Survival in the Sea

Instructional Objectives
Background Information
Elementary and Secondary Extensions

Topic: Life in the Food Chain

Instructional Objectives:

Students will:

  1. Determine the sequential links in a marine food chain.
  2. Identify the roles that various organisms play in this chain.
  3. Develop charts as visual aids for illustrating marine food chains.

Background Information:

The human need for nourishment is satisfied by eating and drinking. Humans consume both plant and animal matter, making us, like certain other animals, omnivores. Like all animals, however, our bodies are unable to produce the chemicals out of which our tissues are made. Only green plants and certain bacteria can perform the task of converting water, carbon dioxide and nutrients into sugar, protein and other sources of nutrition.

Green plants-which include the marine phytoplankton-use energy from the sun to produce their own food. Plants and bacteria that do this are called primary producers. All animals are consumers. Animals that consume only plant matter are called herbivores. Animals that consume other animals are called carnivores. Those carnivores that eat primary consumers are called secondary consumers. Animals that eat secondary consumers are called tertiary consumers, which in turn are eaten by quaternary consumers, and so on. This sequence comprises the food chain. Scientists classify these levels in the food chain according to trophic levels. Producers make up the first trophic level, primary consumers the second, and so on.

Please refer to the Secrets of the Ocean Realm episode "Survival in the Sea" for more information about food chains.

Activity: Chart Marine Food Chains

Time Needed For Activity: One 45-minute period for construction of visual aids, and one 45-minute period for follow-up discussion.

Target Grade Level: Middle School


  • Poster boards or butcher paper
  • Yardsticks
  • Magic markers
  • Construction paper
  • Scissors
  • Illustrated references on marine life


  1. Divide students into groups and have each group develop a chart using large poster boards or large sheets of butcher paper.
  2. Begin by having students divide charts into four vertical columns and five horizontal spaces using yardsticks and magic markers. Each chart should have the following four column headings written in large, bold letters across the top:
  3. "Production/Consumption Roles" (top of first column)
    "Trophic Level Number" (top of second column)
    "Herbivore or Carnivore" (top of third column)
    "Example" (top of fourth column)
  4. Beneath the first column head, label each of the five Production/Consumption Roles, running down the left margin:
  5. "Producers"
    "Primary Consumers"
    "Secondary Consumers"
    "Tertiary Consumers"
    "Quaternary Consumers"
  6. Draw and cut out illustrations of animals identified in both Cathedrals in the Sea and Survival in the Sea. Add additional organisms using other references in order to fill out the chart. Consider the placement and role of humans.
  7. Place the various animals cutouts in the appropriate "Example" box on the chart. Identify primary producers, primary consumers, secondary consumers, etc. See below for a partial list of animals featured or mentioned in the program.*
* algae, plankton, sardines, mackerel, marlin, birds, sailfish, jawfish, scorpionfish, octopus, shrimp, garden eels, stargazer, grunion, dolphins, sharks, barberfish, chubs, sea turtle

Extension for Elementary:

Have students identify as many types of seafood consumed in their homes or in restaurants as they can. Have them then identify the place in their food chain chart where these seafood sources belong, tracking the food chain backward from human consumer to primary producer. Question to consider: How many levels of consumption does it take to reach the human consumer? What eats and gets eaten along the way?

Extension for Secondary:

Using their charts, have students consider the flow of pollutants through marine food chains. Begin by identifying some sources of marine pollution, including chemical effluents, oil spills, sewage, etc. Have students chart the likely points at which these various types of pollution enter the food chain, and how high a trophic level they are likely to reach. Questions to consider: How likely is it that various types of pollution can get back to their human sources by traveling through the marine food chain? To what extent the pollution in marine food chains threaten human consumers?

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