Close-up of bladder wrack's eponymous vesicles

Fucus vesiculosus, known by the common name bladder wrack or bladderwrack, is a seaweed found on the coasts of the North Sea, the western Baltic Sea, and the Atlantic and Pacific Oceans, also known by the common names black tang, rockweed, bladder fucus, sea oak, black tany, cut weed, dyers fucus, red fucus, and rock wrack. It was the original source of iodine, discovered in 1811, and was used extensively to treat goitre, a swelling of the thyroid gland related to iodine deficiency.

Description

The fronds of F. vesiculosus have a prominent midrib and almost spherical air bladders which are usually paired but may be absent in young plants. The margin is smooth and the frond is dichotomously branched. It is sometimes confused with Fucus spiralis with which it hybridises.^[1]

Distribution

Fucus vesiculosus is one of the most common algae on the shores of the British Isles.^[2] It has been recorded from the Atlantic shores of Europe, Northern Russia, the Baltic Sea, Greenland, Azores, Canary Islands, Morocco and Madeira.^[3][4] It is also found on the Atlantic coast of North America from Ellesmere Island, Hudson Bay to North Carolina.^[5]

Ecology

The species is especially common on sheltered shores from the middle littoral to lower intertidal levels.^[5] It is rare on exposed shores where any specimens may be short, stunted and without the air vesicles.^[6] F. vesiculosus supports few colonial organisms but provides a canopy and shelter for the tube worm Spirorbis spirorbis, herbivorous isopods, such as Idotea and surface grazing snails such as Littorina obtusata.^[1] Phlorotannins in Fucus vesiculosus act as chemical defences against the marine herbivorous snail Littorina littorea.^[7]

Biology

Plants of F. vesiculosus are dioecious. Gametes are generally released into the seawater under calm conditions and the eggs are fertilised externally to produce a zygote.^[1] Eggs are fertilised shortly after being released from the receptacle. A study on the coast of Maine showed that there was 100% fertilisation at both exposed and sheltered sites.^[1] Continuously submerged populations in the Baltic Sea are very responsive to turbulent conditions. High fertilisation success is achieved because the gametes are only released when water velocities are low.^[8]

Consumption

Primary chemical constituents of this plant include mucilage, algin, mannitol, beta-carotene, zeaxanthin, iodine, bromine, potassium, volatile oils, and many other minerals. The main use of bladder wrack (and other types of seaweed) in herbal medicine is as a source of iodine, an essential nutrient for the thyroid gland. Bladder wrack has been used in the treatment of underactive thyroid glands (hypothyroidism) and goitre.^[9]

Bladder wrack has been shown to help women with abnormal menstrual cycling patterns and menstrual-related disease histories.^[10] Doses of 700 to 1400 mg/day were found to increase the menstrual cycle lengths, decrease the days of menstruation per cycle, and decrease the serum levels of 17B-estradiol while was later carried out and showed similar effects.^[11]

See also

• Edible seaweed
• Seafood allergy
• Vitamin B₁₂

References