Does bladderwrack always have bladders?

BBC Wildlife contributor Matt Doggett discusses this adaptable seaweed species.

Bladderwrack is a seaweed which is rich in iodine, so extracts from it are sold in health food stores to support a healthy thyroid.

Bladderwrack is a variable species of seaweed © Diane Macdonald / Getty

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No. Like many species of seaweed, bladderwrack varies its growth-form depending on its environment.

It typically occurs in sheltered rocky habitats on the lower end of the shore, where the characteristic air-filled bladders enable the fronds to float up towards the light, maximising growth and helping it to outcompete other species.

Bladderwrack is less common on exposed shores, but where it does occur it can develop without bladders. In fact, the whole plant is smaller, including the fronds, which are narrower.

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By not forming bladders on wave-beaten rocks, bladderwrack is subjected to less drag, which means less chance of it being swept away. This adaptable species does all it can to survive wherever it lives.