Investigation

ENGAGE

(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.

EXTENSIONS

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

EXPLAIN

(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).

4. 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.

5.  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.

6. 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).

7.  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.)

ENGAGE

(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.)

EXTENSIONS

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 https://askabiologist.asu.edu/experiments/sketch-plankton/for-teachers)

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 https://products.coastalscience.noaa.gov/pmn/. This website also has a downloadable mobile app for identifying the most common saltwater phytoplankton and pronouncing their Latin species names correctly: https://coastalscience.noaa.gov/exit/?url=http://www.gano.name/shawn/phyto/

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

ELABORATE: Food Webs

(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.