Reef Builders through Time

Peg Yacobucci, Bowling Green State University-Main Campus
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Initial Publication Date: July 21, 2018 | Reviewed: March 12, 2023


Students will use the Paleobiology Database (PBDB) to explore the history of reef-building animals through time. They will document diversity and extinction patterns through time for seven reef-building marine animal groups, including sponges, corals, brachiopods, and bivalves. They will determine which groups were important components of reefs at different times in Earth history and investigate the relationship between reef builders and global climate and atmospheric carbon dioxide through the Phanerozoic. Finally, they will synthesize their findings to make predictions about how reefs may change in the future due to anthropogenic global warming.

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Upper-level undergraduate invertebrate paleontology course

Skills and concepts that students must have mastered

General familiarity with marine animal clades
General familiarity with geologic time scale
Ability to interpret data tables, bivariate plots, and time series

How the activity is situated in the course

Stand-alone exercise; can be done early in the course to show the relevance of paleontology to modern problems or serve as a synthesizing capstone project


Content/concepts goals for this activity

Key concepts:
- Reefs are biogenic carbonate structures that develop topographic relief upon the seafloor
- Different animals built reefs at different times
- An animal group may have built reefs at some times during its stratigraphic range but not at others
- Earth sometimes experienced episodes of greenhouse warming, alternating with colder icehouse conditions
- Greenhouse warming is associated with other environmental changes, such as sea level rise and ocean acidification
- Greenhouse times may have favored animals that use calcite to make their skeletons while icehouse times may have favored animals that use aragonite
- Reefs are sensitive to climate changes, including greenhouse warming and its associated effects
- Large datasets have both strengths and weaknesses

Higher order thinking skills goals for this activity

Analyze data
Synthesize observations to describe patterns
Recognize temporal trends
Critically evaluate data quality
Apply findings to make predictions

Other skills goals for this activity

Work with online data sources
Interpret graphs, including time series
Express thought processes through writing
Collaborate with others (if students work in groups)
Communicate and present conclusions (if students give class presentations)

Description and Teaching Materials

This activity can be done by individual students or student pairs, either in class or as a take-home assignment. One option is to start the activity in class, so students can get help with using the PBDB and answering the initial questions, and then have students complete the activity outside of class time.

Each student or pair receives a copy of the student worksheet, which includes the background information the students need and detailed, step-by-step instructions for using the Paleobiology Database Navigator web interface. Spaces for all student data compilation and written responses to the questions posed are provided on the worksheet.

To complete the activity, students will need Web access to use the Paleobiology Database and to research the typical mineralogy (calcite vs. aragonite) for the seven targeted reef-building groups. They optionally will also need access to textbooks or other print sources to confirm the mineralogies of the groups.

Time to complete the worksheet will vary from student to student, but it should take at least 1-2 hours. Optionally, different students can be assigned to look up different groups in the PBDB and then share their findings with the rest of the class. This approach can save time by dividing the workload among the students.

It is strongly recommended that the instructor facilitate a class discussion of the students' findings and experiences after students complete the activity worksheet. Optionally, students can be asked to present some of their findings to the rest of the class. The instructor can then prompt students to discuss a range of issues, including challenges they faced, the pros and cons of "big data", and how well they think they can predict future changes to reef ecosystems.

An answer key is provided.
Student Worksheet on Reef Builders through Time (Microsoft Word 2007 (.docx) 3.7MB Jul2 18)
Answer Key for Reef Builders through Time (Microsoft Word 2007 (.docx) 3.7MB Jul2 18)

Teaching Notes and Tips

If the instructor feels it is desirable to do so, s/he can provide a brief introduction to reefs and/or the PBDB before students start the activity. Students should be able to complete the activity, however, with minimal background instruction.

Note that the activity key was prepared in April 2018. Since the PBDB is continually added to and edited, the specific numbers of collections and diversity and extinction plots may vary over time. However, the activity requires students to describe broad temporal patterns that are not likely to be affected by new updates to the PBDB.

Students may struggle in interpreting the data on collection numbers and the diversity and extinction time series, as students tend to focus too much on little details instead of the overarching pattern. For example, tabulate corals show collection numbers above 1,000 in the Silurian and Devonian, bracketed by lower numbers (595 in the Ordovician and 394 in the Mississippian). Should they count the Ordovician and Mississippian as times in which tabulates were important, or not? The instructor can provide guidance here, perhaps by pointing out that it is up to the student to decide how to interpret the data and explain that choice. This can be an entry into a larger class discussion of how "real" scientific data always require interpretation by the scientist and there often is not a single right answer.

The students are likely to encounter some errors in the PBDB, potentially including errors in the original data sources, data entry mistakes, and coding errors in how information is presented in the web interface. Rather than ignore these errors, Question 8 in the activity asks students to identify one possible error and discuss it. As noted in the answer key, scleractinian corals reported from the Ordovician are one good example. As part of a class discussion of students' findings, it's great to ask students to report out on the errors they identified. The class can then talk about the pros and cons of "big data", including the heightened power of analyses using large sample sizes vs. the challenges of rooting out errors among so many data points.

Students may be confused that diversity and extinction patterns differ depending on the level of stratigraphic resolution used. For example, extinctions that look like they appear at period boundaries actually occurred earlier, within a single period, when plotted using stratigraphic stages as the smallest temporal units. A discussion of the pros and cons of different temporal resolutions is helpful here.

Students less familiar with the geologic time scale may need the Carboniferous vs. Mississippian and Pennsylvanian explained. They may also be confused by the plot of Phanerozoic atmospheric CO2 because the time scale on the plot runs in the opposite direction to the PBDB's time scale (right to left vs. left to right).

This activity can be a jumping-off point for more detailed investigations by the students. As one example, groups of students can select one reef-building group or one time when large reefs were common and do independent research into it, resulting in a paper and/or presentation to teach the rest of the class about that group or time. Or students may want to explore in more depth the idea of calcite vs. aragonite seas, or variations in biomineralization through time, or how a specific mass extinction affected reef vs. non-reef ecosystems, or even how the PBDB works. A variety of student-driven, authentic inquiry projects could stem from this initial activity.


Instructor check-ins with individual students or pairs (formative assessment)
Final responses to questions on the worksheet (summative assessment)
Class discussion of students' findings and experiences with the PBDB (summative assessment)

References and Resources

The Paleobiology Database.
Primary data source for the activity.

The Coral Reef Alliance. 2017. Coral reef biodiversity.
Overview of modern coral reef diversity from a non-profit group that conducts research and advocacy for coral reef conservation. Good place to point students who want to "do something" to protect reefs today, with suggestions for action steps anyone can take to protect reef ecosystems.

Hodges, Montana. 2016. Fossil Songs by Dr. George Stanley: The Rudist Rag.
Fossil reef expert Dr. George Stanley (University of Montana) sings an adorable song about rudist bivalves, key reef builders in the Cretaceous. Video intersperses images and information about rudists with Dr. Stanley's delightful performance.

Hughes, T.P., et al. 2018. Global warming transforms coral reef assemblages. Nature 556: 492-496.
Scientific report on recent large-scale coral bleaching on the Great Barrier Reef of Australia due to global warming.

Intergovernmental Panel on Climate Change (IPCC). 2014. Summary for Policymakers. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.
The IPCC Summary for Policymakers provides a detailed, state of the art summary of scientists' current understanding of anthropogenic climate change.

Khaled bin Sultan Living Oceans Foundation. 2015. Coral: What is it?
Visually appealing short (2:31 min) video that briefly explains how modern reef corals make their skeletons. Includes explanation of symbiotic relationship of coral and zooxanthellate algae.

National Geographic. 2017. Coral Reefs 101.
Short (3:52 min) video that explains reefs' importance as hosts of diversity and the threat of bleaching due to warming.

Ries, J.B. 2010. Review: geological and experimental evidence for secular variation in seawater Mg/Ca (calcite-aragonite seas) and its effects on marine biological calcification. Biogeosciences 7: 2795-2849.
Journal article that reviews the concept and evidence for calcite vs. aragonite seas.

Wood, R. 2011. General evolution of carbonate reefs. Pp. 452-469 in: Hopley, D. (ed.) Encyclopedia of Modern Coral Reefs: Structure, Form and Process. Encyclopedia of Earth Sciences Series. Springer, Dordrecht.
Excellent scholarly review of the history of reefs and reef builders through the Phanerozoic.