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Procedure

1. Introduce the term “food chain” to the students. Have the students think of an animal from an environment they are familiar with, such as the ocean, and then construct a food chain around the animal. For example, the students might suggest a shark. From there they might suggest that a shark would eat a smaller fish, the fish would eat a shrimp and the shrimp would eat algae (seaweed). Write their responses on the board so the students can see how the animals link in the food chain.
2. Explain to students that one of the reasons we eat food is to provide energy (calories) for our bodies. This energy passes from one organism to another through a food chain. Ask the students to discuss where the energy comes from that travels through the food chain. For hints, think about how plants get the energy to make food and what provides energy for our entire planet (Answer: the sun). Ask them if all of the energy made by the plants will make it the entire way through the food chain? Is there a point in the food chain where energy no longer gets passed along?
3. In the classroom, divide the class into 6 groups. Groups will be divided up as follows: 18 students will be diatoms, 4 students will be fiddler crabs, 4 students will be marsh snails, 2 students will be blue crabs, 2 students will be diamondback terrapins, and 2 students will be river otters. Adjust the numbers of each group proportionately, according to class size.
4. Pass out signs. Review with the students whom they will be eating in the game and who will eat them. (Fiddler crabs and marsh snails will eat diatoms. Blue crabs will eat marsh snails. Diamondback terrapins will eat fiddler crabs and marsh snails. River otters will eat diamondback terrapins and blue crabs.)
5. Pass out the paper bags with holes in the bottom to each student before the activity begins. The size of the hole should be between the sizes of a quarter and a half dollar. Explain to the students that the objects such as popcorn that falls out of the bags as the game progresses represents energy used by the organism in its life processes (energy used for moving, growing, etc.) or energy in indigestible form, like the energy caught up in bones, and therefore is energy that cannot be transferred to another organism when it is eaten, because it has already been used or lost.
6. Designate an area in the classroom or outdoors as the “salt marsh tidal creek habitat” (an area of at least 15 feet by 15 feet). Have the students stand on the outside of the area in their groups. This activity can be a high-energy event for the students. Set ground rules about running and jumping. The students should walk around in the habitat area or hop on one foot. Also, make sure the students know that they do not need to tackle other students. They only need to tag their prey, take its "stomach" bag and empty the contents into his/her own bag.
7. Start the activity by having the diatoms from both groups enter the habitat area, spread out and sit down (in the saltmarsh the diatoms rest on the bottom).
8. Assign an adult to be the sun. The sun should walk through the habitat area and drop the popcorn or other objects into the bags of the diatoms. The objects represent the sun's energy falling down to the diatoms. If possible, before the activity, count the total number of objects or cups of objects that will be used in the activity. The amounts of “original energy” and “energy in the otters' stomachs’” can be used in a math follow up activity.
9. As the diatoms catch the objects have them say "producer," to remind them that they are the only organisms in this food chain that can  produce food from the sun's energy.
10. Allow the primary consumers from each food chain, the marsh snails and fiddler crabs, to enter the habitat area and tag one or two diatoms (no more than three). Have the snails and crabs say "primary consumer" as they "eat" a diatom and empty their "stomach" bag, because they are the first organism in this food chain to get their food by eating another organism.
11. The diatoms leave the habitat and the secondary consumers, the diamondback terrapins and blue crabs, enter the area and tag the primary consumers. Have the terrapins and crabs say "secondary consumer" as they "eat" a primary consumer.
12. The primary consumers leave the habitat area and the apex consumers, the river otters, enter the area and tag the secondary consumers. Have the otters say "apex consumer" as they "eat" a secondary consumer.
13. After all of the members of the food chain have “eaten” everyone gather in the “salt marsh habitat area.” They should sit down, pretend to die and rot away. The pretend bacteria will then have their turn at being a part of the food chain by decomposing the students.
14. While students are “decomposing,” review the elements of the activity with them. Also pose questions to the students, such as: Where does the energy come from? Can a food chain exist without the sun? Can a food chain exist without producers? How much energy was lost during the activity (measure the objects in the otters’ stomach bags and compare it with the original amount of objects given to the diatoms)? Does all the energy made by the diatoms (the producers) make it to the river otters (the apex consumers)? Is this what happens in a real food chain? If the river otter was the apex consumer in a community and blue crabs were the secondary consumers and the main prey of the river otter, would there be more blue crabs or more river otters in that community? Why?

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Follow-Up Questions

• In a salt marsh community, are there more organisms than the six organisms discussed in this activity? Would a river otter be able to eat other animals besides diamondback terrapins and blue crabs?
• In a community, are you always going to have the same food chain, or can you have many different ones?
• What is a food web?