bladderwrack

Bladderwrack, also known as Fucus vesiculosus, is a species of brown algae in the family Fucaceae. It occurs on cool temperate coasts of the northern hemisphere, especially on rocky shores of the Atlantic and Pacific, where it lives in the intertidal and shallow subtidal zones.

It has a flattened, olive-brown thallus up to about 60 cm long with forked, leaflike fronds. Near the tips the fronds bear rounded air bladders that provide buoyancy. It attaches to rocks by a strong holdfast and lacks true roots.

Bladderwrack plays a role in coastal ecosystems by providing habitat and food for a range of invertebrates and by serving as a subject in studies of seaweed physiology. It reproduces in the intertidal zone via conceptacles on the fronds and can form dense stands in favorable conditions.

Chemically, bladderwrack contains iodine and various polysaccharides such as alginates and fucoidans, as well as laminarin and trace minerals. It has been harvested for alginates used as thickening agents in foods and cosmetics, and for iodine-rich extracts used in dietary supplements. In traditional medicine it has been used to address thyroid-related concerns, though evidence and safety considerations vary.

Because iodine content can be high and variable, excessive or inappropriate use may affect thyroid function, and products should be used with caution by people with thyroid disorders or those taking thyroid medications. Sustainable harvest and regulatory controls govern commercial harvesting in many regions.