Lesson 6: Lethal Legacy*

Lesson Information

Summary: Students role-play species in an Arctic Ocean food chain to illustrate the bioaccumulation of contaminants.
Duration: 45 to 60 minutes
Group size: One group of 20 to 40 students
Materials: At least 40 tokens in four colours per student (coloured beads, marbles, bread bag tags, coffee or popsicle sticks); hoops (one per four students); paper cups, envelopes, or sandwich bags (one per student); armbands or headbands (one per five students)

Learning Outcomes

Students will be able to describe the process of bioaccumulation of contaminants and identify threats to ocean communities, including people.

Background

One of the greatest problems with some contaminants is their tendency to build up and cause toxic effects in wildlife. This process, known as "bioaccumulation" (see Teacher's Notes), can result from contaminants carried through water, food, or air, often originating from more than one source. The contaminants that bioaccumulate most are those that cannot dissolve in water but can dissolve in fats and oils, for example, dioxins and PCBs. More of these contaminants are found in fatty tissues, such as the liver, than in muscle tissues. As a result, older organisms have higher concentrations of certain contaminants, and with each trophic level in the food chain (each link from the bottom to the top), the concentration increases.

Arctic ecosystems are especially vulnerable to contaminants because:

• biodiversity is more limited here, and many northern species have low reproductive capacities;
• the long length of Arctic food chains makes them susceptible to bioaccumulation and disruption if any of the links are damaged;
• many Arctic species are long-lived, and contaminants have a long time to biaccumulate in them;
• many contaminants are found in fatty tissues, which, due to the temperature-regulating properties of fat, make up much of the mass of species, such as seals, whales, and polar bears, at the top of the Arctic food chain; and
• there is high per-capita human consumption of wildlife in the North.

Pollutants from communities worldwide are carried to the Arctic by air, rivers, and oceans. Their transfer from sea water to organisms begins with the contamination of ice algae, or phytoplankton, living in surface ocean waters and on sea ice. Contaminants are then transferred up the food chain, more or less as follows: phytoplankton are eaten by zooplankton, such as copepods, the main food of arctic cod. Arctic cod are eaten by ringed seals, beluga whales, narwhals, and some seabirds. Polar bears, at the fifth trophic level, feed mostly on ringed seals. Northern people, who consume local wildlife as a large part of their diet, join the polar bear at the top of the Arctic food chain.

Procedure

1. Explain to your students that this activity is a simulation of part of the Arctic Ocean food chain. Explain how a food chain works and provide the example described in "Background" above.
2. Divide the class into two groups, one four times larger than the other (for example, in a class of 25, there should be a group of five and a group of 20). The smaller group will role-play arctic cod. The larger group will role-play copepods. Identify each arctic cod with an armband or headband.
3. Select a playing area with a definite boundary, such as a baseball diamond, basketball court, or similar-sized area marked off with rope, to represent an Arctic Ocean habitat. Place five hoops randomly inside this area. Scatter the coloured tokens (representing plankton) around the habitat.
4. Give each fish a small paper cup, envelope, or sandwich bag to represent its stomach.
5. Explain the rules of the role-play as follows. When released into the habitat, the copepods begin to eat plankton tokens by putting them into their cups (stomachs). The cod concentrate on capturing copepods. Any copepod that is tagged by a cod has been eaten and must empty all its plankton tokens into the cod's cup. Since copepods are much more numerous than cod, captured copepods remain in the habitat and continue hunting for plankton. A cod must capture at least one other copepod before it can capture the same one again. The hoops throughout the playing area represent protective cover for copepods, who can hide from cod by standing with both feet inside a hoop. However, a hoop can only protect two copepods at a time.
6. Continue the lesson until there is a severe shortage of plankton, at which time students should stop and sort the tokens in their cups, counting the total of each colour.
7. Inform students that some of the plankton are contaminated by a toxic chemical that is now in their bodies. The chemical is represented by one colour of token (preselected by you). This contaminant has been in the ocean for a long time and has moved up through the food chain. Have students compare tokens and note that larger fish (the ones that have consumed the most) often contain the greatest amount of contaminants. Explain that in the Arctic, dioxins and PCBs are two contaminants that bioaccumulate in animal tissues. Have students hypothesize how these chemicals might end up in the Arctic.
8. Discuss the activity, emphasizing the following points:
• These contaminants originate in products used in human communities and travel by air, rivers, and ocean currents.
• They bioaccumulate as they rise from the bottom to the top of the food chain.
• They threaten the health of animals near the top of the food chain (including people).

Arctic communities are very susceptible to these contaminants.

Evaluation

Have students draw a "flow chart", tracing the path of a contaminant through a food chain and explaining the reason for different amounts of the contaminant at each level.

*This lesson has been adapted from learning activities in Project WILD and Fish Ways activity guides.