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.
The fronds of F. vesiculosus grow to 90 centimetres (35 in) long and 2.5 centimetres (1.0 in) wide and have a prominent midrib throughout. It is attached by a basal disc-shaped holdfast. It has almost spherical air bladders which are usually paired, one on either side of the mid-rib, 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 and is similar to Fucus serratus.
Fucus vesiculosus is a common large alga on the shores of the British Isles. It has been recorded from the Atlantic shores of Europe, Northern Russia, the Baltic Sea, Greenland, Azores, Canary Islands, Morocco and Madeira. It is also found on the Atlantic coast of North America from Ellesmere Island, Hudson Bay to North Carolina.
The species is especially common on sheltered shores from the middle littoral to lower intertidal levels. It is rare on exposed shores where any specimens may be short, stunted and without the air vesicles. 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. Phlorotannins in Fucus vesiculosus act as chemical defences against the marine herbivorous snail Littorina littorea. Nevertheless, galactolipids, rather than phlorotannins, act as herbivore deterrents in this species against the sea urchin Arbacia punctulata. Methyl-jasmonate may induce the phlorotannins production. Fucophlorethol A is a type of phlorotannin found in F. vesiculosus.
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. 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. 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.
Biology in the Baltic Sea
Individuals of F. vesiculosus from the North Sea colonized the Baltic Sea less than 8 000 years ago. Today, F. vesiculosus is found deep inside the Baltic Sea, including areas of strong hypo saline (2–4‰) waters, such as the inner parts of the Gulf of Riga, the Gulf of Finland and the Bothnian Sea.
The colonization of the Baltic Sea is paralleled by a switch from what seems to be obligate sexual recruitment to facultative asexual recruitment. Asexual reproduction in Baltic Sea populations is accomplished by the production of adventitious branches that come loose and reattach to the bottom by the formation of rhizoids. Adventitious branches are present in thalli of F. vesiculosus also in other areas, but asexual formation of new thalli has never been reported outside the Baltic Sea.
The genetic structure of F.vesiculosus in the Baltic Sea is typically fine-scaled, with significant genetic differences among populations as little as 1 kilometer apart. However, between some areas the differences are large, e.g. are populations along the SW Finnish coast and in the Gulf of Finland very different from each other and from the rest of the Baltic Sea.
The ratio of sexual to asexual recruitment varies, even among nearby populations, from no clones to all individuals in the population being of the same clone. Clones seem to be absent in the southern Baltic Sea, less common in Estonia but very common in Gulf of Finland and in the Bothnian Sea. Mostly, clones of F. vesiculosus have a very local distribution, which is different to clones of the closely related sister species Fucus radicans, where a few clones are widely distributed.
Genetic variation is fundamental for a species ability to adapt and survive in new environmental conditions. Thus, to mitigate future losses, management and conservation of Baltic Sea biodiversity should include also the genetic level.
Eutrophication, increased turbidity or cascading effects of overfishing have historically eradicated local populations of F. vesiculosus. Loss of this type is likely to lead to loss of genetic variation including local adaptation. The warming and salinity decrease predicted for the Baltic Sea over the coming 50 to 100 years may result in further population losses. In areas with low levels of sexual reproduction (high clonality) the potential for adaptation to new environmental conditions is low. Here, populations are particularly vulnerable.
According to the Baltic Sea research and development project BONUS BAMBI, management for the long-term conservation of F. vesiculosus should aim to:
- Protect populations with high sexual activity, i.e. many genotypes and thus, capacity for future evolutionary adaptation. This is particularly important in areas where cloning is otherwise predominant, and at range margins in the Bothnian Sea and in the Gulf of Finland,
- maintain large population sizes,
- maintain connectivity between populations at present levels,
- provide management plans for marginal populations, i.e. in the Bothnian Bay, in Gulf of Finland and in the Gulf of Riga,
- consider genetic monitoring,
- consider restoration of earlier lost populations in Gulf of Gdansk, using individuals from areas of similar salinity.
Primary chemical constituents of this organism include mucilage, algin, mannitol, fucitol, beta-carotene, zeaxanthin, iodine, bromine, potassium, volatile oils, and many other minerals.
Recently the researchers found that an extract of Fucus vesiculosus, promotes the contraction of fibroblast-populated collagen gels through increased expression of integrin molecules. In this study, they investigated the effects of topical application of an aqueous extract of this alga on the thickness and the mechanical properties of human skin. A gel formulation that included 1% of the extract was applied topically to human cheek skin twice daily for five weeks. A significant decrease in skin thickness measured by B-mode ultrasound was elicited, as was a significant improvement in elasticity measured with a Cutometer as compared with controls. In cheek skin, the thickness normally increases and the elasticity usually decreases with age. These results suggest that the Fucus vesiculosus extract possesses anti-aging activities and may be useful for a variety of cosmetics.
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