Ocean Acidification and Oysters
Hilary Palevsky
Overview
Note: Additional materials relating the concepts in this lab to general high school chemistry are available. Please contact uwpcc@uw.edu for more details.
Focus Questions:
- How does seawater chemistry –both pH and aragonite saturation state – affect larval oyster growth?
- How do local physical and biological processes control the short-term variability of seawater chemistry in the Pacific Northwest?
- How will seawater chemistry change over the 21st century and how will this affect Pacific Northwest oyster growers?
Part 1:
Students calculate the saturation state of aragonite (the CaCO3 mineral in oyster shells) in the hatchery’s seawater and graph its relationship with the success of larval oyster growth.
Part 2:
Students analyze variations in seawater pH and aragonite saturation state at the hatchery over a two month period and determine how daily cycles of photosynthesis and respiration as well as episodic upwelling cause these variations.
Part 3:
Students compute how ocean acidity is projected to change in the future and predict how this will affect the ability to grow oyster larvae at the hatchery.
Learning Goals:
Students will be able to…
- Explain how increasing carbon dioxide in the atmosphere is changing ocean chemistry.
- Explain how and why organisms with calcium carbonate shells are affected by ocean acidification.
- Connect ocean acidification with its impacts on the local Pacific Northwest economy through the oyster aquaculture industry.
- Identify and explain the dominant processes controlling short-term variability and long-term changes in coastal Pacific Northwest ocean chemistry.
- Calculate changes in ocean acidity and predict how these changes will affect oyster aquaculture.
Background Information for Teachers
As carbon dioxide from burning fossil fuels is added to the atmosphere, much of that carbon – 30% of all fossil fuel carbon dioxide emitted to date – is absorbed by the ocean. The carbon dioxide combines with water to form carbonic acid, leading to an increase in ocean acidity (a decrease in ocean pH). This alters the balance of carbonate chemistry in seawater, decreasing the concentration of the carbonate ion (CO32-), an important building block for the calcium carbonate shells made by many marine organisms. (For more detail see the additional background materials under supplemental resources.)
The oyster aquaculture industry in the Pacific Northwest is a case study in how ocean acidification can impact socially, economically and environmentally-important marine ecosystems worldwide. It also provides a positive example of how scientific information can guide effective human adaptation to the challenges posed by climate change, as oyster hatcheries now routinely use results from coastal water chemistry monitoring programs to guide their decisions about how to schedule larval production and maintain favorable seawater quality.
The data for this activity comes from a collaboration between the Whiskey Creek Hatchery and scientists at Oregon State University, initiated to determine whether ocean acidification was responsible for observed declines in oyster larval production at the hatchery. The same data the students work with in their Excel analyses, and graphs very similar to those the students generate, were published in the journal Limnology and Oceanography in 20121 and have been adapted for this module.
1Barton, A., B. Hales, G.G. Waldbusser, C. Langdon, R.A. Feely (2012). The Pacific oyster, Crassostrea gigas, shows negative correlation to naturally elevated carbon dioxide levels: Implications for near-term ocean acidification effects. Limnology and Oceanography 57(3), 698-710
Prior Knowledge for Students
This module is designed so that it can be used both with students who are already familiar with ocean acidification as well as students who are new to the subject. The introductory lesson and accompanying PowerPoint slides include sufficient background on ocean acidification for all students to complete the rest of the module. Teachers can easily modify the introduction to remove or move more quickly through information already covered. Also see the supplementary materials for additional ocean acidification resources that we recommend for use in combination with this module.
Part 2 assumes that students are already familiar with the biological processes of photosynthesis and respiration and how they consume/produce CO2, as well as the physical process of upwelling in the ocean. If these subjects have not previously been covered, three additional PowerPoint slides have been included to facilitate the teacher giving a very general overview of these subjects prior to students beginning Part 2 in order to prepare students to complete the activity. Be sure to allow for additional time to complete Part 2 if this material needs to be covered.
Anticipated Challenges
Experience has shown that students are more successful in completing the data analysis if they have some prior experience with Microsoft Excel. However, this module can still be completed by students with little to no prior Excel experience as long as extra time is allowed. The detailed instructions provided in the worksheets are written for PC version of Microsoft Excel 2010. If student computers have a different version of the software, worksheet instructions should be modified by the teacher to match the version used in class.
Assessment
If desired, students’ completed worksheets from this module could be collected and graded using the teacher key provided. For a more formal assessment of student learning, exam questions based on the data and learning goals from this module are included in the accompanying teacher materials.
Materials
- Lesson Powerpoint Slides
- Microsoft Excel workbook with data to analyze (in the PCC Google Drive folder)
- Worksheets to accompany each part of the module
- Answer keys (request password from uwpcc@uw.edu)
Procedure
Preparation:
Download both the student and teacher (key) versions of the Microsoft Excel data workbooks and accompanying worksheets, as well as the PowerPoint slides.
Prior to using the lesson in class, teachers should complete the entire module to ensure they are prepared to answer student questions while completing the activity in class. Follow the worksheet instructions to complete the calculations and graphing in the student version of the Microsoft Excel data workbook, and review the worksheet answers provided in the key for teachers. The teacher should also review the accompanying PowerPoint slides to prepare to give the introductory lecture with any necessary modifications to appropriately fit what has been previously covered in the course. Prior to beginning Part 1 in class with the students, ensure that there are computers available with Microsoft Excel and that students will have access to the student version of the data workbook (through a course website, Moodle, Edmodo, etc.).
Introduction: Teachers should select how to introduce this module based on the extent to which ocean acidification has been previously covered in the course. A set of PowerPoint slides with accompanying lecture notes is provided with sufficient information to provide an introduction for classes that have no prior exposure to the topic of ocean acidification. Teachers are encouraged to modify these slides to fit their class. Slide #6 presents the equations that students will be expected to use in Part 1, and slides #9-11 introduce the specific case of the oyster aquaculture industry in the Pacific Northwest that will be addressed in this module, so it is recommended that these slides be used in all classes even if other portions of the introduction are omitted or modified.
Part 1: In this part, students compare their theoretical predictions with actual data showing how changes in the aragonite saturation state of seawater affect larval oyster growth. Students should each individually or in pairs (depending on how many computers are available) to work through Part 1 of the worksheet and complete the calculations and graphing using the Part 1 tab of the Microsoft Excel workbook. The student worksheet gives detailed instructions on how to make the graph in Part 1. However, it is strongly recommended that the teacher work through the worksheet and data analysis in advance using the same version of Excel that the students will use in class in order to check that the instructions match the version of Excel that will be used and in order to anticipate any student challenges.
Questions 1-4 ask students to demonstrate their understanding of the calcium carbonate dissolution reaction, how to calculate the aragonite saturation state, and how to use that information to determine which direction the reaction will proceed. This information will have already been covered in the introduction, but the teacher should observe the students’ answers to ensure that they understand this material before proceeding.
While the students are completing Excel calculations and graphing, the teacher should circulate among the students to answer questions and check for major errors in student progress. If many students are having problems with the same part, it is helpful to have the Excel data loaded onto a computer connected to a projector so that you can demonstrate the correct procedure.
At the end of the class period, review the students’ responses to the worksheet as a class, including showing an example of the final graph they each should have produced (in the accompanying PowerPoint slides) and asking students to share their interpretations of the data in questions 8-9.
Part 2: In this part, students observe how diurnal photosynthesis and respiration and episodic upwelling control short-term variability in seawater chemistry. Students should continue to work individually or in pairs through Part 2 of the worksheet, completing the calculations and graphing in the Part 2 tab of the Microsoft Excel workbook. This part does not include graphic illustrations of how to use Excel, although step-by-step procedures are still provided for graphing. If students have not previously used functions in Excel, the teacher should briefly explain how to do this before they calculate the 1-day running mean in Question 4 using the AVERAGE function. It is again strongly recommended that the teacher work through the worksheet and data analysis in advance of the students completing the activity in class.
At the end of the class period, again review the students’ responses to the worksheet as a class, including showing examples of the final graphs they each should have produced (in the accompanying PowerPoint slides). Ask students to explain the role of photosynthesis, respiration and upwelling in the data and ask them to share their ideas about how the hatchery can use this information to change their practices. This is a good opportunity to conclude the class period on a positive note by explaining that Pacific Northwest oyster hatcheries are in fact using this information to adapt their practices, and that the industry has recovered as a result of improved scientific understanding and monitoring.
Note that three optional slides are provided in the PowerPoint for this part, which are designed for use in classes where students are not already familiar with photosynthesis, respiration and/or upwelling to provide an overview of these concepts prior to students beginning work on Part 2. These slides can be skipped if this material has already been covered.
Part 3: In this part, students calculate how ocean acidity is projected to change over the 21st century, compare this long-term change to the existing variability in Netarts Bay that they described in Part 2 and predict how continued anthropogenic carbon emissions will affect the oyster hatchery. Once students have completed the worksheet, review the students’ responses as a class using the accompanying PowerPoint slides for additional figures showing projections of future changes to pH and aragonite saturation state.
Selected Supplemental Resources
Materials on oyster aquaculture in the Pacific Northwest (suggested for a deeper overview of the social and economic context):
- http://vimeo.com/93272507 – 4-minute video from Taylor Shellfish Farms in Shelton, WA about their business and how it is affected by ocean acidification
- http://apps.seattletimes.com/reports/sea-change/2013/sep/11/oysters-hit-hard – article from the Seattle Times on oyster farmers’ adaptations to ocean acidification (Part 3 of an excellent reporting series on ocean acidification – the entire Sea Change series is recommended if you want readings covering ocean acidification in a variety of contexts)
Additional teaching resources on ocean acidification:
- Institute for Systems Biology Ocean Acidification module (including links to a variety of outside content): http://baliga.systemsbiology.net/drupal/education/?q=content/ocean-acidification-systems-approach-global-problem
- Virtual Urchin online lab from Stanford University: http://virtualurchin.stanford.edu/AcidOcean/AcidOcean.htm
- Center for Microbial Ecology Education and Research (C-MORE) Ocean Acidification science kit (hands-on labs focused on corals): http://cmore.soest.hawaii.edu/education/teachers/science_kits/ocean_acid_kit.htm
- Ocean Carbon and Biogeochemistry (OCB) hands-on labs and demo: http://www.us-ocb.org/publications/OCB-OA_labkit102609.pdf
Additional background on ocean acidification:
- http://www.nanoos.org/education/learning_tools/oa/ocean_acidification.php – Recommended for an excellent collection of additional ocean acidification-related websites and videos in the right sidebar. NANOOS also hosts a Visualization System for exploring ocean chemistry data from all around the Pacific Northwest.
- http://www.skepticalscience.com/docs/OA_not_OK_Mackie_McGraw_Hunter.pdf – Comprehensive but accessible overview of the chemistry behind ocean acidification, also including a lot of additional context about the global carbon cycle
- http://www.aseachange.net/ – 83-minute documentary about ocean acidification, through the eyes of a retired teacher concerned about the world his grandson will live in, who travels around the world to learn from scientists about their current research on ocean acidification (including great footage of field research). Not freely available, but can be rented/purchased from the website.
