This lesson will depict the effect that sharks have in the Caribbean coral reef system and will show students how over-fishing of sharks has a ripple effect on the marine ecosystem. Students will learn about the balance in the reef ecosystem among sharks and other carnivorous fish, their prey, and algae. Students will see that predatory behavior is not inherently negative and that predators are an important part of a balanced ecosystem.
This lesson is one in a series exploring the history, biology, and ecology of the National Marine Sanctuaries. It was developed for National Geographic's Oceans for Life program, in collaboration with and with support from the National Oceanic and Atmospheric Administration.
Show students photographs of several sharks found in Flower Garden Banks NMS:
Whale shark
Nurse shark
Caribbean reef shark
Dusky shark
Great hammerhead
Ask students the following focus questions and write their responses on chart paper:
- Which adjectives describe the pictures?
- What do you know about sharks, what they eat, and how they hunt?
Tell them that sharks are predators, and have students generate a definition for the word
predator. Ask students to make a "value judgment" on predators—are they good or bad? Have them share the reasons for their opinions.
Tell students that all of the sharks in the photos are inhabitants and visitors of
Flower Garden Banks National Marine Sanctuary (FGBNMS). You may want to explain to students that marine sanctuaries are protected areas of the ocean, much like national parks on land. Tell students they will be creating diagrams depicting the ecosystem in FGBNMS. In small groups, they should explore the following Web sites, taking notes on the various inhabitants of the ecosystem for their diagrams. Diagrams should depict each of the components of the ecosystem (reef, algae, fish, sharks, etc.) and should indicate the general level of each inhabitant in the food chain. (Teacher note: students should have a basic understanding of the food chain. If necessary, provide a review of this material.)
Web sites:
Flower Garden Banks
The Living Sanctuary
Flower Garden Banks Profile
National Marine Sanctuaries—Encyclopedia of the Sanctuaries
Bring the class back together to discuss the Web research. Using student input, draw a simple diagram of the FGBNMS food chain on the board or on chart paper. Ask students:
- Which animals are predators and which are prey?
- Are some both?
- Are any only predators or only prey?
- What is the basis for the entire food chain at FGBNMS (algae)?
- How is the algae dependent upon the coral, and vice versa?
Explain to students that the FGBNMS is home to a variety of sharks, barracuda, and parrotfish. Ask students to describe how each of those animals fit into the food chain in that ecosystem. Ask them which animals they eat and the effect that eating, or not eating, those animals has on the ecosystem as a whole.
Show students the video clip of various animals from FGBNMS feeding on their prey, including organisms feeding on algae. Point out the fact that some animals are predators but never prey, and some are only prey.
Ask students if they think it would be a good idea to remove sharks from the FGBNMS ecosystem. Why or why not? Ask them to consider the effects of the removal of sharks on the rest of the food chain. What would happen to the rest of the ecosystem's inhabitants?
Tell students that they'll now be playing a game that simulates such changes in the ecosystem.
Write the following Food Chains on the board:
Food Chain 1: Tiger Shark—Grouper—Parrotfish—Cyanobacteria
Food Chain 2: Reef Shark—Baracuda—Sponges—Seaweed
Food Chain 3: Hammerhead Shark—Sting Rays—Sea Urchins—Coral
Food Chain 4: Dusky Shark—Angelfish—Butterfly Fish—Zooxanthellae
Divide students into groups of five. Distribute a set of Food Chain Game cards (PDF, Adobe Reader required) and four spoons to each group. The spoons should be lined up in the middle of the table, within equal distance of each student. Groups then select one student as the dealer who deals four cards to each student. The goal of the game is to end up with a balanced ecosystem (one of the Food Chain groups.) The dealer draws one card from the pile and either keeps it or passes it on. If the dealer keeps the card, he or she must discard one from their hand. Whatever card the dealer is discarding gets passed to the person on their right, who either keeps that card or passes it on, and so on. When someone has a balanced ecosystem they take one of the four spoons from the center, at which point everyone else must grab for the remaining spoons. The person who doesn't get a spoon gets a point and the game ends when someone gets five points. The person with the fewest points wins.
After students have completed the game, ask them to describe the effects of removing the following components from the food chain:
- coral
- algae
- mid-sized fish
- sharks
Help students understand the interconnectedness of the members of the ecosystem, and the ripple effect that occurs when one part of the food chain is removed or significantly decreased. Ask students:
- What effect would the removal of sharks have on the coral? Why?
- What effect would the removal of secondary consumers have on the coral? On sharks?
- What effect would the destruction of most of the coral reef have on the rest of the food chain? Can you predict the order in which species would begin to feel the effects? How long do you think it would take before the sharks' food source ran out?
Have students revisit their earlier thoughts on predators. Ask them if their opinions have changed at all, and why. Do they consider predators to be a help, or hindrance to the FGBNMS specifically? Why?
Ask students to reflect upon the value of FGBNMS and why they think it should be preserved. Considering what they have learned about ecosystem balance and the food chain, what types of preservation activities do they think would be appropriate? Is there one area or inhabitant of the sanctuary they think is most important? Why? Ask them to predict what might happen to the area without preservation efforts.
This lesson plan was prepared by the National Geographic Society under award #NA04NOS4290216 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions, and recommendations are those of the authors and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration or the Department of Commerce.
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