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News

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Dr Thierry Chopin Aquaculture comes in many shapes and fashions

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lgae periodically make the news, however, not always for positive reasons: harmful micro-algal blooms toxic to marine life and sometimes to humans; Olympic swimming pools turning completely green in Rio de Janeiro in 2016; large recurrent green macro-algal tides in China; brown macro-algal tides unpleasant to tourists in the Caribbean islands; etc. It is time to demystify this ‘obscure’, albeit photosynthetic, group of organisms, as they render key ecosystem services to nature and to humans, who eat them almost everyday, in one form or another, without always knowing it.

In fact, the term ‘algae’ does not mean much!

simple reproductive structures). We now realise, especially with the progress in molecular techniques, that this mixed bag is completely unnatural, with no real cohesion and with species spread over most kingdoms of organisms, encompassing microscopic microalgae (like the unicellular phytoplanktonic forms) and macroscopic macroalgae (like the giant kelps that grow taller than trees) that colonise the oceans, freshwater streams, trees (associated with fungi in lichens), stones, high altitude snow in glaciers, geothermal sources and even deserts. At the molecular and ultra–structural levels, green algae are closer to trees on land than they are to brown algae, which are closer to some fungi. The well-known green alga, sea lettuce (Ulva), is closer, at the molecular level, to a spruce tree than to the well-known red alga, nori (Porphyra), even if their morphology is very similar (a green blade versus a red blade) and they are found close to one another on the shore. So, it is not surprising that, collectively, algae are doing so many different things when it comes to life cycles and the reproductive strategies they have evolved over a very long geological time. Did you know that you start your day with algae in your orange juice (a microscopic mesh of carrageenans, extracted from red algae, keeps the pulp in suspension) and you go to bed with algae (your toothpaste would be a liquid without alginates, extracted from brown algae)? Did you also know that every second molecule of oxygen we inhale was produced by an alga (micro- or macroscopic), and every second molecule of carbon dioxide we exhale will be re-used by an alga? Algae have played a driving role in major processes on this planet: they initiated an irreversible global change leading to the current oxygen-rich atmosphere and, by transferring atmospheric carbon dioxide into organic biomass and sedimentary deposits,

Line of sugar kelp, Saccharina latissima

Giving a simple definition of what algae are is not that simple. Since the time of the Greeks and the Romans, algae have been a misunderstood, unappreciated and underused group of organisms, lumped together in a very artificial manner. When they did not know in which group of organisms to classify a new species, they described them as ‘incertae sedis’ (of uncertain placement). Over time, a lot of algae/ seaweeds became ‘incertae sedis’ … The end result of several centuries of neglect is that, systematically, algae do not have much in common and are an unnatural grouping (what is called a polyphyletic group, i.e. with different ancestors and different evolutionary histories). Algae share only a few characteristics: they are photosynthesising (sequestering carbon dioxide and producing oxygen); they strive on absorbing dissolved inorganic nutrients, such as nitrogen and phosphorus (hence the interest in using them for bioremediation); they do not make flowers and their anatomy is relatively simple (no roots, stems, leaves or vascular tissues, and

they act as carbon sink contributing to the slowing down of global warming. Algae are key primary producers and links in the food web of coastal and estuarine ecosystems. They participate naturally in nutrient recycling and waste management, a property that can be taken advantage of when they are cultivated using the duality of nutrients (essential when limiting/polluting when in excess). Coral reefs would not have been formed without the help of algae and it would be more appropriate to call them coralgal reefs; a lot

16 | July 2018 - International Aquafeed

JUL 2018 - International Aquafeed magazine  
JUL 2018 - International Aquafeed magazine