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Graphing Changes in Marine Life Abundance

Marine biologist observes quadrat on ground.

Want to try your hand at some marine biology? Then grab your raingear and follow the steps below to make a study of the marine life occupying a section, or quadrat, of Mearns Rock (a boulder in Prince William Sound, Alaska, that was oiled in 1989 by the Exxon Valdez oil spill). For your study, you'll use a series of zoomed-in photos of that quadrat. Each shows a different year from 1990 to 2009. Your goal will be to see how the percent cover of mussels, barnacles, and Fucus gardneri (a kind of seaweed, also called rockweed) in this study area has changed during those 19 years.

As you complete this project, you'll be using the same method used by real marine biologists. To study how marine life abundance changes from one year to the next, marine biologists sometimes section off a small plot of land that's representative of the particular habitat they're studying (for example, a rocky shoreline or a bog). They use a frame (generally a 0.25 or 0.5 square meter of rebar or PVC pipe), known as a quadrat (or "quad" for short), which they place on the ground to mark an area to study in depth. Each year, the biologists return to count the organisms or plants that occupy the area inside the quad. In the photo above, one of OR&R's marine biologists is using a quad in his studies of the Mearns Rock site. He's trying to find out how the abundance of Fucus, barnacles, mussels, and other organisms changed over the years following the Exxon Valdez oil spill.

1. Before You Begin

Collect the resources you'll need:

  • Open our mini field guide (Document format: PDF, size: 154.9 K). You'll use it to recognize the species in your quad, estimate their percent cover, and establish the criteria you'll use to make your observations.
  • Open and print out our data table (Document format: PDF, size: 17.6 K). You'll use it to record your estimates of percent cover of species in the quad.

2. Observe and Record

Now, open the series of high-resolution photos of the same quadrat of Mearns Rock, taken each year from 1990 to 2008. As you examine each photo in the series, try to estimate how much of the quadrat that Fucus occupies (as a percent of the total area), how much of the quadrat mussels occupy, and how much of it barnacles occupy. We've prepared some viewing tips to help you observe the marine species. Record your estimates in the data table you printed out.

3. Plot Your Data

Your final step will be to graph your data, so that you can see trends over time in the relative abundance of the three species in the quadrat. Your graphs will look similar to those that marine ecologists make after actually measuring the amount of cover!

Related Photo Collections
  • Mearns Rock Time Series Read our biologists' explanations of the year-to-year changes you see on Mearns Rock. (20 images)
  • Block Island Time Series Our biologists studied the plants and animals living in this quadrat to see how they recovered after the Exxon Valdez oil spill. (6 images)

More Information
  • An Ecosystem In Transition The graph on this page was prepared by our marine biologists, and looks much like the graphs you'll prepare as you complete this project.

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