4. SEAWEEDS USED AS A SOURCE OF ALGINATE

4.1 Genera and species used

Alginate, sometimes shortened to "algin", is present in the cell walls of brown seaweeds, and it is partly responsible for the flexibility of the seaweed. Consequently, brown seaweeds that grow in more turbulent conditions usually have a higher alginate content than those in calmer waters. While any brown seaweed could be used as a source of alginate, the actual chemical structure of the alginate varies from one genus to another, and similar variability is found in the properties of the alginate that is extracted from the seaweed. Since the main applications of alginate are in thickening aqueous solutions and forming gels, its quality is judged on how well it performs in these uses.

A high quality alginate forms strong gels and gives thick aqueous solutions. A good raw material for alginate extraction should also give a high yield of alginate.

Brown seaweeds that fulfil the above criteria are species of Ascophyllum, Durvillaea, Ecklonia, Laminaria, Lessonia, Macrocystis and Sargassum, although the last, Sargassum, is only used when nothing else is available: its alginate is usually borderline quality and the yield usually low.

4.2 Natural habitats

Ascophyllum (Figures 14 and 15) is found in cold waters of the Northern Hemisphere. It grows in the eulittoral zone (see Section 2.2 for definition), forming distinct bands of dark brown, branched plants 1-4 m long. It prefers somewhat sheltered areas and disappears where there is strong wave action.

Durvillaea (Figures 16 and 17) is found only in the Southern Hemisphere, and grows best in rough water, near the top of the sublittoral zone, on rocky shores or offshore reefs. Plants are smaller where summer water temperatures rise to 19°C, but grow best where the temperature does not rise above 15°C. Plants of 5 m length are not uncommon, but 2-3 m is more usual.

Ecklonia species are found in both Northern and Southern Hemispheres, in warm temperate waters, usually on rocky substrates of the upper sublittoral zone (Figure 18).

FIGURE 14
Ascophyllum nodosum (Specimen from National Herbarium, Royal Botanic Gardens, Sydney. Collectors: Alan J.K. Millar and Jacob Larsen.)

Laminaria harvests rely on mainly three species: L. digitata, L. hyperborea and L. saccharina. All three grow in cold temperate water, 10°-15°C, and are harvested in the Northern Hemisphere. L. japonica is sometimes used in China, but it is mainly cultivated there for use as a food, and only surplus production is used in the alginate industry. The cultivation of L. japonica is discussed in Section 8.4.

Laminaria digitata grows in the upper sublittoral zone in rocky, wave-exposed localities and it is well adapted to this because of its flexible stipe (stem) and divided blades (Figures 19 and 20).

FIGURE 15
Ascophyllum nodosum at low tide

PIERRE ARZEL, IFREMER, BREST

FIGURE 16
Durvillaea potatorum on wave-swept rocks, Australia

BRUCE FUHRER

FIGURE 17
Durvillaea potatorum suspended on poles. being transferred to 5-metre high air-drying racks, King Island, Australia.

FIGURE 18
Ecklonia species (Cheju Island, the Republic of Korea).

FIGURE 19
Laminaria digitata (after Lüning, 1990).

FIGURE 20
Laminaria digitata

PIERRE ARZEL, IFREMER, BREST

Laminaria saccharina also grows in the upper sublittoral, usually below L. digitata, but requires more sheltered conditions because of its undivided and mechanically less tolerant blade (Figure 21).

Laminaria hyperborea (Figures 22 and 23) grows on rocky bottoms of the mid-sublittoral zone, in depths of 2-10 m, but in clear water it can be 15-25 m: the limiting factor being sufficient light for growth. It has a strong stipe and the plant stands upright in the water and forms "laminarian forests". They can survive for up to 15 years, in contrast to the Laminaria in the upper sublittoral, which have a life of about 3 years.

Lessonia has two species that are collected in Chile for alginate extraction. They are collected from the northern and central coasts, but the harvests are sometimes disrupted by an El Niño event. This causes the El Niño Current to develop, which flows from north to south with water temperatures as high as 23°-27°C and has been known to destroy almost the entire Lessonia population.

Lessonia nigrescens grows in thick belts in the rocky lower eulittoral zone, where its massive holdfast allows it to survive the rough waters in which it thrives (Figure 24).

Lessonia trabeculata (Figure 25) grows in the sublittoral, 1-20 m depth. It also has a very thick holdfast and stands up underwater, rather like Laminaria hyperborea.

Macrocystis pyrifera grows best in calm, deep waters in temperatures of 15°C or less. It is sensitive to water temperature and does not withstand a rise above 20°C. It grows on rocky bottoms where its holdfast can become established, and can be found as large underwater forests, with plants rising to and growing along the surface, at times up to 20 m in length (Figure 26).

FIGURE 21
Laminaria saccharina (after Lüning, 1990).

FIGURE 22
Laminaria hyperborea (after Chapman and Chapman, 1980).

FIGURE 23
Laminaria hyperborea, , held upright, as it stands on the ocean floor, by Norman Jones.

J.M. JONES

Sargassum species are found worldwide in warm temperate and tropical water-temperature regions. They are found in both the eulittoral and upper sublittoral zones. They exhibit a wide variety in shape and form (Figures 27 and 28). The alginate content is usually low compared to the previously listed genera, and the quality of the alginate poor, although there are exceptions. For alginate extraction, they are regarded as the raw material of last resort.

FIGURE 24
Lessonia nigrescens, held by John Sanderson, Kelco Co.

R.H. MCPEAK

FIGURE 25
Lessonia trabeculata, held by John Sanderson, Kelco Co.

R.H. MCPEAK

FIGURE 26
Macrocystis pyrifera, fixed to the bottom in 10 m depth of water, grows up to and then along the surface, kept afloat by gas-filled bladders (Tasmania, Australia).

FIGURE 27
Sargassum species (Specimen from National Herbarium, Royal Botanic Gardens, Sydney. Collector: S. Skinner).

FIGURE 28
Sargassum flavicans (after a specimen from National Herbarium, Royal Botanic Gardens, Sydney. Collector: Australian Museum).

4.3 Sources of alginophytes

Ascophyllum, also known as rockweed, is widely distributed in cold waters of the Northern Hemisphere. Material for alginate extraction comes from the west coast of Ireland; the Outer Hebrides, off the west coast of Scotland (United Kingdom); Iceland; the west coast of Norway; and, until recently, the coasts of Nova Scotia and New Brunswick (Canada). However, it is no longer harvested for alginate extraction in Canada because of government harvesting restrictions that made it uneconomic. In France, it can only be cut by hand, with some used in the alginate industry and some as a powdered additive to cattle feed. It is also harvested in Iceland.

Durvillaea is collected as beach wash on the west coast of King Island, which lies between Tasmania and the mainland of Australia. Small quantities are also collected in southern Chile.

Ecklonia species are found in both Northern and Southern Hemispheres, but are currently only collected in South Africa. Some of it is exported and some used internally to produce fertilizer. There is no alginate industry in the country. Some ten years ago it was harvested by divers on the coast of Cheju Island (the Republic of Korea), and used in an alginate factory located there. However, the factory has since been closed and sold to real estate developers. Experimental cultivation of Ecklonia in South Africa has been successful, with growth of young plants on rafts.

Laminaria digitata in France is the main raw material for the alginate industry. Laminaria saccharina often grows in close association with L. digitata, and is sometimes harvested at the same time. In Norway, L. digitata grows in masses at the lower end of the eulittoral zone and was previously an important source for the Norwegian industry. In France, it is in the upper sublittoral and is harvested around the coast of Brittany and adjacent islands. Iceland is also a source of L. digitata for the alginate industry in Scotland (United Kingdom).

Laminaria hyperborea is found on the west coast of Ireland; and the Outer Hebrides and the Orkney Islands, Scotland (United Kingdom). On the west coast of Norway, it forms dense forests, 1-2 m high. There are estimates of large quantities growing around the coast of Brittany (France), but commercial harvesting has not yet occurred.

Lessonia species are found in both Northern and Southern Hemispheres, but it is only collected in northern Chile (Regions II, III and IV). Here it grows, especially L. trabeculata, on offshore shoals and is torn off in rough weather.

Macrocystis pyrifera, sometimes called the giant kelp, is harvested from offshore beds that stretch from Monterey in California (United States of America), to Bahia Asuncion in Baja California Sur (Mexico). Smaller quantities are also collected in northern Chile. Collections from large beds in southern Argentina ceased a few years ago. Macrocystis angustifolia has been cultivated on an experimental scale in South Africa with a view to eventually growing it for alginate production or abalone feed.

Sargassum is collected on the south coast of Java (Indonesia) and in the Philippines. In the former country it is used for alginate production while in the latter there are pilot studies for its use in alginate production, but its present use is to produce seaweed meal for animal feed.

4.4 Harvesting methods for wild seaweeds

Ascophyllum

In Ireland, this is cut by hand, leaving about 25 cm for regrowth; it is floated in nets to a point on the shore where it can be loaded on to trucks for transport to premises for drying and milling. In Norway, it was traditionally cut using a sickle, and this is still done in some places. However, most is now mechanically harvested using a flat-bottom vessel specifically designed for the purpose. It operates at high tide and because of the shallow depth, a water jet instead of a propeller is used for manoeuvring. A steel pipe fitted with rotating cutters extends beyond the bow of the vessel and can be lowered onto the seaweed. As the seaweed is cut, it is sucked up through the pipe and into a net on the boat. When the net is full it is thrown overboard (the seaweed floats) and nets are collected by another boat and taken to the factory. The Norwegian vessels were also used in Nova Scotia (Canada), but government restrictions on harvesting led to the alginate company ceasing activity. Ascophyllum is a very dark seaweed, black rather than brown when dried, and alginate extracted from it is dark and must be strongly bleached. Because of this, alginate producers often prefer other seaweeds.

Durvillaea

This is collected only from storm-cast material on King Island (Australia), and it is illegal to harvest the seaweed by cutting it from the rocks. Collection is restricted to 50 percent of the cast kelp, for unsubstantiated environmental reasons. The seaweed is hung on large racks to air dry for several days, then it is broken up, dried in a hot-air oven and milled to a powder that is freighted to Scotland (United Kingdom). The unusually high alginate content of the dried seaweed (40 percent) allows the whole operation to be economic.

Ecklonia

This is collected from beach-cast seaweed on the west coast of South Africa, mainly from beaches south of St Helena Bay.

Laminaria digitata

This was harvested in Norway by hand from the lower eulittoral, but with the advent of mechanical harvesting of L. hyperborea and Ascophyllum, the use of L. digitata has ceased. It is one of the major raw materials for the French alginate industry and it is harvested very efficiently using a mechanical device, the scoubidou, mounted on a boat.

The scoubidou is a curved iron hook which is suspended from a hydraulic arm mounted on the boat. The scoubidou is lowered into the L. digitata bed and rotated. The blades of the seaweed are wound around the rotating scoubidou and the hydraulic arm pulls them out of the sea (Figure 29). Short blades are missed by the device and form the next year's crop. The scoubidou boats operate from May to October, and during the winter are used to collect scallops. Restrictions are placed on the number of boats and their daily harvest to prevent overharvesting of the beds, since demand in France well exceeds its supply of L. digitata.

FIGURE 29
Scoubidou boats harvesting Laminaria digitata off the coast of Brittany, France

PIERRE ARZEL, IFREMER, BREST

FIGURE 30
Harvesting Laminaria hyperborea in Norway. The crane has just lifted aboard the rake and its load of seaweed. Prongs of the rake are visible on the right-hand end.

FMC BIOPOLYMER

Laminaria hyperborea

Beach-cast material has been collected for several decades in Ireland, and in the United Kingdom from the Outer Hebrides and Orkney Islands. The stipes (stems) of this species are thick, strong and have a high content of a good quality alginate and usually it is just the stipes that are collected and dried. In Norway the alginate industry originally used L. digitata but as the company expanded its market, it became necessary to exploit the L. hyperborea "forests". A harvesting vessel was designed specifically for this purpose. The harvesting is done by dragging a large rake-like device through the seaweed bed where it cuts the plant near the holdfast. It is fixed to a crane on the boat and after about two minutes of dragging the crane lifts the rake and its catch (about 2 tonne) into the boat (Figure 30). A boat can carry up to 130 tonne, and when full it takes its load to a storage silo where it is chopped and stored in a formalin solution. When more raw material is required by the factory, it is then taken there by a larger ship. The harvesting areas are divided into five parts and harvesting is by rotation every fifth year, allowing the beds to recover. A study has found that while harvesting by this method removed all the adult kelp plants, small kelp plants were left undisturbed and, with the improved light conditions, they grew to a height of at least 1 m within 2-3 years.

Macrocystis pyrifera

Macrocystis pyrifera grows in relatively deep water (8-25 m) and is harvested by "mowing" it. A vessel is equipped at the front or rear with reciprocating cutters, reaching across the width of the vessel and about 2 m vertically on each side, in a "U" shape. Mounted behind the cutters is a sloping wire mesh belt (Figure 31). As the vessel approaches the seaweed bed, the entire assembly of cutters and wire mesh belt is lowered about one metre into the water. The normal habit of Macrocystis is to grow to the surface and as it continues to grow it floats along the surface (Figure 26). The cutters cut the stipe (stalk) about one metre below the surface and the forward motion of the vessel forces the seaweed onto the moving belt. This transports the seaweed up and into an open hold that runs for most of the length of the vessel. A mechanically driven rake is used to spread the seaweed evenly over the hold. The vessels in California are large and capable of carrying several hundred tonnes of seaweed per trip.

4.5 Cultivation of seaweeds

None of the usual seaweeds for alginate production are cultivated. They cannot be grown by vegetative means, but must go through a reproductive cycle involving an alternation of generations, as outlined in Section 1.5. For alginate production, this makes cultivated brown seaweeds too expensive when compared to the costs of harvesting and transporting wild seaweeds. The only exception is for Laminaria japonica, which is cultivated in China for food but sometimes surplus material is diverted to the alginate industry in China.

FIGURE 31
Cutters mounted on the front of a vessel for harvesting Macrocystis pyrifera. When harvesting, the reciprocating cutters and conveyor belt are lowered one metre below the surface and the cut seaweed is forced onto the belt by the forward motion of the vessel.

4.6 Quantities harvested

The statistics in the following paragraph have been taken mainly from Critchley and Ohno (1998). Many of the values refer to 1995 or 1996 harvests; those for Chile are for 1999. Note that, unless otherwise stated, all the values are in wet tonnes. There are three exceptions, and they are clearly marked as being dry tonnes.

Ascophyllum: Ireland - 32 000; Norway - 25 000; France - 14 000 but used for animal feed as well as alginate extraction; United Kingdom - 8 000; Iceland - see under L. digitata.

Durvillaea: Australia - 4 000 dry tonnes; Chile - 2 000.

Ecklonia: South Africa - 500 dry tonnes.

Laminaria digitata: France - 60 000; Iceland harvests both L. digitata and Ascophyllum and uses geothermal hot water to produce a combined 6 000 tonnes of dried seaweed.

Laminaria hyperborea: Norway - 170 000; United Kingdom - 5 000; Ireland - 2 500; France - 1 000.

Lessonia: Chile - 110 000.

Macrocystis pyrifera: United States of America - 80 000; Mexico - 30 000; Chile - 6 000.

Sargassum/Turbinaria: India - 1 900-3 800 dry tonnes; Indonesia has an alginate factory with a capacity of 300 tonne requiring an input of about 3 000 dry tonnes of Sargassum, but the actual harvest is not available.

Table 4 shows estimates of harvests of alginophyte, all in dry tonnes, grouped into broad geographical regions.

TABLE 4
Alginophyte resources (tonnes dry weight; 2001)

Source: H. Porse, CP regions. pers. Kelco comm. 2002

4.7 Markets

The alginate industry is concentrated into fewer producers than the agar industry so the number of buyers of alginophytes is quite small compared to the market for agarophytes. Nevertheless the alginate producers are still competitive in their buying. They need to secure their sources and like to draw their supplies from a variety of geographic areas so that if one is affected by climatic conditions (e.g. El Niño) there are alternative supplies available. Following recent mergers and acquisitions in the industry, there are now four major alginate producers in Europe and the United States of America; two in Japan; and a smaller one in each of Chile and Indonesia. There are about 20 producers in China, though many are of the cottage industry type; they use mostly Laminaria japonica cultivated in China, but the larger processors also buy seaweed from Chile.

The large alginate producers need to ensure continuity of supply of raw material. The original factories were established where the seaweed was available and any sources located near each producer are usually contracted to that producer. Thus the seaweeds in Ireland and Scotland go to the factory in Scotland; the Norwegian Laminarias go to the Norwegian factory in Haugesund; and the giant kelp, Macrocystis, on the coast of California, United States of America, goes to the factory in San Diego. The brown seaweeds in Chile are the main source available to any buyer, and there are limited supplies of Ecklonia maxima available from South Africa. There are many exporters listed in the Export Directory of ProChile under two items that include both red and brown seaweeds.

The following export brown seaweeds; there may be others in the ProChile lists.

Alginates from different species of seaweed often have variations in their chemical structure, resulting in different physical properties. For example, some may yield an alginate that gives a strong gel, another a weaker gel; one may readily give a cream/white alginate, another may give that only with difficulty and is best used for technical applications where colour does not matter. There are more reasons why alginate producers prefer to buy a mixture of species of seaweeds, this allows them to blend their products to give properties to suit particular uses. So, price permitting, normally there is a market for any brown seaweed that will yield an alginate of medium to high viscosity or high gel strength. Price must include the cost of transport to the processor's factory and that rules out some rich natural beds, such as those found in the Falkland Islands, Chatham Island (New Zealand) and the Kerguelen Islands.

4.8 Future prospects

At present, with a worldwide recession, demand for alginate is flat, but will improve as economic conditions recover, particularly in the textile industry. Because the supply of brown seaweeds from southern California-Baja California and Chile can be curtailed, sometimes severely, by El Niño events, processors are always interested in finding new sources. Well-dried brown seaweeds can also be stored for lengthy periods, so processors are willing to stockpile their raw materials. There appears to be a steady market for alginophytes, though not one that will expand very rapidly.