New faces cause a stir in the New Hampshire crustacean community

Lobsters have long reigned as king among New Hampshire’s shelled sea creatures, but the chances of a coup are growing — and climate change is tipping the scales.

Indeed, said biologist Christopher Peter in an interview this summer, it may already be the case that “the lobster is no longer the king crustacean of the coast of New Hampshire.”

What kind of creature could hope to dethrone the lobster? Only, perhaps, a similarly large, jagged, claw-brandishing arthropod: the Atlantic blue crab, of Chesapeake Bay fame. 

Blue crabs are thriving in the rapidly warming currents of the Eastern Seaboard, expanding northward and becoming more common in places once too cold for them to establish year-round populations. Meanwhile, other newcomers are making their debuts, too, such as the lopsided fiddler crab and aggressive lady crab.

These new faces are an example of the range of ways that climate change is reshaping marsh ecosystems, said Peter, who has been tracking the shifts in New Hampshire’s Great Bay. The influx, he added, raises big questions for coastal researchers, who anticipate other changes for estuaries, marshlands, and the fisheries that depend on them.

Peter and other researchers from the Great Bay National Estuarine Research Reserve, the University of New Hampshire, the New Hampshire Department of Fish and Game, and Plymouth, Mass.-based Manomet Conservation Sciences received funding from New Hampshire Sea Grant this year to approach those big questions. Doing so, he said, is about being proactive and ready for the changes coming up the shore.

Vacationers or transplants?

On the bright afternoon of Monday, Aug. 10, Peter and three teammates boarded a 20-foot University of New Hampshire research boat and cast off from a dock at the Jackson Estuarine Laboratory in Durham.

Skimming over the fast-moving currents of Little Bay, the team made a beeline for a bright yellow buoy ensnared in a tangle of seaweed. Researcher and Great Bay National Estuarine Research Reserve Stewardship Coordinator Lauren White leaned over the gunwale to grab it and proceeded to haul out onto the deck 40-something feet of line, culminating in an immense wire crab trap full of estuary mud, seaweed, and dozens of startled crabs, which skittered over one another and clicked angry claws in the sunlight.

That haul, and each subsequent trap the team would pull that afternoon, contained a mixture of green crabs and rock crabs. Neither species was unexpected: Green crabs, though invasive, have been exploding in population here for decades, while the rock crab is native to the region.

What the team was on the lookout for were the two newcomer crab species that have become the subject of research conducted at the Great Bay Reserve: Atlantic blue crabs and fiddler crabs.

Blue crabs are found sporadically throughout northern New England, but historically had year-round populations only as far north as Cape Cod, Peters said. But in the 2010s, the crabs began moving north, apparently lured by warming waters. Since the early 2020s they have been spotted with increasing frequency in New Hampshire and Maine, according to an online tracker run by Manomet Conservation Sciences.

Fiddler crabs have followed a similar path, with research published by Great Bay Reserve staff earlier this August concluding they have expanded into the warm, brackish estuaries of the New Hampshire coast, though they remain rare in the state overall.

Thus, we are positioned to watch the arrival of more robust populations of these crab species in northern waters play out in real time, Peter said. And their debut has the potential to make a big splash.

“A whole new organism that’s never been here before has come to our shores,” Peter said, raising big questions for scientists.

Those questions include: Why now? Are the crabs visiting only in summer, like, as Peter put it, Massachusetts vacationers? Or are they becoming established here, having taken up residence in northern waters year-round? 

Data collected by Great Bay National Estuarine Research Reserve team members in recent years seems to indicate that some of those newcomers are indeed persisting locally all year long, Peter said. 

The New Hampshire Sea Grant funded work will allow the team to continue tracking the species’ presence, focusing on blue crabs. That will include trapping and data collection like that conducted on the water Monday, as well as lab work: Researchers will collect water samples from the bay, isolate the fragments of DNA floating within it, and sequence them to learn more about which species are cohabitating in the marsh, Peter said.

It’s important to understand how crab populations are changing, according to Peter, because the small creatures can carry big consequences for many parts of the ecosystems they reside in.

“Crabs interact with salt marshes, they interact with seagrass beds, they interact with oysters, mussels, other crabs, lobsters, fish,” to name a few, Peter said. Learning more about whether the expansion of new crab species is affecting those other creatures and habitat types is another aim of the study. 

For example, using a collection of lobster traps, the team is also monitoring lobsters in the bays to assess whether blue crabs are affecting that struggling fishery.

Lobsters are on the decline in New Hampshire and Maine, a phenomenon that’s driven by climate change, Peter said. The species prefers cold water, and appears to be fleeing northward as the Atlantic Ocean warms. The surface of the Gulf of Maine is warming faster than most other water bodies on Earth. 

It’s possible that changing dynamics among the crustaceans on the ocean floor could also play a role in that change, Peter hypothesizes. (After all, both species can be aggressive, he said.)

The researchers also want to know how newcomer animals have carved out space for themselves within the marsh food chain. 

To deduce that, they will use a range of laboratory techniques — including the more invasive method of dissecting some of the crabs they catch and analyzing the DNA in their stomach contents to yield a recent snapshot of what the crabs have been eating. 

The molecular makeup of the crabs’ bodies themselves can also shed light on what the animals have been eating, because, as the saying goes, “you become what you eat,” Peter said. 

Different tiers of the food chain contain different molecular signatures, allowing the researchers to get a sense of whether a crab has, for example, been eating plants or fish, by comparing the atoms within the crab’s body to those found throughout the ecosystem, Peter said.

All this will allow the researchers to get ahead of understanding how the crabs are influencing the ecosystem, Peter said.

Organisms “tend to do strange things out there when they’re in new places,” he said. “We’re not quite sure what they’re going to do, and how they’re going to impact other plants and other animals and other habitats here. That’s one big concern.”

As crabs creep northward, so does knowledge

As the world changes and species expand their ranges to adjust, sometimes the creatures themselves can outpace research and knowledge about them, Peter said. Therefore, a major goal of this project is also community engagement and knowledge-sharing within the scientific community, to help researchers get ahead of the blue crabs, he said. 

Though they may prove disruptive, Peter was careful to note that the presence of new crab species on the northern New England coastline isn’t all bad. The changing behavior of the animals, he said, is simply a reflection of the changes imposed by humans on the natural world.

“These organisms are just responding to the environment,” he said. “We’re changing the environment, they’re not.”

There are some “pros,” too, Peter noted. Blue crabs, like lobster, are commercially popular, prized for their meat. In certain locations in the Mediterranean, where the species has become invasive, blue crab fisheries have developed, Peters noted. 

Yet, ecologically, he concluded, the change can’t be construed as a positive.

“It’s a values question. I think it’s good and bad,” Peter said. “Do we want organisms here, in different spots of the world, that could impact native organisms, even if they are delicious? … It’s probably not a black or white answer.”

New Hampshire Bulletin is part of States Newsroom, a nonprofit news network supported by grants and a coalition of donors as a 501c(3) public charity. New Hampshire Bulletin maintains editorial independence. Contact Editor Dana Wormald for questions: info@newhampshirebulletin.com.