The old-time Maori dried karengo and cooked it as a sort of relish, as Japanese and Welsh coastal dwellers use related species of Porphyra under the names of amanori and laver bread. Bull kelp provided a valued receptacle. A large plant yields a leathery sheet 2–3 ft long by a foot wide by ½ in. thick, and the middle honeycomblike layer is easily slit through to convert the sheet into a bag of rubbery texture. In such a bag the skinned bodies of dozens of young muttonbirds can be preserved, the full sack being protected by an outer wrapping, as of long strips of totara bark.
(a) Carrageenin. New Zealand has about 20 species of Gigartina, closely related to the Irish moss or carrageen of commerce. Technically red seaweeds, they are mostly of a dark-purplish colour when alive, but easily bleach almost white if kept damp in the sun. After soaking in fresh water and boiling for a short time, the fronds easily break up and the liquor sets to a jelly on cooling. A purified extract called carrageenin is extensively produced on the Atlantic coast of North America and is widely used as a stabiliser in chocolate milk and such beverages. The varied properties of New Zealand's many species have not been exploited, but several kinds are gathered, especially from Otago southwards, for making jellied milk puddings, and some dessert preparations are made for sale. Some have proved suitable ingredients in toothpaste, and a few breweries use local seaweed for finings.
(b) Agar. Certain red seaweeds, particularly members of the Gelidiaceae, contain a polysaccharide of large molecular weight and side linkages, called by the Malayan name of agar or agaragar. Extraction requires long boiling or cooking under pressure and impurities are removed by filtering, dialysing, and freezing. A 1–2 per cent agar solution characteristically sets at a low temperature. The jelly, however, remains solid at a comparatively high one, giving a range between about 35 and 90°C where either solid or liquid state can be had at will; further, no permanent change results from sterilising at high temperatures. Agar is familiar as the clear firm jelly in which some canned meats are set. The most important use is for culture media on which fungi and bacteria can be grown for therapeutic and research purposes, and no adequate substitute has been found. For many years Japan supplied the world's requirements, but following research during wartime shortages New Zealand began to produce agar, and from 1945 an export worth some thousands of pounds annually was developed. Two seaweeds are used, mostly Pterocladia lucida and, in smaller quantities, the finer P. capillacea, both collected chiefly from North Island coasts and dried and baled like hay for selling. Air-dry weed yields about 30 per cent agar, which is sold as a fine powder. The gel strength is high and the ash content low.
(c) Alginates. Alginic acid and its salts are colloids extracted from the larger brown algae. None is produced in New Zealand, though some local kelps have a high algin content, for instance, 40 per cent of dry weight in bull kelp and 20 per cent in Macro-cystis pyrifera, the latter a species harvested for alginates on the Californian coast. Alginates are used in the food, paint, pharmaceutical, adhesive, and polish manufacturing industries.
In some maritime countries seaweeds are used for manuring the land. Some supply potash (to 30 per cent KC1 in dry weight) and iodine (to 0.4 per cent) as well as organic matter, though dry meal of two species has been shown to immobilise inorganic nitrogen in soils. Seaweed is used in many home gardens, the best being Macrocystis and the long-stalked Ecklonia. The green sea lettuce, Ulva, thrives in water contaminated with organic matter, and from such places it can act as nitrogenous manure. In sewage outfall areas Ulva can increase to nuisance proportions, especially when it accumulates in putrefying windrows about high-tide level.
by Lucy Beatrice Moore, M.SC., Botany Division, Department of Scientific and Industrial Research, Lincoln.
- Transactions of the New Zealand Institute, Vol. 57 (1926)
- Ibid., Vol. 60 (1930)
- Transactions of the Royal Society of New Zealand, Vol. 69 (1939), “Reference Lists of New Zealand Marine Algae”, Laing, R. M.
- Proceedings of the Seventh Pacific Science Congress, Vol. 5, Botany (1953), “The Utilization of Seaweed in New Zealand”, Schwarz, E. F.
- Plant and Soil, Vol. 12 (1960), “Studies in Manurial Values of Seaweeds”, Francki, R. I. B.