Modeling Marine Food Webs and Human Impacts Overview In this two-part lesson, students will develop food webs and investigate human impacts on marine ecosystems. In Part I, students will explore the ecological role of organisms in an ocean habitat and use information provided on Food Web Cards to develop food chains. In Part ll, students will model the interconnected feeding relationships in the open ocean ecosystem by developing food webs and then use their food webs to explore the impact that different scenarios have on the ecosystem. Grade Levels: 5-8 Learning Objectives Students will be able to: • Analyze the role of organisms as producers, consumers, and decomposers in marine ecosystems. • Develop a model to describe the movement of energy in marine ecosystems. • Use their model to explore impact scenarios in marine ecosystems. NGSS Performance Expectations • 5-LS2-1: Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment. • MS-LS2-3: Develop a model to describe the cycling of matter and flow of energy among living and nonliving parts of an ecosystem. Suggested Time: Two 50-minute class periods Materials • Student Worksheet 1 • Student Worksheet 2 • Poster paper for creating food webs • Markers in multiple colors • Food Web Cards • Food Chain image • Food Chain with Energy Flow Arrows image • Sample Completed Food Web • For the teacher – Computer with Internet access, projector 1 Media Resources • Blue Whale Barrel Roll video • The Tucker Trawl video • Endangered Sea Turtles video • Marine Debris Impacts video Part I: Food Chains in the Open Ocean Students will explore the roles that different organisms play in a marine ecosystem by determining the links that exist between the organisms. Engage • Ask students: o Can anyone tell me why we eat? You are looking for answers that connect food and eating with needing energy to grow and survive. o How about animals in the ocean—what kinds of things do you think that they eat? Let students share their prior knowledge and ideas about what creatures in the ocean eat. If they say animals or plants, prompt them to go into more detail or description. • Tell students: Now we will watch a video showing one kind of ocean animal—a blue whale— eating. Prompt them to look for the following as they watch: o What does the whale eat? o How do scientists learn about what, and how, whales eat? • Play video: Blue Whale Barrel Roll (see box) In this video, students will see how an animal of such enormous size feeds on masses of small, shrimp-like krill (zooplankton), obtaining enough to eat. Interested in a closer look at how scientists “tag” whales to track their behavior in the ocean? Watch Tagging a Humpback Whale. • After viewing the video, discuss with students: o What did you observe the whale eating in this video? o How much krill does a blue whale eat? o Do you think krill are important? 2 o What do you think these krill eat? o How do you think scientists know what whales, fish, and other animals in the ocean eat? Explore • Tell students: Now we are going to watch a short video that will give you a glimpse into how scientists learn about the kinds of food that are in the ocean for marine life to eat. It shows scientists using a system of nets to take samples of small marine organisms at different levels in the water. Let’s see what they find. • Play video: The Tucker Trawl • After viewing the video, ask students: o What kinds of organisms did the trawl bring up? o What did they look like? How big were they? o What animals in the ocean eat these organisms? Explain • Tell students: Who eats whom in an ecosystem can be represented by a food chain. • Download and project this Food Chain image of a sample food chain from a grassy field ecosystem. Then, download and project this Food Chain with Energy Flow Arrows image to show the flow of energy as organisms in the ecosystem eat one another. • “Read” this food chain out loud, creating a concrete meaning for the arrows with your students: Grass is eaten by the grasshopper, which is eaten by the mouse, which is eaten by the owl. The energy flows from the grass to the grasshopper, to the mouse, to the owl. • Explain that a food chain, such as the one shown here, shows the series of steps in which energy, and matter, flow through organisms in an ecosystem as one organism gets eaten by another. The main takeaway: The arrows in a food chain show the flow of energy through the food chain. Follow the arrows to move ”up” the food chain. • Ask students: What role does the Sun play in this food chain? Explain that the Sun is the primary source of energy, which gets transferred through organisms in the food chain in this grassy field and all other ecosystems on land. The Sun is also the primary source of energy for life in the regions of the ocean where sunlight penetrates. • Tell students: Now you are going to build your own food chains to show the feeding relation- ships between some of the creatures that live in the ocean. • Organize students into teams of two to four. • Distribute: Every student should get Student Worksheet 1, and each team should get a set of Food Web Cards. 3 • Give the following directions: Have each team explore the Marine Life Cards. Using the information about diet provided on the cards, challenge teams to build at least five different food chains. They should link as many organisms together in a chain as they can—but use at least two in each one. Tell them that an organism may have relationships with more than one other organism in the stack of Food Web Cards; there is not one right answer. Have students capture their work in Student Worksheet 1. • Call on a few teams to share their food chains with the class. Which team made the most food chains? Which team(s) made the longest chain? • Ask students: o What pattern do you observe when you look at all these different food chains? Sample answers: They all begin with phytoplankton; larger animals eat smaller animals; phytoplankton and zooplankton are the smallest organisms in the chains. o Can animals be in more than one food chain? Are there certain animals that are in more food chains than others? Elaborate • Tell students: Each creature in the food chain has a role in the ecosystem. Write the terms “producer,” “consumer,” and “decomposer” on the board. Discuss the words and what they mean. Definitions: o Producers (or primary producer) can make their own food, converting inorganic compounds into energy-rich organic compounds, usually through photosynthesis. o Consumers obtain energy and nutrients by eating other organisms, which can be plants or other animals; all consumers are animals. o Decomposers obtain energy from dead organisms, breaking down the organic matter and returning the raw material (such as carbon, nitrogen, and phosphorus) to the ecosystem. • Ask students: o Looking at the food chains that you built, who are the producers? Answer: the phytoplankton, which get energy from the sun through photosynthesis o Name some consumers in your ocean food chains. Sample answers include: krill, tuna, sharks • Optional extension: If you would like to go into further detail about feeding levels in a food chain, bring in that learning goal here. Explain to students that each step in a food chain is a different feeding level, like steps up a ladder. Primary producers always make up the first level, 4 followed by primary consumers, secondary consumers, and so on up the food chain. For example, the mouse in the example food chain above is a secondary consumer. The top consumer on a food chain is called an apex predator. Apex predators have few, if any, natural predators of their own. • Point out that as energy flows through an ecosystem “up” through the food chain, matter (such as carbon and oxygen) is recycled at every feeding level. For example, as an animal eats, it takes in from the food what it needs for body repair, growth, and other biological processes and releases the rest as waste. The organic matter in the waste, and in the animal itself when it dies, is broken down into inorganic substances and returned to the environment by decomposers. • Explain that although decomposers (such as bacteria) may not be visible or immediately apparent in an ecosystem, they are there and play a role that is just as important as that of the consumer. Emphasize that decomposers act on all organisms in the food chain: they break down the wastes of living organisms and the organic matter of dead organisms at every feeding level and cycle the nutrients back into the environment, making them available again for primary producers and consumers in the ecosystem. • Discuss the role of phytoplankton as the primary producers in the ecosystem. Explain that, sim- ilar to the role that plants play on land, these tiny photosynthetic organisms convert the Sun’s energy and nutrients into compounds that go on to feed other organisms in the ecosystem, ei- ther directly or indirectly. Point out that all food chains in the ocean begin with phytoplankton or algae, which are consumed directly by zooplankton. The zooplankton are then consumed by other larger animals, including the largest animal to have ever lived on Earth—the blue whale. Evaluate • Direct students to Student Worksheet 1 to study the food chains they drew.