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Ocean and Beach Food Webs
Students investigate marine and intertidal food webs, then collect and observe plankton, and observe food web interactions during a beach field trip. After the field trip, students observe plankton using microscopes and do research to extend their learning about food chains and webs. They construct a model of a food web based on their research and evidence collected on the field trip.
Essential Question(s)
How does matter cycle and energy flow through an ecosystem?
What is the role of plankton in the movement of matter and flow of energy through intertidal and marine food webs?
PDF Investigation
Time Required
4-5 hours over 5-6 sessions
Life Sciences, Physical Science
Investigation Type
Field Trip, Classroom
Grade Level
NGSS Performance Expectations
Materials Needed

Field Trip

  • Plankton nets (one for each pair of students).
  • Magnifying glasses (one for each student)
  • Science Notebooks


  • Microscopes (one/pair or group of students)
  • Plankton sketchbooks or white paper
  • Chart paper and markers
  • Water droppers (one/student)
  • Slides - gridded slides are preferred (one/student)
  • Colored pencils


  • Reference materials
  • Scissors
  • Yarn
  • Glue

NGSS Performance Expectation

Students who demonstrate understanding can:

Students who demonstrate understanding can:
Support an argument that plants get the materials they need for growth chiefly from air and water. 

Use models to describe that energy in animals’ food (used for body repair, growth, motion, and to maintain body warmth) was once energy from the sun. 5-PS3-1

Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment. 5-LS2-1


Knowledge - Students will know that:
  • food provides animals with the materials they need for body repair and growth and the energy they need to maintain body warmth and for motion.
  • plants acquire their material for growth chiefly from air and water.
  • the food of almost any kind of animal can be traced back to plants.
Skills - Students will be able to:
  • use a diagram to explain the flow of energy from the sun through a food web.
  • support an argument with evidence about how plants (i.e., producers) in the food web obtain the matter they need to make their own food.
  • define the health of an ecosystem in terms of multiple species of different types able to meet their needs in a relatively stable web of life.
Local and Cultural Connections
People play critical roles in marine and intertidal food webs and in Alaska, many people depend on the health of these ecosystems for their subsistence or cash income. Look for ways to include local uses and the cultural importance of local seaweeds, intertidal animals, salmon, marine fish and marine mammals. Examples:
- Alaskans harvest and eat mussels, clams and cockles, scallops, chitons, sea cucumbers, sea urchins octopus, crabs, and seaweeds.
- Limpets can be used as an emergency food because since they are not filter-feeders like clams, they don’t accumulate shellfish toxins.
- Shells are used for jewelry and decoration and were traditionally used as money in some places in Alaska.
- Seaweeds are used in many manufactured products as filler and as fertilizer for gardens. The seaweed aquaculture industry is growing in several Alaskan coastal communities.
- A compound found in sea cucumbers is being used as medicine to treat cancer.
- Because the “glue” made by barnacles and byssal threads made by mussels are strong adhesives even under water, the compounds are being imitated and used in medical and surgical applications.
Teacher Preparation

Review the teacher background section and the Alaskan intertidal and ocean food web models (links in the Resource section). NOTE: Not all of these models include the recycling of nutrients through decomposers.

Plankton Tows and Observation

  • Decide on a water source for collecting plankton samples. (You can do this as part of your beach field trip or make another trip to the beach, to a stream or river near the school, to a harbor with a dock you can use, or to a private dock you can get permission to use.)
  • Gather field trip supplies and equipment. You can make your own plankton nets (See link to instructions in the Resources section).
  • Print out copies of plankton identification guides.
  • To extend the learning, decide on a plankton sampling schedule that will allow your students to return to the same water source and compare their results.

Beach Field Trip

Make field trip arrangements - buses, lunches, permission slips, life jackets (if applicable), volunteers, etc.

Research Project

Gather nonfiction books, web links, and other resources for student research and/or schedule library time.

See the Resources section below and the Field Trip Resources page for links to online sources for student research.

Learning Experiences


(20-30 mins.)

  1. Show students a plankton net and ask them what they think it is.
  2. Allow them time to think and share their ideas.
  3. Explain that it is a net to catch tiny plants and animals in water that you may not be able to see with the naked eye.
  4. Ask: What kind of tiny plants and animals do you think you might catch in a plankton net?
  5. Allow them time to think and share with a partner.  
  6. Ask partners to share with the group and write their ideas on a chart paper.
  7. Watch the YouTube video The Power of Plankton.  (5 ¼ mins.) The end of the video shows students how plankton are monitored continuously from ships.


Watch the TedEd Video The Secret Life of Plankton (6 mins.) and/or The Invisible Watery World of Plankton video (5 mins.).


(30-45 mins.)

  1. Ask the students: Where do plankton get their food? Guide them in a discussion about the differences between phytoplankton and zooplankton. (Phytoplankton uses the sun to make its own food through photosynthesis. Zooplankton eat phytoplankton.) You can also review the differences between meroplankton and holoplankton that were described in the video, using barnacle and crab larvae as examples of holoplankton that eventually settle on the beach.

  2. On a large piece of chart paper or a whiteboard, draw the sun and plankton and use arrows to show the flow of energy from the sun to the phytoplankton, to the zooplankton. (The arrows that show the flow of energy should begin at the sun and move out in order to describe the correct flow of energy in the web. The arrows that also show the movement of matter should point in the direction that matter is moving rather than in the direction from “who” is eating a plant or animal to the “whom” they are eating. Students often draw the arrows the other way in food webs.)

  3. Add seaweeds as producers to the base of the food web. Ask students:  What other types of matter are needed for phytoplankton and seaweeds to make their own food? (light and air in the form of gas dissolved into the water) Discuss the reason why seaweeds are only found in shallow water (They have to be able to grow tall enough that their leaf-like blades can float near or at the surface of the water and capture enough light for photosynthesis.) and why phytoplankton are only found in the top layer of the ocean (where there’s enough light for photosynthesis at least part of the year in northern waters).

  1. Ask students what eats plankton and seaweeds. Distinguish between animals that eat phytoplankton and those that eat zooplankton or both. Allow students time to think and share their ideas. Remind them that many types of plankton are one-celled organisms that can be filtered out of the water as a way to capture them for food.

  1.  Guide this discussion and add the names of fish, marine birds, and marine animals to the chart. Distinguish between animals that eat plants (herbivores), animals that eat other animals (carnivores), and animals that eat both animals and plants (omnivores). Have students tell you where to add the arrows to show the direction of flow of energy and the recycling of matter). Include humans in the food web if they don’t think of it. Always start them back at the sun to describe the origin of energy in food webs.

  1. Add dead plankton, seaweeds, and animals, at least one animal that eats dead things (a detrivore – examples: crabs, ravens, gulls) and a decomposer (example: bacteria).

  1.  Show the flow of matter into the phytoplankton and seaweeds after decomposition. (Students often leave the flow of energy and matter that happens through the process of decomposition out of food webs. This way of doing it demonstrates the cycling of matter that occurs after decomposition is completed.)

Field Trip

(1½-2 hrs.)


(30-45 mins.)

After you have provided students an orientation to the field trip site and reviewed beach etiquette and safety rules, provide them with 20-30 minutes to explore within boundaries. Their focus questions are: Who eats whom? What evidence can you find of animals feeding or being eaten? Where on the beach and in the water do you find seaweeds? In what types of places are seaweeds absent?

Chaperones can help the students find evidence that might include:

  • Holes drilled through shells by boring snails
  • Sea stars “humped up” and feeding on a clam or mussel
  • Animals captured by anemones and being digested
  • Sea stars regenerating arms or with chunks removed by gulls

Bring the group back together and have them share their evidence.

EXPLAIN (Structured Investigations)

(1 hour)

Intertidal/Beach Food Chains: Divide the class into groups of three or four. Their task is to move from the lower intertidal zone to the upper intertidal zone (Use a band of mussels or rockweed as an indicator of the middle intertidal if there is one on the beach or kelps as an indicator of the lower zone.) and try to construct at least one food chain in each zone. The food chain needs to include a producer, an herbivore, a carnivore, and a detrivore (that feeds on dead things). They should use the species name if they know it, but if not, they can make a drawing and write a description (e.g., a green film on a rock, a brown kelp with holes in the blades).

Plankton Tow:  Plankton sample can be collected in shallow water offshore of the beach, from a dock,  
or at another predetermined water source.

  1. Demonstrate how to use the plankton net properly and what to do with it when they are done. Tow the net just below the surface of the water as you walk back and forth along a dock; do this while wading through the water, or drop a net with a rope from a bridge or pier into a fast-moving current. Be sure to tow the net against a current so that the current moves the plankton into the net rather than washing them out.  
  2. If there is a lot of plankton in the water, you may need to hold the net upright after a tow and wash down the sides of the net (from the outside) by pouring water from a bucket or a small spray bottle. Do this slowly enough that the plankton are all collected in the jar at the bottom of the net and then release the jar from the net.  
  3. Have students break into pairs to go and collect their samples.
  4. Students can look at their samples with their magnifying glasses and share their observations. They may also notice differences in the color of the water that is a result of the amount of plankton in the water at different times of year and at different places.

Make sure the samples are put into a container with a lid for safe transport back to the classroom. If your net is constructed with a bottle that has a cap, you can simply put the cap on the bottle. If there is no cap, students can pour contents into a clean plastic container with a lid.

Back in the Classroom

EXPLORE: Observing and Sketching Plankton

(45-60 mins)

  1. Back in the classroom, ask students to guess how many different types of plankton are in the samples they collected. Have them share their answers. Tell them:  We are now going to take a close look at what we collected using microscopes.
  2. Model to students how to prepare slides and use the microscopes.
  3. Have them work in pairs to prepare slides and view their samples under the microscope.
  4. Model with a photograph how you might sketch the plankton.  
  5. First, think about the following questions. What shape is it? Is it one organism, or many? What color is it? Can I see any organs inside the body? How large is this organism?
  6. Now begin modeling a sketch. Remind students not to be intimidated. Show them how to:
    - Pay attention to detail and draw what they see.
    - Start with the outline first and then move on to the details.
    -  Sketch lightly and darken it when you add details.
  7. Have students sketch what they can see under their microscopes in their sketchbooks,
    reminding them that scientific sketching takes practice and they should just do their best.
  8. Ask: How many organisms can you see in your water dropper sample? Do you think our estimate was reasonable?  

Provide website links or book for students to use to identify their plankton to a species group (Identification to species is difficult.). (See the Resources section for links.)


Making a technical drawing of plankton

  1. Start with a practice sketch of a familiar item. This lets students practice the detail in which they are sketching. Bring in a fish, apple, plant, soccer ball, or class pet and model the detail in which the students should sketch. This is also a great time to introduce scale as a math extension.

  2. It may be a challenge for some students to find and focus in on live, moving plankton. You can complete this activity in two days; the first day, students can sketch plankton from examples in Zoom Gallery (species shown are pond plankton) and the second day, they can sketch live plankton.

  3. Select four different varieties of plankton and do the activity again. If you are feeling ambitious, have students sketch ALL the varieties of plankton in the Zoom Gallery and arrange them from the smallest to largest!

(Adapted from Catch & Sketch Plankton, Arizona State University School of Life Sciences

Harmful Algal Bloom Monitoring

Involve your students in learning about harmful algal blooms and becoming citizen scientists who monitor phytoplankton in either fresh water or salt water. For more information and training, see This website also has a downloadable mobile app for identifying the most common saltwater phytoplankton and pronouncing their Latin species names correctly:

Other lesson plan and worksheets are available at It’s a Plankton Eat Plankton World Packet.


(45-60 min.)

  1. Refer back to the food web the class constructed before the field trip. Ask:  What evidence did you find at the beach about who eats whom? Compile the answers on a whiteboard.

    Ask:  How do we know what animals eat if we can’t observe them often enough to know everything they eat? Call on students to share their answers and lead the discussion to how scientists look in the stomachs to determine diet or help them recall what they learned about the feeding structures and digestion systems of specific animals they may have observed in animals on previous field trips (e.g., filter-feeders, feeding structure of a sea urchin, clam siphon).

  2. Have students select one local animal they observed on the beach to find out what they eat and what eats them using the evidence listed on the whiteboard, books and/or the Internet to create a food chain poster for their animal.

  3.  Students present their food chain posters to the class.

  4.  When students are finished presenting, facilitate making the creation of a diagram or mural of a food web involving more than one food chain.

  5. After the food webs are completed, ask the students: Where do all of the food chains start? Are there other ways some of these organisms are connected? What is the difference between a food chain and a web?

Adaptations and Variations:

Students can cut and paste pictures, rather than draw.
Students can create a Google Slide or Web Poster instead of a drawn/colored poster.
Students can play a food web game, using the information they have collected to make connections with other species using yarn or string.

EXTENSION: The Alaska Seas and Watersheds unit The Case of the Missing Sea Otters provides an opportunity to explore what happens when a species is removed from the ecosystem and when people and other predators compete for the same prey species.


(45-60 min.)

Use the student posters, class presentations, and participation in the development of a food web diagram to assess student understanding of the following concepts:

  1. All energy in a food chain or web ultimately comes from the sun.
  2. Food chains include at decomposers that break down matter into what can be used by producers to make their own food.
  3. Food webs are more complex than a food chain relationship between one predator and one prey species or between one consumer and one producer.
Building a Plankton Net  
The Invisible Watery World of Plankton  
The Power of Plankton  
The Secret Life of Plankton  
Images of Alaska plankton and other marine species
Phytoplankton Line Drawings  
Zooplankton Line Drawings  
The Kachemak Bay Research Reserve Plankton Coloring Book  
Images of marine organisms including fish and marine invertebrate larvae

NOAA Auke Bay Laboratory, NOAA Fisheries

Photographs of phytoplankton


Plankton Identification Cards and Dichotomous Key

Alaska SeaLife Center

Images of Alaskan species with information about food web connections
Food Web Cards: Rocky Intertidal Habitat  
Food Web Cards: Mudflats  
Mudflat food webKachemak Bay. Dennis Lees.  
Ocean Food Web Cards  
Arctic Ocean Food Web Cards  
Ocean plastic smells like food to marine animals  
Species Profiles on Alaska Department of Fish and Game
Invertebrates - Species Profile  
Fish - Species Profile  
Birds - Species Profile  
Mammals - Species Profile  
Alaska Intertidal and Ocean Food Web Models
North Pacific Food Web  
Gulf of Alaska Food Web  
Marine Food Web  
Arctic Ocean Food Web

Arctic Ocean Food Web includes phytoplankton, zooplankton, and sea ice algae as producers.

Nonfiction Children’s Books
Ocean Sunlight: How Tiny Plants Feed the Sea

By Molly Bang and Shirley Chisholm with an accompanying science/ELA lesson plan

Sea Soup: Phytoplankton

By Mary M. Cerullo

Sea Soup: Zooplankton

By Mary M. Cerullo

This is the Sea that Feeds Us

By Robert F. Baldwin

A Whale’s Tale from the Supper Sea

By C.J. and Ba Rea (written about the Kenai Fjords area)

Resources for Extensions
Catch & Sketch Plankton

ASU School of Life Sciences

PLOSABLE Are Plankton Super Stars  
Whale Jenga Food Web Game  
Meroplankton vs. Holoplankton Video 
Teacher Background

Food Web Concepts

In 5th grade, the emphasis in the NGSS Life Science disciplinary core ideas related to food webs is on tracing the food of animals back to plants and tracing the movement of energy in the food web back to the sun. Students should gain the understanding that plants take in matter that is not food (water, air, and what’s left at the end of the decomposition process) and turn it into food and extend their understanding about “who eats whom” to interconnections within food webs that facilitate the cyclical pattern of movement of matter through ecosystems.

For a brief (approx. 2 minute-long) overview of how scientific thinking has changed about food webs over the last 50 years and the importance of understanding ocean food webs and the role of humans in them, watch this video about marine food webs

Beach field trips provide opportunities to watch food webs in action, with sea stars feeding on mussels or clams, submerged barnacles in tide pools using their cirri to filter the water like the baleen plates of whales, and clams squirting out their waste water after filtering sea water through their body. Many consumers in the intertidal zone graze on producers in the form of seaweeds and algal films on rocks; others filter sea water for both live prey and detritus. Many intertidal invertebrate and fish species are, in turn, prey for larger, more pelagic predators such as larger fish and marine birds and mammals which can also often be observed feeding nearshore.

Plankton: the Base of the Food Web

While plankton are too small to be observed with the naked eye as other than stationary or moving specks, net tows can be taken in shallow water near shore or from docks to provide students the opportunity to view plankton under a field microscope or using microscopes back in the classroom. Green or brown chloroplasts can often be observed within transparent phytoplankton as well as movements of zooplankton seeking prey and moving their food through their digestive system.

The word “plankton” is derived from the Greek word “planktos” and means to drift or wander. Phytoplankton, microscopic, one-celled plankton that are capable of photosynthesis, are the base of the ocean food web. They use the energy from the sun to make their own food and, in the process, produce most of Earth’s oxygen in the ocean, the largest ecosystem on Earth covering 70% of Earth.

One-celled zooplankton eat phytoplankton; multi-cellular drifting animals like jellyfishes eat a variety of zooplankton. Zooplankton can be divided into two categories - meroplankton and holoplankton. Holoplankton spend their whole lives drifting and meroplankton, which include many marine invertebrates, spend the first part of their lives drifting and settle down on the bottom of the ocean or in the intertidal zone when they mature.

Plankton nets are used to collect plankton samples in either coastal waters or aquatic field trip sites like streams and ponds by plankton can also be sampled in the ocean using either nets or continuous plankton recording devices mounted on moving ships.

See the examples of Alaskan intertidal and ocean food web models. (Links in the Resources section.)

Prior Student Knowledge:

Students should have a basic understanding that plants use the energy from the sun and need air and water to make their own food through the process of photosynthesis. They should also know some intertidal ecosystem food chain connections if they have gone on beach field trips in previous years. The emphasis in 3rd grade is on relationships between external and internal structures and their functions so students should have some knowledge of how marine invertebrates capture prey and feed as a basis for thinking about which species they graze on or prey on and which species scavenge dead matter or feed on detritus on the beach.  

Possible learner preconceptions, misconceptions and instructional clarifications:

Learner Preconception/Misconception: The producers in food webs are always plants. Plankton are plants at the base of marine food webs.
Instructional Clarification: There are many different kinds of plankton because the word plankton means that the organism is of a size, shape, and density that it drifts with ocean or stream currents. At this grade level, students can think of phytoplankton as “plant plankton,” although algae and cyanobacteria are both considered phytoplankton. Many zooplankton are one-celled but since the only criterion for being plankton is one of drifting in the currents, large multi-celled animals like jellies are also considered plankton.

The main producers in marine and intertidal food webs are phytoplankton and seaweeds. Their classification is confusing. Even scientists don’t always agree on which kingdom or kingdoms to put them into. Because phytoplankton (phyto – plant-like) are one-celled, they are often classified with one-celled zooplankton (zoo = animal) and other types of one-celled animals as protists in the Kingdom Protista. The instructional emphasis at this grade should be on where different planktonic organisms fit into food webs in terms of making their own food or consuming other plankton.

Learner Preconception/Misconception: Seaweeds are plants.
Instructional Clarification: As fifth graders explore marine food webs which have at their base producers that aren’t classified as members of the Plant Kingdom, it’s a good time to help them understand more about the complexity of grouping organisms and build on their knowledge about what plants need to survive and aspects of plant structure and function from earlier grades.

Seaweeds are macroalgae (macro = big, but there is no agreed-upon definition for algae.) All seaweeds are photosynthesizers and they lack structures that other members of the plant kingdom have. Still, some algologists (scientists who study seaweeds and other algae) place green and red seaweeds in the plant kingdom while they place brown seaweeds, which include the kelps, in a separate kingdom with one-celled diatoms and dinoflagellates. Given the complexity of the science and the lack of agreement, it’s probably best in upper elementary to allow your students to think of seaweeds as “the plants of the sea,” and phytoplankton as the “plant plankton.”

Learner Preconception/Misconception:  Seaweeds aren’t plants because they don’t grow in soil.
Instructional Clarification: While it’s true that seaweeds lack roots which means they can grow on the beach or on the ocean bottom in shallow water, that doesn’t mean plants need soil to get what they need to photosynthesize. Plant matter actually comes mostly from air and water, not soil, and phytoplankton and seaweeds are also able to obtain what they need for photosynthesis from water and air. They can also obtain some of the carbon dioxide they need in the form of gas dissolved into the water. You can ask students about their experience with hydroponic gardening as evidence that plants can grow in water.

Learner Preconception/Misconception: All animals that eat dead plants and animals or detritus are decomposers.
Instructional Clarification: Scavenges like crabs, ravens, and bottom fish are scavengers. They are consumers of organic matter in large lumps which aren’t broken down into inorganic minerals and nutrients that plants can recycle in photosynthesis. Detrivores like some marine worms consume much smaller clumps of detritus much like earthworms on land as do sea slugs. All of these detrivores speed up the decay process. Decomposers like bacteria and fungi complete the process by metabolizing detritus on a microscopic scale. Detritus feeders and decomposers can thus both be considered decomposers in marine food webs but scavengers are not decomposers.

The assessment probe Ecosystem Cycles developed by Page Keely can be used as pre-assessment of student understanding of these concepts.

Components of Next Generation Science Standards Addressed

Science & Engineering Practices

Developing and Using Models
Use models to describe phenomena. (5-PS3-1)

Engaging in Argu-ment from Evidence
Support an argument with evidence, data, or a model. (5-LS1-1)

Developing and Using Models
Develop a model to describe phenomena. (5-LS2-1)

Disciplinary Core Ideas

PS3.D: Energy in Chemical Processes and Everyday Life: The energy released [from] food was once energy from the sun that was captured by plants in the chemical process that forms plant matter (from air and water). (5-PS3-1)

LS1.C: Organization for Matter and Energy Flow in Organisms: Food provides animals with the materials they need for body repair and growth and the energy they need to maintain body warmth and for motion. (secondary to 5-PS3-1)

Plants acquire their material for growth chiefly from air and water. (5-LS1-1)

LS2.A: Interdependent Relationships in Ecosystems: The food of almost any kind of animal can be traced back to plants. Organisms are related in food webs in which some animals eat plants for food and other animals eat the animals that eat plants. Some organisms, such as fungi and bacteria, break down dead organisms (both plants or plants parts and animals) and therefore operate as “decomposers.” Decomposition eventually restores (recycles) some materials back to the soil. Organisms can survive only in environments in which their particular needs are met. A healthy ecosystem is one in which multiple species of different types are each able to meet their needs in a relatively stable web of life. Newly introduced species can damage the balance of an ecosystem. (5-LS2-1)

Cross-Cutting Concepts

Energy and Matter
Energy can be transferred in various ways and between objects. (5-PS3-1)

Matter is transported into, out of, and within systems. (5-LS1-1)

Systems and System Models
A system can be described in terms of its components and their interactions. (5-LS2-1)

Common Core

Draw on information from multiple print or digital sources, demonstrating the ability to locate an answer to a question quickly or to solve a problem efficiently. (5-LS2-1)
Include multimedia components (e.g., graphics, sound) and visual displays in presentations when appropriate to enhance the development of main ideas or themes. (5-LS2-1)
MP.2 Reason abstractly and quantitatively
Alaska Cultural Standards
Developed by Christine Sabin, Juneau School District. Adapted for Alaska Sea Grant by Marilyn Sigman.
Last Updated on
Last Updated by
Marilyn Sigman
Alaska Sea Grant University of Alaska Fairbanks Alaska Department of Education and Early Development NOAA