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Colvin Winner Contributes Explicit Evidence for Impact of Climate Variability and Nutrients on Bermuda Corals


Hannah Barkley ’11 examining juvenile corals under the microscope. (Photos courtesy of Hannah Barkley ’11)

Each spring, the Princeton Environmental Institute (PEI) and the Department of Ecology and Evolutionary Biology jointly award the Becky Colvin ’95 Memorial Award. This prestigious undergraduate research fellowship supports outstanding proposals for environmental field research projects in preparation of the recipients’ senior theses. The prize was established in 1995 by Dr. and Mrs. Robert Colvin in memory of their daughter, Becky Colvin ’95. Becky was an ecology and evolutionary biology major who was committed to field research.

Hannah Barkley '11, the 2010 Colvin Award winner, spent last summer conducting research for her senior thesis at both the Bermuda Institute of Ocean Sciences (BIOS) and at the Woods Hole Oceanographic Institute (WHOI) in Massachusetts. PEI News spoke recently with Hannah about the pioneering research she conducted for her senior thesis.

Please describe your senior thesis project and explain how the Colvin funds supported your research.

The tentative title of my senior thesis is Establishing Links between Basin-Scale Climate Variability and the Growth of Atlantic Corals: The Effect of Temperature and Feeding on Favia fragum. The main goal of my thesis is to understand how changes in the North Atlantic Oscillation affect the growth of Bermuda corals.

Research has shown that the growth of Bermuda corals is tightly linked with different phases of climate phenomena in the Atlantic. The dominant mode of climate variability in the Atlantic is the North Atlantic Oscillation. Like the better-known El Nino Southern Oscillation, the North Atlantic Oscillation causes periodic shifts in atmospheric and ocean conditions in the Atlantic Ocean. These changes, which include shifts in ocean temperatures and nutrient concentrations, have marked effects on coral reefs and ocean life.

During my summer thesis research, supported by Colvin Funds, I explored the mechanism by which variability in climate can affect the growth of corals. I also researched the effects of temperature and feeding on corals to determine how these factors interact and whether increases in food availability and feeding could be responsible for the observed correlation between coral growth and North Atlantic Oscillation events. To do this, I conducted a four-week experiment at the Bermuda Institute of Ocean Sciences (BIOS). I collected adult corals from Bermuda reefs and gathered the larvae that they released. I then raised the juvenile corals in different temperature and feeding conditions and quantified the effect of each condition on the physiology and skeletal growth of the corals. After finishing my experiments in Bermuda, I traveled to Woods Hole Oceanographic Institute (WHOI) in Massachusetts to analyze my samples. I found that both temperature and feeding had positive effects on coral growth, but that the effect of feeding was much greater than that of temperature. Because feeding appears to drive coral growth rates, my results may explain the patterns we are observing in Bermuda corals in relation to climate variability.


Hannah Barkley ’11 in Bermuda, preparing to collect adult corals from near-shore reefs.

Why is your research important, and do you hope it will have an impact beyond the campus?

It is extremely important that we understand these effects because models predict that North Atlantic Oscillation events will shift toward phases of higher temperature and lower nutrient availability in the future in response to climate change. We therefore must understand how the phases of the North Atlantic Oscillation affect coral growth if we are to anticipate how reefs will react and to establish any necessary conservation measures. While my work is a preliminary finding in a new field, I intend in the near future to publish my results to increase scientific dialogue concerning the interaction of coral reefs and climate.

Please provide details about particularly innovative aspects of your research or results.

My senior thesis is the first experimental study that addresses the effects of North Atlantic climate variability on corals. While many studies have acknowledged the relationship between climate phenomena and coral growth, none have conducted experimental studies to test the effects. My experiment is also the first to examine the interaction of temperature and feeding in a tropical coral species. We still understand very little about the effect of coral feeding on skeletal growth, especially in juvenile corals, and this research provides some of the first evidence that feeding can influence skeletal growth rates in corals.

What surprised you the most about your results?

I was most surprised by how much of an impact a coral’s ability to feed itself has on its own growth. Reef-building corals have photosynthetic algae that live within their tissues and transfer the products of photosynthesis to their coral host. Until recently, this endosymbiotic relationship between the coral and the photosynthetic algae was believed to be the sole source of food for reef-building corals, and therefore the sole genesis of coral growth. It is now better understood that corals also obtain nutrients directly from the water, but I was surprised that these external energetic inputs from feeding had such a significant effect on coral growth.

Were you able to accomplish what you originally intended, or did the parameters of the project change once you began?

I was fortunate that, due in large part to the help of my advisers, my experiment ran smoothly, which meant that I was able to conduct the research that I originally intended at BIOS and WHOI. However, I did initially have problems obtaining juvenile corals for my research. I was unable to use the first coral species I collected because the adults didn’t spawn, so I had to use a different species than I first intended.

My adviser at Princeton is Professor Stephen Pacala, and I’ve also worked very closely with Dr. Samantha de Putron at BIOS and Dr. Anne Cohen at WHOI (who conducted the original research off of which my project was based). All three of my advisers have contributed enormously to my project: Dr. de Putron in her knowledge of coral biology and recruitment and her guidance in Bermuda, Dr. Cohen in her expertise in coral biogeochemistry and assistance with my lab analyses at WHOI, and Professor Pacala in helping me to analyze, understand, and write up my results.

What were the most important lessons you learned while conducting your research?

I learned a lot about coral biology from this research, but the most valuable lessons I learned were about conducting field research. This was my second summer doing research at BIOS, and so while I was familiar with coral research and the challenges associated with it, I still learned a lot about carrying out field and lab studies. I especially learned how to think quickly to solve problems and adapt my methods in response to challenges. Going through the process of designing, carrying out, analyzing, and writing up my own research has been extremely valuable.

Will this experience have an impact upon your career path following graduation?

This research experience has had a huge impact on my future career path! I am actually going to graduate school next year to continue my research on corals. I will continue to work with Dr. Anne Cohen as a student in the joint program between MIT and WHOI. My research at Princeton has focused on understanding the effects of environmental stressors on coral growth and calcification. For my graduate research I hope to extend this understanding to research effective conservation strategies to save threatened coral reef ecosystems. I ultimately hope to work in conservation, especially in developing strategies for coral reef conservation.

Do you have any advice for next year’s Colvin winner?

Plan ahead! This experience has taught me how important it is to have every aspect of a study planned out, including experimental design, analytical techniques, and statistical analyses. At the same time, field research is unpredictable and it almost never goes as planned! It is important to have a plan, but it is equally important to be able to revise it quickly and as needed.

Tag(s): ss-2011