Scotland provides a home to a wide variety of seaweed species, with different species thriving in different coastal areas. One of the most abundant is wrack, also known as rockweed. Wrack is a large brown seaweed that grows along the Scottish coastline. There are five species of wrack native to Scotland – Ascophyllum nodosum, Pelvetia canaliculata, Fucus vesiculosus, Fucus spiralis, and Fucus serratus.
Wracks are predominantly found growing on intertidal rocky shores, but can also be found on sheltered mud, sand, or gravel shores. It has a structure called a holdfast which grips onto rocks. The holdfast is visually similar to the roots of a plant, but doesn’t penetrate the seabed or draw nutrients from it in the same way as land plants. Instead of stems, seaweeds have a stiff stipe that holds them upwards towards the sunlight. From this, long fronds grow. These vary in shape depending on the species and may be long, strap-like and dotted with air bladders in the case of the knotted wrack (Ascophyllum nodosum), or flat strap-like branching fronds with jagged edges in the case of the serrated wrack (Fucus serratus).
With the exception of serrated wrack (Fucus serratus), all members of the wrack family have distinct “bladders” which fill with air, or in the case of spiral wrack (Fucus spiralis) a gelatinous material that is part of the seaweeds reproductive cycle. These bladders hold the seaweed afloat in water to gain the maximum amount of light. The knotted wrack (Ascophyllum nodosum), also called egg wrack, grows approximately one bladder per frond per year which means you can determine its age by counting its bladders.
Wracks are one of the most common seaweeds found on beaches in Scotland and across Britain, and a dense mass of wrack seaweed at low tide will be a familiar sight to many people. These dense masses of wrack provide shelter for many species on the rocky shores – from grazing molluscs to tiny fish.
Wrack seaweeds are abundant along the majority of the Scottish coastline, but appear to grow especially well on the west coast of Scotland, around the Inner and Outer Hebrides, and around the Orkney and Shetland islands. Smaller areas of wracks are also found along the southeast coast of Scotland.
Different species of wrack can be found growing in different depths of water:
A common wrack seaweed known as knotted wrack or egg wrack which grows on sheltered rocky shores, around the mid shore zone. It is a long lived species, with individual plants growing slowly for decades. It can be found year round.
A very common seaweed known as Channelled wrack which grows around the high water mark on sheltered, rocky shores. Living on the upper shore, it is very tolerant of desiccation – it traps water in channels in the fronds and can survive for up to eight days out of the water. In fact, if it is fully submerged for too long, it may die. It can be found year round.
A common wrack seaweed known as bladder wrack which grows between the high and low water marks on rocky shores. It forms dense beds on the mid shore, often together with egg wrack. It can be found year round.
A common wrack seaweed known as spiral wrack or twisted wrack that grows just below the high water mark on rocky shores all around the country. It is very tolerant of desiccation and can survive out of the water for long periods. It can be found year round.
A common wrack seaweed known as serrated or toothed wrack that grows just above the low water mark on rocky shores. Other seaweeds, including Dulse, can often be found to grow on its fronds. It can be found year round.
Scotland is also home to an unusual subspecies of Ascophyllum nodosum which is only found in the head of west coast sea lochs. Known as “sea loch egg wrack” this uniquely Scottish seaweed doesn’t attach to rocks like most seaweeds do, but instead rolls with the gentle tides.
Seaweeds have a long history in Scotland of being harvested for commercial purposes, although it is an industry which has been dormant for many years. Historically, it was harvested to extract iodine, produce alginates, and used as a food source. The climate emergency that we are now facing globally has caused many people to look again at seaweedas a crop which has the potential to be used in sustainable, environmentally friendly ways and there is growing interest in how Scotland’s natural seaweed resources can be used.
Seaweed has been in increasing demand by small food and cosmetic businesses in recent years, and is mainly harvested for their alginates. The harvested alginates are widely used as thickening agents in many products from ice cream to toothpaste, as well as being used in pharmaceuticals for their ability to encapsulate medicine and treatments.
Wrack seaweeds are very effective at accumulating and storing nutrients and minerals from the surrounding seawater and this has made them hugely popular in the cosmetics industry. One example is serrated wrack (Fucus serratus), which is widely used by the cosmetics company Lush to create face masks, hair treatments, and moisturisers as it is rich in vitamins, minerals, and trace elements that form a barrier on the skin that helps retain moisture. Lush also use bladder wrack (Fucus vesiculosus) to create “seaweed absolute” – a deep green or greenish brown liquid with an intense green, herbaceous and woody odour. It is used in perfumery when a marine or seashore fragrance is required.
Historically, harvested wrack has been a popular home remedy for many skin conditions including psoriasis, eczema and to ease arthritis and rheumatic pains – and one of the most popular suggestions for using collected wrack at home is to put it in a bath to help draw out the minerals and nutrients stored inside.
In recent years, there has been an increase in the use of wrack seaweeds to create textile fibres. Ascophyllum nodosum (commonly known as egg wrack or knotted wrack) is used to create a textile fibre called Seacell produced in Austria by German company Smartfiber AG. Seacell is produced using knotted wrack that has been washed, dried, and ground before being combined with eucalyptus to create a biodegradable fibre that can then be woven or knitted to create textiles. This innovative fibre is used by a textile artist in Scotland called Jasmine Lingington who dyes the fibres using knotted wrack collected on the southeast coast of Scotland to create fashion garments (called “Seaweed Girl”), home textiles, and fibre art. She extracts the pigment from the knotted wrack to create a subtle coloured natural dye, and the by-product is used to create a seaweed bead which she pairs with kelp sequins for embellishment.
On a small, individual scale, wracks can be harvested by hand on the shore and brought home to use in making a rich stock powder to be used in soups, stews, and sauces. They can also be pickled, and used as vegetables and added to stir-fries. And the gelatinous bladders on spiral wrack can also be used in a similar way to olives or capers.
Seaweeds can also be used as a fertiliser or soil conditioner, and many island communities use beach-cast seaweed (including wrack species) gathered from the shore to spread on land, and there is also some commercial use of seaweeds – mainly Ascophyllum nodosum – as organic fertiliser.
There is also growing interest in Scotland around how seaweeds, including the wrack species, could be harvested on a large-scale to produce biofuel.
Currently there is no large scale harvesting of wrack or other seaweed species in the UK, but there are a number of businesses and individuals harvesting wild seaweed on a small scale in Scotland. Wrack along the shoreline is accessible at low tide, and can be harvested by hand using a small knife or sickle. Seaweed is cut 15cm to 30cm above the holdfast (depending on species) to allow regrowth.
Ascophyllum nodosum is the most commonly harvested wrack in Scotland, and it may also be collected using a mechanical seaweed harvester in addition to being collected by hand. The seaweed is generally cut around 30cm above the holdfast to allow regrowth – the stump that is left will regenerate in 3 to 4 years.
As well as wild harvesting, seaweed can also be sustainably farmed for large-scale harvesting. Seaweed farming doesn’t require land to be cleared, freshwater, or any insecticides or fertilisers, and seaweed farms can also play an important role in carbon capture. Seaweed has the ability to absorb up to 47kg per pet tonne, which equates to approximately one tonne of carbon per hectare annually. They can also encourage responsible coastal management and provide areas for sea life to thrive.
Seaweed aquaculture is already a huge industry globally. Around 95% of farmed seaweed is currently grown in southeast Asia, and other countries in northern Europe – including the Faroe Islands, Norway, Iceland, Denmark, the Netherlands, and Ireland – have a growing industry. There is considerable potential for growth of a kelp and seaweed industry in Scotland that operates in a sustainable and careful way.
“The Power of seaweed in a fibre”. Smartfiber AG, https://www.smartfiber.de/en/seacell-fiber/. Accessed 10th February 2021.
“Wild Seaweed and Seagrass Harvesting”.Wild seaweed harvesting: strategic environmental assessment – environmental report, Scottish Government, 2016. https://www.gov.scot/publications/wild-seaweed-harvesting-strategic-environmental-assessment-environmental-report/pages/4/. Accessed 10th February 2021.
“Seaweeds and Seagrasses”. The Wildlife Trusts, https://www.wildlifetrusts.org/wildlife-explorer/marine/seaweeds-and-seagrass. Accessed 5th February 2021.