Bladder wrack (Fucus vesiculosus)

GenusFucus (1)
SizeSize: up to 2 m (2)

Common and widespread (2).

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).

Occurs around the coastline of Britain, and is also known from Ireland, the Baltic Sea, Norway, the Atlantic coast of France, Spain and Morocco, as well as Greenland, and the eastern coasts of Canada and the USA (2).

Bladder wrack occurs intertidally on the middle-shore, where it grows attached to rocky substrates, and is often associated with knotted wrack (Acophyllum nodosum) in the zone above toothed wrack (Fucus serratus) (3). It can survive in a wide range of exposures (3).

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).

This seaweed is not currently threatened.

No conservation action has been targeted at this species.

For more on this species see the Marine Link Information Network (MarLIN) species account:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. National Biodiversity Network Species Dictionary (November, 2002)
  2. White, N., (2000) Fucus vesiculosus. Bladder wrack. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth:Marine Biological Association of the United Kingdom. (November, 2002)
  3. Fish, J.D. and Fish, S. (1996) A student's guide to the seashore. Second Edition. Cambridge University Press, Cambridge.
  4. The Seaweed Site. Michael D. Guiry (November, 2002)