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 other types of 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 when herbivores are present and are eating algae on the reef corals have less competition for 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!


Do invasive species escape their enemies?

One of the invasive plants found in the experiment, Dianthus armeria

One of the invasive plants found in the experiment, Dianthus armeria

The activities are as follows:

Invasive species, like zebra mussels and garlic mustard, are species that have been introduced by humans to a new area. Where they invade they cause harm. For example, invasive species outcompete native species and reduce diversity, damage habitats, and interfere with human interests. Damage from invasive species costs the United States over $100 billion per year.

Scientists want to know, what makes an invasive species become such a problem once it is introduced? Is there something that is different for an invasive species compared to native species that have not been moved to a new area? Many things change for an invasive species when it is introduced somewhere new. For example, a plant that is moved across oceans may not bring enemies (like disease, predators, and herbivores) along for the ride. Now that the plant is in a new area with no enemies, it may do very well and become invasive.


Scientists at Michigan State University wanted to test whether invasive species are successful because they have escaped their enemies. They predicted invasive species would get less damage from enemies, compared to native species that still live near to their enemies. If native plants have tons of insects that can eat them, while an invasive plant has few or none, this would support enemy escape explaining invasiveness. However, if researchers find that native and invasive species have the same levels of herbivory, this would no support enemy escape. To test this hypothesis, a lab collected data on invasive and native plant species in Kalamazoo County. They measured how many insects were found on each species of plant, and the percent of leaves that had been damaged by insect herbivores. The data they collected is found below and can be used to test whether invasive plants are successful because they get less damage from insects compared to native plants.

Featured scientist: Elizabeth Schultheis from Michigan State University

Flesch–Kincaid Reading Grade Level = 11.3

  • For a lesson plan on the Enemy Release Hypothesis, click here.
  • For a great scientific paper discussing the Enemy Release Hypothesis, click here.
  • The Denver Museum of Nature and Science has a short video giving background on invasive species, here

Do insects prefer local or foreign foods?

One of the invasive plants found in the experiment, Centaurea stoebe.

One of the invasive plants found in the experiment, Centaurea stoebe.

The activities are as follows:

Insects that feed on plants, called herbivores, can have big effects on how plants grow. Herbivory can change the size and shape of plants, the number of flowers and seeds, and even which plant species can survive in a habitat. A plant with leaves eaten by herbivores will likely do worse than a plant that is not eaten.

Plants are those that naturally occur in an area without human interference are called native plants. When a plant is moved by humans to a new area and grows outside of its natural range, it is called an exotic plant. Sometimes exotic plants become invasive, meaning they grow large and fast, take over habitats, and push out native species. What determines if an exotic species will become invasive? Scientists are very interested in this question. Understanding what makes a species become invasive could help control invasions already underway and prevent new ones in the future.

Because herbivory affects how big and fast a plant can grow, herbivores may determine if an exotic plant thrives in its new habitat and becomes invasive. Elizabeth, a plant biologist, is fascinated by invasive species and wanted to know why they are able to grow bigger and faster than native and exotic species. She thought that invasive species might get less damage from herbivores, which would allow them to grow more and could explain how they become invasive.

To test this hypothesis, Elizabeth planted 25 native, 25 exotic, and 11 invasive species in a field in Michigan. This field was already full of many plants and had many insect herbivores. The experimental plants grew from 2011 to 2013. Each year, Elizabeth measured herbivory on 10 individuals of each of the 61 species, for a total of 610 plants. To measure herbivory, she looked at the leaves on each plant and determined how much of each leaf was eaten by herbivores. She then compared the area that was eaten to the total area of the leaf and calculated the proportion leaf area eaten by herbivores. Elizabeth predicted that invasive species would have a lower proportion of leaf area eaten compared to native and noninvasive exotic plants.


Featured scientist: Elizabeth Schultheis from Michigan State University

Flesch–Kincaid Reading Grade Level = 10.9

There is one scientific paper associated with the data in this Data Nugget. The citation and PDF of the paper is below, as well as a link to access the full dataset from the study:

For two lesson plans covering the Enemy Release Hypothesis, click here and here. For another great paper discussing the Enemy Release Hypothesis, click here.

Aerial view of the experiments discussed in this activity:

ERH Field site 2