocks, sand but some seaweeds establish a “holdfast” to keep them from floating away.  But some seaweeds do just float in the water.   Show examples of how some seaweed has “bladder balls” (THEY POP REALLY LOUD!)  that provides buoyancy so the plant grows up toward the surface.

5) Describe the 3 basic colors of seaweed – Green, Brown and Red.  Describe the different sizes and shapes.  Some seaweed is too small to see and some grows over 100 feet tall.  Seaweeds in Hawaii can grow up to 12 inches per week although that is not normal.  The large kelp beds of California can grow up to 2 feet a day!  They cut it weekly to make fertilizers.


6) Show the students how we are going to rinse the seaweed that was collected from the beach.  Remind them that there may be small snails in the seaweed.  We rinse the seaweed to remove the salt before we will put in the garden. Have students take a handful and rinse it,  dunk it again to rinse and put on a screen.

7) Have the kids sort through the seaweed on the screen identifying as many different forms of seaweed as they can. Put the excess seaweed in the buckets for the last step.

8) As they find a new seaweed, have them place it in a container on the table. Observe how the seaweed changes as it it placed in water. Some look like slime but become beautiful underwater. Kids will stuff the bottles if you let them so encourage them to put in just enough to clearly see and identify.

9) If you have older kids and/or more time, have the kids go through the additional resources and identify the different seaweeds. Is it alien, endemic or unknown. Is it edible?

10) Have the students take the buckets of seaweed and toss them around the garden adding great minerals and fertilizer!

Answers to Tough Questions: (Beware)

  • Can I take this seaweed home?  No – Your mom won’t want stinky seaweed!  or   Sure, after we spread it on the garden soil, you can come back with your mom or dad and take home whatever you want.
  • Can I eat this seaweed?  No – even if it is edible, we do not have the correct cleaning facilities for seaweed.
  • Is this a piece of coral? Yes, dead coral is often used by seaweed as a holdfast.  When waves are strong it gets washed up to the beach.  Did you know that coral is actually a colony of small animals (polyps) and has a symbiotic relationship with a special algae (seaweed) called zooxanthellae.  If the algae dies, so does the coral.  This is often referred to as coral bleaching because the coral will turn white.
  • Is this a new seaweed? There is always at least one child who will keep bringing the same type of seaweed up and asking this.  Ask them to describe the color, size and texture of the leaves and make them conclude that it is the same as the last one they brought up.
  • Do fish eat seaweed?  Yes, but not all fish.  Many fish hide in seaweed.  Some even change colors so they are very hard to see when in their favorite seaweed.  Turtles also eat seaweed as well as many crabs, star fish,  and other sea animals.

ADDITIONAL RESOURCES:

Id of Hawaii Seaweeds: http://www.hawaii.edu/reefalgae/natives/sgfieldguide.htm

Id of Edible Limu in Hawaii: http://www.hawaii.edu/reefalgae/publications/ediblelimu/