Draft Seaweed Policy Statement Consultation Paper

Consultation paper on policy options for seaweed cultivation in Scotland

5 Background to Seaweed

5.1 Introduction

5.1.1 In order to establish the environmental effects of the proposed SPS and the policies contained within the Consultation Document, it was necessary to develop an understanding of the seaweed industry and, through this, establish the features of the environment that are likely to be affected. This section of the report forms the start of the baseline for this SEA, presenting background information on Scotland's seaweed resources, the important role seaweed plays in the marine environment and an introduction to the commercial aspects that will likely fuel industry growth.

5.2 Algae and Seaweed

5.2.1 Algae are plant-like organisms with simple reproductive structures that live in the aquatic environment including the sea, freshwater and even damp conditions on land. They are usually photosynthetic and aquatic-based but, unlike terrestrial plants, do not have true roots, stems, leaves or vascular tissue. Algae can be classified into two distinct types. The first, and smallest, is micro-algae which are unicellular or multi-cellular (less than 0.4 mm in diameter) and typically possess high oil content. The second, called macro-algae, are multicellular with differentiated cell structure and function, with lower oil content than micro-algae and can have high carbohydrate and sugar contents [15] .

5.2.2 The term 'seaweed' is the collective name for a number of different groups of macro-algae living on seashores and in shallow marine waters, such as intertidal and subtidal habitats, throughout the world [16] . Seaweeds are considered to be near the base of marine food webs, and as such, play an important role in marine ecosystems with many marine animals relying on the food and shelter they provide. Seaweed also forms the basis for a large worldwide industry built upon the harvesting of wild seaweed and, more recently, the cultivation and production of seaweed for a variety of uses.

5.2.3 The collective macro-algal group is often classified into three broad groups, based largely on their pigmentation and shared biological characteristics [17] . The three broad groups include:

  • Brown seaweeds ( Phaeophyceae) are usually large in size, ranging from giant kelp (often 20m long) to thick and leather-like seaweeds (2-4m long) and much smaller species (30-60cm in length). They include species such as the kelps and wrack.
  • Red seaweeds ( Rhodophyceae) are usually smaller and generally range from a few centimetres to a metre in length. They also include seaweeds of purple and brown-red pigmentation.
  • Green seaweeds ( Chlorophyceae) are also small, with a similar size range to the red seaweeds.

5.2.4 Different species of seaweed have developed through different evolutionary processes, and as such, the differences between three types involves more than colour [18] . It is estimated that there are some 10,000 species of red, brown and green seaweed globally [19] , and as such, seaweeds exhibit a wide variety of diverse life forms.

5.2.5 All seaweed species are allocated to Ecological Status Groups ( ESG) under the Water Framework Directive ( WFD), with each classified either ESG1, comprising late successional or perennial species, or ESG2 comprising opportunistic or annual species that are simpler in structure [20] . The life span of different species of seaweeds varies markedly, ranging from weeks for annual species, to many years for some perennial species [21] such as Laminaria hyperborea (a kelp) which can survive for up to 15 years [22] .

5.3 Habitat Requirements

5.3.1 The major environmental factors affecting seaweeds are light, temperature, salinity, water motion and nutrient availability [23],[24] . The presence of seawater (or at least brackish water) and sufficient light to enable photosynthesis are the main common requirements for seaweed species to survive. All types of seaweed use sunlight, carbon dioxide and water to create food, and as such, seaweed grow within the reach of sunlight. Many areas around Scottish and UK coastlines contain the suitable habitats, high natural nutrient levels and current flows considered to be necessary for seaweed growth [25] .

5.3.2 Most seaweeds live attached to hard substrata so that they hold their position in tidal areas [26] , and hence seaweeds are found in the rocky intertidal areas in most of the world's oceans and, in temperate and polar regions, attached to rock surfaces in shallow subtidal areas [27] .

5.3.3 However, with the wide variety of seaweed species, there is wide variation in the specific requirements and sensitivities of different seaweed species. For example, some species are more suited to warm climates, others require less sunlight to survive than others and can grow in deeper areas, while others, such as maerl [28] , do not require an attachment and therefore grow unattached on the seabed.

5.4 The Role of Seaweed in Marine and Coastal Environments

Biodiversity and Ecosystem Processes

5.4.1 Seaweed plays a number of important roles in marine ecosystems, the most important being its support for marine biodiversity. Scotland's seaweed communities provide a range of different and unique habitats for marine plants and animals. For example, Scotland's kelp forests provide living spaces for a wide range of animals and plants, e.g. small animals such as worms and crustaceans living in gaps in branching holdfasts of the kelp on the seabed, fish seeking shelter from predators in the shade of plants, and other marine plants living amongst the kelp forest [29],[30] . Maerl provides similar conditions: the 2010 site condition monitoring survey conducted by SNH found some 236 animal species living in the maerl within the Sound of Arisaig, with a further 185 animal and algal species associated with the surface of the maerl [31] .

5.4.2 Seaweed's position at the base of the marine food chain means that many different animals rely on it both as a food source and for the shelter a seaweed community can provide. Marine fauna such as fish, sea urchins and molluscs graze on seaweed, and the presence of these attracts other marine species that use them such as birds and mammals. For example, seabirds are known to use gaps in the seaweed forests to hunt for small fish and crabs.

5.4.3 This attraction of marine fauna is in part due to seaweed's role in the production of organic material. Like terrestrial plants, seaweeds grow by fixing carbon dioxide ( CO 2) through photosynthesis, and when the seaweed dies, it breaks down and becomes a food source for bacteria and single-celled organisms [32] . Different types of seaweed capture sediment and nutrients, which can significantly improve surrounding ecosystems and food supplies for these biological communities. In addition, the relatively sheltered environment that seaweed can help to create provides protection for many marine animals from the high physical stresses found on high-energy coasts [33] .

5.4.4 Seaweed provides important habitats for many fish and crustacean species. As such, disturbance of these communities can also disturb the fauna that use these areas [34] . Unattached seaweed (cast seaweed or driftweed) washing up in coastal areas and on beaches can play a key role in supporting coastal habitats. As they degrade, these plants provide vital habitats for small creatures, such as crustaceans and insect larvae that hatch amongst the cast seaweed, and provide a vital source of food. These areas often become a valuable food source for other creatures, such as seabirds, that hunt through cast weed for food [35] .

Water Quality

5.4.5 Seaweed's nutrient absorption properties have been widely investigated for commercial industry, but are also very useful in its role in the marine environment. The ability of many seaweeds to bio-accumulate nutrients and pollutants (including heavy metals), contribute to improving water quality, assisting in reducing eutrophication and delivering associated benefits for the marine and coastal communities they inhabit.

Coastal Processes

5.4.6 Seaweed can contribute to wave attenuation and to reducing the erosive impact of waves on our coastlines, and has been shown to play an important role in protecting marine and coastal areas, particularly in storm events. For example, the large kelp forests ( Laminaria hyperborea) west of the Western Isles have been observed to play an important role in reducing wave energy reaching the coast [36],[37] .

5.4.7 Driftweed or cast-weed, terms given to seaweed that has been washed ashore by the wind and sea, can also play a role in changing coastal processes by stabilising beach areas and assisting sand dune development, and enabling pioneering salt-tolerant plants to establish along the driftline amongst cast seaweed areas [38] .

5.5 Scotland's Wild Seaweed Stocks

5.5.1 Hundreds of species of seaweed have been identified in the UK [39] . Four broad groups of seaweed have been identified by SNH in Scotland's coastal waters [40] , each containing a wide variety of species:

  • Kelp: a brown seaweed growing on underwater rocks all around Scotland's coasts. It grows best in areas of strong water movement, requires good levels of sunlight and can grow in depths of 5m in sheltered sea lochs or greater than 30m in the clear waters around St Kilda [41] . While five varieties of kelp grow around Scotland (Tangle ( Laminaria digitata), Cuvie, Dabberlocks ( Alaria esculenta), Sugar kelp ( Laminaria saccharina) and Furbellows ( Saccorhiza polyschides)) [42] , in general terms, Scotland's kelp forests mainly comprise cuvie ( Laminaria hyperborea). These communities are found on suitable rocky areas all around the Scottish coastline, most extensively around Skye and the nearby mainland, along the west coast of the Outer Hebrides, and around Orkney and Shetland. They are far less common on the east coast, where much of the sea bed is composed of sand [43] . Certain kelp habitats are Priority Marine Features ( PMF) [44] . Several have been listed as Marine Protected Area ( MPA) search features, with kelp and seaweed communities on sublittoral habitats included in four possible MPAs [45] .
  • Wrack: a brown seaweed which can grow either anchored to rocks between the tides on the seashore (egg wrack), or unattached and flowing with sea loch tides (sea loch egg wrack or wig wrack) [46] . Wig wrack ( Ascophyllum nodosum) only grows on sheltered, muddy, sandy or gravel shores in Western Scotland and Ireland [47] . The species forms in the special conditions of Scotland's fjordic sealochs, and has been identified as a priority for action under the UK Biodiversity Action Plan ( UKBAP) [48] taken forward as part of the Scottish Biodiversity Strategy. Sea loch egg wrack was also included in the list of MPA search features developed in 2012 [49] .
  • Maerl: a purple/pink 'coraline' (or coral-like) seaweed that provides shelter for a wide range of marine creatures, that grows unattached on the seabed. Maerl is widespread along the west coast of Scotland, in the Western Isles, Orkney, Shetland and the north coast ( e.g. Loch Eriboll), but is absent from the east coast. The occurrence of Maerl beds is typically associated with sounds or estuaries that are exposed to currents but protected from strong waves [50] . Coral maerl ( Lithothamnion coralloides) and common maerl ( Phymatolithon calcareum) have been identified within the UKBAP as a priority species, and maerl beds are identified in the UKBAP list of habitats [51] . Maerl beds or maerl with coarse shell gravel with burrowing sea cucumbers were included in four possible MPAs. [52]
  • Stoneworts: a green algae with some 33 known species identified in the UK, grows in clear fresh and brackish water in coastal pools, such as those found amongst the machair in Scotland's Western Isles. Stoneworts are highly sensitive to pollution and many species are now rare in the UK [53] . A total of 44 important stonewart areas ( ISAs) were identified in 2004 in Scotland, 16 of which were also considered to be of European importance. These areas were mainly found in the Western Isles, Shetland, Orkney, and the western and northern Scottish coasts [54] . While a macro-algal species, stoneworts are not generally considered a seaweed.

5.5.2 Research into the commercial availability of wild seaweed stocks has been undertaken in many parts of the world, and Scotland has been the subject of a number of surveys in the past [55] . However, many of these studies were undertaken decades ago, and recent surveys of Scotland's wild seaweed stocks appear to be limited to specific locations, such as the Western Isles.

5.5.3 One such study, undertaken in 1994, assessed littoral seaweed resources and management options in the Western Isles, by surveying the distribution and abundance of potentially exploitable seaweeds ( i.e. A. nodosum, Porphyra umbilicalis, Mastocarpus stellatus, Chondrus crispus and Palmaria palmata) [56] . Another study, undertaken for SEPA in 2003, employed a wider geographic scope and used existing and new survey data on the presence and abundance of macrophyte species in 147 coastal sites on the west and east coasts, Outer Hebrides, Shetland and Orkney Isles [57] .

5.5.4 The most recent such study, undertaken in the Outer Hebrides in 2010 [58] , focused specifically on the extent of the species A. nodosum and investigated the viability of sustainable harvesting of the wild stocks of this species. This study, commissioned by Scottish Enterprise ( SE) and Highlands and Islands Enterprise ( HIE), followed on from previous surveys undertaken in the mid-20 th century, and estimated a biomass of over 170,000 tonnes of wild stocks present within the isles. These resources were found be predominantly located offshore in Lewis, North and South Uist, and Harris.

5.5.5 The PMF identified by Joint Nature Conservation Committee ( JNCC) and SNH include a number of habitats (including kelp and seaweed communities of sublittoral sediments, sea loch egg wrack beds, maerl beds and tide-swept algal communities) [59] .

5.6 Commercial and Industrial Use of Seaweed

Historical Uses

5.6.1 Seaweed production and harvesting of wild stocks has a long history, particularly in South-East Asia. Seaweed has been a key food source in some parts of the world for centuries, with many species of red, green and brown seaweeds consumed [60] . Today, harvesting of natural populations of seaweeds is primarily for human consumption in South East Asia, and for hydrocolloid (phycocolloid) production, producing algin, agar and carrageenan [61] and much of the seaweed eaten today is in the form of these products. Today, large quantities of seaweed are cultivated, mostly in China, to meet the demand for seaweed product.

5.6.2 In terms of species, red and brown seaweeds are largely used to produce hydrocolloid extracts, non-crystalline substances with very large molecules that dissolve in water to make a viscous solution [62] . Alginate, agar and carrageenan are water-soluble carbohydrates that are used to thicken aqueous solutions, and are used to form gels, water-soluble films, and in the stabilisation of some products. Green seaweeds are also widely harvested for human consumption.

5.6.3 Over the last two centuries, seaweed has also been used in the production of products such as potash, methane, acetone and butanol. Today, seaweed extracts are commonly used in a range of different products, often in niche markets, including animal feed (or seaweed meal), shampoo, toothpaste, cosmetics, medicines, fertilisers and bathing gels, amongst others [63],[64] .

Research and Development

5.6.4 Over the past two decades, the potential use of seaweed products has expanded considerably, with much research and investigation conducted into its potential use and in developing technologies for its efficient cultivation.

5.6.5 The nutrient absorption properties of seaweeds, particularly in the accumulation of heavy metals (such as cadmium, copper, nickel, lead and zinc) have been widely investigated. These properties have been investigated and applied in research, particularly in the use of seaweed in waste treatment processes. The successful treatment of sewage and some agricultural wastes, through reducing nitrogen and phosphorus-containing compounds and the removal of toxic metals from industrial wastewater, have been demonstrated in scientific studies [65] .

5.6.6 The use of specific native seaweeds for commercial purposes has also been investigated. For example, the commercial-scale extraction of the rich lime resource in maerl has been proposed in the Western Isles in the past, but has not been taken forward [66] . The use of seaweed as part of an integrated aquaculture system ( i.e. in IMTA with finfish and/or shellfish aquaculture) has been widely investigated as a method of reducing nutrient wastes and associated impacts on the surrounding marine environment from marine aquaculture [67] . The cultivation of seaweed for IMTA is a key component of the Consultation Document, and as such, is discussed in greater detail in Section 7 of this report.

5.6.7 A significant amount of research has been undertaken into the use of seaweed as a source of biofuel. Global interest in the use of algae (both micro and macro-algae) for biofuels, primarily ethanol and biodiesel, is rising [68] . However, both knowledge gaps and questions remain over the economic viability of bioenergy production using algae in the short to medium-term. While the future viability of this industry is presently subject to debate, the potential remains for the proposal of large-scale seaweed cultivation operations in the future, specifically for the production of biofuels.

5.6.8 In terms of cultivation techniques, several strategies for algal culture have been trialled since the 1950s, including land-based tanks, ponds, coastal lagoons and open waters. Although still in their infancy, many advanced propagation techniques are being investigated for application to the cultivation of a wide of variety seaweeds [69] including research in Scotland [70] .


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