Fucus vesiculosus is in the family of brown seaweeds that includes rockweed, sugar kelp, and Alaria. Mature plants are usually olive-green but can range from yellow to greenish-yellow to dark brown.  Plants are generally anywhere from 20cm (8”) to 59cm (35”) long, but lengths up to two meters (6.5 feet) have been reported.  The fronds are attached by a short wiry stipe (stalk) to a discoid holdfast, and they’re moderately narrow and leathery with a prominent midrib. The most recognizable feature of F. vesiculosus is its air bladders paired on either side of each fronds’ midrib, which give a satisfying pop when stepped upon. The paired bladders and midrib make it easy to distinguish Fucus from rockweed, which has single bladders and lacks a midrib.  In both species, the air bladders help float submerged fronds up towards the water surface for photosynthesis. Mature Fucus plants also have football shaped bulges - breeding receptacles – at the tips of the fronds.  These are orange in males and olive-green in females.

Two Fucus species related to F. vesiculosus and with a somewhat similar appearance are spiraled wrack Fucus spiralis and toothed wrack Fucus serratus.  However, both species lack air bladders and their fronds are quite different: F. spiralis fronds grow in a spiral pattern whereas F. serratus fronds are broader and have a serrated margin.  All three species are found in Maine but only two are considered native; Fucus serratus is thought to have been introduced to North America from Europe in the early 1800’s.  The three species can cross-fertilize in nature, resulting in intermediate hybrid forms.

Scientific & Common Names

The derivation of the word Fucus is believed to be from the Greek work phykos, meaning algae, and the word vesiculosus comes from the Latin word vesicula, referring to blisters.  Fucus vesiculosus is a common, widely distributed seaweed along both North Atlantic coasts that has been commercially important for hundreds of years, and coastal people know it by several common names.  These include bladderwrack, paddy tang, black tang, swine tang, rockweed, bladder fucus, sea oak, cut weed, dyers fucus, red fucus, and rock wrack. In Maine it’s usually called bladderwrack or rockweed; we prefer bladderwrack or simply Fucus and to reserve the name rockweed only for A. nodosum.

Life History & Ecology

Bladderwrack is a cold to temperate water species found on both North Atlantic Coasts, the North Sea, and the western Baltic Sea.  Fucus plays an especially important role in the Baltic, where it’s the only large, brown algae that naturally occurs there and the predominate canopy species. Some sources state that F. vesiculosus is also found in the North Pacific, but this may be due to confusing it with other similar species such as Fucus distichus or Fucus gardneri.

Bladderwrack often occurs with or in proximity to Ascophyllum nodosum beds.  It usually grows in a narrow band in the middle intertidal zone along rocky shorelines in protected coves, bays, and estuaries. Bladderwrack can tolerate a range of temperatures from -2°C to 28°C (82°F), and salinities from brackish to very salty water.  Bladderwrack may flourish above or below the Ascophyllum band depending on local conditions, and both species occur above where Fucus serratus is found in the lowest area of the shore zone. Ascophyllum tends to dominate in more protected areas but as exposure increases bladderwrack becomes more dominant. Bladderwrack withstands greater wave action and more ice scour than Ascophyllum and it can recolonize areas where Ascophyllum has been removed due to these natural causes or from harvesting. Over time, however, the slower growing Ascophyllum usually returns to dominance.

Bladderwrack has a long reproductive season extending from spring until the onset of winter, though peak timing can vary between locales.  In Maine, peak reproduction occurs from September to December during periods of calm water, which is an adaptive mechanism to prevent eggs and sperm from being washed away before fertilization happens.  Bladderwrack is dioecious (separate male and female plants) and has a fairly simple reproductive cycle compared to many other macroalgae.  Individuals mature at about two years of age, when reproductive receptacles form on the tips of the fronds.  The receptacles contain many cone or flask shaped conceptacles, each opening to the surface through a pore.  These release structures called antheridia containing 64 sperm each, or oogonia containing eight eggs each. The antheridia and oogonia quickly break down to release their sperm or eggs.  The eggs release a pheromone that attracts sperm, and fertilized zygotes adhere to the bottom within hours. Tiny germlings become visible to the naked eye within a few weeks.  Mortality is very high at this stage, mostly because of mollusk predation, but the plants are highly prolific and fertilization is said to be close to 100%.

Bladderwrack is an “ecosystem engineer” that creates habitat, changes the environment by its physical presence, and affects multiple other species. Fucus, like many other macroalgae species, grows in dense, canopy forming stands.  F. vesiculosus and Ascophyllum are often the dominant near-shore canopy species in the North Atlantic.  Their thick beds absorb wave and wind action and help slow coastal erosion.  The sweeping motion of the fronds from wave and tidal surge prevents some animals, such as barnacles, from becoming established within the canopy.  Other species, however, find shelter there and may use the beds as nursery grounds. In Alaska, Fucus distichus is important spawning habitat for the Pacific herring; the Atlantic herring is also known to lay eggs within and upon F. vesiculosus, though not to the same extent as its Pacific cousin.   

Although its tender germlings are heavily grazed upon by herbivorous snails and other animals, once it becomes established Fucus has few natural predators.   Many seaweed species, including Fucus, produce chemical deterrents to inhibit herbivores, and some of the first studies to identify the nature of these deterrents were done on Fucus.  Several such compounds have been identified, including phlorotannins, phytotannins, and galactolipids.  Fucus galactolipids have been shown to repel sea urchins, which may be one reason Fucus is not their preferred food. Other studies show that Fucus increases its production of phlorotannins as a defensive response to grazing from snails and other small invertebrates.  Fucus appears to have no natural bacterial pathogens.  This may be because a probiotic bacterial biofilm on the fronds inhibits colonization by other, potentially harmful bacteria.

History of Use

Bladderwrack has a long history of use dating back at least to the early 1300’s, when King Denis of Portugal (known as the Farmer King) regulated the harvest of cast ashore seaweeds, Fucus being one of them.  Fucus was an important species in the Northern European kelp industry of the 1600’s, which we describe in more detail in our Ascophyllum profile.  Entire villages worked together to harvest prolific beds of Fucus, Ascophyllum, and other brown seaweeds to extract soda, potash, and iodine.  Fucus played a seminal role in the discovery of iodine in 1811, when the French chemist Bernard Courtois first extracted it from Fucus and Laminaria, two brown seaweeds abundant on rocky French Atlantic coasts.  Like many great scientific discoveries, his was accidental, but in subsequent years it led to the exploitation of Fucus for iodine. Today, Fucus still has a reputation as the best sea vegetable to supplement iodine in the diet.



Culinary Attributes

Freshly harvested bladderwrack is rather leathery and slippery to the touch. When dried it becomes brittle but it can be rehydrated to a softer texture. Freshly harvested or reconstituted whole leaf imparts flavor when steaming clams, fish or lobster…the seafood is nestled within a bed of bladderwrack during steaming.  This can be done on the stovetop, or better yet on the beach in a stone-lined fire-pit, using freshly gathered bladderwrack.  Wrap the seafood in cheesecloth, bladderwrack (or Ascophyllum), and foil and lay it directly on the hot embers.

Whole dried leaf is often used to make broth, added as is to stews and soups, or cooked with grains and vegetables.  The flavor is strong but pleasantly briny, with some people detecting an undertone of sweetness. Cooking in liquid for 20 minutes or more tenderizes the fronds, or they can be removed before eating. Bladderwrack is also available in milled form as coarse flakes or powder.  Milled bladderwrack can be easily included in small quantities (1-2 tsp or tbs) in a variety of recipes to add flavor and nutrition   Some people prefer purchasing dried whole leaf and then grinding it to the desired consistency with a mortar and pestle. 

Nutritional & Medicinal Attributes

As food, bladderwrack contains protein, dietary fiber, vitamins, and especially minerals.  One teaspoon of coarse cut bladderwrack flakes weighing about 4 grams contains 4% of the Reference Daily Intake (RDI) for calcium; 8% RDI iron; 3% RDI potassium; 7% RDI magnesium; and an impressive 15% RDI manganese.  This same serving size also contributes 1,500 micrograms of iodine.  This is above the daily maximum recommended iodine intake, so iodine sensitive individuals should consult with a health practitioner before consuming bladderwrack, or modify their intake.

Most people spill excess iodine from their bodies with no ill effect, and then there are those who desire a high iodine intake for their own personal health reasons.  Vegans, vegetarians, and people who avoid iodine enriched salt or foods such as processed bread may be iodine deficient. Bladderwrack is often preferred by customers for iodine supplementation because of its long history as an iodine source dating back to 1811, when Courtois first extracted it from Fucus.  We continue that tradition today by including bladderwrack in our Seaweed Support Supplement – Iodine Formula.  The formulation contains bladderwrack and four other seaweed species blended to provide 270 micrograms of iodine in two tablets.

As a brown seaweed, Fucus contains the same sulfated polysaccharides we’ve described previously for Alaria and Ascophyllum. These dietary fibers show a number of beneficial biological properties when used as extracts in lab studies, including anti-inflammatory, anti-cancer, and anti-microbial.  One of the most well studied sulfated polysaccharide is fucoidan, which was first extracted from F. vesiculosus in 1913.  Fucoidan demonstrates an amazing range of activities in lab studies and is especially well studied for its anticoagulant properties.  Although various forms are extracted from other brown algae and even some invertebrates, fucoidan extracted from F. vesiculosus is still considered the ‘gold standard’.   

Bladderwrack is applied in folk medicine to ‘cure’ obesity, cleanse the kidneys, fight rheumatism and rheumatoid arthritis, and for skin care.  A clinical study done in Italy in 1976 showed that patients taking bladderwrack lost more weight than those in the control group.  The iodine content of bladderwrack is thought to increase the metabolic rate by increasing the production of thyroid hormone.

A popular use for bladderwrack is in thalassotherapy, therapeutic saltwater or seaweed baths.  Dried, whole leaf bladderwrack contained in a mesh bag is added to a hot bath to release beneficial minerals, iodine, and mucilaginous alginates into the water.  While one can buy seaweed bath kits from specialty vendors, if you like to regularly enjoy this treatment it may be more cost effective to buy bladderwrack leaf in bulk. One pound of dried bladderwrack leaf should be enough for 2-4 baths.  Epsom salts, oats, and lavender or other aromatic herbs can be added to enhance the experience.  Our blog post on Seaweed Bath Hydrotherapy describes this application in detail.

Wild Harvest & Processing

Most bladderwrack is harvested in Canada and Northern Europe, chiefly France and Ireland.  A small amount is also harvested in Maine.  Harvesting is prohibited in the Baltic due to bladderwrack’s vital ecological role there and concern about recent dramatic declines in abundance.  These declines are thought to be due to environmental factors and not because of harvesting.

Bladderwrack has never been as heavily exploited as its fucoid relative Ascophyllum. There are several reasons for this.  Although bladderwrack, like Ascophyllum, contains alginates highly valued in food and industrial applications, it doesn’t contain them at the same high levels.  Bladderwrack isn’t as naturally abundant as Ascophyllum, and harvest is more difficult and time consuming due to its shorter height and its location along more exposed shorelines.  Mechanical harvesting methods developed for Ascophyllum can’t be efficiently applied to bladderwrack, which is typically hand cut or raked.

Bladderwrack is traditionally harvested during the spring and summer months.  Submerged fronds are harvested at intermediate tides from a boat with a cutting rake, or with a knife or sickle at low tide when plants are exposed.   The Maine Seaweed Council sustainable harvesting guidelines call for harvesting no more than 30% of a bed and for cutting plants above the holdfast to allow regeneration.  The freshly harvested crop needs to be dried as soon as possible; ideally, it should be bone dry (about 10% water content) within 48 hours of harvest.  Traditional drying methods rely on the sun and temperatures of about 85°F.  This relatively gentle approach preserves nutrients and enzymes, and results in a raw food with long storage potential.


Bladderwrack is not currently commercially farmed anywhere, although experimental trials have recently taken place in the Baltic, where wild harvest is prohibited.  Researchers cultivated it from thalli detached from wild plants and freely floated in submerged net cages and baskets.  Fouling from barnacles, mussels, and bryozoans proved to be one of the biggest challenges.  The researchers found this could be remedied by subjecting the plants to periods of desiccation (air drying), without affecting growth rates.  This research was published in 2020 and bladderwrack aquaculture still remains in very early stages of development.