Nearly all life in the ocean is dependent on photosynthetic organisms. Only they and some very specialized organisms have the ability to manufacture their own food. with few exceptions, all animals are dependent on the photosynthetic organisms. Plants produce. Animals consume. Producers form the first link in the food chain. The food chain represents the transfer of energy from one organism to another.

An example of an ocean food web includes: diatoms (phytoplankton) that are the basis of the food web; zooplankton such as copepods and crab larvae may eat other zooplankton and phytoplankton; filter-feeding bivalves such as mussels and cockles filter zooplankton out of the water; codfish eat the bivalves; killer whales and humans eat the codfish. In the ocean, many individual food chains overlap and intersect to form complex food webs. Most marine creatures eat a variety of foods. This flexibility allows them to switch if one link in the chain is depleted.
Food webs usually end with a top predator on which nothing else preys. But, all living things die. Animals eat the dead organisms, and then bacteria and fungi attack and decompose the remains. Currents may carry the nutrients back to the surface where phytoplankton use them in photosynthesis.
  • Students construct a typical ocean food web using string and cards

One "Food Web Card" for each student, String (long enough to make a loop to go over a student's head), Index cards, Marker, Hole punch, Yarn or string

  1. Make enough "Food Web Cards" so each student will have one card.
  2. Organize your class into a circle.
  3. Hand one card to ech student to hang around his / her neck. Have each student familiarize himself / herself with their card. Is their organism an herbivore (plant-eater)? A carnivore (animal-eater)? Omnivore (eats plants and animals)? A producer (i.e., photosynthesizes)?
  4. Give the end of the yarn or string to the "Sun" person. Discuss why the food web begins with the sun.
  5. The students decide which organisms depend on the sun. Pass the yarn to one "producer" and back to the sun; then to another producer and back to the sun.
  6. Then pass the yarn from herbivores back and forth to the producers. Each herbivore should say something about what they eat and their role in the food web.
  7. Then pass the yarn from herbivores to the predators that prey on those herbivores. Again, each organism should announce its role in the food web.
  8. Eventually the yarn will pass to the top predators. They should describe to the class how they are dependent on the other organisms. When each student has had the yarn passed to him / her at least once, the game stops. Note how interconnected everyone is.
  • The teacher may introduce an environmental problem into the food web. What is the impact of a pollutant such as plastic bag (which may be eaten by a sea turtle who mistakes it for a jellyfish)? How does that compare with the impact of six-pack rings? how that compare with the impact of a fishing net that catches all the fish? And finally, how does that compare with the impact of a pollutant such as an herbicide that kills all the phytoplankton?
Adapted from Sea Soup Teacher's Guide: Discovering the Watery World of Phytoplankton and Zooplankton, Copyright 1999, by Betsy T. Stevens, Tilbury House, Publishers. Inquiry-based activities for use with Sea Soup: Phytoplankton and Sea Soup: Zooplankton, children's picture books by Mary R. Cerullo, photography by Bill Curtsinger, Tilbury House, Publishers