Instructions

Class Period One:

1) Show the video, Hawaiʻi’s Reefs: Oceanic Oasis (8 minutes). Rewind the tape when you finish, so it’s ready to be played again later in the class.

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2) Hold a brief discussion about the video: Did students learn anything new? What struck them from the video?

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3) Pass out a copy of the Student Page “Reef Fish Checklist” to each student and review the instructions. Also pass out the “Reef Fish Identification Chart” to each student or small group.

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4) Play the video again, this time with the sound off. Students will be filling in the 1st Survey Column of the “Reef Fish Checklist” as they watch the video. Once again, rewind the tape when you finish, so it’s ready to be played again.

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5) Briefly discuss students’ experience with this exercise by asking, “What are some of the challenges facing divers who do underwater fish surveys?”

Some of the answers might include the numbers of fish to count, the fact that the fish are moving, uncertainty about whether a particular fish has been counted before, and having to recognize species quickly.

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6) Ask students whether they think it would be easier to accurately count fish if they could see the video again.

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7) Test their predictions by playing the video again (with the sound off) and having students fill in the 2nd Survey column of the “Reef Fish Checklist.”

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8) Ask students whether they see a difference in their counts. If so, do they think their counts were more accurate the first time or the second time? Why?

For anyone conducting fish surveys, there is a learning curve during which they become more familiar with the species of fish they are likely to see. Their observations become more accurate as they learn.

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9) Have students pair up with a partner and compare their findings by filling in the second page of the Student Page “Reef Fish Checklist.” Students should simply compare observations with each other. Each student should fill in his or her partner’s tallies from the second video survey where indicated on the student page. Students should not complete the calculations at this time.

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10) Bring the class back together and ask whether they saw differences in their partner’s observations and theirs. If so, why do students think these differences might occur? How do they think that differences between observers might influence the results of a coral reef monitoring study? How could researchers compensate for those effects?

This effect is called “observer bias” in research studies. Even with extensive training, underwater observers generally do not record exactly the same data. One way to compensate for observer bias is to pair researchers to make observations and adjust the data to reflect the differences in data sets.

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11) Assign the remainder of the student page as homework.

Class Period Two:

1) Hand out the Student Page “Estimating Percent Cover.”

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2) Tell students that researchers often use “percent cover” as a way of estimating the species composition of a coral reef. This means they are looking at how much of the ocean’s floor is covered by corals, and which types of corals. Tracking changes over time helps them describe and evaluate the health of the coral as well as growth and change within the reef community. Changes in the relative proportions of coral reef species, as well as in total coral coverage, are both important. Percent cover is used to evaluate other types of marine and terrestrial habitats, as well.

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3) Have students work through the activity, making all estimates and calculations.

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4) Write the actual percent black cover for each of the figures on the board. Figure #1 is 36 percent black. Figure #2 is 34.5 percent black.

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5) Review student results using the following discussion questions:

• Were students more accurate at estimating cover when the shapes have straight sides or when they are rounded? What implications might this have for the study of coral reefs?

Coral reef researchers must estimate percent cover of irregularly shaped coral, adding difficulty to an already tricky task.

• Were students more accurate at estimating cover with or without the grid? What might explain this? What implications does it have for studying percent cover on coral reefs?

Breaking up a larger area into smaller areas typically increases accuracy. For even more accurate analysis, many studies of coral cover use a system in which slides of the reef taken at designated locations along a transect are projected over an image containing many randomly selected coordinates. At each set of coordinates, the substrate/cover is recorded and an average made based on those data.

• Which was more accurate, using all of the cells in the grid, or just a sample?

Although using all of the cells may be more accurate than just a sample, it is not feasible for researchers to examine every bit of the extensive coral reefs they study. The trick is to make the sample size large enough to estimate coverage with confidence but small enough to be manageable. Researchers have spent much effort testing the validity of their sampling schemes.

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6) Divide students into pairs. Give each pair one copy of the Student Page “Get the Point.”

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7) Explain that researchers collect data about the presence and abundance of marine species in different ways.

• One way is to set up a “transect” (a line across the reef) and swim along it, counting and recording fish and other species, or stopping at predetermined points to make and record observations. The exercise with the video observations was something like this, only there was not a continuous transect.
• In the “visual strip-transect search” method, for example, two divers swim side-by-side down either side of a transect, counting all fishes seen within a corridor three meters wide and extending to the surface. In another method, divers make one pass along the transect, recording fish they see swimming above the reef and a return pass to search for organisms sheltered in cracks and crevices.
• Another approach, most often used when looking at coral cover or at invertebrate species that live on the reef, is to set up a transect and then to sample at points along that transect.
• One sampling method, called the “point-intercept” method, involves identifying the type of cover at various sampling points along the transect.
• Another sampling method is called the “photoquadrat” method. With this method, researchers use an underwater camera fitted with a square frame that enables researchers to take a picture of a small square portion of the ocean bottom, and then to analyze what is in that photograph later. Researchers may set up fixed locations for these photoquadrats that they return to again and again to track changes over time. This is called the “fixed photoquadrat” method.

When researchers analyze the photographs, they generate a number of points that they overlay onto the photograph, recording the type of cover that lies directly underneath each point. Researchers then extrapolate percent cover of various corals based on this sample.

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8) Have student partners work through the photo analysis exercise on the student page. (Note: The area in the photo not covered by the blue leather coral is the rock substratum and small growths of algae, sponges, or other organisms.)

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9) If there is time left, briefly discuss the photo analysis by asking, “Why is this a good way to estimate percent cover?” and “What do researchers need to know or do to make this technique accurate?”

Photo analysis is a good way to estimate percent cover because the analysis itself takes place out of the water and can be more rigorous than analyses conducted underwater. It also allows researchers to track changes in particular areas over time. To make this technique accurate, researchers must take all photographs from the same distance away from the ocean bottom and must be able to identify organisms based on the photographs.

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10) If students need more time to finish their photo analysis, have each partner take home the photo he or she was working on during class, and allow partners some time during the following class period to compare results. During this time, you may also wish to discuss student responses to the questions in the Student Page “Get the Point.”