Seaweed is on the rise again. For decades, the once important food, fodder and fertiliser has been side-lined, described as slimy, smelly and generally uncool. Now, with the seaweed industry growing at nearly six percent a year, seaweed is back.

Seaweed is actually a catch-all name for large algae growing in the marine and freshwater environments and are typically split by colour into reds, greens and browns. Each colour-group is evolutionarily distinct from the others and all are more different to each other than all land plants are together. One impact of this is that there are different compounds, not present in land plants or fungi, found in different kinds of seaweeds with interesting or valuable properties.

The National Wales: 'Seaweed' is a catch-all name for large algae growing in marine and freshwater environments. Photo: Alamy/PA'Seaweed' is a catch-all name for large algae growing in marine and freshwater environments. Photo: Alamy/PA

Brown seaweeds contain alginate, a thickener and gelling agent used in everything from food stabilisers to textile printing; and fucoidan, a health-boosting and antimicrobial compound.

Red seaweeds contain carrageenan or agar, both of which are also thickeners and gelling agents and used extensively in the food industries within dairy, meat and bread products.

Agar has a secondary use for the production of agar plates, which are used in scientific and medical settings for culturing microbes. Greens don’t have strongly gelling compounds, but, like the others, have unique molecules which have health benefits.

All seaweeds are also bio-accumulators, meaning that they deliberately take up minerals found in the water and subsequently have relatively high concentrations of a wide range of trace elements, including calcium and iodine.


On top of those benefits, seaweeds are also low in fat and high in protein and fibre. It is therefore unsurprising that most of the forecast growth in this industry is in food. However, this overshadows some other new areas of seaweed use where some fascinating science is occurring.

Feeding animals seaweed can significantly reduce emissions of methane. Cows and sheep are responsible for 18 percent of global methane emissions, which is a massive contributor to climate change.

Back in 2014, a group in Australia showed that certain tropical seaweeds decreased methane emissions from cattle rumen fluid by 92-99 percent and later identified the key compound involved. It was later shown that this methane reduction occurred in sheep as well as in bottles in a laboratory, reducing the animals’ methane production by up to 80%. Subsequent studies showed a methane decrease from cattle of 50-80% whilst not appearing to affect livestock weights.

Seaweeds also store a lot of carbon, and protect our climate as a result. With an estimated three-and-a-half million square kilometres of macroalgae growing worldwide, they are locking up a significant quantity of carbon each year, and should be included in climate change mitigation plans in the future. More than 40 percent of carbon locked up by seaweeds is typically lost each year as the ends of the seaweeds break off because of storms, grazers and other algae growing on them.

Dissolved organic carbon, such as sugars and other small molecules, also leaches or is secreted out. An estimated 11 percent of the lost seaweed ends up sinking into deep water where it is broken down so slowly it is considered sequestered or stored, keeping this former carbon dioxide locked away. There will be a high level of localised variance here due to different seaweed species, currents and tides, depths, grazer populations and other factors. But, as a resource, there is no doubt that these carbon-storing seaweeds will be more important in the future, particularly as ocean warming and acidification leads to an overall reduction in kelp forests.

The National Wales: The seaweed Porphyra umbilicalis used to make laver bread or bara lawr has long been a staple in the Welsh diet. Photo: Rosser1954 CC BY-SA 4.0The seaweed Porphyra umbilicalis used to make laver bread or bara lawr has long been a staple in the Welsh diet. Photo: Rosser1954 CC BY-SA 4.0

Seaweeds can be used to make a broad range of products from plastics to textiles to pharmaceuticals; compounds currently generated from the petrochemical industry. Seaweeds contain a high concentration of water compared to a lot of land-based crops, which can be a problem if the seaweed needs to be transported far from the sea.

Cultivation is still a nascent industry in the UK, with much of our seaweeds being wild-harvested, potentially damaging natural stocks if scaled up. But using seaweeds as a feedstock source has a number of big advantages too. Some species can grow up to 60cm a day and as they grow up the water column can generate more organic carbon per square metre than high-yielding crops such as sugar cane. Importantly, they do not require land, fresh water or fertilisers to grow, all constraints for land plants which will be an increasing issue with a rising global population and resource demands in the future.

Seaweeds have many uses and that versatility should be considered: they are far more than something eaten in sushi, or an ingredient in ice cream. We have a long history of eating seaweed - laver bread or bara lawr -  in Wales, now it is time to embrace some of its other great benefits.

Dr Jessica Adams is a Senior Research Scientist at Aberystwyth University with research interests in seaweed composition and its applications.

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