What he’s looking for: kelp blades streaked with sorus tissue, a dark band teeming with millions of spores. A wiry man in his 60s, Lindell has developed relationships with homeowners and researchers across hundreds of miles of New England’s coast so he can access the kelp integral to his work—and, potentially, to the future of seaweed farming in the United States.

After several dives, Lindell has filled his mesh collection bag with cuttings and swims to shore. He stores the prized tissue in a cooler to keep it damp and cool for the five-hour drive, and then sets off for his laboratory at Woods Hole Oceanographic Institution in Massachusetts. Here, over the next 45 days, the spores will be carefully cultivated into seed for farmers and scientists to outplant in the ocean.

Every year, every ounce of any kelp variety farmed commercially in the U.S.—now approaching millions of tons—begins with this process. Many growers see it as a bottleneck: Propagation from wild-harvested seaweed is costly, lengthy, and ties rural coastal communities to laboratories that are often hours, if not days, away. It also shortens the seaweed growing season, as sorus tissue can only be harvested for a few months of the year. And, most frustrating to farmers, relying on wild stocks for farmed kelp means that growers have very little control over the final product. What could look underwater like a yummy blade may turn out to be a varietal better suited to feeding snails than pleasing the human palate.

Lindell’s eponymous lab at Woods Hole may look humble, with low ceilings and cement floors, but it’s meticulously organized, with hundreds of seaweed varietals catalogued and floating in refrigerated containers. As ferry horns punctuate the rushing sound of seawater piped into scores of tanks, a team of scientists toils away at an ambitious project: revolutionizing kelp propagation. They have just mapped a single sugar kelp genome for the first time, and the results are about to be publicized through the Joint Genome Institute in Berkeley, California. Next, they plan to map a genome for the entire species. The project is supported by a $5.9 million grant from the U.S. Department of Energy MARINER program, part of more than $66 million that the agency has invested in American seaweed production since 2018.

If successful, their work will put Americans at the front of seaweed science globally, making it possible for laboratories like theirs to select wild kelp with ideal traits and create new kelp “seeds” in two weeks. This breakthrough in selective breeding would be the biggest advance in mariculture in the past hundred years, akin to Punnett’s Square, which revolutionized plant breeding in the early 1900s.

A Keystone Species in Decline

Different varieties of kelp have thrived in the world’s oceans for more than 100 million years, along the equator and up toward the poles. In 2023, scientists estimated that kelp forests suck up about a third of the world’s atmospheric carbon; kelp also supports fisheries and removes nitrogen pollution. Together, these benefits are valued at as much as $500 billion annually.

Now, this complex, ancient species is in jeopardy. Globally, kelp forests are receding at a rate of 1.8 percent a year, due in part to climate change and human impact. In 15 years, marine scientists say there may not be enough wild stock for farmers to rely on, especially in states like Maine, where kelp forests are rapidly declining. On the West Coast, kelp loss has been even more extreme, with 96 percent of forests from San Francisco to northern Oregon dying off over the past decade, according to The Nature Conservancy. Beginning in 2013, a series of cascading events wreaked havoc: First, a massive heat wave plunged the kelp into stressed conditions at the same time that purple sea urchins—which feed on kelp—lost their biggest predator, the sunflower sea star. Without sea stars to keep them in check, the urchins multiplied and, in a behavioral shift, left their customary nooks and crannies and began devouring the kelp forests.

Scientists believe Lindell’s work could help save the future of seaweed. By mapping sugar kelp, Lindell is creating a Rosetta Stone of kelp traits and corresponding DNA that can then be used by researchers globally to better understand, and protect, their wild kelp populations.

For example, for a kelp forest stressed by increasingly warmer waters, conservationists could identify and plant strains of kelp that are more heat tolerant. Tristin Anoush McHugh, kelp project director at The Nature Conservancy, monitors California’s remaining forests regularly, and believes that Lindell’s advances in seaweed reproductive technology could bolster restoration efforts. Scientists could isolate kelp that survive mass die-off events, propagate them in the lab, and then plant them in the open ocean, creating kelp refuges. “We can’t go and remediate 350 kilometers of coastline, but we can certainly create oases along the way,” she says.

A Market Worth Millions

For decades, China has led the industry, valued at $643.4 million in 2022, a slice of the larger $5.6 billion global seaweed market. According to the U.N.’s Food and Agriculture Organization, China produces 89 percent of the world’s farmed kelp; the U.S. produces less than .01 percent—what one hatchery specialist in Maine calls a “rounding error.”

Many kelp companies in the U.S. cite America’s small appetite for seaweed as an impediment, especially compared to Asia, where seaweed is consumed regularly and in many forms. But minimal demand is only one reason for the low market share. The high cost of farming is another.

American farmers can expect to pay about $1 a foot for string inoculated with kelp seed. The yield is an average of 4 pounds of mature kelp per foot, which nets about 50 cents a pound, according to Lindell. “I don’t know any other agricultural or aquaculture industry where the cost of seed can be as much as 50 percent of the farmer’s revenue,” he says with a scoff.

Compared to other seaweed-farming countries, America is an outlier. Korean seed string is sold for 5 cents a foot and yields 30 pounds per foot, according to Jang K. Kim, a professor in the department of marine science at Incheon National University in South Korea. In China, the seed string cost-to-yield ratio is similar, because the government subsidizes that industry, according to scientists there.

Selectively Bred Spores, on Demand

When the sorus tissue is clean, Lindell’s scientists dry it overnight and then immerse it again in sterile seawater, prompting the tissue to release its spores. These develop into gametophytes—tiny, feathery clumps, male and female—that are selected for desired traits and then bred to create zygotes (fertilized eggs) that develop into kelp seed (or, technically, juvenile sporophytes). Using gametophytes for seed instead of wild-harvested sorus tissue would greatly decrease the costs, since using gametophytes requires no sanitizing and they can be bred for multiple seasons.

“[Gametophytes] allow us to do what animal breeders and plants have been doing for millennia now—make a single-pair cross that we can then ascertain some value to,” explains Lindell. “We can measure—how long is that blade? How sweet is it? Does it resist high temperature?”

Every harvest season for the past five years, his lab has measured these crosses for 30 to 50 traits, creating a tremendous amount of information for breeding commercially attractive future generations—and for potentially restoring wild kelp one day. The lab publishes all of its breeding information on Sugar Kelp Base, an open-source website for global seaweed researchers.

In Asia, selective breeding is common in mariculture, and is why yields can be four to six times larger than on American farms. But in recent years, Asia’s yields have flatlined, possibly due to a lack of genetic diversity after 50 generations of breeding the same genetic lines of kelp.

Instead, Lindell’s genomic selection approach allows his team to conserve genetic diversity while still selecting for specific traits. They’ve also worked closely with Cornell University and the U.S. Department of Agriculture, borrowing crossbreeding techniques from terrestrial agriculture. “In the last five years, we’ve been able to make achievements that took the Asian countries 30 or 40 years to accomplish,” says Lindell.

What is the No. 1 thing they’re breeding for? “Yield. And No. 2 is yield. And No. 3 is probably yield,” says Lindell, laughing. “Every farmer’s business plan and projections are based on yield. Every 10 percent improvement in yield produces probably a 5 percent improvement in their bottom line.”

Increasing yield is part of the focus of the MARINER grant. Currently, the average U.S. farm yield is about 4 pounds per foot. So far, Lindell’s team has been able to triple that yield on average, with hopes of isolating a strain that can produce 25 pounds per foot, approaching the yields of China and South Korea. Lindell is also looking at kelp traits like a strong umami flavor, or thicker blades that make them easier to use as wraps for food, or an ability to resist predation by other marine organisms.

Creating gametophytes, says Lindell, allows seaweed farmers to become “the orchestrator of your own symphony when it comes to the seaweed planting season. You could start it as early or as late as you choose.” Growers would be able to time their own planting, instead of waiting for wild kelp to mature and produce sorus tissue—and they would have a longer growing season and therefore a larger yield.

Gametophytes also mean less nursery time. Currently, beginning with wild-harvested sorus tissue requires around 50 days to produce kelp “strings”—strings of kelp seeds grown out in a nursery until ready to deploy on a farm. With gametophytes, that time is cut to around 30 days. Additionally, farmers can choose varietals based on their traits, similar to the way apple growers select for flavor, color, juiciness, or other qualities.

The Near Future of Seaweed Farming

Except for the warming waters. The Gulf of Maine is warming 99 percent faster than the rest of the ocean, with devastating repercussions for all marine life, from kelp to finfish to lobster. “It’s harder and harder to find reproductive kelp in September to have ready by, say, Halloween,” says Thew Suskiewicz, a seaweed scientist at Maine’s Atlantic Sea Farms, the largest seaweed aquaculture operation in the country. The company provides seed to partner farmers to outplant. For the 2023-2024 season, Atlantic Sea Farms pulled in a record-breaking 1.3 million pounds of kelp for its line of foods.

Suskiewicz operates the farm’s hatchery after a career of studying algae, including at the seaweed food company Monterey Bay Seaweeds. “I’ve been looking at how kelp assemblages have changed in the Gulf of Maine in the last 30 years—and we’ve seen profound changes. Most of the species here have some life stage that is very dependent on the kelp,” he says, noting lobster as an important example. Lobstering is a nearly $400 million annual industry in Maine alone, according to NOAA. Wild kelp’s decline, he predicts, “is going to have a lot of cascading effects.”

Many of Maine’s lobstermen and commercial fishers are already experiencing huge shifts in the marine populations they harvest. That has led some to get into the farmed seaweed industry to diversify their incomes and businesses in the face of warming waters. Establishing gametophyte cultures would make kelp seed string cheaper, offer more predictability, and make kelp farming less dependent on wild kelp beds. Suskiewicz is working closely with Lindell’s lab, and next season will begin raising gametophyte-spawned kelp in Maine’s waters.

“Next year will be the first year we put them out, and we’ll just measure performance—including, how much did they grow? How do they taste? What is their blade length?” says Suskiewicz.

Suskiewicz believes that the American seaweed industry is at an inflection point, and that selective breeding is arriving at the perfect time. Five years ago, Atlantic Sea Farms seaweed salads were available only in specialty food stores. Now, they’re found across the country, thanks in part to the company’s intensive marketing efforts to introduce the average American to kelp.

Now that seaweed is a bit more familiar, Suskiewicz believes that if the cost of kelp seed drops through widespread adoption of gametophytes, the industry will be able to scale up and finally compete with Asia. “People can purchase their kelp from the U.S., from known monitored waters, by farmers in their community, rather than stuff that primarily comes over from China through [South] Korea—dried, dyed, and then shipped over,” he says.

As for Lindell, he sees enormous potential not just for sugar kelp, the species his lab is mapping. His team’s work could help regenerate other kelp species, too, including giant kelp in California and bull kelp in Alaska. And the kelp-farming industry could be the driver. More funding goes into farming kelp than preserving it in the wild, but the science applies equally: “All the learnings of the industry around resilience, growth, health, and disease resistance is going to carry over to conservation.”

This story was produced in partnership with the Pulitzer Center’s Ocean Reporting Network.