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Icon of ocean food web

Ocean Food Webs Module

Module Activities

Grade level

High School



There are 7 activities in this module. Each activity will require 1-2 class periods (assuming 50-minute class periods) to complete.


This module uses the concepts of food webs and trophic levels to explore populations of marine species in ocean ecosystems. Students will explore simulated marine environments using a computer-based virtual reality (VR) data visualization tool called VES-V (The Virtual Ecosystem Scenario Viewer). VES-V displays marine environments as though one was SCUBA diving in those habitats. The numbers and types of fish and other aquatic creatures displayed in different locations in the VES-V simulations are based on actual abundances of marine creatures and how the abundances respond to a variety of conditions.

Students will explore a marine environment in VES-V. Each student will conduct research about one of the species found in that environment, determining what it eats and what preys upon it. Students will combine their data in a whole-class jigsaw activity to create a food web diagram for this marine environment.

Next, students will gather data about populations of predators and their prey in two specific ocean environments. The first case study, based in the Gulf of Maine, explores the relationship between herring and cod that feed on them. Students will collect cod and herring biomass data during “virtual dives” in VES-V. Students will determine the relationship between trophic level and biomass for herring and cod. The second case study is set in kelp forests in Monterey Bay. Students will again “dive” in VES-V to collect biomass data. The key species in the second case study are sardines, sea lions that eat sardines, and orcas that eat sea lions. Students will again collect biomass data for the species in VES-V, then compare biomass with trophic level to reinforce their understanding of the relationship between those two quantities.

Finally, students will explore an ecosystem in the Florida Keys to see how their knowledge of trophic levels and biomass can be used to help predict the supply of a commercially important fish. Students will use biomass data for mackerel, collected in VES-V, to predict the biomass of tuna which feed on mackerel. Students will then compare estimates of tuna biomass with actual data about tuna biomass to see whether the trophic level and biomass relationship is useful for making predictions. The lesson wraps up with a discussion of the future availability of fish, such as tuna, that people are fond of eating.


Modern techniques and technologies make fishing so efficient that it is possible for humans to deplete populations of marine species. People must therefore monitor and manage populations of marine creatures to ensure that they are sustainable. This usually involves placing upper limits on the number of fish or other marine species allowed to be caught each year. Government agencies, such as NOAA Fisheries, strive to set catch limits that balance peoples’ desire for fish as a food source with the need to keep fish stocks above critical thresholds that ensure sustainable populations.

Fishery management experts need data about fish populations to assess the size and health of those populations, so they can set appropriately balanced catch limits. It is impossible to count all the fish in the sea, so fishery scientists use different methods to estimate populations of marine species. Sometimes it is very difficult to get an accurate count of a certain type of species. In some cases, one can infer general trends in a population of fish based on the population levels of a different fish that it preys upon if the second type of fish is easier to count than the first. Sometimes one can get a decent estimate of population size of a predatory fish by collecting data about its prey.

Learning Objectives

  • Students will conduct research about a specific marine species, including what it eats and what preys upon it and communicate their findings to the class.
  • Students will construct a food web diagram, as a whole-class “jigsaw” activity, by combining data about individual species that each student researched.
  • Students will use a virtual reality software environment (VES-V) to visualize marine habitats and gather data about species in those habitats.
  • Students will collect biomass data as well as analyze food webs and trophic levels.
  • Students will use their knowledge of trophic levels to estimate the unknown biomass for one species based on the known biomass of another (predator or prey) species.
  • Students will discuss the extent to which knowledge of food webs and trophic levels can help improve predictions about population levels of marine species that are difficult to directly observe.

Key Words - Vocabulary

  • Biomass - the total mass of a group of organisms combined. The biomass is the sum of the masses of all the individuals in the group.
  • Consumer - a species that eats other creatures, instead of producing its own food source internally.
  • Food Chain - a simple diagram showing a sequence of species that feed on one another.
  • Food Web - a complex diagram showing the organisms in an ecosystem and the relationships between them in terms of what-eats-what.
  • Primary Consumer - a consumer that feeds on producers, such as sheep grazing on grass.
  • Producer - a species that produces its own food internally, usually via photosynthesis. Producers don’t eat other species.
  • Secondary Consumer - a consumer that feeds on primary consumers, such as a wolf that eats sheep.
  • Tertiary Consumer - a consumer that feeds on secondary consumers. A shark that eats a fish that itself is a predator is an example of a tertiary consumer.
  • Trophic Level (model validation) - a number that represents the place of a species in a food web based on what they eat. Producers are trophic level 1, primary consumers are trophic level 2, secondary consumers are level 3, and tertiary consumers are level 4.
  • Trophic Pyramid (model validation) - a diagram that shows the species in an ecosystem based on trophic level, with the lowest trophic level at the bottom. The diagram is pyramid-shaped to indicate that most energy and biomass resides in the lowest trophic levels.


Introduction: Introduce the Ocean Food Webs Module with a Big Question: “How do Individuals, communities or governments ensure that there is enough seafood for people to eat in the future?”

  1. Ask students whether they eat any seafood. Since some students may not like or care about seafood, also ask them whether they work in a restaurant that serves seafood, or hope to get a job in food service. What might happen to the seafood they eat, or to jobs in those restaurants, if seafood prices rose because of limited supplies?
  2. Discussion: Engage students in a discussion with the following suggested prompts:
    • Ask students what happens if we notice that some marine species becomes severely depleted? What might that mean for the health of the rest of the ecosystem?
    • How can we make sure that there are adequate supplies of seafood (or any other limited resource) for people to eat/use in the future?
    • How can we predict the population sizes for various kinds of marine species, or the amount of other potentially limited resources people consume, or use in the future?
    • If we are interested in a certain type of fish (such as tuna), and we notice large changes in the populations of other fish that tuna eat, does that tell us anything about the likely future tuna population?


  • Activity I: Introduce VES-V with a “Virtual Dive”
    In this activity students will conduct a “virtual dive” using the VES-V simulation software to become familiar with its features and to generate student interest in using it. VES-V will be used to support activities throughout this module.

  • Activity II: Introduction or Review of Food Webs and Trophic Levels
    Three closely-related concepts are used throughout this lesson: food webs, trophic levels, and biomass. This activity provides a brief introduction to key aspects from these concepts that are used throughout this lesson. If your students are familiar with these ideas, we suggest you review them in the context of marine ecosystems.

  • Activity III: Food Web Jigsaw
    Students will investigate the food web and trophic levels of a specific marine habitat in the Gulf of Maine. Using data gathered in VES-V, students will compare the biomass of a predator (Atlantic cod) with one of its prey (Atlantic herring). Based on this data, students will infer a relationship between the trophic level and biomass of a type of species in a food web.

  • Activity IV: Case Study 1 - Cod and Herring
    Students will analyze graphs of hare and lynx populations produced by the predator-prey spreadsheet model. This analysis will provide students with the opportunity to observe the relationships between the two populations, and how each population changes in relation to the other. Ultimately, students will formulate and state a principle about how the two populations change in response to each other. Students will make connections between the graphs and mathematical model and the basic behaviors of lynx and hares that generate the patterns observed in the graphs.

  • Activity V: Case Study 2 - Sardines, Sea Lions and Orcas
    This activity is similar to Activity IV but adds more species and complexity to the system examined. Students will investigate the food web and trophic levels of another marine habitat, collect biomass data for multiple species in a kelp forest habitat in Monterey Bay, CA and compare the biomass data for species at different trophic levels. The key species in this activity are sardines, California sea lions, orcas (killer whales) and blue whales. This activity reinforces the concept that trophic level and biomass are usually inversely related; there is generally more biomass at lower trophic levels, and less biomass at higher trophic levels.

  • Activity VI: Food Webs and Changing Biomass
    Students will use their knowledge of biomass ratios of species at different trophic levels to predict the new biomass of a species when the biomass of its prey changes. Students will discuss the complex relationships in food webs, and how that complexity affects the ability to predict the outcomes of changes in a food web.

  • Activity VII: Revisit Initial Question - Enough Seafood?
    Students will revisit the initial Big Question: “How do Individuals, communities or governments ensure that there is enough seafood for people to eat in the future? ” Students will use their knowledge of food webs and trophic levels to address the Big Question. In this activity students will collect data about Spanish mackerel, a fish that is a major food source for other creatures in the Gulf of Mexico. After examining the trend in mackerel biomass, students will form a hypothesis about the biomass of a predator that feeds on mackerel, Bluefin tuna. Finally, students will compare biomass data for tuna with their hypothesis to see how knowledge about trophic levels can help answer the Big Question.

Module References