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Coral Reef Cake

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Reef Indicators Lab
University of South Florida, St. Petersburg
College of Marine Science

Slide Presentation for Coral Reef Cake Activity

The following are pictures that I use; captions provide a sample "narration".

Questions: What is this? Why are coral reefs important?
Key points: Coral reefs are very special places. The corals build the reef structure that provides food and shelter for many kinds of marine plants and animals. Coral reefs are also popular places to scuba dive.


Photo by J. C. Halas.

This is an aerial view of Looe Key Reef in the Florida Keys. There are three small boats in the picture for scale. The top half of the picture shows the back reef, including sandy areas and seagrass beds. The lower half of the picture shows the reef with its characteristic spur and groove formation. Most coral growth is in the spurs, which are the dark areas. The grooves are the brighter areas and are sand channels that allow sand to move between the backreef (top of the picture) and the forereef (bottom of the picture). Branching corals grow most abundantly in the shallower water over the spurs, brain corals grow most abundantly at intermediate depths, and plate corals are most common either on shaded sides of the spur or on deeper parts of the spurs.

Aerial View of Looe Key Reef

Photo by Walt Jaap.

Question: What are these?
Key points: Branching corals like these historically were the major reef builder in the Florida Keys and much of the Caribbean. Unfortunately, most of these corals have died from disease in recent years.
Optional: On our cake reef, we will represent branching corals with pretzels.

Branching Coral (Acropora palmata)

Question: What is this?
Key points: This is a brain coral growing out of a star coral. Brain corals are also important reef builders and live abundantly on the coral spurs. Notice the Christmas-Tree Worms on the brain coral.
Optional: On our reef, muffins will represent brain corals.

Head Coral

Question: Can you guess what these are?
Key points: Plate corals grow under relatively low light conditions. Some species always grow as plates. Star corals grow as large heads in shallower water where there is lots of light and as plates in deeper water where light is limited.
Optional: Bite-sized cookies will play the role of plate coral on our edible reef.

Plate Coral

Question: Does anyone have any idea what this is?
Key points: Encrusting coralline algae is the most important plant on the coral reef. It grows as a crust over dead coral, sand, and loose rubble, holding the reef together.
Optional: We will use pink frosting to play the role of coralline algae.

Coralline Algae

Question: What are these?
Key points: Seagrass beds are found behind the reef, in the backreef. Large barrel sponges can often be found in the seagrass.
Optional: Green-tinted coconut and brown-tinted marshmallows will represent seagrass and sponges on our reef.

Sponge surrounded by Seagrass

Question: What do you see here?
Key points: Patch reefs are also found in among the seagrass beds in the back reef. Brain corals, sea fans and sponges are common on patch reefs. Fish like this large parrot fish find shelter among the sea fans and graze upon the coral and algae with their massive beaks, which is why they are called "parrotfish".
Optional: Corn-chip sea fans and fish-shaped crackers will populate our seagrass bed.

Sea Fans and Parrot Fish

Question: Anyone know what these are? Do you know what they eat?
Key points: Sea urchins are found on coral reefs. They eat by scraping away at algae living on dead coral.
Optional: Raisins or chocolate chips can play sea urchins on a cake reef.

Sea Urchin, Diadema antillarum

Photo courtesy of J. C. Halas.

Both parrotfish and sea urchins are important "bioeroders" because their grazing activity breaks coral down to coral sand. Other bioeroders on the reef include sponges and clams. Who do you think will be the "bioeroders" of our reef?

Bioerosion Diagram

Illustration courtesy of N. P. James.

Question: Can anyone guess what this is?
Key point: This is a mound of sand built by a special kind of shrimp. The shells and skeletons of snails, urchins, corals, and many other plants and animals make up the sands on the reef.

Pile of Sediment

If we look at reef sand closely using a magnifying glass or stereomicroscope, we can see shells and spines as well as fragments of larger shells and skeletons. We will use frosting sprinkles for sand on our reef.

Close up of Sand Particles

Question: Anyone know what kind of fish these are? [Surgeon fish]
Key points: The reef provides food and shelter for fish, so an incredible variety and abundance of fish live on the reef.

Let's summarize now. In the Florida Keys, the reef grows upon fossil reef limestone called the Key Largo Limestone. Notice the spurs and grooves in this diagram. [Review with the students where each kind of organism lives.]

Block Diagram of a Reef

Illustration courtesy of N. P. James.

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