How to identify seaweed

Seaweeds require enough light to photosynthesise, so are most abundant in the intertidal zone – especially along rocky shores. Here are 12 for you to spot. 

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All illustrations by Dan Cole / The Art Agency 

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1 Purple laver Porphyra umbilicalis (above

Small and purple, with broad, tough fronds. Found in upper zone of rocky shores. Edible; eaten as laver bread.

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2 Oarweed Laminaria digitata

A glossy, golden-brown kelp up to 2m long, with distinctive ‘fingers’ on broad fronds. Exposed at low tide.

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3 Furbelows Saccorhiza polyschides

A brown kelp with a frilled stem and large bulbous holdfast that attaches to rocks. Revealed at low spring tides.

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4 Bladderwrack Fucus vesiculosus

Olive-brown and up to 2m long, with air bladders at the frond ends. Forms beds in mid-zone of rocky shores.

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5 Channelled wrack Pelvetia canaliculata

Brown and up to 15cm long, with fronds that curve inwards to create a channel. Found at top of the shore.

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6 Pepper dulse Osmundea pinnatifida

Small, red or brown, fern-shaped seaweed of sheltered rocky coves. Edible; used as a curry-like spice.

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7 Coral weed Corallina officinalis

Small, pink or purple seaweed with a feathery structure. Forms a dense carpet in pools on rocky shores.

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8 Carrageen Chondrus crispus

Purple, with flat fronds up to 20cm long. Found on rocks on lower shore. Edible; used as a thickening agent.

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9 Sugar kelp Saccharina latissima 

A brown kelp up to 2m long, with frilly fronds. Found below low-tide mark. Edible; used as a sugar substitute.

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10 Gut weed Enteromorpha intestinalis

Green, grass-like seaweed with tubular fronds. Found on rocks, sand or mud at all levels of the shore.

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11 Velvet horn Codium tomentosum

Green seaweed with spongy texture resembling deer antler ‘velvet’. Found in rockpools and on lower shore.

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12 Sea lettuce Ulva lactuca

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Small and green, with crumpled, lettuce-like fronds. Grows on rocks in mid-zone of shores. Edible.