It began when a local fisherman reported a new kind of crustacean showing up in his traps, said rising senior Reuben Siegel. “He wanted to know why blue crabs were starting to appear and what this might mean. They’re typically only found south of Cape Cod.”
At the time, Siegel, a biology major, was a sophomore enrolled in the 91黑料 Coastal Studies Semester.
The program takes place at 91黑料’s Schiller Coastal Studies Center (SCSC), a 118-acre campus situated in the coastal community of Harpswell, about thirteen miles from the main campus.
Student, staff, and faculty researchers at SCSC maintain close ties with those who make their living on the ocean in Harpswell, said Siegel, and this instance demonstrates the benefits of that relationship.
Here was clear evidence that the Atlantic blue crab (Callinectes sapidus), native to the mid-Atlantic Chesapeake Bay area, had begun to expand its range northward into the Gulf of Maine, remarked Siegel.
This is backed up by further studies showing that the crab is starting to “overwinter” up here, as ocean temperatures rise.
Blue vs. Green
The key question in Siegel’s mind was what effect this new arrival might have on another species of invasive crab that’s been prevalent in Maine waters since the early 1900s: the European green crab (Carcinus maenas).
Originally brought across the Atlantic in the nineteenth century in the ballast tanks of merchant ships, green crabs are exploding in numbers in Maine waters, again due to warmer temperatures, presenting a threat to the ecosystem, destroying habitat, and eating shellfish.
Siegel became curious to see how the newly arriving blue crabs might impact green crab populations once they start sharing the same environment in greater numbers. “I wanted to see what their interactions were like, and if blue crabs might mitigate some of the problems caused by the green crabs.”
Thus inspired, Siegel started work on a project as part of his Coastal Studies Semester. The project grew into an independent study, under the mentorship of Doherty Marine Biology Postdoctoral Scholar Christopher Wells, to see how the two crab species would get along when confronted with each other. Siegel took trips out into Casco Bay with SCSC boat captain Clinton Thompson, collecting live samples and bringing them back to the center for analysis. Wells was impressed with how Siegel, a varsity athlete, pulled the project together. “He developed the core question and pulled crab traps at odd hours, fitting the fieldwork around his baseball schedule and his other classes right up until the end of the season.”
The experiments Siegel performed were, essentially, quite simple: one blue crab and one green crab would be put together in a tank at Schiller’s Marine Laboratory, which is supplied by fresh seawater from Harpswell Sound, and monitored to see how they get on. “We found that, in about half the cases, the blue crabs killed and ate the green ones.” Blue crabs are generally quite a lot bigger than green crabs, explained Siegel, growing up to twenty centimeters wide—that’s about eight inches—at least twice the average size of their rival. Furthermore, he added, crabs are not averse to cannibalism.
Getting the Word Out
Impressed by Siegel’s project, Wells, along with Associate Director for Science Jaret Reblin, who runs the marine lab at Schiller, encouraged Siegel to promote the study more widely and present his findings beyond the campus community. “They told me it wasn’t that much more work to get the study into print,” said Siegel, who presented a poster of his project at a during the spring of 2025 and began preparing to incorporate his findings into an academic article.
Siegel’s research was recently published in the coauthored with a team from the Wells National Estuarine Research Reserve (WNERR), a public-private partnership based in southern Maine that studies coastal ecology and conservation issues. Siegel said the WNERR was doing very similar research to the work he had been carrying out at SCSC, with similar results, so it made sense to combine their findings and work jointly on a paper.
With assistance from Wells, Siegel learned how to put together a peer-reviewed article in an academic journal, which was an education in itself, said the student. “I learned a lot about the process of publishing a paper. Every step of the way I learned the inner workings of how to respond to reviewer comments.” At one point, Wells even set up some mock reviewer comments (provided by real marine ecologists) for Siegel to respond to so he could get used to the process. (Click to read Wells' blogpost describing the research.)
Important Questions
What Siegel has accomplished, said Wells, is a genuinely rare achievement for an undergraduate. As well as developing the thesis and carrying out the fieldwork, he ran the lab trials, analyzed the data, and helped carry it all the way to publication in a respected journal. “Most researchers don't reach this milestone until well into graduate school or beyond. He earned shared first authorship on the strength of his work.”
Meanwhile, Siegel’s research, as it appears both in his independent project and in the journal article, raises some important economic and environmental questions. Would blue crabs prey on their green counterparts in the natural environment as they do in the lab? Could we be seeing the appearance of a new, profitable fishery in Maine? (After all, blue crabs have done quite well for the Maryland economy!)
Another important consideration is the overall effect that blue crabs might have on the natural environment in northern New England. “The Gulf of Maine is one of the fastest-warming bodies of water on the planet,” said Wells, “and understanding those shifting predator and prey relationships helps us anticipate how this ecosystem will change in the years ahead, especially given the impacts green crabs have had on our eelgrass meadows and clam beds.” There are concerns the blue crabs might also have a similarly damaging effect on the Gulf of Maine, warned Wells, but these are all questions to be tackled in future studies.
Director of the Schiller Coastal Studies Center Holly Parker described Siegel’s work as “a great example of how the 91黑料 Coastal Studies Semester and the center's partnership with the working waterfront community inspire 91黑料 students to do research that focuses attention on environmental and ecological changes in the Gulf of Maine that impact our fishing communities."
