Assessing the impact of ocean acidification on reef building corals

Summary
This activity introduces students to an actual data set that explores the impacts of ocean acidification on tropical coral reef ecosystems. Students are first given a scenario for a field site in the Caribbean and are asked to design an experiment that answers the question: How will a decline in surface ocean pH by the 21st century impact tropical coral growth? Students then gather actual data (from coral images collected from the field site) to calculate calcification rates of different coral samples. Finally, students use the provided saturation state values to predict the extent to which coral calcification is expected to decline by the 21st century.

Context

Audience

This lab has been mainly used as an activity in an upper-division writing course for Earth System Science majors, although it can be tailored to a lower division lab class that is covering the impacts of ocean acidification on marine ecosystems.

Skills and concepts that students must have mastered

Basic knowledge of climate change and ocean acidification are useful before beginning this activity, as well as a working knowledge of density. Usually this lab is prefaced with a short lecture on ocean acidification and the impacts of CO2 on ocean chemistry. Concepts related to pH, acidity, and saturation state are reviewed in this activity. Students would also benefit from having some knowledge of excel before beginning this activity, as well as how to calculate a set of averages.

How the activity is situated in the course

The activity is a standalone assignment designed to pull together many different stages of the writing process, from experimental design through data interpretation and analysis. Students are given a background lecture on ocean acidification and its impact on marine chemistry, and how ecosystems may be impacted by ocean acidification in the future. This lab serves to reinforce the concepts learned in relation to ocean acidification (pH, saturation state, calcification) while at the same time giving students practice with writing in science. Generally, this lab is done during the “results” section of the writing process, in which data is gathered and graphs are made. Therefore, concepts of hypothesis and experimental design are reviewed before the data collection portion of the lab. However, this lab can be tailored to a non-writing course as well by omitting the experimental design portion of the lab and simply focusing on the data collection and analysis. Additionally, students who have mastered excel can use excel to generate graphs and error bars, but those who have not had this practice can simply use the graphs provided in the worksheet (for less skilled students I have also omitted the standard deviation calculations and error bars). For the upper division students, I omit the tables and graphs provided and ask them to use excel to generate their tables and figures.

Goals

Content/concepts goals for this activity

Students should be able to accurately describe concepts of coral growth (extension, density, calcification). Additionally, students should be able to describe saturation state and the overall impact of ocean acidification on coral calcification during the 21st century.

Higher order thinking skills goals for this activity

Students should be able to design an experiment related to a real-world field-work scenario. Using their experimental design, they should then formulate a hypothesis that they will then test with data collected in the field. After collecting the data and constructing graphs, students should be able to interpret the data to predict how ocean acidification will impact coral calcification by the year 2100.

Other skills goals for this activity

This activity has been used in an upper-division writing course for Earth Systems majors, and is meant to reinforce the scientific method and the science writing process (from experimental design through data interpretation). Even if this portion of the activity is omitted, by the end of the activity students should be able to calculate averages and standard deviations in excel, make graphs, and produce error bars on their figures.

Description and Teaching Materials

If done in full, this activity takes approximately 3 hours to complete. In a prior class, students are first given a background lecture on ocean acidification and the impacts of OA on various biological and chemical processes in the ocean. This allows them to complete the activity with minimal interruption. However, the activity can be condensed by omitting the lab write-up portions, or by using hand-drawn graphs rather than excel. Typically, I ask students to work in groups of 3 on this assignment.
Students are first asked to read the introduction on the worksheet and discuss with their partners how the field site in question can be used to explore the impacts of ocean acidification on coral reef ecosystems. Once they have brainstormed ideas, students then design an experiment to answer the guiding question. At this point, the experimental design is very open ended and it is meant to test their ability to see the big picture. Students are asked to write their experimental design in the form of a methods section of a paper.
After writing their own methods section, students are then introduced to the actual study and how the scientists collected their data. They watch a short clip on data collection in the field, then proceed to collect their own “data” by making measurements similar to those made on real corals. For this part of the activity, they will need printed copies of the attached “Coral Image” file. I have found that the black and white images do not photocopy well, so use a fairly high quality printer. Students will require a ruler or other measurement device to measure the annual extension of the coral images. Because the scale bars on the image file don’t often match up with an actual ruler (depending on printing, etc), I have found it easiest to give my students a blank strip of paper that they can then use to measure distances based on the scale bar provided.
At this point, students can either use excel to calculate averages and generate figures (upper division students), or they can simply calculate averages and use the empty figures provided on the worksheet. Students then complete the worksheet in sequence, answering the questions and producing graphs in excel. For an instructor’s guide, please see the Instructor’s Guide attached.
Student Handout (Microsoft Word 2007 (.docx) 731kB Aug31 17)
Instructor Guide (Microsoft Word 2007 (.docx) 733kB Aug31 17)
Coral Image Files (Acrobat (PDF) 897kB Aug31 17)
Underwater Coring Video ( 13.5MB Aug31 17)

Teaching Notes and Tips

When printing the coral image files, it is best to use a high quality printer for each image rather than a photocopier, as I have found photocopies can be harder to see. Students often struggle with error bars and how they are interpreted, so it is often necessary to walk them through the first portion on coral skeletal extension so they have an easier time later on with the data interpretation. See the Instructor’s Guide for more details on the specifics of the activity and an answer key.

Assessment

Assessment will vary depending on whether this activity is being used to reinforce writing skills or ocean acidification-related content. To assess content accuracy, the worksheet can be used. To assess writing skills or figure preparation in excel, students are provided with a rubric before the activity so they understand the key points they need to address in their writing or figures.
Elizabeth Derse Crook, University of California-Irvine, August 2017. Activity.

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