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Food Web

Grade Level(s): 3-5
Time: 30-45 minutes
Group Size: 10-30

NYS Learning Standards Core Curriculum

Standard 4: Living Environment
Students will: understand and apply scientific concepts, principles, and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science.

  • Key Idea 5: Organisms maintain a dynamic equilibrium that sustains life.
  • Key Idea 6: Plants and animals depend on each other and their physical environment.

Summary

Students will be introduced to some of the organisms in an aquatic ecosystem. The concept of food webs and the many roles organisms play as consumers, producers, and decomposers will be introduced. Students will participate in an activity to learn how humans play a role in the aquatic food web as anglers and consumers.

Objectives

  • Students will be able to identify 1-3 fish specific to fishing site
  • Students will be able to construct an aquatic food web
  • Students will be able to explain how humans play a role in the aquatic food web
  • Students will be able to identify species as producers, consumers, or decomposers

Materials

Vocabulary

  • Abiotic Factors - non-living aspects; i.e., water, sunlight, rocks, oxygen
  • Autotrophs - producers; those that produce oxygen through photosynthesis; i.e., plants
  • Bioaccumulation - the increase in concentration of a chemical or substance in an organism's body from intake (respiration or ingestion) to which the level of concentration is higher than the surrounding environment (the higher in the food chain an organism is, the higher the concentration levels of toxins will be).
  • Biotic Factors - living aspects of the environment; i.e., plants and animals
  • Carnivores - feed solely on other consumers, meat eaters
  • Consumers - see heterotrophs
  • Decomposers - consume dead organisms; heterotroph; i.e., bacteria, some insects, and fungi
  • Ecosystem - community of organisms and their environment; working together
  • Food Chain - an arrangement of the organisms of an ecological community according to the order of predation in which each uses the next usually lower member as a food source
  • Food Web - interactive food chains in an ecosystem
  • Herbivores - primary consumers; feed solely on plants
  • Heterotrophs - consumers; those that cannot perform photosynthesis; use organic substrates to get energy; i.e., herbivores, carnivores, and decomposers
  • Omnivores - feed on both plants and other animals
  • Overfishing - when so many fish are taken from a stock that the population is unable to recover
  • Photic - sunlit portion of the water
  • Phytoplankton - microscopic free floating aquatic plants that live in the water
  • Plankton - tiny free floating aquatic organisms that live in the water
  • Primary Consumers - see herbivores
  • Producers - see autotrophs
  • Secondary Consumers - carnivores, omnivores, and decomposers
  • Tertiary Consumers - top predators of an ecosystem
  • Zooplankton - tiny free floating aquatic animals that live in the water

Background

Every living organism needs energy to sustain life. Organisms within a community depend on one another for food to create energy. The simplest of these feeding relationships is referred to as a food chain. A food chain is a linear arrangement of at least three organisms in which each uses the organism below as its food source. Within an ecosystem, there are many interactive food chains which create a food web. Both abiotic and biotic factors are involved in food webs.

Biotic Factors

At the base of a food web are producers, or autotrophs, which produce their own food through photosynthesis, such as trees and shrubs. Consumers, or heterotrophs, are those organisms that cannot make their own food, and therefore must eat producers or other consumers to gain energy. Primary consumers or herbivores feed solely on producers. There are three types of secondary consumers: omnivores, carnivores, and decomposers. Omnivores eat both plants and animals, carnivores eat only other consumers, and decomposers are those organisms that consume dead materials. Decomposers are not to be confused with scavengers, as scavengers are considered carnivores that eat parts of dead animals. Decomposers are recyclers and consume dead materials. Without them, nutrients would not cycle back into the environment, therefore making it impossible for other organisms to sustain life. Last are tertiary consumers, or top predators of an ecosystem.

Abiotic Factors

Although not often included in the food web, abiotic factors or the non-living aspects of an ecosystem (water, sunlight, temperature, etc.) play an important role. Climate will decide which food resources, and how much water and sunlight, are available to organisms in any given environment. Water and sunlight are necessary for plant growth and photosynthesis, and also provide animals with the basic needs of survival.

Food Webs and Food Chains

In every environment there are different food webs. For example, as a raccoon leaves the forest at low tide to feed on exposed mussels, the nutrients of one food web can transfer to another. Although the organisms may be different, the order, producers, primary consumers, secondary consumers, and tertiary consumers, is always the same. For the purpose of this lesson, we will focus on aquatic food webs, both salt and freshwater.

Saltwater Food Web

Illustrations of zooplankton

Illustration by Ann Ezelius

Micro-organisms known as plankton are key players in the food web of a marine environment. Occupying the photic or sunlit portion of the water are two types of plankton, phytoplankton and zooplankton. Phytoplankton or plant plankton account for 95% of the primary productivity in the ocean. Zooplankton or animal plankton eat phytoplankton, and thus are primary consumers. In addition, larger zooplankton will eat smaller zooplankton; small bait fish will eat larger zooplankton; and large predatory fishes will eat the small bait fish. This series of feeding relationships make up the marine food chain. When you factor in other species that feed on the same organism, then the chain becomes a web.

Freshwater Food Web

At the base of the freshwater food web are producers such as algae, duckweed, and lily pads. Because many freshwater systems are small relative to the nearby terrestrial systems, much of the energy in freshwater systems can come from terrestrial sources, such as leaves falling into the water. Consequently, decomposers are often very important in freshwater systems. Just like on land, aquatic plants undergo photosynthesis and provide aquatic organisms with oxygen. Freshwater primary consumers include zooplankton and invertebrates. Smaller prey fish that consume the invertebrates are secondary consumers. Predators at the top level include largemouth bass, smallmouth bass, walleye, chain pickerel, and perch. Humans and carnivorous birds (ospreys) are also included in the freshwater food chain.

Human Impacts

In many food webs, humans can be the top predator and are responsible for the decline in population, or in some cases, the endangerment or even extinction of many species. In aquatic food webs, humans are the top predator when they fish or when they buy and sell fish. Humans can negatively impact aquatic food webs in many ways: by overfishing, introducing non native species, or polluting the aquatic ecosystem.

Bioaccumulation in the Food Web

Pollution can accumulate from species to species, moving up the food chain until it eventually affects the whole food web. This process is known as bioaccumulation. For example, in a saltwater ecosystem, clams filter out pollutants in the water such as heavy metals, coliform bacteria from sewage contamination, and oil. However, when pollutant levels are high, they build up inside of the clams, concentrating the toxic substances. Higher on the food chain, a blackfish eats the clams and stores the toxins in its body.

Main Activity

Introduction

  1. Introduce yourself
  2. Introduce the day's activities:
  3. Prep for upcoming fishing tripFish identification
  4. Aquatic ecosystems and the ecological interactions in that ecosystem, making a food web

Brainstorming

  1. Have students brainstorm a list of plants and animals that live in an aquatic (freshwater or saltwater) ecosystem.
  2. Write answers on the board.
  3. Option for older students: Introduce the following concepts: abiotic, biotic, producers, photosynthesis, and consumers.
  4. Say: Ecosystems have abiotic factors and biotic factors:
    1. The abiotic environment (non-living; i.e., water, sunlight, atmospheric gases, temperature, wind, and climate)
    2. The biotic environment (living organisms; i.e., plants, animals, insects, and bacteria.)

Making a Food Web

  • Invite a student volunteer to choose an Organism Identification Card and read it aloud. That student then pretends to be that organism in the food web. Give that student the Organism Prop corresponding to that organism and ask the student to stand at their desk.
    • Crab: tongs
    • Plankton: hair band with springs
    • Sun: sunglasses
    • Algae: toothpaste or plastic fish tank plant
    • Bird: noise maker or feathers
    • Bait: air freshener
    • Shellfish: fake pearl necklace
    • Fish: models or nose plugs
    • Skate: elbow & knee pads
    • Squid: apron
    • Angler: fishing rod with thick fishing line
  • When a student becomes a fish, show the class the fish mount, discuss some features of the fish and then hand the student the prop.
  • Continue having students take turns choosing Organism Identification Cards, reading them aloud, and then standing at their desks with the props. Be sure that the last Organism Identification Card you share is the "Angler."
  • Demonstrate how the food web works; begin with the angler and continue working your way through the ecosystem by asking each student questions about his/her organism, such as, "What do you eat?" and/or "What other organism(s) do you depend on?"
    1. The prop for the angler is a fishing rod. Use the fishing line to make the web; moving from organism to organism.
    2. Each time the web may be different, depending on the student's interjections.
  • After the web is formed, discuss the relationships and dependency of the food web. For example, remove one of the organisms from the web. Discuss and show the breakdown of the web when a link is removed.
  • When finished with the exercise, reel in by having each student, one at a time, release the fishing line. Start with the last organism chosen and continue on to the next student whose line went slack.

Wrap up

Relation to Fishing

If going fishing following the lesson, conclude by relating the exercise to fishing. Explain that by knowing how organisms interact in an aquatic food web, we can tell what bait to use when fishing for a specific species. Also explain that as anglers and consumers of fish, we are part of the aquatic food web. We should follow fishing rules and regulations to avoid overfishing certain species.

Review

  • Review the fish species introduced during the lesson
  • Go over terms producers, consumers, or decomposers
  • Assign species to categories (producer, consumer, or decomposer)
  • Have the students construct their own aquatic food web or complete the Food Web Worksheet. Ask the students to explain how humans play a role in the aquatic food web

Questions for Discussion

Q: What can a producer do that a consumer cannot?
A: Creates energy by undergoing photosynthesis

Q: What do you call an organism that feeds on dead organisms and or plant material?
A: A decomposer

Q: What is the difference between phytoplankton and zooplankton?
A: Phytoplankton are plant plankton, while zooplankton are tiny aquatic animals

Q: Name a top predator in the aquatic food web
A: Answers can vary: human, osprey, largemouth bass, striped bass

Q: How can humans negatively impact the aquatic food web?
A: Answers can vary: overfishing, not following rules and regulations, polluting

Q: Name an organism that eats zooplankton
A: Larger zooplankton will eat small zooplankton and small baitfish will eat large zooplankton

Q: How can humans help protect the aquatic ecosystem?
A: Answers can vary: By not polluting, following fishing regulations, educating others about fishing rules/pollution

Q: What is overfishing?
A: Taking so many of a species of fish that the population is unable to recover

Q: What do herbivores eat?
A: Plants

The instructor can also have students complete the Food Web Worksheet for assessment.

Web Resources

Biodiversity & Species Conservation - NYSDEC web page on biodiversity and the human/natural threats to biodiversity

The Food Web - [Leaving NYSDEC website] Website provides information on the physical, chemical, and biological components of Lake Ecology. Useful food web vocabulary and food chain/web diagrams.

Freshwater Fishes - NYSDEC site providing information on a variety of species, with over ten series on fish including: true bass, common minnows, common prey fish, sunfish, and trout.

Marine Fish - NYSDEC site providing additional information on common marine species in NY waters


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