You use seaweeds for that?

ABOVE: Encrusting coralline red seaweeds are important in the ecology of near-shore marine ecosystems andalso present a number of economic benefits. Photo: Gavin Maneveldt.

by Gavin W Maneveldt, Department of

Biodiversity and Conservation Biology,

University of the Western Cape

The word seaweed is commonly used,yet to refer to these marine algae as'weeds' is very far from the truth.Together with microscopic algae called

phytoplankton and other photosyntheticorganisms, seaweeds are responsiblefor all primary production in the oceansand therefore form the basis of thefood chain in the sea. Although we

often cannot smell or taste them, manyingredients in our foods and householdproducts come from the sea and fromseaweeds.

They are therefore both directlyand indirectly valuable to humans.

Seaweeds assimilate minerals directlyfrom the sea and are thought to be thesingle most nutritious foods that youcan eat. Rich in trace elements andvitamins, many of them may frequently

contain more protein than meat andmore calcium than milk.

Green seaweedsSea lettuce (Ulva species) as a whole

plant has long been eaten in the FarEast as a green vegetable in saladsand soups. Rich in carotenoids (anantioxidant) of which beta-carotene isthe most popular, green seaweeds arenow believed to help in the preventionof cancer, heart disease and strokes. In

fact, beta-carotene is being referred toas 'the age-fighting antioxidant.' Beta­carotene, as a natural pigment derivedfrom green seaweeds, is often also usedas a yellow-orange food colourant incheese, coffee creamers, egg substitute,

margarine, .mayonnaise, multivitaminsand salad dressings.

Brown seaweeds

A characteristic feature of brownseaweed is their cell wall which is made

of cellulose strengthened by calciumalginate. Whole brown seaweeds (notgranulated) such as kelp, for example,are considered excellent 'detoxifying'agents. The alginate in their tissuesare said to bind with any toxins in theintestines and render them indigestible.

24 March 2006 Veld&Flora

Not many people will, however, readily

eat whole kelp.In South Africa, the seaweed industry

is based largely on sea bamboo(Ecklonia maxima) and split-fan kelp(Laminaria pallidal. Kelp is harvestedextensively along our west and south­west coasts as feed for commerciallyfarmed abalone and is even used as a

nutritional supplement for farm animalsin local agriculture. Kelp is widely usedas a fertilizer and is even harvested ona large scale for the production of avery successful plant growth stimulanthaving been shown to be a great source

of micronutrients and beneficial plantgrowth promoters.

Furthermore, alginate is a substanceof considerable economic importance as

it is used as a gelling and emulsifYingagent in a number of industries.Surprisingly though, at present it is only

the kelp that is harvested commercially

in South Africa for alginate extraction.Perhaps it is because no other groupof brown seaweed occurs in largeenough biomass to be commerciallyviable. Internationally, however, a huge

market exists for the harvesting of kelpand other brown seaweed for alginate

production. In the food industry itmakes water-based products thicker,

creamier and more stable over extremes

in temperature, pH and time. Forexample, alginates prevent the formationof ice crystals in ice cream. Otherproducts containing alginate includebrownie mix, frozen foods, desserts,

relishes, salad dressing, sauces, graviesand even beer foam. Similarly, in thecosmetics, pharmaceutical, paint,textile and welding industries, alginateaids in the suspension and stabilizationof agents over ranges of temperature

and pH. In the paper industry, forexample, alginate is important as itenables sizing and polishing of thefinished paper product. Did you knowthat alginate from kelp is even usedto make fibres for high quality audiospeakers?

Kelp is especially important to themedical industry. Alginate is used toencapsulate many things such as tabletsin powder form, fracture castings and

moulds, and even organs for transplant.Kelp also contains an astonishing

amount of vitamins and minerals, themost important of these being iodine.Iodine has a normalizing effect onthe thyroid gland (which controls thebody's growth and development). InNamibia, scientists are looking into

the use of kelp as a treatment of goitre

and prevention or reduction in theoccurrence of cretinism in southernMrica. Similarly, because iodine feedsthe thyroid, kelp is even used in weight­

loss formulas.

Red seaweeds (fleshy)

While the seaweed industry in theWestern world is based mainly on

seaweed extracts, in the East seaweedsare cultivated in huge volumes forhuman consumption; much of thisindustry being based on red seaweeds.The genus Porphyra (purple laver) in

particular, consitutes at least 80% of allseaweed harvested allover the world.In Asia, Porphyra (known as nori) iseaten as a whole seaweed either dried

or in soups, and globally as a tastywrapping for sushi. The iodine andhigh vitamin and protein content ofnori makes it attractive, as does therelative simplicity of its mariculture

(sea farming), which began more than300 years ago in Japan.

Beside food for direct consumption,red seaweeds are also important for theirphycocolloid extracts. Phycocolloidsare seaweed derivatives that cause

particles to remain suspended insolution and are therefore excellentas stabilizing and gelling agents. The

main phycocolloids derived from redseaweeds are carrageenan and agar.

Carrageenan is highly sought afterin western societies where it is espe­

cially important in the dairy industry.Milkshakes, cheese, yoghurts, pow­

dered milk (including baby formula),all possess red seaweed carrageenanextracts. Believe it or not, carrageenanis even used in toothpaste, cosmet­

ics, shampoos, paints and pet food. Anumber of carrageenophyte seaweedsare being investigated in South Africa.These include Hypnea spicifera (greentips), and various species of Gigartina(tongue weed), Sarcothalia (twistedgigartina) and Aeodes (slippery orbits).

Agar on the other hand, has its mostimportant use as a medium on whichto culture fungi and bacteria in micro­biological and medical pathological

research. In food for human consump­tion, however, agar can be found inbaking and confectionary products andis also widely used to clarify wine, juiceand vinegars because of its excellent

protein binding properties. In largerindustries, agar is used to make adhe­sives and capsules for tablets. South

Mrican agarophytes include species ofseaweed from the genera Gracilaria(which is harvested extensively inSaldanha Bay) and especially Gelidium.

Red seaweeds (calcified)

Encrusting coralline (made of limedeposits) red seaweeds are importantin the ecology of near-shore marineecosystems where they serve as foodand shelter for many marine animals.

Because of their hard, calcified nature,they have a number of economic uses.In modern medical science corallinealgae are used in the preparation of

dental bone implants. Coralline rubbleknown as maerl is used in calcium min­eral supplements, as soil pH condition­ers, in the filtration of acidic drinkingwater and even as food additives forlivestock. Coralline algae are commonlyused as 1ive rock' in the marine aquar­

ium industry and did you know that inmany tropical communities, corallinerock is used as building stones?

The commercial use of seaweeds in

South Mrica comprises but a smallindustry utilizing mostly brown andfleshy red seaweeds. The increasinguse of local representatives of seaweeds

has resulted in a state policy to ensurethe sustainable use of these commer­

cial resources and this awareness hasgreatly facilitated research on local sea­weeds and considerably increased our

knowledge of most of the species. It

is only with this increased awareness

that we've been able to bring to you theknowledge that we've gained regardingthis fascinating group of marine organ­

isms. ~

ABOVE LEFT: Ecologically, kelp provides an important complex, three-dimensional habitat for thousandsof species of fish, invertebrates and other seaweeds. Kelp is also economically valuable to South Africanindustries.ABOVE RIGHT: The sea lettuce Viva is rich in beta-carotene, anatural antioxidant and cancer-fighting agent.BELOW: Looking like wrinkled cellophane, Porphyra species are extremely low in calories and contain lots ofiodine, which is good for healthy thyroid function. Photos: Gavin Maneveldt.

What does that mean?Antioxidant A compound (vitamins A [which isconverted from beta-carotene], C and E, sele­nium [a mineral], and carotenoids) that protectsagainst cell damage caused by molecules calledoxygen-free radicals (oxidation) that are amajorcause of disease and ageing.

Cretinism A type of mental and physical retar­dation caused by severe, uncorrected thyroiddeficiency in infancy and early childhood.

Goitre An enlargement of the thyroid gland quiteoften due to a lack of iodine in the diet.

Primary production The production of organicmatter (plant tissue) from carbon dioxide, waterand sunlight through photosynthesis.

March 2006 Veld&Flora 25