How Marine Life Adapts to a Warming World: Estefany Argueta Herrera Investigates how the Reproductive Behavior of Green Sea Turtles and the Movement of Black Sea Bass are Re-shaping Marine Ecosystems
by Chamini Kulathunga
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Story by Chamini Kulathunga, UMass Amherst Public Writing Fellow
On a moonlit beach in northeastern Brazil, a green sea turtle lays her eggs in the chamber she’s been digging with her back flippers for the past hour. Next to her is a group of ecologists doing fieldwork in experimental physiology, witnessing the birth of a resilient species that has been swimming in Earth's oceans for more than 100 million years, surviving since the extinction of the dinosaurs. “Once they start laying their eggs is when we approach the turtle because they go into almost a trance-like state, barely moving. That's when we could touch them. We apply metal tags, take measurements, and snap a photo of their faces for visual ID. It's always magical. We hear their breath with every push and see their little tears,” says Estefany Argueta Herrera, a PhD student researcher in the Organismic and Evolutionary Biology (OEB) program at the University of Massachusetts Amherst.
For Argueta, moments like these are more than opportunities to witness nature’s oldest rituals. They contain artifacts that hold answers to an important question of our time: how does marine life adapt to a rapidly changing climate? Argueta’s research focuses on the effects of global warming on two marine organisms. In one of her projects, she observes green sea turtles on Fernando de Noronha island in Brazil to estimate how many male turtles, whose numbers may decline as rising beach temperatures produce more female hatchlings, are currently contributing to reproduction.In another, she looks at the expansion of black sea bass in the Gulf of Maine. They are traditionally found in the warm water of Gulf of Mexico, Florida, and North Carolina but they are now expanding into the cold waters.
What is remarkable about both projects is that they allow Argueta to ask questions about the evolution of these organisms at different levels of their biological hierarchy—from the smallest DNA, protein, and cellular levels to organs, whole animals, populations, and eventually, how it manifests at the level of entire ecosystems. “In a way, my work as an ecologist allows me to ask questions at the source”, explains Argueta. Exploring how these changes affect organisms and their performance—whether it is energy use, thermal tolerance, or stress tolerance—also sheds light on how changes in marine ecology at this biological level affect communities whose livelihoods depend on them, such as local fishers.
Argueta grew up in the landlocked state of Iowa, far from the oceans where she now spends much of her time studying marine life. A high school marine biology program and pre-college STEM program, during which she spent two weeks camping and studying painted turtles and their nesting biology along the Mississippi River, sparked her interest in aquatic ecosystems. She later joined Iowa State University to study animal ecology as an undergraduate. Every summer, she made sure to nourish her love for marine biology through internships and ecology courses, which took her to places like Oregon, Chile, and Alaska.
At UMass Amherst, Argueta's research on turtles is based on the Temperature-Dependent Sex (TDS) determination of turtles. Unlike in humans and all mammals, turtle sex is not determined by chromosomes; it is driven by the temperatures of the sand where the eggs are incubated. “In cool temperatures, we get males, and in warm temperatures, we get females. As beach sand temperatures warm globally, it poses a global problem because our models are projecting over 90% female production in eggs. So, there's a concern that there might not be enough males to sustain sea turtle populations,” explains Argueta. Her research strives to understand how many males are currently taking part in reproduction in the regions she studies, and what mechanisms or behaviors could sustain those numbers.
However, male sea turtles are notoriously difficult to study because they rarely come ashore. To solve this mystery, Argueta and her team conducted what she calls "a big paternity test on sea turtles." The team collected over 13,000 skin samples from turtle mothers and their babies off the coast of Northeast Brazil. Using these samples, they subtracted the mother’s information to produce the father's genetic information, which allowed them to calculate how many male turtles are contributing reproductively to the population even without seeing them. Another aspect that Argueta looks at is multiple paternity in turtles. Because female turtles mate every 4 to 6 years and males can mate every year or 2 years, Argueta says, “Maybe it's okay to have an off-skew ratio of males to females. This is something I am trying to understand”.
Argueta describes field work in marine systems as an almost spiritual experience, where one is at the mercy of nature. “When I was doing field work on turtles, I was nocturnal for 3 months because that’s when they come out of the ocean to lay their eggs. With the fish project, it was early mornings because you are at the whim of the ocean and its tides, which affect their behavior. Nature is in control, and it waits for no one. My schedule is determined by that,” she explains.
Argueta chose UMass Amherst for her graduate studies specifically to work with her advisor, Dr. Lisa Komoroske, whose research on sea turtles aligned with her own interests. Although her initial interest was to join the Brazil sea turtle project, she also discovered a collaborative community at UMass that extended beyond a single laboratory. Faculty members, researchers, and mentors across campus and at the nearby U.S. Geological Survey's Conte Anadromous Fish Research Center helped shape her current research, introducing her to new techniques and collaborations that expanded her work from sea turtles to marine fish. She also credits the Department of Organismic and Evolutionary Biology's collaborative culture, including its interdisciplinary Behavior, Morphology, Physiology, Ecology, Evolution (BAMPHEE) seminar series, for fostering a community where researchers freely exchange ideas, mentor one another, and support ambitious scientific questions. "I've been lucky to be around people who do great research and who want me to be part of their team," says Estefany. “I also want to give a shout-out to Dr. Steve McCormick, who is a retired faculty member but who provides me with continuous feedback and advice. He believes in my work, and he sometimes comes out of his retirement to take me fishing on his boat to get the animals I need to observe for my research,” she added.
Apart from her research, Argueta also tutors K-12 students from underrepresented backgrounds, reflecting her commitment to improving access to STEM education. She hopes to continue supporting programs that foster a sense of belonging and opportunity for aspiring young scientists, motivated by the programs that similarly supported her to find her way into science. As the first person in her immigrant family to pursue a PhD, she sees education as a way of expanding possibilities. "I love to learn, and I want others to understand that they all have the ability to learn and excel in these subjects. It’s astounding to think that my curiosity could take me this far. I now get to be a part of these massive projects in these remarkable areas of the world where I witness nature at its rawest forms. I'm living a life bigger than what I dreamed of,” says Argueta with a gentle smile.
Argueta is the recipient of the NSF Graduate Research Fellowship Program, the Armstrong Graduate Student Research Grant, the Richard Cronin Fisheries Research Award, and the Spaulding-Smith Fellowship. She also thanks the Projeto TAMAR, Florida State University, and Oregon State University for the Brazil/sea turtle work, the U.S. Geological Survey’s S.O. Conte Anadromous Fish Research Center and Gloucester Marine Station for their collaborative support. Following graduation, Argueta hopes to pursue future research opportunities that would allow her to return to Brazil and expand her work on sea turtle reproductive ecology, while continuing to build research questions across both fish and turtle systems.
Argueta’s work is a reminder that every species has a story to tell about our changing planet and understanding them at different levels of their shifting biology helps reveal the delicate connections that sustain entire ecosystems.