Seaweed | Growing & Harvesting Farms

Seaweed, the weed of the sea! Why not make the most of this nutritious sea vegetable? Here’s how British seaweed farms are growing and harvesting this sea plant.

You probably don’t realise it, but you use products containing seaweed every day. You can find it in toothpaste, cosmetics, beer, ice cream and paints. On an industrial level, it is used as a green fuel, in fertiliser and animal feed - all with little environmental repercussions.

Seaweed is quickly becoming a unique staple ingredient in our food. Known for its umami flavour and as an alternative to salt, Michelin-star chefs have embraced the range of edible seaweeds as an exotic addition to ocean-inspired plates. Seaweed is high in protein, omega oils and a range of vitamins and minerals, so it’s easy to see why it is growing in popularity among our health-conscious society.

But how are seaweed farmers meeting these growing demands for seaweed?

Traditional Seaweed Harvesting

Seaweed has long been a significant part of East Asian diets. And for centuries, wild seaweed harvesting has been part of coastal community culture across Northern Europe and the British Isles. How did they grow and harvest seaweed?

Picture a rugged coastline. Local townsfolk wade into the murky seawater among the rocks to hand pick rubbery leaves of dark green and brown. Or in the calm after a storm, they wander along a shoreline gathering washed up seaweed fronds. Back then, people knew the seasons for picking, and how to use each type of seaweed. In many communities, women would take the lead in gathering seaweed for food to sell locally.¹

Today, harvesting wild seaweed contributes to the majority of seaweed production in Europe, with the largest producers being in France, Norway, Ireland, Iceland and Russia. In Ireland, 10,000 wet tonnes of seaweed are gathered each year from a single beach in Cork.¹

Fun fact: Consider for example the rich history of “Irish Moss”. In 19th century Ireland, seaweed was gathered and dried for use in flans, tonic and beer, and was even thought to have medicinal properties.

Modern Seaweed Farms

But traditional methods of gathering wild seaweed is by its nature unreliable. The work is labour intensive and costly. Experts observed that the “increasing demand for seaweeds as food products can only be adequately met by cultivation.”¹ According to FAO, 96% of global seaweed production is now in cultivated farms rather than wild harvesting (including other uses like fuel, as well as food).²

The type of cultivation depends on how the species of seaweed replicates and reproduces. The simplest and most common cultivation method is to attach pieces of seaweed to rope lines or nets that are suspended in the sea often near the coast. They hang on wooden stakes or on a floating wooden framework dug down into the seabed.

Nori, the black seaweed used in sushi, is grown using nets that spores settle onto. The nets are hung at a depth that allows the seaweed to be exposed to the air for a few hours a day when the tide is out. Another technique, used to grow Sea Grapes or “Green Caviar”, is simply planting a cutting of seaweed (about 100g) into the seabed to help it take root.³ 

Harvesting Seaweed

While the majority of seaweed harvesting in the UK is still gathered by hand at low tide, other countries harvest wild seaweed with boats and machinery, using a rake or trawler methods. This is much more efficient than hand collection, but, if used excessively, can have a severe habitat impact as it can pull up other seaweeds and disrupt sea animal homes.⁴

But, seaweed harvesters have given an encouraging amount of thought and attention to this issue. For example, in Norway the rake method only removes the top floating canopy of seaweed, which allows the seaweed to regrow over the next two years and minimises disruption of the seabed.⁵

Seaweed's Sustainability

In addition to providing food and shelter to all the creatures inhabiting its aqua ecosystem, seaweed forests can decrease carbon dioxide on the surface of the sea and in the atmosphere.⁶ Seaweed also absorb dissolved nutrients from the water, which can decrease eutrophication caused by water pollution.⁷ 

Fun fact: Adding dried seaweed to cow feed can reduce their production of the greenhouse gas methane by 99%.⁷

One cautionary warning is that as a natural filter, seaweed can have high levels of iodine and metals if exposed to polluted water.⁷ This means that although nutritious in many ways, seaweed can be harmful if consumed too much.

Now that you know a bit more about seaweed and how it’s grown, would you eat more of this sea vegetable? Let us know in the comments below!