Nature and Biodiversity

How scientists are working to restore the world’s embattled kelp forests

The world’s kelp forests grow along more than one-quarter of all seacoasts

Kelp forests are one of the most extensive marine life plant habitats on Earth. Image: Unsplash/Shane Stagner

Elizabeth Devitt
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SDG 14: Life Below Water

  • Kelp forests grow along more than one-quarter of the world’s coastlines and are among the most biodiverse ecosystems.
  • But these critical habitats are disappearing due to warming oceans, pollution, overharvesting and other human impacts.
  • Losing wild kelp forests causes biodiversity loss, reduces the protection of coastal communities from storm surges and removes a vital carbon sink.
  • Global interest in studying seaweed for food, carbon storage and other uses could help improve wild kelp restoration methods.

Hidden beneath the waterline, the world’s kelp forests grow along more than one-quarter of all seacoasts, supporting a richness of biodiversity that naturalist Charles Darwin believed could rival that of tropical rainforests. But also unseen, these critical habitats are vanishing due to warming ocean currents, pollution, overharvesting and other human impacts.

Despite centuries of accumulated knowledge gained from seaweed cultivation in Pacific Rim countries, the regional declines of kelp beds and recent sudden wipeouts of vast kelp strongholds have underscored just how little conservationists know about protecting or restoring these vital undersea forests, says Karen Filbee-Dexter, a University of Western Australia marine ecologist who studies climate change impacts on kelp.

“Kelp forests are under appreciated and understudied compared to other coastal ecosystems,” says Filbee-Dexter. “But we need to better understand them. They are one of the most extensive marine life plant habitats that we have on Earth, [while] the evidence is overwhelming showing that they are changing really rapidly.”

Researchers first got a wakeup call when marine heatwaves abruptly devastated entire kelp forests on the Tasmanian coast in 2011, and in Northern California in 2014. When the towering stalks and blades of kelp went away, so too did many marine species they supported. And as rock lobster, abalone and fish vanished, commercial fisheries worth millions shut down. Additionally, losing wild kelp forests reduces protection of coastal communities from storm surges and removes an important carbon sink. Scientists estimate that the world’s kelp forests store anywhere from

The good news is that scientists are finding ways to successfully restore kelp. But these newly discovered methodologies need to be scaled up significantly — and fast — to reverse the massive losses that have occurred in some regions, including Australia, Norway, Nova Scotia, and California.

Kelp forests complex ecosystems Bull kelp underwater.
Kelp forests are very dynamic, productive, complex ecosystems. Pictured: Bull kelp underwater. Image: Dan Hershman via Flickr

The challenges of scientific kelp forest management

Kelp has been in the headlines lately as a seaweed with significant carbon-sequestering capability. So far, farmed kelp has gotten most of the spotlight, but whether wild or farmed, the discoveries scientists make today could assist all kinds of kelp in thriving in a rapidly climate-changing world.

There are more than 100 kelp species — a large brown algae found in the cooler, shallower waters of the world, but most studies to date have focused on just two: the disappearing canopy-forming macroalgae of giant kelp (Macrocystis pyrifera) and bull kelp (Nereocystis luetkeana). These dense underwater forests can quickly grow up to 40 meters tall (130 feet), creating a complex habitat from seafloor to sea surface.

Some causes of kelp forest decline are well understood. Warming ocean currents or marine heatwaves, for example, are pushing these cool-water kelp beyond their physiological comfort zone when water temperatures rise above 20° Celsius (72° F), at which point they die. Coastal development, pollution and sedimentation, which degrade water quality, add survival challenges. But it still isn’t always clear why stressed kelp may vanish from some places, yet continue flourishing in others.

That’s partly due to difficulties in studying these forests. Often, it can even be hard to find them. Historically, kelp beds have been tracked by ship, satellite, and small plane. But these surveys miss a lot. Only canopy-forming kelp are visible on the sea surface. And although giant kelp is a perennial, bull kelp dies off in winter and reappears in summer, making detection tricky. Also, kelp can be a moving target: Severe storms can uproot entire forests overnight.

Accurate maps are critical to improved management of existing kelp beds, offering an early warning for declining forests while providing a vital baseline for monitoring recovery and restoration projects, says postdoctoral researcher Sara Hamilton at the University of California at Davis. Without a true assessment of inventory, it’s also hard to sustainably regulate the amount of wild kelp harvested commercially.

Seaweed farm formations, Xiapu, China kelp forest
Increasing interest in farmed kelp could benefit wild kelp as scientists research what helps kelp species thrive. Image: Alex Berger via Flickr

Worldwide, more than one million tons of wild kelp are harvested each year, according to 2019 data from the United Nation’s Food and Agriculture Organization. Much of that, about 40%, is collected off the coast of Chile, with wild brown seaweeds sold to commercial markets for diverse purposes, including food production, pharmaceuticals, textiles, and biotechnology.

Countries that regulate kelp harvests often set annual amounts of biomass that harvesters can take. But even regulation comes with problems. When Hamilton analyzed kelp harvest management in Chile, California and British Columbia, she found that a lack of regularly updated kelp inventory in all three places is “a major barrier” to effective management.

“There is good scientific literature on how kelp forests work, but we need to take that a step further and develop the science of how we manage them effectively,” Hamilton says.

In Chile, for example, the kelp harvest is governed by a complicated mix of management regimes that include no-take Marine Protected Areas (MPAs), exclusive access areas overseen by consortiums of local fishers, and unprotected-open access areas. Accurate monitoring of the kelp take among the various harvests may not always be maintained, Hamilton notes.

Further, scientists don’t know precisely how much kelp is too much to harvest before forests are too depleted to grow back. Although far less kelp tonnage is taken in California and British Columbia than in Chile, Hamilton says that regulators in these areas rely on self-reporting for the commercial harvest, which can be unreliable, while only loosely tracking the recreational harvest — leaving major data gaps. Recreational harvesters forage kelp for personal use.

Echoing Hamilton’s analysis, in the U.S. the California Department of Fish and Wildlife released an enhanced status report in 2022 on bull kelp and giant kelp that included recommendations for more accurate monitoring, better understanding of harvest impacts, and the roles of top predators in kelp forests. Similar conservation concerns led to a new law in Washington State intended to protect and restore 10,000 acres of bull kelp forest and eelgrass meadow by 2040.

kelp forest Lessonia trabeculata
Lessonia trabeculata is common along the coastline of Chile where brown algae is part of the world’s largest wild kelp harvesting operation. Image: Dick Culbert from Gibsons via Wikimedia Commons

Challenges posed by kelp restoration

One thing scientists know for sure is that it’s better to protect kelp forests than try to bring them back. All too often, regulatory action comes too late — after kelp forests are greatly diminished or gone.

Kelp was already decimated in the aftermath of marine heatwaves along 100 kilometers (about 62 miles) of Tasmania’s coast before the Australian government declared giant kelp marine forests an endangered ecological community in 2012. And this year, nearshore trawling was banned along a swath of Sussex coast, in the U.K., only after fishing practices razed once-thriving kelp beds and ravaged commercial fisheries.

Local and regional policy changes can mitigate wild kelp over-harvest, pollution, coastal development, sedimentation, and unsustainable fishing practices. But those actions can’t cool warming oceans. “Kelp forests are very dynamic, productive, complex ecosystems,” says marine ecologist Cayne Layton at the University of Tasmania in Hobart, Australia. “Trying to replicate that is quite tricky.”

Historically, restoration projects have relied on artificial reefs, made of everything from cement blocks to old tires and decommissioned oil rigs, to provide a surface where kelp can attach. The Wheeler North Reef, one of the world’s largest artificial reefs at 152 hectares (376 acres), was built with quarry rock to mitigate the loss of kelp forests and marine life resulting from warming waters off the coast of San Clemente, Southern California caused by outflow from the San Onofre nuclear power plant. Started in 1998, and completed in 2021, the reef is now considered a success in kelp restoration.

Marine scientist Aaron Eger dives into a vibrant kelp forest of Ecklonia radiata.
Marine scientist Aaron Eger dives into a vibrant kelp forest of Ecklonia radiata. Image: Aaron Eger

On Tasmania’s eastern coast — a hotspot where seawater is warming faster than the global average — Layton and professor Craig Johnson, at the Institute for Marine and Antarctic Studies at the University of Tasmania, are focusing their restoration efforts on “future-proofing” the new kelp forests. They’re “outplanting” baby giant kelp propagated from algae that possess a higher tolerance for warmer waters. “It’s not genetic manipulation,” notes Layton. “We’re just identifying giant kelp individuals that are naturally more [temperature change] tolerant.”

Of the 50-plus genotypes they’ve tested so far, about 10 to 15% can survive in water up to seven degrees warmer than the 16-17° C (60-62° F) waters where the kelp typically thrive. “It’s pretty amazing that some actually survive up to the maximum recorded temperature for giant kelp,” he says.

The researchers started outplanting these “super kelp” more than 18 months ago in three different 100-square meter (1,076.4-square foot) plots. But it’s a labor-intensive process to lab-rear thousands of juvenile kelp, each about a millimeter in size, then fasten them onto small plastic plates, and finally dive down to drill the plates into rocky reef.

Kelp forest restoration methods Cayne Layton marine ecologist University of Tasmania Hobart
Kelp forest restoration methods are often labor intense. Image: Cayne Layton

The researchers’ goal is to get about one adult kelp growing per square meter — similar to a natural Tasmanian giant kelp forest. Since 2020 they’ve achieved about 50 surviving adults, growing up to 12 meters tall, in two of the three plots. Layton hopes to start seeing the first major “pulse” of natural recruitment of baby kelp from those adults.

Thousands of miles away in the U.S., at the University of Washington’s Friday Harbor Lab, postdoctoral researcher Brooke Weigel is conducting studies on the temperature and nitrate sensitivities of surviving bull kelp populations near Puget Sound.

Although most kelp beds there made a comeback after the 2014 West Coast marine heatwave, bull kelp sites in southern Puget Sound saw significant ongoing declines, according to mapping by ecologists. “There are all these hints about environmental factors that might be contributing to these declines,” says Weigel. But those clues “haven’t been experimentally tested in the lab much at all.”

Map of bull kelp forests along shorelines in South Puget Sound between 1873 and 2018.
Bull kelp forest sites in southern Puget Sound are seeing significant ongoing decline. Image: Washington State Department of Natural Resources.

Weigel is starting her second round of lab-growing the microscopic phase of bull kelp (known as gametophytes) across a range of temperatures. She’s found that surprisingly the gametophytes can survive up to a toasty 20° C (68° F) temperature — typically lethal for adult kelp. But above 16° C (60°F) the gametophytes can’t be successfully fertilized to produce the sporophytes that make up towering forests.

“That’s a pretty marked cut off,” she says. Conservationists “need to know if there are [temperature] thresholds for kelp survival and reproduction as they select sites to restore kelp forests.”

It’s not yet known what allows some kelp to survive higher temperatures. In previous work, Weigel looked for clues in microbiomes, studying the bacteria in the slime layer that coats kelp blades. Layton is also trying to unlock the temperature resilience puzzle, looking at kelp physiology and metabolism: Is temperature change resilience determined by variations in cellular membranes? Or in photosynthetic machinery?

“It’s probably going to be a whole bunch of different things,” he suggests.

The process of spore release and culturing of kelp in Cayne Layton’s lab at the University of Tasmania.
Answers to why some kelp survive at higher temperatures may be encoded in bull kelp’s genetic make-up. Image: Cayne Layton

Answers may be encoded in bull kelp’s genetic make-up, says population geneticist Filipe Alberto, at the U.S. University of Wisconsin–Milwaukee. In his “kelp forensics lab,” Alberto analyzes kelp DNA collected from Pacific Northwest sites. Working with the Puget Sound Restoration Fund, he is determining how much genetic diversity exists within populations, whether they’re related, and if variations are associated with warmer or cooler waters. Alberto is also creating the bull kelp version of a seed bank to preserve regional genetic diversity. Instead of seeds, Alberto preserves gametophytes by keeping them dormant in a reduced-light and temperature-controlled environment.

“We might not ever be able to put this diversity back where it was originally from,” says Alberto. But if the gametophytes aren’t preserved now, it will be impossible to restore that diversity if the kelp disappear.

Soon, Alberto and his collaborators at the University of California at Santa Cruz and the California Conservation Genomics Project hope to complete sequencing of the bull kelp genome. This reference genome will be a resource for scientists looking for genetic variations that might help the kelp survive coming environmental changes.

bull kelp gametophyte kelp forest
The impact of temperature and nitrate levels on bull kelp gametophytes is hard to study in nature as the kelp live on ocean bottoms. Image: Brooke Weigel

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Challenges posed to scaling up kelp forests

As kelp forest losses increase globally, scientists warn that the viable paths to successful restorations vary from region to region. Each barren seascape presents unique challenges — maybe there’s an overabundance of sea urchins or degraded aquatic habitat, poor water quality, or varying amounts of warming.

”We are driven by an insatiable desire to understand the distribution and trends of kelp,” says Helen Berry, marine ecologist with Washington state’s Department of Natural Resources (DNR). “The key point: There isn’t a single summary — we are losing in some spots and gaining in others. To manage natural kelp it’s critical to understand that,” she says.

To help kelp researchers and restorationists learn from each other’s efforts, marine scientist Aaron Eger, at the University of New South Wales in Sydney, analyzed more than 250 kelp restoration efforts. Then he created an open-source database, searchable by problem type (overgrazing sea urchins, for example), to make it easy to see which methods best fit with which problems and circumstances. Additionally, with extensive collaboration and funding from The Nature Conservancy, Eger became one of the lead authors on The Kelp Restoration Guidebook. “There’s a lot of tools at our disposal to try and overcome these wicked problems that we face,” he says.

Eger’s meta-survey showed that successes were more likely when excess “disturbance events,” such as overgrazing by sea urchins, were removed and when outplanting sites were close to other kelp forests.

His analysis also highlighted an unexpected challenge: legal resistance. Most coastal environmental laws are designed to protect what is already in the ocean, Eger explained. But these laws often prohibit taking something out, like sea urchins, or adding something manmade, such as structures to support new kelp growth.

Purple sea urchins underwater kelp forest restoration pollution
Successful kelp forest restoration requires strategies to remove key stressors, such as too many sea urchins, pollution, sedimentation and over-harvesting. Image: Ed Bierman via Flickr

The biggest takeaway from Eger’s study was that the majority of restoration efforts (62%) have been led by academics, conducted on plot sizes of less than one hectare (80%), over time spans of less than two years. “For scalable restorations of entire forests, we need to take this out of the academic realm. We need partnerships,” he emphasizes.

One such partnership is being led by SeaForester, a for-profit seaweed restoration company that is working with kelp reforesters around the world using an innovation called “green gravel.”

This method requires no labor-intensive divers with baby kelp on plastic plates or other substrates. Instead, small rocks are seeded with baby kelp, then tossed into the ocean from a boat. Kelp establish themselves within a few years. “This is still super-fast, compared with how long it takes to regrow a forest [on land],” notes Thomas Wernberg, a marine ecologist at the University of Western Australia, Perth, and co-founder of the Green Gravel Action Group, an international network of researchers testing this method.

Originally developed in Norway, green gravel has found success in several pilot projects including the restoration of golden kelp (Laminaria ochroleuca) along Portugal’s coast. Testing of kelp-seeded gravel is currently underway under different coastal and ocean conditions in Europe, North America, and Australia.

“There’s a lot of excitement around this [idea], but it’s not a panacea,” warns Wernberg, also a senior researcher at Norway’s Institute of Marine Research. It didn’t work, for example, in a coastal California project when a storm surge rolled away all the kelp-bearing gravel.

“We still need to treat the root cause [of kelp loss]. In a lot of circumstances that is human-induced degradation of the marine environment,” Wernberg notes. That requires the winning over of officials and the public.

Kelp forests underwater.
In a lot of circumstances kelp forest loss is caused by the human-induced degradation of the marine environment. Image: Karen Filbee-Dexter (A), Thomas Wernberg (B), Stein Fredriksen (C)
The ideal recipe for kelp forest restoration with green gravel
The ideal recipe for kelp forest restoration with green gravel: (A) Collect fertile plants from wild kelp; (B) Isolate reproductive tissue (sorus) to get zoospores; (C) Add spore solution to small rocks in trays; (D) Wait several weeks for small sporophytes to appear; (E) Scatter green gravel on a reef; (F) Watch the baby kelp grow. Image: Henning Steen, Institute of Marine Research, Norway

One way of achieving that goal is to link kelp forests to valuable ecosystem services such as carbon sequestration, says Filbee-Dexter, who is part of the Green Gravel Action Group. Although kelp forests may not be as charismatic to people as coral reefs, the “blue economy” is ramping up with investors keen to capitalize on using seaweeds for carbon credits, sources of alternate protein, or biomass for fuel.” Developing more accurate measures of wild kelps’ carbon-storage potential could get them the protections they need. “People pay attention to what they care about,” she says.

The farmed seaweed industry could also contribute more to science’s fundamental understanding of wild kelp morphology, genetics, and optimal nutrient needs, says Helen Berry. But she cautions that comparing cultured kelp to wild kelp can be challenging, like “equating a Christmas tree farm to an old growth forest.”

However, researchers of farmed kelp may be able to fill in knowledge gaps around the role wild kelp plays in building biodiversity. One major difference between wild and farmed kelp, for example, is where it grows in the water column, explains Carrie Byron, an associate professor at the University of New England’s School of Marine and Environmental Programs, in Biddeford, Maine. Wild kelp is attached to the seafloor, while farmed kelp is suspended above it on lines or platforms.

Byron, funded by The Nature Conservancy, is studying whether farmed kelp — despite these structural differences — can still provide suitable habitat for the same diversity of species. More baseline data is needed to determine the biodiversity that comprises a healthy kelp ecosystem.

Underwater kelp forest seaweed farming of Eucheuma in the Philippines
Increasing interest in farmed kelp could benefit wild kelp as scientists pursue fundamental knowledge about what helps kelp species thrive. Image: Derek Keats via Wikimedia Commons
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Choosing change

Change is not always bad, says Filbee-Dexter. “One of the things you do as an ecologist is understand how ecosystems are functioning.” And in the case of kelp populations altered by human influences, that means determining if those changes will result in a resilient ecosystem that while functioning differently, still offers similar and valuable ecoservices. She provides an example of the Arctic kelp she has researched, populations of which could eventually be crowded out of existence by warmer-water species.

Researchers also have to grapple with the ethics of “assisted evolution,” or outright genetic manipulation, to help kelp continue to grow under increasingly adverse conditions. “We don’t have a good history of meddling and having it turn out very well,” says Filbee-Dexter.

One kind of change that Cayne Layton would like to see is the industrialization of kelp restoration is the kind of change Cayne Layton would rather see. He envisions cultured kelp farms, hatcheries for baby kelp known as sporophytes, and urchin fisheries as just a few ways of generating revenue from kelp — money that could be fed back into conserving wild kelp ecosystems.

“It’s not just about pouring money into this hole and saying let’s go restore kelp forests,” Layton says. “There’s so much value in doing this.”


Berry HD, Mumford TF, Christiaen B, Dowty P, Calloway M, Ferrier L, Grossman EE, VanArendonk NR. Long-term changes in kelp forests in an inner basin of the Salish Sea. PLoS One. 2021 Feb 17;16(2):e0229703. doi: 10.1371/journal.pone.0229703

Cavanaugh KC, Bell T, Costa M, Eddy NE, Gendall L, Gleason MG, Hessing-Lewis M, Martone R, McPherson M, Pontier O, Reshitnyk L, Beas-Luna R, Carr M, Caselle JE, Cavanaugh KC, Flores Miller R, Hamilton S, Heady WN, Hirsh HK, Hohman R, Lee LC, Lorda J, Ray J, Reed DC, Saccomanno VR and Schroeder SB. A Review of the Opportunities and Challenges for Using Remote Sensing for Management of Surface-Canopy Forming Kelps. Front. Mar. Sci. 2021 8:753531. doi: 10.3389/fmars.2021.753531

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Filbee-Dexter K, Wernberg T, Barreiro R, Coleman MA, de Bettignies T, Feehan CJ, Franco JN, Hasler B, Louro I, Norderhaug KM, Staehr PAU, Tuya F, Verbeek J. Leveraging the blue economy to transform marine forest restoration. J Phycol. 2022 Apr; 58(2):198-207. doi: 10.1111/jpy.13239

Filbee-Dexter K and Smajdor A. Ethics of Assisted Evolution in Marine Conservation. Front. Mar. Sci. 2019 6:20. doi: 10.3389/fmars.2019.00020

Giant kelp (Macrocystis pyrifera) healthy kelp forest ecosystem biodoversity
More data is needed to determine the biodiversity that comprises a healthy kelp forest ecosystem. Image: Claire Fackler, CINMS, NOAA, Flickr

Fredriksen S, Filbee-Dexter K, Norderhaug KM, Steen H, Bodvin T, Coleman MA, Moy F, Wernberg T. Green gravel: a novel restoration tool to combat kelp forest decline. Sci Rep. 2020 Mar 4;10(1):3983. doi: 10.1038/s41598-020-60553-x

Gouraguine, A., Moore, P., Burrows, M.T. et al. The intensity of kelp harvesting shapes the population structure of the foundation species Lessonia trabeculata along the Chilean coastline. Mar Biol 2021 168, 66. doi: 10.1007/s00227-021-03870-7

Hamilton SL, Gleason MG, Godoy N, Eddy N, and Grorud-Colvert K. Ecosystem-based management for kelp forest ecosystems, Marine Policy, 2022 Vol 136, doi: 10.1016/j.marpol.2021.104919

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