Kelp forests provide key habitat for ocean life and help clean water to create a thriving marine ecosystem. But these underwater forests are in flux due to changes in modern fisheries and, a new study published in the journal “Ecology” revealed, rapid ocean warming.
Douglas Rasher, a senior research scientist at Bigelow Laboratory for Ocean Sciences, steered his team in documenting the first comprehensive census of Maine’s kelp forests in nearly two decades. Their work highlights the significant impact of climate change on ecological relationships in Gulf of Maine waters, showing the widespread collapse of kelp forests along the southern coast compared to their resilience in cooler, northern reaches.
Prior theories indicated that changes in the food chain mainly influenced wild kelp beds. The collapse of Atlantic cod, for example, led to a proliferation of kelp-eating sea urchins, deforesting much of the coast until the 1980s when several grazers were removed due to fisheries management.
Now, a new threat has emerged: rising water temperatures.
“Absolute temperatures in the south are higher, so forests there have already reached their tipping point,” Rasher said. “The forests in the cooler reaches are likely to persist for decades and should receive targeted management to continue to provide key ecosystem services.”
Rasher’s lab conducted dive surveys along over 200 miles of coastline. They recreated Robert Steneck’s in-depth kelp census from the early 2000s, combined their data with information on temperature from Jarret Brynes, a co-author from the University of Massachusetts Boston, and nearly 20 years of annual survey data tracking sea urchins from the Maine Department of Marine Resources.
“Data sets that cover this much space and time are rare,” said Thew Suskiewicz, a former postdoctoral researcher at Bigelow and the study’s first author. “They are powerful for detecting emergent and important changes in our ecosystem.”
Study findings revealed that small, filamentous red algae thrived in areas where forests had collapsed, creating a dense “turf” on the seafloor rather than a protective canopy structure. Still, there’s cause for hope.
Kelp forests from Mount Desert Island to the Canadian border are slowly declining, but if protected, they will continue to provide key services: photosynthesis, food supply and habitat for creatures like fish, crabs and lobsters.
‘The tale of two coasts’
As Rasher says, “It’s the tale of two coasts.” But how long will the dense forests in more northern stretches of the Gulf of Maine last?
“In the early 2000s, kelp covered 85-100% of a square meter area, but it has since declined to 50-70%,” Rasher said. “Over 90% of the forests in the southern region have collapsed, and the average area covered by kelp has significantly declined to the point where existing habitat is sparse.”
Though the paper’s data ends in 2018, Rasher’s team has continued to record the loss of forests and rise of red algae along the Midcoast, citing drastic changes near Boothbay Harbor.
“The indication that northern forests will continue to persist is positive,” Rasher said. “But even those aren’t immune to the impacts of climate change. If global carbon emissions aren’t curbed, we’ll unlikely be able to maintain them long-term.”
Rasher outlined what can be done: continued fisheries management, keeping sea urchin numbers in check and developing best practices for sustainable kelp harvesting to ensure genetic diversity.
Enter: kelp aquaculture
As director of seaweed science at Atlantic Sea Farms, Suskiewicz now leads a team in the early stages of kelp cultivation.
His cohort is piloting two new species: sea lettuce (Ulva) and dulse (Palmaria palmate). Once the kelp reaches a suitable size on the spools, it is delivered to farmers and fishermen, who help raise it during the winter and harvest it in springtime. The idea is to spark a halo effect; as the oceans grow more acidic, the kelp, in greater abundance, counters the rising pH levels.
Atlantic Sea Farms, the largest seaweed cultivation company in the U.S., harvested over 1.3 million pounds of kelp this year. The company has grown the supply of line-grown kelp and its market, teaming up with 30 partners — soon to be 50, Suskiewicz said.
Maine fishermen are leading in growing some of the most climate-friendly food during their “off-season.”
The company offers its partners free seeds, technical assistance and a buy-back guarantee. After harvesting, the kelp is returned to the Biddeford facility to be transformed into value-added products.
“It’s counterintuitive,” Suskiewicz said. “In the winter, lobstermen can improve the conditions in the Gulf. They are already stewards. We’re tapping into that, making kelp available to consumers, lifting carbon from the oceans and expanding opportunities to our fishing communities.”
The 2024 kelp harvest season paid over $1 million to fishing families in Maine, Rhode Island, and Alaska, a reprieve after facing instability in the fisheries they’ve long relied on.
“Projects like Green Gravel are restoring wild kelp beds using similar techniques as ours,” said Suskiewicz, showing how his work on the ecology paper and at Atlantic Sea Farms intersect. “They seed rocks with kelp spores and deploy them onto natural reefs. The decline is shocking, but what keeps me hopeful is the progress made across our coast, diversifying Maine’s waterfront in recent years.”
Further research
Rashers’ team is now monitoring the impact of kelp loss on the ecosystem, from microbes to large fish. Thanks to funding from the National Science Foundation, his lab began a project called “Species on the Move. ”
This project uses scuba-based surveys, like the ones in the ecology paper, and a tool called environmental DNA (eDNA) — a method for detecting “rare” species through water samples. Several projects under this umbrella focus on understanding changes in the physiochemical environment, how animals use kelp forests, and the energy flow in the ecosystem from algae to commercial fish.
One study aims to establish how much fish rely on kelp forests during their juvenile stages, similar to how sea grass, mangroves, and oyster/coral reefs function as nurseries. Another study investigates the level of gene flow between kelp forests, which could be useful for improving best practices in the kelp aquaculture industry.
“If the southern coast becomes suitable for kelp forests in the future, current research will be crucial for restoration,” Rasher said. “Climate change has rewritten the rules. We need to adjust the way we conduct science, manage resources and ask questions if we are to adapt to our changing ocean.”
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