In a simple food chain, the primary way the sun's energy and atmospheric carbon dioxide (CO2) gas is transferred to the marine ecosystem is through a relatively simple chain of interactions: phytoplankton convert CO2 into organic carbon via photosynthesis, zooplankton get carbon by consuming phytoplankton, small fish eat zooplankton, bigger fish prey on small fish, and so on.

The complexities within food webs makes it difficult to predict exactly how other organisms may be affected. In general, however, it is well known that toxic algae (i.e., some phytoplankton) can pose serious risks to other organisms, even those human and other animals "way up the food chain."
NOTE: An interesting related activity is "Where's the energy going?"
  • Players will understand how toxic algal blooms may affect simple food chains
  • Students will recognize the consequences of Harmful Algal Blooms (HABs)


White and red pipe cleaners: two-thirds white and one-third red (or use "Phytoplankton" cards, marking one-third with red ink), 1 small paper or plastic bag for each "student copepod", armband (or "Copepod card") for each "student Copepod," armband of different color (or "Herring card") for each "student Herring," armband of different color (or "Seal card") for each "student Seal"

You may wish to issue "Food web cards" for your students to wear instead of armbands. You can download an Adobe Acrobat Reader version of the cards by clicking here. You'll need to make several copies of the phytoplankton, copepod and herring cards.
  1. Review the concept of food chains, if needed.
  2. Divide the players into three groups. In a class of 26 students, there would be two Seals, six fish, and eighteen copepods (a type of zooplankton). Work with approximately three times as many copepods as herring, and three times as many herring as seals. Note it would take many times more plankton to satisfy a herring, however! Give each group an identifying label (e.g., various color armbands or "Food Web Cards.").
  3. Hand each copepod a small paper bag. The bag represents each copepod's "stomach."
  4. With the players eyes closed, or otherwise not watching, distribute the pipe cleaners out in a large open playing space.
  5. Give the players their instructions. The copepods are the first to go find food. The herring and seals are to sit quietly on the sidelines watching the activity. The copepods have 30 SECONDS to gather, or "eat," as much phytoplankton (e.g., pipe cleaners or "Food Web Cards") as they can. At the end of 30 seconds, they must stop gathering.
  6. The herring are now allowed to "hunt" the copepods. The seals are still on the sidelines. Give the herring between 15- 60 seconds to hunt depending on the size of the area. Each herring should have time to catch one copepod. Any copepod caught by a herring must give his or her bag of phytoplankton to the herring and then sit out.
  7. Then release the seals to "hunt" herring. The same time limit and rules apply. Any herring still alive should continue grazing copepods. Copepods should still prey on phytoplankton. If a seal catches a herring, then the seal gets the food bag and the herring goes to the sidelines. At the end of the designated time, ask all players to come together, in a circle and bring their food bags.
  • Ask the players to go through their food bags and count the number of white markers and the number of red markers.
  • Inform the students that some of the phytoplankton were toxic: i.e., all of the red markers (i.e., pipe cleaners or marked "Food Web Cards").
    • Any copepod still alive may now be considered dead, if he/she has any red markers in his/her food supply.
    • Any herring with half or more of its food supply colored red may be considered dead.
    • The seal with the fewest number of red pieces is "sick," and the one with the most may be considered dead.
  • Record the numbers for use in discussion about the activity:
    • How many Seals survived?
    • How many Herring survived?
    • How many Copepods survived?
  • Discuss what conclusions can be learned from this activity.
  • (OPTIONAL) Switch roles and food choices.
Adapted from the Western Regional Environmental Education Council, Copyright 1983, 1985