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Mar 07, 2002

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vol. 23, no. 5

I view exploring seaweeds as an introduction to some aquatic deity's imagination, the opening of a new and real world and the path to Zen-like satisfaction.

By Louis Druehl
Are seaweeds the next great health panacea? Certainly, seaweeds are
well positioned to replace fungi, the sources of antibiotics. French researchers have reported on the antitumor effects of an algal slime extracted from a brown seaweed. They conclude it “is a very potent antitumor agent in cancer therapy.”

Other researchers have demonstrated the potential efficacy of kelp-derived constituents in the treatment of thrombosis (stroke) and blood coagulation, and prostaglandin-synthesis (anti-inflammatory activity). These and other studies emphasize the importance of understanding seaweeds and the excitement associated with this marine group.

I view exploring seaweeds as an introduction to some aquatic deity's imagination, the opening of a new and real world and the path to Zen-like satisfaction.

Environmentalist Briony Penn described her discovery of seaweeds, through my book Pacific Seaweeds, as an experience akin to following Alice down the rabbit hole. Seaweeds justify these fanciful statements.

For convenience's sake, the approximately 600 species along our shores are placed into three natural groups - red, green and brown seaweeds. In reality, seaweeds can project any colour you can master on your palate, in addition to providing glossy or matte finish and in some instances an iridescence approaching that of a Rufus hummingbird.

Their shapes are bewildering, ranging from tiny green dots that colour otherwise drab sea anemones or change tide pools into tureens of rich pea soup, through a myriad of branching forms, to giant brown onions (bull kelp or Nereocystis) sometimes exceeding 35 metres in length. One, Derbesia, is a perfect little single-celled green ball about one centimetre across that lives only where the waves are strongest. Another, Codium, or the stag-horn alga, resembles a deer's antlers in felt, which in reality consists of numerous cells all exceeding 30 centimetres in length. A red seaweed has taken on the form of a cactus and derives its name from this resemblance (Opuntiella).

Seaweeds do not live in isolation but in competitive and supportive associations with other forms of marine life. On the beach, where everything competes for space, you must have a home. Some seaweeds capture and retain space in much the same mode as does crabgrass, others simply overwhelm adversaries by unleashing literally billions of spores, any one of which has the potential of occupying space.

Of course seaweeds nourish local animal inhabitants by providing energy-rich materials they have produced using sunlight. One study has shown that the carbon making up the body of a cormorant is composed of up to 48 per cent kelp-derived carbon. This is all the more remarkable when you consider that there are several links in the food chain separating the bird from whatever it was that first ate the raw kelp-carbon. A bizarre feeding interaction involves Codium that is fed upon by a sea slug that enslaves the algal chloroplasts in a special pouch were they are compelled to produce the slime required for the slug's motility.

Seaweeds do resist being eaten. Some are calcareous, being as hard as your teeth, and others produce noxious chemicals to deter herbivores. The acid kelp, Desmarestia produces sulfuric acid, having the same acidity as human gastric juices, to discourage sea urchins. This acid literally digests the sea urchin's eating apparatus. Other seaweeds produce chemicals that destroy the herbivore's digestive enzymes. What is astounding is that some of these seaweeds produce their chemical defences only when they have been attacked, thus conserving the energy necessary for the construction of their biotoxins. This type of activity belies the notion of dumb weeds.

Seaweeds face environmental problems beyond grazers. Waves often limit the distribution of seaweeds. Some seaweeds can live only where there is significant wave action. The sea palm (Postelsia) encounters wave forces exceeding 41 times the pull of gravity. Many seaweeds are excluded from this harsh environment but some modify their form to accommodate the greater drag forces. The five-ribbed kelp (Costaria) is about 10 centimetres wide and tough as leather in wave-exposed situations and up to 80 centimeters wide and fragile in wave-sheltered places. If you take a wave-exposed Costaria and transplant it to a sheltered area its new growth will conform to the sheltered situation. We call this ability phenotypic plasticity. Animals do not show this type of plasticity, but then, they can just walk away from stress.

And then there is sex. Seaweed sex is so varied as to confuse Comte Donatien Alphonse Francois de Sade. Consider the large brown seaweeds, like the bull kelp. These large plants will produce zillions of spores, half of which will grow into microscopic males and half into microscopic females. It only takes one male and female to reproduce the giant parent plant. The female produces eggs which, when mature, release a perfume that causes the male to release his sperm and then attracts the sperm to the egg. The individual resulting from this union overgrows its mother. Kelp perfume was discovered by a German scientist who noted the smell of gin in the culture room where he was rearing the little kelp males and females. I find it interesting that not only do kelp perfume and gin smell similar but that they elicit similar responses.

The little surf-loving green ball, Derbesia, has a totally different approach to procreation. Each ball is either a male or a female. They sit next to each other through the fortnight tidal cycle, each creating little sperm or egg-like cells until their unicellular bodies are packed with these structures. When the tide is lowest and the first light strikes the little green balls, they tear open, violently emptying their reproductive agents into the surf. Somehow these find each other and a new generation is born, but this generation is not a green ball but a green filament. The now exhausted little green balls mend their ripped cells, re-inflate themselves and produce a new crop of reproductive cells for the next extreme low tide and the anticipated explosion. At some later time the filament produces spores that grow into little green balls.

My small book, Pacific Seaweeds, contains comments on seaweeds for human health, marine conservation, farming and recipes - all richly illustrated with lots of colour photographs and black and white drawings.

If you decide to explore seaweeds you will learn things no one else knows, and that is a very satisfying feeling.

Louis Druehl is an SFU professor of biology who teaches and conducts research at the Bamfield marine research station.















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