Home‎ > ‎

Dennis Hubbard - Coral reef ecology - Geology


This model illustrates the relationships between nutrients which encourage reef algae and grazers that consume them. Recently, the algae/coral balance on many modern reefs has been impacted by some combination of overfishing and nutrification/pollution. This exercise uses a NetLogo computer model to demonstrate specifically how losses of grazing fish and the addition of nutrients to the reef system change the relative abundance of corals and algae on the reef. On a larger scale, it demonstrates the non-linearity of environmental decline in most natural systems.


This exercise is designed for geology majors, biology majors and non-science majors with an interest in coral reefs and environmental science or environmental studies. While an introductory Biology, Geology or Marine Science course would be helpful, they are not necessary.

Skills and concepts that students must have mastered

The only requirement is a reasonable ability to read graphs and make inferences from the output of the computer model. Accompanying materials provide the necessary background for instructors and students.

How the activity is situated in the course

The modeling exercise consists of the following materials that can be downloaded from the area at the end of this page:

1) a short background lecture (Powerpoint provided)
2) instructions and hands-on demo of the model
3) homework assignment or lab exercise to use the model
4) discussion of model outcomes
5) The CoralReefs model (v.5.1)


Content/concepts goals for this activity

This activity consists of a mixture of 1) in-class lecture, 2) hands-on activities guided by a series of scenarios and 3) a follow-up discussion of outcomes and their significance. This allows students with a variety of learning styles to internalize the lessons included in this exercise.
It also provides practical examples of how natural systems work and how this information can be used to inform important environmental policy decisions using cross-disciplinary principles. Finally, it serves to reduce anxieties common in students from non-technical majors or that consider math "too difficult".

Higher order thinking skills goals for this activity

Students will learn to 1) run and manipulate the model, 2) use graphic output to generate data from multiple runs and then 3) use those data to understand specific changes in coral reefs in response to the most common anthropogenic stresses operating at local or regional scales. They will also develop some degree of comfort working with computer simulations and deciding how to best use the output. Finally, they will learn about the inherent non-linearity of most natural systems.

Other skills goals for this activity

Each student is asked to prepare an "op ed" piece to relate the outcome to the general public. They are encouraged to make sound policy and economic arguments based on the model data.

Teaching Notes and Tips

Detailed teaching notes are provided in the materials on the SERC site. A detailed manual that described specifically how to set up and run the model is also provided at the SERC site.


Handout 2 includes a model-specific set of questions that lead students through the logic process and also allow the instructor to assess a student's level of comprehension. We created a detailed assessment that examined both what and where students learned in this exercise. A copy can be requested.

References and Resources

Introduction to Ocean Sciences by Douglas Segar

The model illustrates how models are useful in general while also enhancing the student's understanding of field specific information?

OMnI Survey Questions:

Did students build models, manipulate parameters/variables in models and/or was the model simply demonstrated by the instructor?
The topic is generally described in a class along with a demonstration of the model (students download the model and free NetLogo software prior to class and bring laptops). A background document on reef modeling is provided for the teacher (downloadable below). A Powerpoint lecture is also available. General information for students is provided in Handout 1: A Modeling Primer. Each student uses Handout-2: Model Instructions and Questions to complete an exercise at home. The results are discussed in a second class; we typically set up a spreadsheet to show values and outcomes (e.g., How many student runs showed marked decline at a nutrient level of X?). Because the model is non-linear, each student will get slightly (or sometimes, dramatically) different outcomes - just like nature. The exercise demonstrates how natural systems work in general, focusing on how the various factors interact. Also, the model demonstrates that it is much harder (and more costly) to "fix" the reef once you "broke it" than to keep it "healthy" in the first place.

How did you assess the affect of students having used/been exposed to the model?

Handout 2 includes a model-specific set of questions that lead students through the logic process and also allow the instructor to assess a student's level of comprehension. We created a detailed assessment that examined both what and where students learned in this exercise. A copy can be requested.

How did it go in class? What advice would you give to someone trying to implement your model in their class?

The exercise went very smoothly. It was also demonstrated at the NSF-sponsored Cutting Edge Workshop on Teaching Environmental Geology. A parallel web page can be found at Carlton COllege's Science Education Resource Center web page (http://serc.carleton.edu/index.html) along with numerous other exercises (some are models). This exercise is described at that site and can be accessed at:


Courses Impacted

Geol 115: Coral Reefs: Biology, Geology and Politics

Please upload most recent model as an attachment or create link to model.

Dennis Hubbard,
Aug 22, 2012, 2:22 PM
Dennis Hubbard,
Aug 22, 2012, 2:22 PM
Dennis Hubbard,
Aug 22, 2012, 1:47 PM
Dennis Hubbard,
Aug 22, 2012, 2:23 PM
Dennis Hubbard,
Aug 22, 2012, 2:23 PM