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Fast-growing, easily utilised marine algae which fix carbon dioxide


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The importance of seaweed across the ages

A short history of seaweed exploitation in the western British Isles


Seaweed has formed a part of the diet of Irish and Scottish coastal dwellers for at least 4,000 years.  The earliest recorded account of its use is in a poem dated around AD563 and attributed to St Columba, a native of Donegal, after his move to Iona in the west of Scotland. Dulse (Palmaria palmate), a red seaweed, was traditionally eaten with oatmeal in a thick broth or served boiled and tossed in butter.  The monks on Iona collected it to provide food for themselves and for the poor. Indeed, seaweed has associations with poverty in both Scotland, where it supplemented the diet of those displaced from their lands and forced to coastal locations to make way for sheep between 1790 and 1820, and Ireland, where it also became part of the diet during the potato famine after 1846.

Dulse, dillesk in Ireland and Carageen (Chondrus crispus), known in Ireland as Irish moss, or carrageen moss, continue to be harvested for food in small quantities in both Ireland and Scotland and purple laver (Porphyra umilicalis), a traditional component of the better known Welsh lavabread (‘Bara lafwr’), remains the key ingredient of laverbread or pudding in Scotland and Ireland, where it is known as slake, sloke or slocan.  Sea lettuce (Ulva lactuca) – ‘green laver’ - can also be used in a similar way to purple laver but is regarded as inferior.  Recently suppliers of “sea vegetables” have also sought to market some kelps and wracks for human consumption.


For many generations, seaweeds have played a much larger part in the production of foodstuff, being used as fertilisers.   Their ability to concentrate minerals and trace elements from the sea render them a potent source of nutrients for vegetable cultivation.  Traditionally storm-caste seaweeds were collected from the shore, especially in the western coastal areas of Scotland and Ireland, briefly composted and dug into the soil as a fertiliser and soil conditioner providing high levels of nitrogen and potassium, particularly useful in the shallow, often low potassium, soils of these west coast areas.  Crofters still use this method to the present day.

Later, with increasing coastal population, lazy bed cultivation became commonplace.  Wide trenches were dug and the seaweed thrown up by winter storms was laid on the earth piles for several weeks.  Eventually the piles of earth were turned back into the trenches and root crops, especially potatoes, planted.  No further fertilisation was undertaken, the seaweed providing all necessary nutrients.
Old areas of lazy beds are still visible on the islands and in western coastal areas of both Ireland and Highland Scotland.


From the later part of the 17th Century seaweed was found to have a number of industrial uses. In Europe, burning kelp to produce an alkaline ash probably started in France. It began in the British Isles in 1694, first in Fife and later, around 1720, in the Orkneys.  By the 1740s the practice was well established in western Ireland and the Hebrides and by 1800 Scotland alone was producing 20,000 tonnes p.a..

Kelp ash contains soda and potash and was used initially in glazing and glass-making.  It was an effective substitute for expensive Spanish “Barilla Soda” prepared from salt marsh plants.  During the Napoleonic Wars, Britain was largely isolated from Europe and Barilla Soda became unavailable.  As a result the value of kelp ash rose, especially as it became increasingly used in soap making.  During the first 15 years of the 19th century Laminaria spp. (kelp) collected as cast after storms, and Ascophyllum (knotted or egg wrack), cut from rocky shores at low tide, was collected and dried in increasing quantities.  Such seaweeds could be burned in round, stone-lined pits or shore kilns (as soon as two days after collection in good weather conditions).  20 tonnes of wet weed yielded five tonnes of dry and one tonne of kelp ash.  Many kilns were established along Irish and Scottish shorelines.

During these early 19th century boom years, Scotland produced 20,000 tonnes of burnt kelp from Orkney, the Western Isles and the west of Scotland, implying a harvest of 400,000 tonnes p.a. of wet seaweed.   One might expect that, given a 4-month cutting season and west coast weather, this would need an army of at least 3,000 cutters.  It is said that as many as 40,000 souls may have depended on kelp harvesting at its 19th century peak.  The harvesting was all by hand, supported first by horses to carry the weed from the shore in “creels” and later by adapted hand and horse carts for which special paths – “wrack roads” (now often corrupted to Wreck Road) were constructed.

A few made fortunes from seaweed.  Most Scottish soap and glass factories were in Glasgow and at one time a single Glasgow merchant handled 80% of the Scottish harvest.  In 1720 kelp ash sold for about £2 per ton, between 1740 and 1760 it was sold at £7 to £8 per ton.  By 1800 this had risen to £18 to £22 per ton.  Around 1810 the price of Barilla Soda from Spain fell to £10 per ton and following the end of the Napoleonic Wars, after British victory at the Battle of Waterloo in 1815, and the removal of import duty in 1820, the price of kelp ash rapidly fell back to the £2 per ton of 100 years earlier.  Kelp burning was over and its collapse contributed to Highland poverty and the misery of the clearances.

Iodine extraction from kelp began as the burning of kelp became less commercially attractive.  It was a much more skilled process.  The weed had to be fresh and protected from rain.  The burning temperature had to be controlled and stopped at precisely the correct time.   It was important not to burn weed contaminated with sand such as storm cast kelp because this affected burning temperature and thus iodine yield. Iodine pricing was speculative.  From 1841 to 1845 it averaged 11s-9d per lb.  By 1860 it was 8s per lb.  Cheaper mineral deposits were later imported from Chile and by 1900 the industry was petering out.  The last Highland shipment left South Uist in 1933 and by the start of World War II, it had ceased in Ireland too.


In 1893 the English chemist Edward Curtis Stanford, a specialist in iodine extraction, isolated alginate from seaweed. In 1864 he had established an iodine extraction plant for the North British Chemical Company at Middleton on Tiree (known as the “glassary”). As well as producing iodine and, eventually, alginates, this plant also produced charcoal, used as a fertiliser and deodorant for earth closets, and biogas used to light the buildings.

West Highland alginate production began in Argyll in 1935 when another English chemist, C. W. Bonniksen set up “Cefoil” at Putechantuy (Putechan, near Bellochantuy in Kintyre).  His aim was to produce a wrapping film which he began to sell in 1939, just as war started and “cellophane”, a much superior product, was launched.  The business failed but the Ministry of Supply recognised the benefits of alginates to the war effort.  It was known that chromium alginate could be spun into green yarn and used for manufacture of camouflage netting.  Outputs of the wartime work are vague but there is a story that alginic acid was used as a substitute for balsa wood and that at least one de Haviland “Mosquito” aircraft was built of it.  Other wartime products such as camouflage paint, custard and artificial silk for parachutes were reputedly made from alginates.

The Ministry of Supply built factories at Kames and Barcaldine (Argyll) and Girvan (South Ayrshire) which were managed by Cefoil.  A weed collection and drying station was established at Orosay (South Uist) in 1944. When war ended, Cefoil bought these factories and subsequently changed its name to Alginate Industries.  The small factory in Bellochantuy was subsequently closed and later, in 1956, Kames was also shut down.

During the second half of the 20th century extensive uses were found for alginates. Sodium alginate is a jelly-like carbohydrate and was used in a variety of ways to hold water, gel, emulsify and stabilise in the food, pharmaceutical and industrial sectors.   It was widely incorporated into foods and drinks to thicken drinks, form gels in pies and jellies, and to stabilise pet foods, meringues and ice cream.  It improved the head on beer and allowed fast setting of puddings and was used in textile printing to produce sharp edges and to thicken textile pastes.  When dried it could coat quality paper to produce a sheen.  The dental business used it in toothpastes and as a dental impression powder and it was used to coat tablets in the pharmaceutical industry.   Alginate’s properties were useful in cosmetics, paints and medical products and sodium alginate could also be used to form alkali-soluble fibres.

Alginate Industries grew apace through the 1960’s and 70’s.  In addition to the Orosay collecting station, further stations were set up in Sponish (North Uist) in 1955 and Keose (Lewis) in 1965 in addition to local collecting in Argyll and Ayrshire.  Nevertheless, Scotland could not meet the increasing demand for seaweed and supplies were eventually imported to Scotland from Ireland, Iceland, Norway, South Africa, Chile and Tasmania. 

In 1979 Alginate Industries was sold to Kelco, a Californian company, and renamed Kelco/AIL Limited.   This was a time of competition from Chinese producers of alginates and other competing products.  The 1980’s saw production reducing and staff being laid off.  The name changed to Kelco International and its then parent, Merck, in 1996 sold the company to Monsanto.  It was renamed Nutrasweet Kelco Company in 1996, when Barcaldine was closed and production focussed in Girvan.  Alginate production finally ceased in Scotland, after acquisition in 2008 of the Girvan plant by FMC Corporation of the USA.  At its peak, the world alginate industry probably utilised a quantity of wet seaweed similar to that harvested in the western British Isles in 1814.


Although Edward Curtis Stanford was using algal derived biogas to light his factory in Tiree in the 19th century, the history of seaweeds as a source of bioenergy – biogas and alcohols – is just beginning.  US experiments in the 1970s demonstrated methane production but failed to be followed through primarily because of a lack of adequate supply.  This is no longer a significant constraint and the economic and social importance of renewable energy have been revolutionised in the past 25 years.

We expect BioMara to be at the forefront of the novel developments upon which the next, and possibly the greatest, seaweed- based industry in Ireland and Scotland will be based.   The production of transport fuels, particularly in remote, rural, isolated and island communities, such as many in rural Scotland and Ireland, may well come to depend upon liquefied algal-derived biogas and bioalcohols.  Watch this space…

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