Seaweed: Food, Health, Farming and Climate Change

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seaweed branches
"Seaweed" is the common name for countless species of marine plants and algae that grow in the ocean as well as in rivers, lakes, and other water bodies. Some seaweeds are microscopic, such as the phytoplankton that live suspended in the water column and provide the base for most marine food chains. Some are enormous, like the giant kelp that grow in abundant “forests” and tower like underwater redwoods from their roots at the bottom of the sea. Most are medium-sized, come in colors of red, green, brown, and black, and randomly wash up on beaches and shorelines just about everywhere. [Source: NOAA]

The vernacular “seaweed” is a misnomer, because a weed is a plant that spreads so profusely it can harm the habitat where it takes hold. (Consider kudzu, the infamous “mile-a-minute vine” that chokes waterways throughout the U.S. Southeast). Not only are the fixed and free-floating “weeds” of the sea utterly essential to innumerable marine creatures, both as food and as habitat, they also provide many benefits to land-dwellers, notably those of the human variety.

There are about 9,000 species of seaweed. Lucy Sherriff wrote in Fortune: Seaweed is having its moment in the sun: Use of the marine plant is a rapidly growing trend that could aid in everything from global food security to climate change. Seaweed grows quickly, contains many vitamins and minerals, and produces up to 11 times the biomass of wheat and corn. It’s vastly underutilized despite its rapid growth rate, and recent studies reveal it could absorb as much carbon as the Amazon.” [Source: Lucy Sherriff, Fortune, November 8, 2022]

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 ; Fishbase ; Encyclopedia of Life ; Smithsonian Oceans Portal ; Woods Hole Oceanographic Institute ; Cousteau Society ; Monterey Bay Aquarium ; MarineBio

Seaweed Characteristics and Benefits

In some ways seaweed lacks the complexity of terrestrial plants because many of the structures that land plants have — roots of collecting water, flowers for attracting insects and dispersing pollen — are not necessary. The ocean environment of seaweeds provides them with all the nutrients and support the need. Most are not edible to humans or fish.

Most seaweed float or attach themselves to rocks in shallow water and are generally found near shores. Many types are covered with slimy mucous which prevents them from drying out when exposed to the air at low tide.

Seaweed is an incredibly resilient organism, and some species, such as giant kelp, can grow up to 60 centimeters (two feet) a day and as tall as 53 meters (175 feet). Underwater vegetation in shallow coastal waters also supports a wide diversity of marine creatures by providing spawning, nursery, refuge, and foraging grounds for many species. It is also highly nutritious, containing high levels of protein, essential minerals, and vitamins.

Underwater plants provide oxygen, food, and shelter. Eel grass, a type of submerged aquatic vegetation, supports the life cycle of many fish and shellfish. The health of submerged aquatic vegetation is an important environmental indicator of overall ocean and estuary health. Seagrasses in bays and lagoons, for instance, are vital to the success of small invertebrates and fish. These small creatures are a food source for commercial and recreational fish. Seagrasses also stabilize sediments, generate organic material needed by small invertebrates, and add oxygen to the surrounding water. [Source: NOAA]


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Kelp is a kind of seaweed that forms long strips that hold rocks at the sea bottom with a claw-like fasteners that serves as anchors but provide no root like functions. Kelp need to anchored to the bottom of the sea or it washes away. There are 300 species of kelp. Most are not edible. Some of the edible species are brown when they are harvested but turn bright green when they are cooked.

Kelps are designed to live offshore in places with crashing surf. The have inflatable bladders that keep them afloat and strong, flexible leaves that move in the moving water without breaking. Some have slippery mucous coating to protect them from exposure to sun and air. Large masses of kelp are sometimes called kelp forests. A number of species that live among kelp are unique to kelp forests.

Kelps dominate the reefs of cool seas. Relatively little is known of their origins, Some think they originated 5 to 10 million years ago in the Northern Hemisphere when the northern seas were cool and full of nutrients, This theory is hard to prove because the soft tissues of kelps don’t mineralize into fossils very well. Studies of large abalone shells that feed primarily on kelp suggest that kelp first appeared in large amounts in the Northern Hemisphere about 5 million years ago.

Large kelp forest lie off the coasts of New Zealand, Japan and California. Before World War I, 1,500 companies harvested kelp off the coast of California to supply potash for making gunpowder.

Kelp Forests

Kelp forests provide habitat for a variety of invertebrates, fish, marine mammals, and birds. A kelp forest Many species of fish and marine mammals inhabit kelp forests for protection and food. In kelp forests, the most commonly found invertebrates are bristle worms, scud, prawn, snails, and brittle stars. These animals feed on the holdfasts that keep kelp anchored to the bottom of the ocean and algae that are abundant in kelp forests. Sea urchins will often completely remove kelp plants by eating through their holdfasts. Other invertebrates found in kelp forests are sea stars, anemones, crabs, and jellyfish. [Source: NOAA]

A wide range of fish can be found in kelp forests, many of which are important to commercial fishermen. For example, many types of rockfish such as black rockfish, blue rockfish, olive rockfish, and kelp rockfish are found in kelp forests and are important to fishermen.

A wide range of marine mammals inhabit kelp forests for protection and food. Sea lions and seals feed on the fish that live in kelp forests. Grey whales have also been observed in kelp forests, most likely using the forest as a safe haven from the predatory killer whale. The grey whale will eat the abundant invertebrates and crustaceans in kelp forests. One of the most important mammals in a kelp forest is the sea otter, who takes refuge from sharks and storms in these forests. The sea otter eats the red sea urchin that can destroy a kelp forest if left to multiply freely.

Kelp forests are a natural buffet for birds such as crows, warblers, starlings, and black phoebes which feed on flies, maggots, and small crustaceans that are abundant in kelp forests. Gulls, terns, egrets, great blue herons, and cormorants dine on the many fish and invertebrates living in the kelp. Kelp forests also provide birds with a refuge from storms.

Seaweed as Food

Kelp and other kinds of seaweed are widely eaten and put to various used in Japan, China, Korea and other places. About 15 million metric tons was harvested in 35 countries in 2007, nearly double the total of a decade earlier, according to U.N.’s Food and Agriculture Organization. China is the largest producer and exporter, with huge crops filling entire bays and estuaries. Japan also produces a lot, much of it consumed domestically. [Source: Los Angeles Times, December 2009]

Seaweed is a $7 billion global industry. In the Philippines, it is added to noodles. In Wales it is mixed with oats to bake bread. In Belize it is mixed with nutmeg and milk to make a popular drink. In Japan it used as a topping for rice, an ingredient for soup and a wrapping for sushi. Kelp is processed to extract food gums — texturizing agents called agars, alginates and carrageenan — used as additives to make toothpaste thick, yogurt creamy, beer foamy, skin moisturizers moist and hundreds of other uses.

Seaweed farm in Zanzibar

Seaweed is being seriously considered as a food source in placed that haven’t traditionally eaten it. Among its advantages are that it doesn’t need arable land, fresh water or fertilizer. Some species of kelp grow 60 centimeters a day. From an environmental point of view sea weed agriculture doesn’t produce any erosion or run off and cleans the water of excess nutrients and absorbs carbon dioxide.

There is nothing radically new about this idea. A 1966 article published in Time magazine predicted that by the year 2000 “huge fields of kelp and other kinds of seaweed will be tended by undersea “farmers” — frogmen who live for months at a time in submerged bunkhouses.” Their seaweed probably would be “regenerated chemically to taste like anything from steak to bourbon.”

On seaweed bacon, Hicks Wogan wrote in National Geographic: Aquaculturists in Oregon are developing a specialty food industry centered on a marine alga that’s been called “the most productive protein source on Earth,” “the superfood of the future,” and — intriguing to many people — “bacon of the sea.” Dulse (rhymes with “pulse”) is a seaweed found in the northern Atlantic and Pacific Oceans. Northern Europeans have eaten it for centuries; most Americans haven’t tried it or even heard of it. Oregon State University researchers patented a strain that can be grown in tanks on land using only seawater and sunlight — all while absorbing carbon dioxide in the course of photosynthesis. As a food product, dulse’s benefits are several. It grows rapidly. It’s rich in vitamins, minerals, antioxidants, and protein. And some say that when strips are smoked and fried, it does taste like bacon (with which it’s plated above). Chuck Toombs’s company farms dulse on the Oregon coast and sells it fresh to restaurants and dried in stores. “People are demanding more plant protein,” Toombs told Oregon Public Broadcasting. “And we’re going to be able to supply that.” [Source: Hicks Wogan, National Geographic, May 18, 2021]

Health Benefits of Seaweed

Seaweed is chock-full of vitamins, minerals, and fiber, and can be tasty. For at least 1,500 years, the Japanese have enrobed a mixture of raw fish, sticky rice, and other ingredients in a seaweed called nori. The delectable result is a sushi roll.[Source: NOAA]

Scientists are studying sea weed for future drugs. Like other plants they produce chemicals that fight pathogens that are not harmful to humans and they thrive in an environment filled with fungi, virus and bacteria. A substance isolated from a nonedible seaweed’sargassum piluliferum — fights flu viruses in much smaller doses than in existing flu medication and produces few side effects.

Many seaweeds contain anti-inflammatory and anti-microbial agents. Their known medicinal effects have been legion for thousands of years; the ancient Romans used them to treat wounds, burns, and rashes. Anecdotal evidence also suggests that the ancient Egyptians may have used them as a treatment for breast cancer.

healthy sargassum ecosystem

Certain seaweeds do, in fact, possess powerful cancer-fighting agents that researchers hope will eventually prove effective in the treatment of malignant tumors and leukemia in people. While dietary soy was long credited for the low rate of cancer in Japan, this indicator of robust health is now attributed to dietary seaweed.

Seaweed Farming

According to the FAO: 36 million tonnes (wet weight) of algae and sea weed were produced in 2020, of which 97 percent originated from aquaculture. Production of algae has experienced an impressive growth in the past few decades as it was at 12 million tonnes in 2000 and 21 million tonnes in 2010. However, it increased by only 2 percent in 2020 compared with 2019. Asian countries confirmed their role as major producers with a share of 97 percent of the total production of algae. China alone as leading producer accounted for 58 percent of the overall total in 2020, followed by Indonesia (27 percent) and the Republic of Korea (5 percent). [Source: “The State of World Fisheries and Aquaculture 2022" by the Food and Agriculture Organization of the United Nations (FAO)]

On China’s Fujian coast, seaweed farmers head out at dawn to tend their aquatic fields. Such farms help China grow 12 million tons of food a year with no soil or fresh water and no fertilizer except runoff from the land.

Joel K. Bourne, Jr. Wrote in National Geographic: ““A few hundred miles north, in the clear, frigid waters off Casco Bay, two Maine watermen, Paul Dobbins and Tollef Olson, launched the first commercial kelp farm in the U.S., in 2009. They started with 3,000 linear feet of kelp line and last year farmed 30,000, harvesting three species that can grow up to five inches a day, even in winter. Their company, Ocean Approved, sells kelp as fresh-frozen, highly nutritious salad greens, slaw, and pasta to restaurants, schools, and hospitals along the Maine coast. Delegations from China, Japan, and South Korea have visited the farm — the seaweed industry is a five-billion-dollar business in East Asia. [Source: Joel K. Bourne, Jr., National Geographic, June 2014]

Describing kelp farmers at work in the northeast United States, Bob Drogin wrote in the Los Angeles Times, “They usually wear wet suits and...tend their underwater crop by hand...As the boat bobbed one recent morning...they tied three species of kelp seedlings to long mesh sleeves. They lowered each sleeve about 25 feet into the tidal current on ropes tied to a large raft that was anchored on the bottom...By spring each frond should be 6 to 8 feet long. The kelp will be cut by hand, briefly boiled to kill bacteria.”

Could Seaweed Feed the World?

Lucy Sherriff wrote in Fortune: Oceans cover more than 70 percent of the world’s surface and yet contribute to 2 percent of the world’s food. Seaweed remains an untapped food source potential. The UN’s Food and Agriculture Organization even went so far as to describe seaweed as a “precious ally” in the fight against hunger. [Source: Lucy Sherriff, Fortune, November 8, 2022]

Research published in September 2022 revealed just how extensive ocean forests are — covering an area twice the size of India — amounting to a vast trove of nutritious food that requires no additional resources to produce. The study found these forests produce, on average, between two and 11 times as much biomass per area as intensely farmed crops such as corn and wheat, meaning they could hold the key to fighting food insecurity. “This feels like the most exciting climate resilience story we’ve seen…They’re farming something that is done with no arable land, no fresh water is used, and carbon and nitrogen are taken out from the water, making the ocean healthier.”

“Seaweed has historically been assigned to the specialty food aisle and, as a result, has remained largely inaccessible to the public,” says Eliza Harrison, program manager for Ocean Rainforest, a company that grows seaweed for animal feed, food, and cosmetic producers. “By exploring alternative applications, such as meat replacement products, seaweed could be incorporated into more familiar foods — thereby increasing consumption within the U.S.”

Economic Benefits of Seaweed

Marine plants and algae have contributed to economic growth. The seaweed business is worth an estimated $14 billion globally. Among their many uses in manufacturing, they are effective binding agents (emulsifiers) in such commercial goods as toothpaste and fruit jelly, and popular softeners (emollients) in organic cosmetics and skin-care products. [Source: NOAA]

Lucy Sherriff wrote in Fortune: Along the coastlines, seaweed can provide a sustainable livelihood for communities that traditionally relied on fishing, one seaweed farming benefit that Warner’s company has been focusing on. But there have been challenges in Asia’s intensive seaweed farming process, including changes in marine ecosystems and an increase in disease.

In a study released in May 2022 Renewable and Sustainable Energy Reviews said that seaweed farming provides potential alternatives for future energy, decarbonization, food security, and mitigating global climate change. But there are barriers to the implementation of such operations — including farm permit acquisition, a lack of farming knowledge, and little consumer demand for the product.[Source: Lucy Sherriff, Fortune, November 8, 2022]

Seaweed in Japan

More than 1,200 varieties of seaweed are found in Japanese waters. Only about three are commonly eaten. Dried seaweed (“nori”) is processed into crumbly dark green sheets and can be made into gelatin used in jelly, ice cream and soy sauce. It is most commonly used to wrap rice balls and sushi rolls. Kelp is used a flavor enhancer in soups, noodles and sauces. Seaweed is an important source if iodine.

Japanese eat an average of 14 grams of seaweed a day. The most commonly consumed sea weed in Japan are “kombu“ (kelp), “nori“ ( “Porphrya“), and “wakame“ (“Undaria pinnatfida“). They are eaten outright and served with rice and used as a flavoring. Studies has shown that seaweeds helps to lower cholesterol, reduce high blood pressure and promote healthy digestion.

Five different kinds of edible seaweed are harvested on the small island of Futagama Jima and prepared for consumption through boiling in heavy iron pots and drying on racks. According to an article in Nature by French scientists Japanese have an intestinal bacteria similar to marine bacteria found in the sea that helps them digest sushi and is believed to have been derived from eating seaweed.

Nori, also called laver, is grown on farms off the coast in nets. It is harvested in the autumn when its is 30 to 40 centimeters long with easy-to maneuver square boats and a special machine that pulls aboard the laver-bearing nets.

About 40 percent of Japan's seaweed crop is grown in the Ariake Sea. In recent years the seaweed harvest has been less than expected as a result of the loss of important tidal areas due land reclamation.

Seaweed Industry in the U.S.

Lucy Sherriff wrote in Fortune: “Despite its far-reaching benefits, America has been slow to adopt seaweed farming. In fact, around 95 percent of edible seaweed in the U.S. is imported. This is in part the result of an arduous and expensive permitting process, as well as a lack of public understanding about the benefits of seaweed and how it can be farmed. [Source: Lucy Sherriff, Fortune, November 8, 2022]

Although seaweed is part of the daily diet in Asia and among coastal indigenous people in North America, it remains a niche ingredient in most of the Western Hemisphere. “We have been slow to adopt seaweed farming,” says Paul Dobbins, director of seaweed and shellfish farming for WWF U.S., “in part because there needs to be a market for it.”

Although America’s seaweed industry is relatively nascent, there are signs that the market is shifting domestically: The amount of U.S. imports has been declining, even as consumption has risen by around 7 percent a year. A recent projection for the seaweed snacks market showed that 30 percent of global market growth will originate in North America. That’s starting to happen, albeit slowly. Companies such as Atlantic Sea Farms, Umaro Foods, and AKUA have launched sea veggie burgers, seaweed bacon, and kelp jerky as seaweed-based protein options.

Raising awareness of how to farm seaweed and the algae’s capabilities is crucial, Dobbins notes. “There is a lack of understanding about how it is farmed. How do you create the seed? How do you design and engineer a farm? How do you process it? How do you market it?” Companies like Blue Dot Sea Farms, with their “Seacharrones” — a seaweed take on pork chicharrones — and Blue Ocean Goods — which partners with chefs to put seaweed on plates — have been working hard to change this. “It’s a strategically important crop for food security,” says Dobbins. “But we don’t see seaweed farming in our waters the way you would if you lived in one of the countries in the West Pacific that have top-producing seaweed industries.”

The industry, according to Dobbins, has expanded by 8 percent year on year since 2010. “If it continues at that pace seaweed will surpass potato production by around 2051.” Seaweed may seem like a wonder crop, but there are still numerous barriers that need to be overcome in order for it to surpass potato production: A lack of access to capital for potential farmers, a public acceptance of seaweed farming, and a more streamlined permitting process all stand in the way of growth, Dobbins notes. Briana Warner of Atlantic Sea Farms, an American seaweed company, believes that the state-led permitting process, which can take up to three years in some states, will ensure the industry grows responsibly. Currently, states have jurisdiction over the three miles of ocean closest to the coastline. “We’re creating an entirely new market for seaweed in the U.S.,” she explains. “But it needs to be thoughtful. It needs to be done carefully.” “We don’t want to make the same mistakes we made in terrestrial farming,” adds Dobbins. “There’s a lot going for seaweed, but we want to make sure it’s going to be done well.”

Atlantic Sea Farms

Lucy Sherriff wrote in Fortune: Every winter, Briana Warner searches for scraps of seaweed from the cutting room floor, so she can spread it over her garden before putting it to bed for the season, but it’s often gone. “I work at a seaweed company, and even then it’s hard to get hold of,” the CEO of Atlantic Sea Farms says with a laugh. “The farmers take the scraps at the end of every week so they can feed it to their pigs. It’s in high demand.” [Source: Lucy Sherriff, Fortune, November 8, 2022]

Atlantic Sea Farms was the first, and is still the biggest, seaweed farm in the U.S. The Maine-based company opened in 2009, with the goal of bringing job security to coastal fishers, who have seen their livelihoods decimated owing to climate change, new federal regulations designed to protect whale populations, and overfishing. In Maine, lobster fisheries are pretty much the dominant way that people make money,” Warner explains. “We’re finding ways for fishermen to diversify their income as climate change increasingly threatens the fisheries they work in.”

In 2021 alone, the company produced around 1 million pounds of kelp with 30 of their partner farmers, who are provided with kelp seed, training, and infrastructure to start operating. This feels like the most exciting climate resilience story we’ve seen,” Warner continues. “They’re farming something that is done with no arable land, no fresh water is used, and carbon and nitrogen are taken out from the water, making the ocean healthier.”

Seaweed and Global Warming

Lucy Sherriff wrote in Fortune: Numerous recent studies have highlighted seaweed as one of the most viable solutions to climate change, including the recent September study which estimated that kelp may take up as much carbon as the Amazon rain forest. “Seaweed has all the features required to be classified as a blue carbon habitat and a massive carbon sink,” write the authors of a study published in May 2022 in Renewable and Sustainable Energy Reviews.[Source: Lucy Sherriff, Fortune, November 8, 2022]

“Seaweed farming could contribute to carbon sequestration in the deep sea, but there are many ‘buts,’” cautions Schery Umanzor, assistant professor of aquaculture at University of Alaska Fairbanks. “In brief, seaweeds may be one of the hundreds of strategies we need to mitigate climate change.”

Alongside acting as a natural carbon sink and a nutritious snack, kelp has also been utilized in some more innovative experiments. In Maine, a startup named Running Tide is pioneering a model that uses kelp to pull carbon dioxide from the atmosphere. In Alaska, GreenWave, a company started by a former fisherman, is training indigenous communities to build kelp hatcheries. And in California, a dairy producer is trialing a seaweed-derived feed which reduces the amount of methane cows release when they burp. Considering that one cow belches 220 pounds of methane each year, equivalent to burning 900 gallons of gasoline, that could make quite a difference.

Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

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