WEBVTT

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Welcome to the introduction 
chapter about seaweed basics.


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Brown algae are macroalgae, the 
other ones are red and green algae.


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 They are distinct from microalgae in 
the fact that they are multicellular.


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Brown algae are also eukaryotic and 
photosynthetic organisms and that's why 


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we find them mainly in coastal areas. 
There, they are attached to the seabed 


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and because of that, for them to
 be able to capture enough light, 


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the water column has to
 remain relatively shallow.


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We find brown algae everywhere around the
world, mainly in moderate and cold waters 


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and very few are found in warmer waters.

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There they play several 
important ecological roles. 


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As you noticed, there are very 
large organisms and because of that 


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they are used as habitat and food for 
many animals, many marine animals,


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 including mammals, but also finned and 
shellfishes, mollusks, and even birds. 


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Therefore brown algae are important
 to maintain marine biodiversity.


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 They also protect the ecosystem
 by limiting erosion,


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sequestering carbon, and also fixing nitrate
 and phosphate waste from estuaries.


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As such, their value has been estimated to
be up to 28,000 Int$ per hectare per year, 


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and since the European coast is 68,000 
kilometers long, their value reaches


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  several billion euros per year.

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 Seaweeds are also used as a source of 
nutrition. In Ireland, Scotland, and even


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 here in Brittany, people used to collect
 them to either fertilise their fields or to


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extract iodine, and even sheep
 and cattle eat them.


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In southern Chile, archaeologists have found
 on a site dating from 14,000 years ago, 


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some remnants of seaweed, suggesting
 again that these people used to eat them 


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or to use them as medicine, again
 because of their high iodine content. 


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People in Asia have integrated them several
 centuries ago in their daily food and still do. 


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This is because this large kelp, large 
brown algae, are rich in protein,


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 microelements, and poor in fat.

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It is even thought that kelp have played 
a significant role in the evolution of the 


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human brain because of their content in 
unsaturated Omega-3 and Omega-6 


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fatty acids in addition to other components
 like zinc, magnesium, and vitamin B12.


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Today they are collected, picked here and 
there by connoisseurs who know a good 


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spot like for mushrooms and are
 included in culinary recipes. 


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This is what we named "phycogastronomy".

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In addition, when dried they can be easily
 conserved and transported for long periods.


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 Nowadays the overall value of seaweeds for
 food or extraction of chemical compounds 


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reaches 8 billion euros for a production
 of about 30 million tonnes per year 


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and most of it is produced by aquaculture. 

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Another key feature of brown algae is their 
evolution, and in this tree here I have 


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simplified the eurkaryotic phylogeny by
 showing you only the multicellular organisms 


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Brown algae belong to the stramenopile 
division and actually they have no 


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relationship whatsoever with the other 
multicellular organisms except their


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 common ancestor, a unicell, which would
have diverged 1.6 billion years ago.


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 Because of their specific evolution, their 
genome and cellular components are unique.


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For example, at the level of their cell wall
 there is a unique cocktail of polysaccharides


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 which is not found in other organisms. 
It is made mainly of alginate, found also


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in bacteria, but which is heavily
 exploited by industry,


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 and also fucans, which 
are found in animals.


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Their pigments are also different: they
 contain chlorophyll A, chlorophyll C, 


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and also fucoxanthin, which gives 
these organisms their brown colour.


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Finally, their cytoskeleton is different
 from that of land plant cells. 


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It has centrioles and cortical actin
 filaments like animal cells.


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 Altogether that makes these organisms 
very unique and challenging to study.


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 In other words, when you think about brown 
algae, just let your imagination do it freely.