Knocking Out a Predator: A Study of Coastal Top-Down Effects

Spurred by the gap in knowledge on North Carolina stingrays and the urgency of understanding oyster reef ecology, Paalman chose to delve into the ecological effects of stingrays on wild oyster reefs. “Since we are changing reefs as well, how are they further degraded by predators, [such as stingrays]?” asked Paalman.

Her approach itself is unique. By zooming into the higher trophic level occupied by stingrays, Paalman is investigating species interactions and how a large-boded bioturbator (an animal that shapes sediment structure) influences oyster reef stability. According to Paalman, “A lot of oyster research right now is looking at abiotic effects, especially with water temperature and sea level rising,” making her research approach more unorthodox. 

While Paalman’s project may seem straightforward on paper, actually answering it in the field is a much more perplexing task. The first step? Finding the stingrays themselves. In her project, Paalman is including four species of stingrays: Atlantic rays, butterfly rays, southern rays and cownose rays. As foraging creatures, stingrays participate in extensive migration throughout their respective habitats, with some species even travelling hundreds of kilometers around the cape of Africa. This behavior, combined with their preference for dwelling in the benthic zone, makes finding them akin to a needle in a haystack. 

Above: A cownose stingray foraging on the ocean floor. Image courtesy of Georgia Aquarium.

Fortunately, Paalman does not have to start from scratch. Following in the footsteps of a previous PhD student in Silliman’s lab who examined stingrays in seagrasses, Paalman is in the midst of probing through as many stingray sites as possible. 

“I'll be looking at all these sites with super fresh eyes, which can get overwhelming,” said Paalman, “but I think a great part of that is there is a lot of people who do know the area and it's fun to learn about [each] area.” 

Above: Paalman at a field site in Hoop Pole Creek, Atlantic Beach, NC. Image courtesy of Tiffany Paalman (MSC Program ‘30).

At each site with a known presence of foraging rays, identified by the presence of foraging pits, Paalman is excluding benthic rays. Armed with thick PVC pipes, a tough net, and a determined mindset, she is constructing “jails” to prevent stingrays from foraging in certain areas. 

Following the construction of these cages, Paalman collects data, both biological and physical. A lot of data. Indeed, the Silliman lab’s philosophy is to “get as much data as possible, and let nature speak.” 

To look at community-wide changes in the absence of foraging rays, Paalman uses a combination of excavation and coring techniques. Specifically, she employed a PVC pipe as a makeshift fishing rod. Except, in this case, the “fish” is really just sediment from the ground. Once the PVC pipe has been pulled up with a block of sediment, the sediment is sieved and the number of organisms are counted and measured, providing an assessment of species abundance and diversity. 

Other metrics that Paalman plans to measure include water temperature and wave action, both of which can influence the foraging behavior of stingrays, and thus, the coastal ecosystem. Once all the data has been collected, Paalman hopes to see a significant difference between the exclusion zones and control zones, which may explain the mechanism by which stingrays mold oyster reefs.

Above: Paalman records notes at a newly installed living shoreline at Cherry Point, NC. Image courtesy of Tiffany Paalman (MSC Program ‘30).

Supplementing her field data, Paalman plans to harness the surveying capabilities of drones to investigate how benthic ray foraging may be influencing oyster reef conditions. Specifically, she will use LiDAR (Light Detection and Ranging) imagery, a remote sensing technique that uses a pulsed laser to generate detailed, three-dimensional topographic maps of oyster reefs. With these tools, she hopes to assess how reef cover responds in the absence of benthic ray foraging.

Above: A LiDAR generated image of a forest. Image courtesy of LiDAR News.  

In the end, Paalman hopes to better understand the  “spatiotemporal relationships between benthic ray disturbance, habitat contiguity, and reef dynamics,” as well as how such biogeomorphic disturbances from benthic ray foraging influence oyster reef stability.

Despite the random and rough nature of field science, Paalman enjoys the accessibility of working with a coastal ecosystem. “I like the idea that I can just walk and go to my ecosystem, rather than planning with a timeline to complete all the work,” said Paalman, “I can head out to the reef whenever I want (weather-permitting)!”

On the Court and In the Lab: Balancing a Ph.D Program and Varsity Athletics

Paalman’s typical first year was not like a normal Ph.D student’s. While most students would spend their mornings surrounded by computers and lab equipment, Paalman’s days often began with the blow of a whistle and reverberating echoes of volleyballs being hit across a net. Having played NCAA Division I volleyball for five years in Wisconsin, Paalman’s transition to Duke didn’t slow her athletic career down one bit. In her first year at Duke, Paalman was a critical piece as a middle blocker on the Duke Women’s Volleyball team.

Above: Paalman as a middle blocker on Duke’s Women's Volleyball team in a match against Virginia Tech. Image courtesy of GoDuke.

Balancing a PhD program and D1 athletics was no easy feat. Although Paalman had 5 years of experience as a student-athlete, a PhD program is a whole “different beast” altogether. In the midst of the volleyball season, Paalman often found herself hustling from morning volleyball practice in Cameron Stadium to a Marine Biology and Ecology course in LSRC where she served as a teaching assistant, all while squeezing in seminars, lab meetings and her own graduate classes. At the end of the day, Paalman even went back to the gym, putting in extra reps and film analysis to make up for the practice times she had lost.

Despite having to juggle so many responsibilities at once, Paalman enjoyed the unique perspectives athletics offered her. Strangely enough, a PhD program and varsity athletics share a lot in common. 

“Being in athletics, you make mistakes all the time, you make mistakes everyday in practice, and volleyball is a game of mistakes,” explained Paalman, “That reflected the PhD life a lot because in undergrad, your success is determined on your tests and grades, while in PhD it’s determined based on scientific publications, and that's more based on day to day work and making mistakes. . . Having that sort of perspective and being able to bring it into my professional life is really cool.”

“It was definitely a lot, but really rewarding at the same time,” said Paalman.

To prospective scientists, Paalman encourages students to remain determined and committed, no matter the setbacks they may encounter. Paalman herself once felt that she would never be able to join a PhD program. “I felt so out of the loop of marine science for a while because I wasn't from a marine environment and my undergrad wasn't a research institution,” said Paalman, “but I learned from athletics to connect and use your resources as much as possible.”

Just like how athletes get recruited, Paalman actively cold-called and emailed professors from all over the country, including her current mentor. And just like in sports, success in academics is dictated by the effort and drive of the student. “Whatever you put into it is what you're going to get out of it.”

Paalman also emphasizes the importance of a supportive environment. Especially in science, where collaboration is essentially present in every step, being with people you genuinely enjoy working with and who share the same goals is extremely helpful.  

“Be as authentic as you can,” said Paalman, “and hope that you receive the same.”