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Seaweeds are only a group within the algae; they are the macroalgae found in the sea. Referring to them as ‘seaweeds’ in English is most unfortunate, as they are far from being the weeds of the sea. They are ‘algues marines’ in French, ‘algas marinas’ in Spanish, ‘Meeres Algen’ in German, and to the Chinese, who have a long tradition of using them, they are ‘海藻 (haizao)’ or the colourful/beautiful plants of the sea. Should they be called ‘sea vegetables’? But seaweeds can be used in many applications beyond food. There are approximately 10,500 known species of seaweeds (generally divided into three large groups: the brown, the red and the green seaweeds). Around 500 species have been used for centuries for human food and medicinal purposes, directly as food or indirectly for the compounds that can be extracted from them. While minimally known by the general public and aquaculturists, especially in the western world, seaweeds represent the largest group of organisms cultured at sea: 47.5 percent of the total world aquaculture in the marine environment, while fish mariculture represents only 11 percent. Because they have very different life histories, their culture techniques vary widely. It is imperative to know the biology, physiology, biochemistry, etc. of these organisms very well

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Now you are talking seaweeds… what is the difference?

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of the world’s beautiful tropical white ‘sandy’ beaches are, in fact, made of fine debris of dead calcified green seaweeds.

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before attempting their cultivation, as they are definitely not the ‘low-hanging fruits’ of aquaculture. To cultivate seaweeds appropriately, understanding their biological cycles, and developing adapted strategies accordingly, is key to success. One of the most cultivated and used seaweeds are kelps.

Now you are confusing me with the term kelps…

Kelps are large brown seaweeds, mostly found at good low tides. They belong to the class Phaeophyceae and the order Laminariales. Kelps can form ‘underwater forests’ in coastal waters where they have significant ecological roles and provide key ecosystem services. They are among the fastest-growing organisms on this planet (up to several centimetres per day), capable of reaching more than 50m in length in the case of the giant kelps in the Pacific Ocean (2-12m in the case of the Atlantic kelps). Their anatomy is among the most advanced in seaweeds. They are attached by holdfasts, which only have an anchoring function (no absorption of nutrients like roots do). From the holdfast originate elongated stem-like structures called stipes, from which blades develop that are not as physiologically sophisticated as leaves. To help maintain the blades close to the surface, some large kelps have developed gas-filled bladders. Now that you know the differences between these different terms, we will present, in the next issue of International Aquafeed, a global perspective on seaweed aquaculture.

Dr. Thierry Chopin is Professor of Marine Biology, and Director of the Seaweed and Integrated MultiTrophic Aquaculture Research Laboratory, at the University of New Brunswick in Canada.

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International Aquafeed - July 2018 | 17

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