Symbiotic Relationships in Science

When BIOS coral reef ecologist Samantha de Putron began tackling a project that required multiple, ongoing experiments to address a major portion of an overarching research question, she turned to a resource that scientists have long relied on: interns. And, much like the symbiotic algae in the corals that de Putron studies, this arrangement benefited everyone involved, including two Princeton University students who are using the opportunity to conduct their senior thesis research at BIOS.

Both fourth-year students at Princeton, Zoe Sims is majoring in ecology and evolutionary biology and Vivian Yao is pre-med and also majoring in geosciences. They were also both interns at BIOS in 2015, which allowed them to become familiar with the day-to-day operations of a research station and gave them the opportunity to collect preliminary data that would serve as a baseline for their work this year.

“It’s a mentor’s dream to have interns return as they can achieve a comprehensive study that is not always possible to complete in one summer, especially when working in the field or with animals in experimental treatments,” said de Putron of working with senior thesis students on her National Science Foundation (NSF)-funded research.

For her part, Yao is studying Bermuda’s corals to understand how nutrients are recycled between the coral animal and the symbiotic algae, called zooxanthellae, that live within coral tissues. Working with de Putron, as well as her advisor at Princeton, Danny Sigman, and Woods Hole Oceanographic Institution collaborator Anne Cohen, Yao is using a series of laboratory experiments to look at how corals respond under varying light conditions and feeding levels.

Yao’s research is an important component of the larger NSF-funded project, which is investigating the role of primary productivity in coral growth. Traditionally people think of ocean acidification and warming ocean temperatures as two major factors that negatively affect corals. But research shows that reduced nutrient supply due to changing ocean circulation could be a third significant impact on coral growth and survival, Yao said. Many global climate models predict that vertical mixing—in which water rich in plankton and other organic matter is carried from the deep to the surface layers—will be weakened. Without this crucial nutrient supply many corals might experience reduced growth rates.

Related to this, as well as a separate project in its own right, is Sims’ study on how groundwater discharge affects Bermuda’s coral reefs. Land-based groundwater is an often-overlooked source of nutrient input for coastal ecosystems, particularly in densely populated locations like Bermuda. The two-pronged approach to understanding the influence of groundwater on reef health involves both an ecological and a hydrologic component.

“The first question was, can we actually detect groundwater discharge along the coastline and, if so, what are the signatures and traits of that discharge?” Sims said. The next question was whether the groundwater nutrients are causing an ecological shift on the reefs—such as increased algal growth or loss of biodiversity—or if grazing pressure from algae-eating fish is keeping the ecosystem in check.

Under the guidance of Cohen, and assisted by de Putron, Sims is conducting field experiments to measure this grazing pressure from fish. She is also working to quantify groundwater discharge in nearshore waters, a topic of interest to the Bermuda government.

For both Yao and Sims, the opportunity to participate in independent research with a strong fieldwork component was an important part of their decision to conduct their senior thesis research at BIOS.

“This is the first time I’m undertaking a project of this size independently,” Sims said. “It’s an exciting experience getting used to having that kind of responsibility and being my own decision-maker, being able to choose the direction of the project for myself.”

De Putron, who has mentored four other senior thesis students from Princeton in the past six years, is excited to see Yao and Sims grow as scientists. “With returning students, and especially senior thesis students, you have this extra level of dedication and commitment,” she said. “It’s not just their work here during the summer, but they are taking data back with them and spending time analyzing it, so it’s a great opportunity for them to really see how longer-term research projects play out.”