BU student researcher Sierra Koerber-Marx (CAS’26) works underwater at Nubble Light on Maine’s southern coast, while her sugar kelp subjects crowd the foreground. Photo by Lizzie McNamee (CAS’10)

Marine Biology

Protecting Maine’s Coastal Heritage—and Her Own

Student researcher and daughter of a lobsterman Sierra Koerber-Marx (CAS’26) dives to help save sugar kelp in a changing ocean

Sierra Koerber-Marx grew up salty on the Maine coast. Her family lived most of the time on Monhegan or North Haven islands. Her father and uncle made part or all of their living lobstering. A hardworking life for the adults, mostly idyllic for Koerber-Marx and her two sisters. 

“When I was little, we used to make the crossing out to Monhegan in this tiny outboard. I used to always lie up in the bow. We would make beds out of the life jackets and lie on them,” says Koerber-Marx (CAS’26).

Now, with climate change, she wonders what life on the Gulf of Maine will be like for future generations.

“In Maine, especially on island communities, most of the people have lived there for so many generations that you hear a lot about how much the ocean has changed,” she says. “That was a big part of me becoming interested in studying the oceans in New England, because I’ve never seen a cod as big as the cod that my dad used to catch when he was a kid, because they just don’t exist anymore. Which is kind of crazy, because that’s within one lifetime.”

And that’s why the Boston University junior is in a wet suit and fins on a windy, gray Monday in May, scuba diving the frigid, 46-degree Atlantic waters at Nubble Light on Maine’s southern coast. “That’s refreshing,” one member of her dive party insists, tongue possibly in cheek.

Koerber-Marx is a biology and marine science double major and plans to become a marine biologist. This summer, an Undergraduate Research Opportunities Program project has her studying sugar kelp (Saccharina latissima), which looks a bit like lasagna noodles and is one of the most common types of seaweed here. Specifically, she is studying how sugar kelp adapts to thermal variations in New England’s coastal ecosystems. 

She will make multiple dives at Nubble and at Folly Cove in Gloucester, Mass., to assess whether the common kelp does better in the colder, more open water of Nubble, or in the warmer, more sheltered cove, trying to shed light on its adaptability.

For nearly an hour at Nubble, a small red buoy waving a red-and-white flag is the only sign that she and three others are under the surface, working. 

Health Checkup for the Kelp

“Kelp beds are vital coastal ecosystems in New England, supporting commercially important fisheries,” Koerber-Marx wrote in her UROP proposal, “including Atlantic cod (Gadus morhua) and green sea urchins (Strongylocentrotus droebachiensis), while also buffering high wave energy, and improving water quality.”

But, she wrote, New England’s kelp forests have declined substantially in recent decades due to multiple stressors, including overgrazing by sea urchins after the collapse of cod populations that preyed on the urchins. The spread of the invasive sea lace or sea mat (Membranipora membranacea) has furthered the decline, covering kelp blades, increasing their brittleness and susceptibility to breakage. And there are other challenges.

Koerber-Marx’s project will measure the size and density of kelp at the two locations at different times. This will allow a comparison of the seasonal changes in kelp health. Even if the kelp in warmer waters is not doing as well as in the colder spot, it might have adapted in ways other kelp hasn’t. “They can potentially adapt to survive in higher temperatures, so then when you’re restoring the kelp, you want to use those populations that have that adaptation.” In early fall, she will conduct lab tank experiments on field samples at BU to test her hypotheses. 

Koerber-Marx and Scavo Lord working in the kelp field below Nubble Light. Video by McNamee

Another reason Koerber-Marx is at Nubble is that the kelp there grows on the sloping face of rock ledges as well as on the seafloor. “We’ve noticed that the kelp is a lot healthier looking on the walls, so we’re trying to figure out why that difference exists,” she says.

“Sierra is awesome at this and very experienced” after diving in the BU Marine Semester last fall, says Karina Scavo Lord (GRS’21), a College of Arts & Sciences lecturer in biology. She’s Koerber-Marx’s adviser on the UROP project and joins her on every dive. “It’s never easy getting in the freezing cold water after months of being out of the water. And we have gotten data every dive—every dive has been productive, which is great.”

Understanding how kelp responds to warming temperatures could be key to stewards of the marine ecosystem as the climate changes. And it could also be important to the growing aquaculture industry that is trying to find ways to market kelp as a food source. “They’re trying to rebrand it by calling it sea vegetable, not seaweed,” Scavo Lord says. They’re even making pickles out of it.

The project is supported by a $3,000 student research award from UROP and BU’s Kilachand Honors College; it will be the subject of Koerber-Marx’s honors thesis. Dive tanks and gear are provided by the BU scientific diving program, and the marine science program will provide the lab equipment.

Two friends from the Marine Semester dive with Koerber-Marx on and off and help with data collection: Sophie Martorana (CAS’26), who’s at Nubble on this day, and Maeva Vasquez (Questrom’25). Lizzie McNamee (CAS’10), BU’s dive safety program manager, also sometimes joins them.

“Her project has tremendous broader implications,” says Scavo Lord, “and this is so close to home for Sierra. We talked a lot about her growing up in Maine and seeing these ecosystems and wanting to study them more, because she’s observed them changing and heard about them changing from her family. It’s neat that we can build on that.”

Protecting Her Heritage

When the divers emerge from the water and rush to dry off, it’s clear that the dive itself has required some personal thermal adaptation. “It is soooo cold,” Koerber-Marx says, shivering.

While underwater, they set out a five-meter line used for observation and sampling, called a transect, multiple times—on the ocean bottom and on the rock wall—counting and measuring kelp blades for one meter on either side of the line. They also count the number of kelp individuals and urchins within the sampling area.

Scientific diving has “a very niche skill set,” Koerber-Marx says. “When you’re underwater, you have a lot of things to think about already. And then you add in trying to do science, taking measurements and trying to remember all the numbers, carrying everything, but also remembering to check your air and communicate.” But, so far, “this project’s gone really smoothly,” she adds. “We actually collected data on our first dive, which is rare.”

Does Koerber-Marx feel any “climate grief” about what is happening in the Gulf of Maine?

“Definitely. I have thought about how it’s sad that I’ll never see the same ecosystems that my dad did or my great-grandpa did,” she says. “There’s this one tide pool that we grew up playing in as kids, and the way I see it now, there’s so much more algae, and the whole ecosystem has changed.

“But it also is motivating to make sure that I’m working to conserve that area for my future kids and for future generations. It does feel good to contribute to conserving it.”