Seaweed under the spotlight

Seaweed plays a vital role in the natural world
Seaweed plays a vital role in the natural world

Kerri Whiteside

Living Seas Officer

Ulster Wildlife Trust

WE all know seaweed, that slimy stuff that tangles around your feet when having a dip or a paddle in the sea, but there is a lot more to it than meets the eye.

Seaweed is actually rather fascinating, and just as plants form the basis of life on land, seaweed plays the same role in the ocean.

Seaweed isn’t a plant though; it is in fact algae and as such, doesn’t have a vascular system or extensive roots. Instead, it produces extremely strong adhesives which help it attach to rocks by its base, known as the holdfast.

Seaweed can be easily categorised into three main types - green, brown and red – which have evolved over billions of years and possess various capabilities of surviving on either the lower, middle or upper shore.

It plays a vital role in the natural world and actually makes up the greater bulk of our oceans’ vegetation whilst also providing valuable shelter for fish and invertebrates; dense kelp forests, for example, support entire underwater communities. Not only is seaweed of huge ecological importance, it is also widely used by people whether eaten fresh or preserved in a jelly or in a dehydrated state. It’s more commonly eaten in Asia than in Europe, but we actually use seaweed quite a lot in products and treatments, and in laboratories.

Have you ever heard of agar and alginates? Agar is obtained from red seaweed and is used in labs as a culture for bacteria. Alginates are extracted from large brown seaweed and are used in various things from the food we eat to pharmaceutical and cosmetic products as emulsifiers, stabilisers and thickeners. Common products you may be surprised to discover, containing seaweed include toothpaste, ice-cream and beer!

Alginates are also used as coatings for paper, leather and textiles!

Some of the most familiar species of seaweed found in Northern Ireland include channelled wrack sea lettuce, bladder wrack, dulse, sea spaghetti and various varieties of kelp.

Channelled wrack is found on the more extreme upper shore growing in tufts on the open rock. It is known to survive out of water for up to eight days due to the channels that run along its fronds which hold in moisture - in fact, if submerged for any length of time it won’t survive! Channelled wrack is actually very nice to nibble on fresh from the shore - it has quite a sweet taste.

Sea spaghetti can be commonly spotted floating along the shallows and in rock pools. It starts its life shaped like a tiny button and takes this form for its first year until the long spaghetti-like reproductive receptacles grow in spring and summer before breaking off. Sea spaghetti is quite popular in France where it is served fresh with garlic and capers - perhaps a recipe worth a try!

So, the next time you are out for a stroll along the shore why not try and identify some of the seaweed at your feet and if you’re feeling particularly intrepid, take a handful home for dinner or a relaxing ‘home-spa’ treatment!

If you’d like to discover more about seaweed and meet some real life sea creatures, why not join us at Titanic Belfast this week for the Under the Sea Festival. For more information visit