Assistant Professor of Marine Biosciences Jonathan
Cohen studies the visual ecology of marine
invertebrates like Scina crassicornia, the red-eyed
amphipod pictured below.
Above photo by Lisa Tossey
Ralph Waldo Emerson once said, “People only see what they are prepared to see.” The same could be said of krill.
The tiny crustaceans’ eyes are specialized into two parts, one to detect the color the green and the other to see violet. Why would they need such unusual eyes? That is just the kind of question that fascinates Assistant Professor of Marine Biosciences Jonathan H. Cohen, who joined the College of Earth, Ocean, and Environment last fall.
“As humans looking at sensory systems, we put our view of how we perceive onto different animals and assume they function the way we do,” he said. “It’s better to ask: How does the world appear to the organism?”
Cohen is using physiological experiments, microscopy, and mathematical modeling to understand how krill eyes work, exploring whether their vision aids in schooling behavior or an improved ability to observe contrast between objects. The research is part of his broader focus on the visual ecology of marine invertebrates, from microscopic coral larvae to Atlantic brief squid. His work encompasses how vision impacts predation, mating, orientation, and habitat selection, as well as how zooplankton responds to oil spills.
The son of an optometrist, Cohen was first exposed to both the world of vision and aquatic biology at a young age while growing up near the Chesapeake Bay in Maryland’s Harford County. He studied biology and environmental science at Dickinson College in Carlisle, Pa., where he benefited from the opportunity to conduct research with a neurobiologist. He spent a semester with the Duke University Marine Lab and developed an interest in zooplankton and the vertical migration of deep-sea animals while on a course-related trip to Bermuda.
His undergraduate experience demonstrated to Cohen that science was a potential career path, and he went on to earn his doctorate in biology from Duke University in 2004. He was a postdoctoral fellow at Harbor Branch Oceanographic Institution and served as assistant professor of biology and marine science at Eckerd College in St. Petersburg, Fla. Expanding his research efforts was part of his desire to join the University of Delaware.
“I was looking for a place where I could still teach the courses I love and have solid student interaction, but also do research in the lab,” he said.
His research interests complement those of other UD faculty interested in the ecological role of light, whether with respect to bacteria, coral, or harmful algal blooms. Also, like many of his colleagues, he has conducted research in the Antarctic.
Most recently however he traveled to the Gulf of Mexico to study the biological effects of oil and chemical dispersants following the Deepwater Horizon spill. So far, he has found that there is wide variability in the vulnerability of different animals. Young blue crabs, for example, survive oil and dispersant exposure, but may have an altered molting response. Comb jellies, on the other hand, can tolerate oil fairly well but struggle when there is dispersant in the water.
Cohen’s upcoming projects relate to how linked sensory modalities, such as vision, smell, and vibration detection, influence marine invertebrates’ behavior. For example, crab larvae vision is altered by smell: When they smell fish, their eyes become more sensitive to light. Part of what he enjoys about his research is the balance between observing animal behavior out in the field and back in the lab.
“You observe something complicated in the world, and then, elegantly if you can, measure it in the lab,” Cohen said. “Then you model how you think it should be working and check it back in the world.”