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Trichodesmium Response to Ocean Acidification

Adviser: François M. M. Morel

Darcie E. Ryan


“Quitting never crossed my mind, even as I lay on the rocking ship deck, staring longingly at Bermuda’s silhouette on the distant horizon.”


Trichodesmium organisms are magnificent cyanobacteria that inhabit the surface ocean, fix nitrogen, and form spherical and raft-shaped colonies fittingly named “puffs” and “tufts.” Despite their size—colonies span just two millimeters—the ecologically important genus fascinates me, and I enjoyed completing my thesis about their response to ocean acidification. However, before my senior year, I barely knew what Trichodesmium were, much less how markedly they would change my life.

I began thesis topic-hunting during my junior year, fall semester, knowing three things. First, I wanted to study the ocean. A freshman introductory oceanography course inspired me to join the Princeton Department of Geosciences. The subject simply made me happy. Second, I wanted to incorporate climate change into my senior thesis to sate my desire for environmental stewardship. And third, I fancied conducting fieldwork on a research vessel, since the hands-on experience would aid future graduate school work.

When I expressed my thesis aspirations to a junior adviser, he introduced me to Professor François Morel, a professor whose research interests complemented mine. Though I originally intended to focus on calcifying phytoplankton and ocean acidification, Professor Morel suggested a less-studied organism: Trichodesmium. Since the Industrial Revolution, mean surface ocean pH has decreased; this phenomenon is called ocean acidification. Trichodesmium are important components of tropical and subtropical marine ecosystems, and lab-based work already had suggested that pH variations influence their carbon and nitrogen fixation rates. Fieldwork investigating the topic would provide new information, thus rendering my senior thesis relevant. With help from the Princeton Environmental Institute, the Bermuda Institute of Ocean Sciences (BIOS), and the Morel lab group, I started working that summer.

In brief, I collected Trichodesmium thiebautii colonies from the Sargasso Sea, incubated them in three pH scenarios on the RV Atlantic Explorer, and analyzed the samples later, on land. I will not pretend that the fieldwork progressed without a hitch. In fact, during my first cruise, seasickness felled me. Imagine catching the stomach flu on a spinning amusement park ride that never ends: This is seasickness. However, quitting never crossed my mind, even as I lay on the rocking ship deck, staring longingly at Bermuda’s silhouette on the distant horizon. My persistence stemmed from genuine fascination with Trichodesmium and ocean acidification. Trust me, if the subject had not been interesting (to me), I would have caught the first plane home after docking. I therefore recommend finding a thesis topic, no matter how obscure or unusual, that catches your fancy. Though not every senior weathers seasickness for their work, all will endure trying times, and the ultimate reward should exceed this inevitable adversity.

That summer, the fates eventually smiled on me, because after two sick days, I adjusted to life at sea. My experiments proceeded smoothly. Professor Morel, Dr. Michael Lomas of BIOS, and Dalin Shi of the Morel lab group supervised my work from beginning to end, and I cannot stress how important their assistance proved as I researched and wrote my thesis. In fact, my prime piece of advice to seniors embarking on their thesis journey is: When faculty or graduate students in your department offer help, accept it. They have more experience and knowledge than you, hands down. During my senior year, I met Dalin weekly and scheduled monthly conferences with Professor Morel. Their insight proved invaluable.

My thesis offered surprises as well. To strengthen the field results, I conducted laboratory research—basically, I studied protein concentrations in Trichodesmium erythraeum exposed to three pH regimes—during my fall and early spring semesters. Though my summer work yielded strong data, the lab work was ambiguous. I thereby learned that science can (and often will) be unpredictable. Even the best-planned thesis projects may not produce clear data trends. However, one should not be discouraged by inconclusive results because they are clues. Simply present your results honestly; during the Princeton Undergraduate Research Symposium, I described both successes and failures and still managed to snag a finalist prize.

In my humble opinion, seniors should treat their theses as beginnings, not ends. The project may directly or indirectly jump-start your career or graduate school work. In fact, as I study invasive tunicates during my current internship, I constantly draw upon my thesis experiences. The methodological approach to which I adhered during laboratory sessions, the communication skills I sharpened during research presentations, the time-management tricks I employed during spring thesis crunch time: These things help me daily. More importantly, perhaps, are the personal changes I underwent during senior year. Almost unconsciously, my work ethic and critical thinking skills improved. As I stepped through FitzRandolph Gate during the graduation ceremony, I felt like a more mature individual; I had accomplished something; I was prepared to move on.

So, to every person approaching his or her senior year, I wish you the best. Hopefully, you will find your own Trichodesmium.

Trichodesmium Response to Ocean Acidification

Darcie E. Ryan

François M. M. Morel

Albert G. Blanke Jr. Professor of Geosciences

“As I see it, the senior thesis plays a catalytic role in helping students transition from youth to adulthood.”

When I first met Darcie Ryan during her junior year, she struck me as an original. I was amused by her hat (she always wears a hat) and her forthright demeanor. From talking to her, it also became clear that she was bright (no surprise) and that she shared the optimistic idealism of many Princeton students: She wanted to save the world. All good reasons, it seemed to me, to make her grapple with the world, to push her gently into an experimental thesis. 

As I see it, the senior thesis plays a catalytic role in helping students transition from youth to adulthood. Experiments bring the messiness of the real world into the Princeton experience: Beakers break, well-planned experiments fail, great ideas require tedious verifications, and one gets seasick on the great blue ocean. All of that happened. And it was wonderful to see. Darcie took it in and got over it. She worked hard. She learned a lot about the world and about herself. She grew up several inches. And she still wears a hat.

Darcie’s thesis contributed a bit to our knowledge of the world. It also changed her. A great success by all measures.