Krill, a thumb-sized, shrimplike animal, is a keystone species in the Antarctic ecosystem. In recent years, scientists have discovered evidence of declining krill populations, which could spell big trouble for other animals that depend on it for food. This lesson asks students to investigate the importance of krill to the Antarctic ecosystem by researching the animals that depend on it and drawing a food web. They will conclude by writing paragraphs explaining the potential consequences of a decline in krill populations.

Geography, life science

Standard 8: "The characteristics and spatial distribution of ecosystems on Earth's surface"

Two hours

• Computer with Internet access
• Writing and drawing materials

Students will

• read and answer questions about krill;
• research Antarctic animals and take note of each animal's place on the food chain;
• draw an Antarctic food web, using the animals they have researched; and
• write paragraphs explaining the potential consequences of a decline in krill populations.

Show students this picture of krill (click on "Krill"). Then have them look at this picture of a leopard seal. Explain that the krill, a thumb-sized crustacean, is crucial to the survival of this large seal. Have students explain why they think this would be the case.

Have students go to National Geographic's SeaLab—Antarctica. Ask them to read this page and the page about krill (click on "Krill").

Ask students to answer these questions in writing:

• What are krill?
• Why are they important in the Antarctic ecosystem?
• Why are their populations in trouble?

Explain to the class that, in addition to overfishing, krill populations may be declining due to global warming. This phenomenon has reduced sea ice and therefore reduced populations of the algae and phytoplankton that krill eat.

Write the names of the following Antarctic animals on the board, and have students copy the list on their own paper: emperor penguin, Adélie penguin, leopard seal, crabeater seal, Weddell seal, humpback whale, orca, pelagic fish, skua, plankton, krill. They should be sure to leave about 1/4 of a page under each species so they will have room to take notes.

Divide the class into small groups or pairs, and have them research the animals on their list. The following Web sites will help them get started:

National Geographic: SeaLab—Antarctica
National Geographic News: Penguin Decline in Antarctica Linked to Climate Change
70 South: Antarctic Animals
Australian Antarctic Division: Antarctic Wildlife

As students go through the sites, ask them to answer these two questions for each species:

• What does this species eat?
• What other species eat this species, if any?

Have students use pencils and paper to draw a simple Antarctic food web about the animals they have been exploring. They should place krill at the middle of the web and the other species on other parts of the page. Ask them to write each species' name in a circle or box and draw an arrow from that species to the species it eats.

Students' diagrams should have an arrow from krill to plankton and arrows from all other species to krill. Additionally, they should have drawn arrows between several of the other species, including an arrow from the emperor penguin to the fish, and the leopard seal to the penguins and the crabeater seal.

Have a class discussion about the importance of krill in the Antarctic ecosystem.

Have students write paragraphs answering this question: "What might happen to the Antarctic ecosystem if krill populations decline?" Ask them to name at least five species besides krill and explain the chain of events that could occur.

• Have students read the information at these Web sites:
  
  National Geographic News: Camera-Fitted Seals Spy Antarctic Sea Life
  The Why Files: SealCam
  
  Ask them to write paragraphs describing how this camera technology is being used and predicting what the cameras might teach us about Antarctic life, including seals and krill.
  
  
• Have students research two of the most ferocious predators of the Antarctic, the leopard seal and the killer whale (orca). Ask them to write paragraphs answering these questions: What roles do these species play in the Antarctic ecosystem? How might these species be affected by declining krill populations?

70 South: Antarctic Animals
Australian Antarctic Division: Antarctic Wildlife
National Geographic News: Camera-Fitted Seals Spy Antarctic Sea Life
National Geographic: SeaLab—Antarctica
The Why Files: SealCam