Project title
Reconstructing reef shark communities in the Tropical Eastern Pacific over millennia
Photo credit:Mentor name
Dr. Aaron O’Dea, STRI Staff, ODeaA@si.edu
Co-mentor name and position: Dr. Erin Dillon, STRI Postdoctoral Fellow
DillonE@si.edu; emdillon23@gmail.com
Location
Naos Marine Laboratory
Project summary and objectives
What were baseline levels of shark abundance and ecological function on coral reefs before humans? Historical accounts tell tales of seas teeming with sharks and other large predators in places where these animals are rarely seen today. Many shark populations have rapidly declined over the last half century due to overfishing, habitat degradation, and other human impacts. These losses have heightened sharks’ extinction risk, particularly in tropical ecosystems such as coral reefs. They have also resulted in complex and sometimes surprising consequences for ecosystem structure and function.
Yet, empirical evidence of past shark abundances is limited. Because humans began harvesting sharks prior to surveying their populations, available monitoring data do not extend far enough back in time to capture the full extent of shark declines. As such, we know little about the historical range of variability in shark abundance or the drivers of that variability. Without long-term data to contextualize what has been lost, it is challenging to design effective management targets informed by historical shark abundances and understand sharks’ natural functions as mobile predators on reefs.
Our research looks to the past for answers. We combine different types of paleontological, historical, and ecological records to reconstruct natural variability and patterns of change in reef shark communities over long ecological timescales. In particular, this project will use fossilized shark scales (dermal denticles) accumulating in marine sediments to reconstruct millennial-scale trends in shark abundance along the Caribbean and Pacific coasts of Panama. This new technique provides us with a “time machine” to explore the deeper ecological history of sharks on coral reefs before human impact and ask important questions about sharks’ ecological roles and historical baselines to inform shark conservation.
Using this approach, we aim to:
• Quantify variability in shark baselines. How abundant were sharks on coral reefs before human impact? How much do their populations vary naturally? What drives natural variability in shark baselines?
• Assess the magnitude and trajectory of millennial-scale change in shark communities. How much have reef shark communities changed over millennia in different regions, and why? How do sharks’ susceptibility to human impacts vary with environmental conditions? What might that tell us about their future recovery potential, especially in the face of rapid environmental change?
• Explore the functional consequences of shark declines. How have sharks’ ecological roles changed following their removal from reef ecosystems? How have shifts in shark abundance away from pre-exploitation baselines altered reef food web structure and energy flow?
Mentorship goals
Interns will work with an international and multidisciplinary research team, and they will have weekly meetings with mentors to discuss project goals and progress. Interns will learn how to process paleoecological samples in the lab and will gain experience working with microfossils under a microscope, analyzing data, and communicating their research with diverse audiences. They will also gain exposure to the fields of historical ecology and paleoecology in tropical marine ecosystems, including how data about past ecosystems can be used to inform current conservation efforts. There may be opportunities to participate in occasional field work to collect samples, although this project is primarily lab-based. Interns will be encouraged to attend lab meetings as well as seminars, professional development workshops, and networking opportunities at STRI.
Desired Background
Interns will assist with sampling and processing coral reef matrix cores to isolate tiny fossilized shark dermal denticles. This work involves sieving and weighing sediment samples, treating those samples with acetic acid, and sorting through sediment grains under a microscope to recover the dermal denticles and other microfossils, which requires patience and organization. Interns will also photograph and measure dermal denticles under a microscope. The internship could result in deliverables such as a scientific poster, conference talk, and/or contribution to a peer-reviewed article. Interns will take part in sharing their research with the public through lab tours and other outreach activities.
Desired qualifications include: previous experience working with ecological or paleontological data (preferred but not required); previous experience with microscopy (preferred but not required); knowledge of statistical methods (preferred but not required); willingness to learn programming languages such at R; ability to work independently and with groups of people from diverse backgrounds; attention to detail; and commitment to science communication and public outreach.
This internship opportunity is funded by the project. Interested candidates that meet the desired background are welcome to send their CV or resume, and a statement of your interest in pursuing this position to Dr. Erin Dillon to DillonE@si.edu
List of suggested readings
Dietl, G. P., and Flessa, K. W. (2011). Conservation paleobiology: putting the dead to work. Trends Ecol. Evol. 26, 30–37. doi: 10.1016/j.tree.2010.09.010.
Dillon, E. M., McCauley, D. J., Morales-Saldaña, J. M., Leonard, N. D., Zhao, J., and O’Dea, A. (2021). Fossil dermal denticles reveal the preexploitation baseline of a Caribbean coral reef shark community. Proc. Natl. Acad. Sci. 118, e2017735118. doi: 10.1073/pnas.2017735118.
Dillon, E. M., Norris, R. D., and O’Dea, A. (2017). Dermal denticles as a tool to reconstruct shark communities. Mar. Ecol. Prog. Ser. 566, 117–134. doi: 10.3354/meps12018.
Jackson, J. B. C. (2001). What was natural in the coastal oceans? Proc. Natl. Acad. Sci. 98, 5411–5418. doi: 10.1073/pnas.091092898.
Jackson, J. B. C., Kirby, M. X., Berger, W. H., Bjorndal, K. A., Botsford, L. W., Bourque, B. J., et al. (2001). Historical overfishing and the recent collapse of coastal ecosystems. Science. 293, 629–638. doi: 10.1126/science.1059199.
Lotze, H. K., and Worm, B. (2009). Historical baselines for large marine animals. Trends Ecol. Evol. 24, 254–262. doi: 10.1016/j.tree.2008.12.004.
Pacoureau, N., Rigby, C. L., Kyne, P. M., Sherley, R. B., Winker, H., Carlson, J. K., et al. (2021). Half a century of global decline in oceanic sharks and rays. Nature 589, 567–571. doi: 10.1038/s41586-020-03173-9.
Roff, G., Doropoulos, C., Rogers, A., Bozec, Y.-M., Krueck, N. C., Aurellado, E., et al. (2016). The ecological role of sharks on coral reefs. Trends Ecol. Evol. 31, 395–407. doi: 10.1016/j.tree.2016.02.014.
Sibert, E., Cramer, K., Hastings, P., and Norris, R. (2017). Methods for isolation and quantification of microfossil fish teeth and elasmobranch dermal denticles (ichthyoliths) from marine sediments. Palaeontol. Electron. 20, 1–14. doi: 10.26879/677.
