Review the definition of symbiosis from Lesson 2, and read the following description to students, asking them to try to determine which kind of symbiosis it is: “All corals are animals, but like lichens on land, which are part fungi and part algae, they have a symbiotic relationship with algae. Most corals contain symbiotic algae called zooxanthellae (note: pronounced zo-zan-thel-ee), within their tissues. The coral provides the algae with protection and the compounds it needs to carry out photosynthesis. In return, the zooxanthellae are the corals’ ‘solar panels,’ providing the reef building corals with enough energy to extract calcium from the seawater to build their skeletons quickly. The zooxanthellae use sunlight for photosynthesis and produce oxygen and sugars which the corals can use. This symbiosis is so successful that fast-growing species of corals can grow up to 20 cm (8 inches) per year. What kind of symbiosis is this?”
Elicit from students that this is mutualism, a relationship in which both organisms benefit. (It may be helpful to provide choices: mutualism, amensalism, parasitism, and commensalism.)
Tell students, “Many other coral reef animals, including sea anemones, soft corals, and giant clams, also have symbiotic relationships with these algae and with each other.” Provide an example of a coral reef food chain or food web (S-8-9-3_Coral Reef Food Web.doc). Have students identify relationships among organisms in the coral reef ecosystem. Also, have students describe the flow of energy through the coral reef ecosystem.
If computers with Internet access are available and time permits, have students view the video clip at the “Energy Flow in the Coral Reef Ecosystem” Web site and write answers for the “Discussion Questions,” and/or do the interactive coral reef activity at the “Coral Reef Connections: Great Barrier Reef” Web site at www.pbs.org/wgbh/evolution/survival/coral/index.html.
Provide students with instruction on coral reefs, including what they are, their importance, and the impact of humans on them. Display the outline on Coral Reef Ecosystems (S-8-9-3_Coral Reef Outline.doc). Have students copy the outline into their notes.
Display the Coral Reef Locations Map (S-8-9-3_Coral Reef Locations Map.doc) and explain why coral reefs are found in tropical locations (i.e., they need sunlight for photosynthesis and warm water for the survival of organisms).
Hand out the Human Threats to Coral Reef Ecosystems–Student Version (S-8-9-3_Human Threats to Coral Reef Ecosystems-Student Version.doc and S-8-9-3_Human Threats to Coral Reef Ecosystems-Teacher Version.doc). Have students examine the data and answer the Analysis Questions.
- Students who might need an opportunity for additional learning can use a copy of the Coral Reef Food Web (S-8-9-3_Coral Reef Food Web.doc). Have them review vocabulary from this unit by identifying: producers, consumers, herbivores, carnivores, omnivores, and trophic levels. Have them describe the flow of energy through one food chain in the web.
- Students who may be going beyond the standards can design a 2–3 minute public service announcement (for television or radio) to improve understanding of human threats to coral reefs, and actions we can take to protect coral reef ecosystems. The Save a Reef Web site may be useful for this extension (see Related Resources).