Seaweeds are algal organisms of which there are about 4000 species worldwide, diverse in form, biology and chemistry. Seaweeds fall into three distinct groups and are simply identified as brown, red and green seaweed. Brown seaweeds range in size from the giant kelp, which is often 20 metres long, to thick, leather-like seaweeds 2–4 m long, to small species, 30–60 cm long. Red seaweeds range from a few centimetres to about one metre in length; and in colour from red, to brownish red, to purple. Green seaweeds are similar sized to the red seaweeds. In their natural habitat, seaweeds are the natural diet of many marine grazing organisms.

Seaweed is widely used as a food source throughout Asia particularly in Japan, China and Korea. Traditional food species include Porphyra sp. (nori) and Undaria sp. (wakame). In coastal regions of the world, seaweed has a long history of use as fertiliser and in industrial processes. Seaweeds also provide a source of compounds and chemicals that are used in food, cosmetic and health food manufacturing, such as agar.

In Australia, as at 2014, the seaweed industry is based on the harvest of stormcast kelp for the production of alginate and fertiliser; or wild-harvest of the introduced species of Undaria for extraction of bioactive compounds. Future opportunities are anticipated with the cultivation of seaweed for high value end uses, through identifying the functional properties of different seaweed species, and supplying compounds for the nutraceutical and pharmaceutical markets. Opportunities also exist for the selection and growing of species that command high value as fresh and dried food in the restaurant and specialty food markets.

Seaweed has particular potential for cultivation, when it is used in an Integrated Multi Trophic Aquaculture system, or adaptations of the system. The role of seaweed in the system is dual purpose. First, to provide a food source for fish, crustaceans and mollusc species grown in the system, and second to use the organic waste generated by the farmed species. The system is well established in Asia, growing in popularity in Canada and internationally recognised as promising for future sustainable aquaculture.

The principles of Integrated Multi Trophic Aquaculture systems are attractive in Australia because they can be applied to existing land-based aquaculture (e.g. finfish, abalone or prawns) or sea-based aquaculture (e.g. blue-fin tuna or salmon production). The system also has potential where manufacturers or land managers are looking for options to use wastewater and reduce run-off, particularly to avoid eutrophication of coastal waters. In Australia, there has been little validation of Integrated Multi Trophic Aquaculture in a commercial context.

Production of cultivated seaweed could also have great potential for industrial or rural blocks of land adjacent to resources capable of feeding seaweed such as saline water basins.

The development and establishment of a commercial seaweed enterprise in Australia is not for the faint-hearted—technically or financially. However, aquaculture farmers will have many of the skills required. There is much to be learnt about the biology and cultivation of Australian seaweed species and prospective seaweed farmers are advised to consult and potentially establish cooperative research relationships with seaweed scientists in their state, to determine the best species for their situation.

As at 2014, there was no industry body for seaweed producers in Australia. The University of Wollongong hostsSeaweeds Australia, a networking forum for research, development, marketing and commercialisation of seaweed in Australia.

Facts and figures

• Of the 1000s species of seaweed found in southern Australian waters, over 60% do not occur anywhere else in the world
• Seaweeds are not plants, in botanical terms, they are macroalgae
• Chocolate milk, yoghurt, health drinks and some beers contain hydrocolloids (agars, carrageenans or alginates) derived from seaweeds
• Australian seaweed production is very small by world standards, and as at 2014, the commercial focus is mainly on collection of stormcast kelp for alginate and fertiliser production
• Seaweeds are the fastest growing ‘plants’ on earth
• Future Australian opportunities are anticipated for the cultivation of seaweed for high value end uses

The uses for seaweed are diverse. It forms part of a substantial and traditional diet throughout the world but particularly in north Asia, where is accounts for up to 10 per cent of the diet in some regions. The majority of cultivated seaweed production is for food. A smaller but important industry extracts alginate, agar and carrageenan from seaweed for the gelling, water-retention and emulsifying properties of the compounds. Other seaweed compounds can be used in dietary supplements, pharmaceuticals, food supplements and colourings. Seaweed is also widely used as fertiliser, animal feed and animal nutrition products, and for ornamental plants in aquariums.

The opportunity for Australian cultivated seaweed is to produce high-value product based on health benefits. Extracts from seaweeds contain a complex mixture of hundreds of compounds, which are beneficial to human health, such as antioxidants, anti-cancer compounds such as kinase inhibitors, and compounds with anti-inflammatory and immuno-stimulatory properties.

Growing regions

As at 2014, seaweed is grown or trialled on a large scale, in sea-based farms in Western Australia, South Australia, and New South Wales or in land-based saline ponds in Western Australia, South Australia, Victoria and New South Wales.

The cultivation of seaweed can be adapted to any region, so long as saline water of the correct chemical balance is available, matched by a suitable seaweed species for the conditions.

Soil type

As seaweed is grown in constructed troughs, soil type is not a necessary consideration. However, for inland saline ponds, physical and chemical soil properties will need to be taken into consideration, in terms of the soil’s influence on water holding capacity of ponds and chemical makeup of the water.

Climate

If seaweed cultivation is based on locally-adapted species, enterprise location will not be limited by climate zone.

Varieties

As seaweed cultivation is a fledgling industry, there has been no varietal development of seaweed species for commercial production. Seaweed cultivation pilot trials show that there are many species of seaweed that have marketable properties and are possibly suited to commercial cultivation in south eastern Australia, with Ulva and Porphyra species showing the most promise. The determining criteria for species selection will be suitability to local conditions, growth rates in cultivation and marketable product benefits.

Generally, the different types of seaweed have different chemical properties, and therefore different end uses.

• Brown seaweed is mainly used as a source of the hydrocolloid, alginate; but the genera Laminaria, Undaria and Hizikia are used for food. These species do not exist in Australia and therefore alternative or equivalent species need to be chosen.
• Red seaweed is used for food and as sources of two hydrocolloids: agar and carrageenan. Porphyra species are the largest source of food from red seaweeds, commonly known as nori and laver, and used as the wrapping for sushi. There are native species of Porphyra which have not yet been domesticated.
• Green seaweed is used for foods or compounds.For example Caulerpa lentillifera has been commericalised for production by the James Cook University.

Planting and crop management

Parent stock of the species selected for cultivation will be maintained in a hatchery and are reproduced sexually, after a spawning cycle ropes that the seaweed will grow on are submerged in hatchery tanks for a period of time to allow the spores to establish on the ropes. If the seaweed is to grow in troughs, the spores are introduced to the growing medium.

A vital component of both sea and land cultivation systems is to ensure that the water and seaweed are in constant motion. In sea-based systems this is achieved by wave action; in land-based systems, movement is achieved by paddle-wheels or aeration devices. Constant movement ensures the seaweed intercepts adequate light and carbon dioxide.

For land-based systems, water quality must be constantly monitored and managed, to the same extent as an aquaculture system. Appropriate seaweed density and adequate aeration will help maintain good water quality.