Agar is a by-product of some red seaweeds. An agar industry developed in New Zealand during the Second World War, when supplies from Japan dwindled. Agar was needed as a culture medium for growing bacteria and other micro-organisms, and also as a jelly for preserving the canned meat sent to soldiers overseas. In 1941 a young botanist, Lucy Moore, was directed by the Department of Scientific and Industrial Research to search for agar-producing seaweeds. She found vast quantities of Pterocladia lucida on the east coast of the North Island, and arranged for local children to collect and dry the seaweed. After hours of boiling in water, agar dissolved out of the fronds.
New Zealand agar proved to be of very high quality and has been commercially produced since 1943. Today most of the seaweed is collected from south Wairarapa and sent to Ōpōtiki, where the agar is extracted.
Seaweeds and shellfish farms
Washed-up seaweed that is covered in tiny young mussels (mussel spat) is collected from Ninety Mile Beach in Northland and sent to mussel farms. In the 2001–2 fishing year, 250 tonnes of seaweed was harvested and transported to mussel farms in the Marlborough Sounds, where it was transferred to cultivation ropes.
Marine farmers harvested 300 tonnes of beach-cast and free-floating giant kelp in 2001–2 in order to feed young pāua (abalone).
Karengo has been sustainably harvested from the Kaikōura coast since the mid-1980s. At first it was just sold locally, but eventually it was air-dried and milled into flakes for food seasoning, and made available around New Zealand. An annual average of 2.5 tonnes of karengo was collected in the 10 years to 2002.
Two other important seaweed products are carrageenans and alginates. Like agar, these are jelly-forming chemicals. Carrageenans are useful thickeners, used in the food industry in syrups, custards, chocolates and yogurts. They also appear in shampoos, toothpastes and body lotions. Alginates are used to make water-based products creamier, and are added to ice cream and other dairy products to stop ice crystals from forming. In dentistry, impressions of teeth are usually made on an alginate base. Alginates have applications in the paper and textile industries for coatings and dyeing.
Carrageenans and alginates are not commercially produced in New Zealand, although Gigartina, a carrageenan-producing seaweed, grows prolifically around the country, as does bull kelp, which has the highest alginate content of any seaweed.
In 2020, research into the red seaweed Asparagopsis suggested that including small amounts in the feed of beef cattle could cut their methane emissions by up to 98% while enabling them to gain weight more quickly. The potential for reducing New Zealand’s carbon footprint was obvious.
With its long coastline and abundant seaweed resources, New Zealand has the potential for a thriving seaweed industry. However, the labour-intensive nature of harvesting and aquaculture has prevented the country from competing against bigger producers in Asia.