What is Sugar Kelp Seaweed? Ecology and Human History of Saccharina latissima
Description
Saccharina latissima is in the family of brown seaweeds popularly referred to as kelp and scientifically known as laminarians. S. latissima is a large seaweed with a fairly broad blade, up to 20 cm (8 inches) wide, that can grow up to 5 meters (16 feet) long or longer. Live plants are a yellowish-brown color with shades varying between golden to olive brown, but the fronds turn dark green or olive brown after drying. The stipe is typically short, stout, and very flexible, and the frond is long and undivided, often with a characteristic frilly and undulating margin. The blade is sometimes described as leathery or strap-like. The holdfast is relatively small, especially compared to the overall size of the plant, but it is strong and claw-like with multiple branching fingers.
The morphology of S. latissima varies depending on habitat, resulting in several varieties. This is known as phenotypic plasticity. A form distinguished by having a long, hollow stipe was once considered a different species (Saccharina longicruris), but more recent genetic analysis indicates it’s actually a variety of S. latissima. Other varieties of S. latissima have flat, smooth fronds. Sugar kelp growing in highly wave exposed areas develops strap-like blades as an adaptation to hydrodynamic stress. Recently, a variety of sugar kelp colloquially known as skinny kelp was found inhabiting a small band of islands, ledges, and peninsulas in southern Maine exposed to heavy ocean surf. This variety retained its narrow form even when grown at a protected aquaculture site and it’s since been re-named as Saccharina latissima forma angustissima.
Other brown kelp species with a somewhat similar appearance are found within the same range as S. lattisima. Laminaria digitata (oarweed or horsetail kelp) and Laminaria hyperborea (tangle) are easily distinguished from sugar kelp by having divided blades, longer stipes, and a darker color. Winged kelp Alaria esculenta is superficially similar to sugar kelp but has a distinctive midrib running up the blade and “wings”, or fingerlike growths, at the base of the blade.
Scientific & Common Names
Saccharina lattisima was formerly known by the scientific names Laminaria longicruris or Laminaria saccharina. Publications older than about 2012 generally use one or both names. A further complication is that L. longicruris and L. saccharina were considered separate species until fairly recently. It’s now thought these different forms of sugar kelp represent evolution in progress, or what scientists’ term “incipient speciation”.
S.latissima is commonly known as sugar kelp, sweet kelp, or sweet tang due to the sweet white powder found on dried fronds. As sugar kelp dries, natural mannitol sugars from within the plant rise to the surface. S. latissima is also sometimes known as sea belt because of its strap-like blade, or less commonly as Devil’s apron for the broader, frillier form (leading to a kelp infused Canadian beer of the same name). In Old English sugar kelp and related kelp species were often known as sea tangle. Another name for sugar kelp that may be peculiar to Ireland is “Poor Man’s Weather-Glass”, due to its tendency to go limp during humid conditions and rigid during dry conditions when exposed to the air.
Life History & Ecology
Saccharina latissima is a widely distributed temperate water species found in the North Atlantic and North Pacific. Its optimum temperature range is between 10-15°C but it can survive beneath the ice in winter and will tolerate temperatures as warm as about 24°C (75°F). It ranges from Northern California to Alaska along the North American Pacific coastline, and from Long Island Sound north to Nova Scotia along the Atlantic coastline. Along the Atlantic European coast, it grows from Northern Portugal, through the British Isles, north to Norway, and around Iceland.
S. latissima is one of the dominant kelp species in the Gulf of Maine. It usually occurs in sheltered locations from the sublittoral fringe, where it may be exposed at low tides, down to depths of 30 meters (about 100 feet). It can attach to solid substrata such as ledge but often grows attached to less stable substrata such as boulders, or even very small rocks and lobster trap lines. Sugar kelp is often found in dense stands popularly known as kelp forests.
Sugar kelp is a perennial and individual plants can live for between 2 – 5 years. It grows fastest in late winter through spring, but growth slows or even ceases altogether during summer. This results in annual growth rings within the stipe that can help age the plant just like growth rings in a tree. Sugar kelp grows quickly, from ½ inch to 2 ½ inches per day. Growth is from the bottom up, with new tissue gained at the base of the blade just above the stipe, and old tissue lost at the tip of the blade through erosion and decay. This regenerative process deposits kelp fragments into the ocean, especially during summer. Most of this is recycled into detrital food webs but some of it drifts and settles into deep sediments where it sequesters carbon from the earth’s atmosphere.
The life cycle of S. latissima follows a heteromorphic alternation of generations, typical of other laminarian kelps, where a diploid sporophyte (the visible plant) alternates with a microscopic haploid gametophyte. The reproductive season varies depending on location and latitude, but in the Gulf of Maine it peaks in fall and winter (Oct – Dec). Male and female reproductive sorus tissue, visible as a dark, thickened band on the blade, develops on separate plants when they’re between 8 -16 months old. The sorus tissue produces millions of haploid bi-flagellated meiospores (also known as zoospores) with limited swimming capacity, which generally settle to the substratum within 48 hours. Although most spores settle close to the parents, some may be dispersed great distances. After settling the spores develop into tiny, filamentous male or female gametophytes, representing the sexual phase of the plant.
Within 3 -4 weeks, or longer depending on environmental conditions, the gametophytes become sexually mature and produce eggs or sperm. Females release the hormone lamoxirene, which attracts nearby spermatozoids for fertilization. The fertilized egg generally remains attached to the female gametophyte where it develops into a small juvenile sporophyte, and then eventually into a mature kelp plant.
Sugar kelp is a canopy forming species that often grows in dense stands; the ocean’s version of terrestrial forests. These forests may consist entirely of sugar kelp but they can also be complex, with three, four, or even up to seven different kelp species growing within the same forest. Kelp forests play a vital ecological role in providing habitat for other species, assimilating and cycling nutrients, and absorbing storm surge.
In the past few decades, kelp forests have come under increasing threat from human activities that have led to a changing climate, invasive species, and ecological changes triggered by overfishing. Sea urchins are a major kelp grazer that are held in check by predation in a balanced ecosystem. However, when humans over-harvest predators such as seals, lobsters, or cod, sea urchin populations can increase to where they devastate kelp forests, leading to what’s known as urchin barrens. This occurred in the Gulf of Maine in the 1980’s - 90’s until the urchins themselves became a fishing target. Kelp forests have been known to recover quickly once sea urchins are removed, but in many cases, they don’t return for decades.
Sea urchin barren at former kelp bed site. Photo Larry Harris
It’s estimated that in some regions around the world kelp abundance has declined by 40% or more. Sugar kelp declines in Nova Scotia are blamed in part to the invasive encrusting bryozoan Membranipora membranacea, which colonizes mature kelp blades and weakens them. In some parts of the southern Gulf of Maine, kelp forests have been replaced by turf algae. Turf algae communities trap sediments and make the substrate unsuitable for kelp, which prefers harder substrate like rock or cobble. Recruitment of sugar kelp and other kelp species into these areas is further hindered by ocean warming and conditions that favor herbivorous invertebrates, which like to consume juvenile sporophytes. A similar shift to turf algae observed in Norway beginning in 2000 was attributed to eutrophication and warming.
It shouldn’t be necessarily concluded, though, that sugar kelp populations are endangered. It remains plentiful throughout much of its range. Sugar kelp is considered to be more efficient than Laminaria spp. when it comes to dispersal and colonization, and it’s often found in isolated stands even in areas where kelp forests have all but disappeared. These patchwork colonies can rapidly recolonize available habitat through spore dispersal. However, the loss of kelp beds in some areas is a warning that research, monitoring, and high standards for sustainable harvesting are all highly important.
History of Use
Humans have eaten laminarian kelps for a very long time. The giant kelp Macrocystis was identified as one of several seaweed species found in hearth remains at the 14,000-year-old Monte Verde archeological site in Chile. The large brown kelp Ecklonia kurome was consumed in China over 1,000 years ago to cure goiter, and Saccharina japonica (kombu), which is closely related to sugar kelp, has been a food staple in Japan for 1,500 years or more. The Japanese people eat kelp on an almost daily basis, and it has long been so important in Japan that at one time kelp was used as payment for taxes.
Europeans have also likely used Saccharina latissima for at least as long, though there’s no written documentation of this prior to about the 1700’s. The earliest written record of sugar kelp consumption may be from the Scottish botanist Sir Robert Sibbald’s Provision for the Poor in Time of Dearth and Scarcity, published in 1709. He notes that “sea tangle…is of a pleasant taste betwixt salt and sweet: it's Eaten as a salad."
In addition to its culinary uses sugar kelp was harvested for industrial purposes, along with other brown algae such as rockweed and bladderwrack. Potash, soda ash (sodium carbonate), and later iodine were extracted from burnt kelp ash beginning in the early 1700’s, before major mineral deposits of these useful elemental compounds were discovered. This industry was especially prominent (and exploitative) in Scotland. Wealthy landowners profited at the expense of their crofters (tenant farmers) who harvested and burned kelp during the summer months to pay their rent. Kelping was extremely arduous physical labor (and it still is!) and crofters often neglected their fields while they enriched coastal landlords in what was, for a while, a lucrative kelp extraction industry.
By the mid 1800’s this industry was all but over, but just prior to the Second World War the discovery of useful applications for seaweed alginates led to a new industry. Seaweed alginates have water holding, gelling, emulsifying, and stabilizing properties that can be put to use in food manufacturing, medicine, paints, and fibers. Laminarian and fucoid kelps were the main targets of this industry as they contain the most exploitable levels of alginates, about 30-45% dry weight. Two main types of alginates are produced from kelp species: sodium alginate is water soluble and used as a stabilizer and emulsifier in inks and dairy products, and calcium alginate is insoluble in water and used to make fibers for textiles and bandages, along with other uses. Kelp alginates are also good in cosmetic applications such as the Maine made shampoos and soaps offered on our website.
The alginate industry really took off during World War II, and sugar kelp alginate was even used in the manufacture of camouflage netting. New uses for kelp alginates continue to be invented to this day, but most of the world’s alginate now comes from the farmed kelp Laminaria japonica (kombu) and wild harvested Ascophyllum nodosum (rockweed) and Laminaria hyperborean (tangle). Today, most wild harvested or farm raised S. latissima is now destined for use as human food.
Culinary Attributes
Sugar kelp is delicious fresh or dried, and in both forms can be eaten either raw or cooked. It has a mild, salty/sweet, umami flavor. The umami comes from the amino acid glutamate, which is naturally abundant in most kelp species, making them one of the preferred “Umami Foods” important in Japanese cuisine. The closely related Japanese kelp known as kombu (S. japonica) is an essential ingredient in traditional dashi, a stock or broth made by boiling a strip of kombu with fish (bonito) flakes. S. latissima can be used in a similar fashion, earning it the name “Wild Atlantic kombu”.
Dried sugar kelp leaf often has a white powder on its surface consisting of mineral salts such as sodium and potassium and considerable quantities of sugar mannitol. Mannitol gives sugar kelp its pleasant, slightly sweet flavor, and in combination with the salts makes it an interesting and versatile flavor enhancer. We put these qualities to good use in our delicious Kelp Krunch™ bars!
Dried sugar kelp is easily reconstituted by soaking it in cool water for 5-10 minutes. The soak water can be used as stock or discarded if one is concerned about iodine intake. Sugar kelp has the highest iodine content of the eight species we sell, but soaking, blanching, or boiling can all leach 50% or more of kelp’s iodine into the water. This step may be preferred by those who want to enjoy the culinary delights of sugar kelp with less iodine. Once sugar kelp has been processed in this fashion it can be used as a main ingredient in seaweed salads or other recipes.
Sugar kelp is also good without the soaking or blanching step as a minor ingredient in any number of recipes. As a minor ingredient, it doesn’t contribute as much iodine to the dish but it does boost mineral content and impart flavor. We’ve found that sugar kelp is a great addition to baked bean recipes. It adds umami to this traditional New England dish while making the beans more tender and digestible.
Nutritional & Medicinal Attributes
Sugar kelp has a high mineral content, a trait shared by all edible seaweeds, but it’s distinguished in having the highest potassium level of the eight commercial species we sell. It also contains appreciable levels of calcium and iron, minerals which the FDA has identified as being potentially lacking in the American diet. All told, studies show that sugar kelp contains at least 30 minerals. Of the trace minerals, it is highest in strontium, an alkaline earth mineral that plays an important but not well understood role in bone and tooth health. Sugar kelp’s composition is about 35% dietary fiber, with a large proportion of that consisting of highly beneficial sulfated seaweed polysaccharides. Vitamins found in sugar kelp include A, folate and other B vitamins, C, and it’s also thought to be high in vitamin K.
Sugar kelp’s high iodine content makes it attractive to those wanting to boost their dietary iodine intake. It consistently has one of the highest iodine contents of all commercially available seaweeds, although seaweed iodine does vary seasonally, by location, and with the age of the plant. Levels as high as 6,500 ppm have been reported, but data from eleven sources including our own testing shows the median iodine content of sugar kelp to be 2,782 ppm. At this level, a one gram serving delivers 2,782 micrograms of iodine…more than 18 times the Recommended Dietary Intake (RDI) of 150 mcg.
There are several health reasons why one may want to ingest iodine above the RDI. Kelps have been used in Chinese medicine for over 1,000 years to treat goiter, a condition often caused by a lack of dietary iodine. Iodine deficiency is still a modern-day problem and including sugar kelp in one’s diet adds more than enough naturally produced iodine to compensate. Another reason to ensure adequate or high iodine intake is because it can confer protection against radiation poisoning, a topic we cover in our FAQs. Finally, there is a school of thought that attributes the longevity of the Japanese people and their low rates of certain cancers, especially of the prostate gland and the breast, to their high iodine intake. Traditional Japanese cuisine favors seafood and usually includes daily servings of sea vegetables, both of which are high in iodine compared to terrestrial foods. It’s estimated that the average Japanese citizen consumes about 1.2 mg of iodine per day (1,200 mcg), with some people regularly consuming as much as 3mg per day.
However, it should be cautioned that there can be too much of a good thing when it comes to iodine. The accepted tolerable upper intake level is 1,200 mcg iodine per day, and even though most people safely spill excess iodine from their systems, some people are sensitive and can develop adverse symptoms. Also, those receiving radiation treatment for thyroid cancer should not eat kelp or otherwise consume iodine, as this can interfere with the treatment. We advise consulting a medical professional before embarking on a program of iodine supplementation (also known as orthoiodosupplementation) with kelp or iodine supplements.
Beyond iodine, sugar kelp contains fucoidans and fucoxanthins, which are found in most brown seaweed species. Fucoidan is a seaweed sulfated polysaccharide and fucoxanthin is a brown carotenoid pigment. Both have bioactive properties investigated for their anti-viral, anti-cancer, anti-oxidant, and anti-diabetic properties. Fucoxanthin is of particular interest in treating metabolic syndrome, a cluster of health problems that includes obesity (especially excess abdominal fat), high blood pressure, hyperlipidemia, and diabetes. There is little doubt that sugar kelp can be an important part of a healthy diet, even when just a little bit is eaten every day.
Wild Harvest & Processing
Laminarian kelps are wild harvested in about 20 countries around the world, mostly to produce alginates. Much of this wild harvest is of Laminarian species other than sugar kelp. Norway is one of the biggest producers, where 170,000 tons per year of laminarians, primarily Laminaria hyperborea, are mechanically harvested with cutting machines or by dredges pulled along the sea floor with vessels. The Iroise Sea in the northwest of Brittany, France, has one of Europe’s largest kelp forests, mostly of L. digitata and L. hyporborea, but also S. latissima. The kelp is mechanically harvested with a special device known as a “scoubidou” (a curved iron hook attached to the end of a hydraulically driven mechanical arm), or with a type of comb invented in Norway.
Outside of Norway, France, and Iceland, most wild harvest of laminarian kelps is done by hand-cutting, or, as in Chile, by gathering beach cast kelp. Scotland, Ireland, Canada, and Maine account for most of the world’s wild harvested sugar kelp, and it’s all hand cut. In Scotland, recent proposals to mechanically harvest kelp beds have met with fierce resistance.
The highest quality sugar kelp is harvested mid spring into early summer, after the fresh growth of spring has occurred but before the kelp fronds become colonized by epiphytes (other algae) and epibionts (small animals such as barnacles). Harvesting is done at low tide, usually from small boats, though it can also be done by wading into the water to access partially submerged beds. The entire frond is removed above the holdfast and stipe. Sustainable harvesting entails cutting only a portion of the plants in any one bed (about 25%) and rotating harvest between beds. Besides practicing these sustainable methods, harvesters supplying MCSV with sugar kelp follow Organic Certification standards. These include practices such as not harvesting near marinas, fish pens, or other areas where contaminants could be present, and handling the crop in a way that ensures no chemicals are used or accidentally introduced during transport or processing.
Sugar kelp is traditionally dried by hanging from lines for about 48 hours. Drying is one of humanity’s oldest forms of food preservation and it benefits from simplicity; it can be done under the open sky with nothing but the sun and wind. More commonly, though, drying is done in greenhouses, which offer more control over the process and ensure that unexpected rain showers don’t damage the crop. Greenhouse drying can be enhanced with heat from furnaces, and with fans and humidistats to control ventilation and humidity levels.
Traditional drying is the best method for long-term preservation and easy shipping. One pound of dried wild kelp is equivalent to about ten pounds of fresh undried kelp, and once dried it has a shelf life that easily exceeds three years. Sugar kelp’s versatility as a food ingredient lends it well to other forms of processing and presentation as well. These include blanched, flash frozen kelp, fermented sugar kelp ‘Sea-chi”, and kelp puree. These product innovations are a response to the growing popularity of sugar kelp and its increased availability from mariculture (also known as aquaculture).
Mariculture
Although most sugar kelp on the North American market is still wild harvested, interest in farming it has surged in recent years. There are now companies growing sugar kelp in places such as the Faroe Islands, Norway, the Netherlands, and right here in Maine. Sugar kelp has proven to be one of the easiest seaweed species to farm in Maine and a good start towards growing other, more difficult species.
The kelp species Saccharina japonica (kombu) and Undaria pinnatifida (wakame) are two of the most commercially important farmed seaweed species. Most production for these species occurs in China, Korea, and Japan, but Asian farming methods are readily adapted for sugar kelp. The process starts on land, where seed spools are generated and nurtured in climate-controlled nurseries, usually in early fall. The seed spools are planted out at sea when tiny sugar kelp sporophytes become visible on the seed twine, usually after about 1-2 months in the hatchery. The seed spools are wrapped around horizontal grow ropes held in place by anchors and floats. These ropes are usually suspended 1-2 meters below the water surface, but the depth can be changed to suit local conditions. Once out-planted, they require little attention. No land, fresh water, fertilizer, or chemicals are required, making sugar kelp a highly sustainable and low impact crop. The crop grows through the winter months, when other marine activities such as lobster fishing and recreational boating are at an ebb. By mid to late spring the fronds are 1-2 meters long and ready for harvest. From this point on the crop is treated in much the same fashion as wild harvested sugar kelp, although, as described earlier, farmers are innovating new product forms for it.
Farmed sugar kelp is nutritionally similar to wild sugar kelp and can be used in recipes and consumed in much the same way. However, we’ve found in our experience that the texture, color, and size of farmed kelp fronds often differs from the wild plant. Farmed kelp fronds tend to be smaller and thinner than wild kelp, with a more delicate texture. They are often lighter colored as well, retaining a light brown or golden color even after drying. Farmed sugar kelp may be better suited for use as a milled product than as whole leaf. We don’t currently offer sugar kelp powder, granules, or flakes like we do with many of our other species. Either way we anticipate offering farmed sugar kelp soon and when we do it will be packaged and described as coming from mariculture.