Won’t you be my urchin?

The vegetarian sea urchin Diadema antillarum.

The vegetarian sea urchin Diadema antillarum.

The activities are as follows:

Imagine you are snorkeling on a coral reef! You see a lot of plants and animals living together. Some animals, such as sharks, are predators and eat other animals. Other animals, like anemones and the fish that live in them, are mutualists and protect each other from predators. There are also herbivores, such as urchins, on the reef that eat plants and algae. All of these species, and many more, need the coral reef to survive.

Experimental setup with tiles in bins. Some bins have sea urchins and some do not.

Experimental setup with tiles in bins. Some bins have sea urchins and some do not.

Corals are animals that build coral reefs. When you look at a coral you may see what looks like one large rock. In fact, corals are made up of thousands of tiny animals, called polyps. Coral polyps are white but look brown and green because microscopic plants, called zooxanthellae, live inside them. Corals provide the plants a safe home, and in return the plants make food for corals. Sadly, today corals around the world are dying. Scientists want to figure out ways to help corals since they are such important animals.

Corals are picky and only like to live in certain places. Corals compete with algae, like seaweed, for space to grow. Sarah is a marine biologist who is interested in corals because they are such important animals on the reef. She wanted to understand how to help corals. She thought that if there were more herbivores eating algae on the reef then corals would have less competition. Then they would have more space to grow.

Sarah set up an experiment where she put tiles in bins out on the reef. Tiles provided space for animals to grow, including corals. Sarah also put sea urchins in half of the bins. Sea urchins are important herbivores and one of the species that like to eat algae. The other half of the bins had no urchins so the algae would be free to grow there. She had 4 bins with urchins and 4 bins with no urchins. After a few months, Sarah counted how many corals were growing on tiles. She counted corals found in the bins with and without sea urchins. Because sea urchins eat algae, they should free up space for coral to grow. Sarah expected that more corals would grow on the tiles in sea urchin bins compared to the bins with no sea urchins.

B. Photograph of Agaricia juvenile on experimental substratum. C. Photograph of Porites juvenile on experimental substratum

B. Photograph of coral species Agaricia juvenile on experimental tile. C. Photograph of coral species Porites juvenile on experimental tile.

Featured scientist: Sarah W. Davies from University of Texas at Austin

Flesch–Kincaid Reading Grade Level = 6.1

The lab webpage can be found here. There is one scientific paper associated with the data in this Data Nugget. The citation and PDF of the paper is below.

Davies SW, MV Matz, PD Vize (2013) Ecological Complexity of Coral Recruitment Processes: Effects of Invertebrate Herbivores on Coral Recruitment and Growth Depends Upon Substratum Properties and Coral Species. PLOS ONE 8(9):e72830

After students have completed the Data Nugget, you can have them discuss the management implications of this research. Watch the news story below and have students consider how urchins can be used as a management tool to help restore coral reefs!

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