Bladder Wrack (Marine Algae of Cape Cod, Massachusetts and Adjacent Islands)

Bladder Wrack

Fucus vesiculosus

Summary ¹³

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...

Description ¹⁴

Bladder wrack is a familiar large olive-brown coloured seaweed (3), which attaches to rocky substrates by means of a small disc (4). The flattened, branching fronds, which grow up to 2m in length, have an obvious midrib, and are covered with spherical air bladders, which tend to occur in pairs on either side of the mid-rib (3). In small plants, however, air bladders may be entirely absent (3). Forked and pointed reproductive structures occur at the tips of the fronds (3). The appearance of bladder wrack varies depending on the environmental conditions in which it occurs; in more sheltered areas there are many air bladders, whereas there are fewer in more exposed conditions (3). In very exposed areas, a form of bladder wrack called Fucus vesiculosus forma linearis may arise, which completely lacks bladders (3).

Biology ¹⁵

The air bladders keep the fronds of the wrack in illuminated waters, where it is able to photosynthesise (3). In exposed areas, it is beneficial for the wrack to lack bladders, as this decreases the potential for severe damage, and minimises the risk of it being detached and swept away (3). Bladder wrack may live for up to three years. There are separate male and female plants, and reproduction takes place once a year (2). Sex cells are produced in structures known as 'receptacles' located at the tips of the fronds. Eggs and sperm are released simultaneously into the water; the eggs release a pheromone that attracts the sperm (4), and fertilisation occurs externally. The fertilised egg settles to the substrate where it becomes attached after just a few hours (2). Bladder wrack provides shelter for a number of marine species, including the tubeworm Spirobis spirobis, various isopods, and snails (2). It has been harvested by humans for use as a food source, and in various health products (2).

Taxon biology ¹⁶

Some seaweeds can have a greenish color, but yet are not green seaweeds. Bladder wrack is a good example. It can vary from olive-green to brown. Like all brown seaweeds, it is much sturdier than green seaweeds, which easily tear apart. Bladder wrack is easy to recognize by its bladders along the fronds. The floating bladders help the plant to stand straight up in the water. Bladder wrack grows along dikes, on wooden poles and on mud flats. It attaches itself to mussels, stones or other objects. It can grow up to 0.5 meters long. In earlier days, bladder wrack was used as a fertilizer as well as for a remedy for pain in the joints, swellings and skin diseases. Sometimes, there are no floating bladders and then it is easily confused with spiral wrack.

Habitat ¹⁷

The species is found intertidally on rocky shores in a wide range of exposures. It is common on the mid shore often with Ascophyllum nodosum, below Fucus spiralis and in a zone further up the shore from Fucus serratus.

Habitat ¹⁸

Depth range based on 176 specimens in 6 taxa.
Water temperature and chemistry ranges based on 31 samples.

Environmental ranges
  Depth range (m): 0 - 23.77
  Temperature range (°C): 11.471 - 12.348
  Nitrate (umol/L): 4.729 - 7.121
  Salinity (PPS): 35.035 - 35.363
  Oxygen (ml/l): 6.069 - 6.339
  Phosphate (umol/l): 0.336 - 0.439
  Silicate (umol/l): 2.315 - 3.388

Graphical representation

Depth range (m): 0 - 23.77

Temperature range (°C): 11.471 - 12.348

Nitrate (umol/L): 4.729 - 7.121

Salinity (PPS): 35.035 - 35.363

Oxygen (ml/l): 6.069 - 6.339

Phosphate (umol/l): 0.336 - 0.439

Silicate (umol/l): 2.315 - 3.388

Note: this information has not been validated. Check this note. Your feedback is most welcome.