Types of seaweed
Globally there are over 9,000 species of seaweed divided into three major
types: green, brown and red. Red is the most species-rich group (6,000) followed
by brown (2,000) and green (1,200). Around 600 species are found on UK shores.
Like land plants, all seaweeds depend on light for growth, so they only occupy
the intertidal area or relatively shallow photic (light penetrating) zone.
Green seaweeds tend to be found towards the top of the shore, browns from
the top to deeper waters, and, since they are adapted to photosynthesise at
lower lights levels, red seaweeds tend to dominate the deeper, darker waters
and also beneath kelp canopies and in shady rockpools.
Seaweed farming
In 2002, world aquaculture production of seaweeds reached over 11.5 million
tonnes with a value of over $6 billion, with China accounting for almost 9
million tonnes of that total. In Europe, seaweed cultivation occurs only on
a small scale, with France being the only commercial producer in 2002, growing
35 tonnes (Source FAO 2002).
Uses of seaweed
 Seaweed is not only used as a food source (particularly in Japanese cooking),
it has a range of other uses. It can be used in agriculture and horticulture
as an organic fertiliser and soil dressing; in beauty treatments, not only
as an ingredient in products such as moisturisers but also in seaweed baths;
as a health supplement and also as a source of agar and alginates for a range
of products including ice cream, yoghurt and pet food.
Polyculture
Polyculture or integrated aquaculture is the term used to describe the farming
of one or more species simultaneously in the same area. Within the aquaculture
industry, trials are currently taking place to see if growing seaweed and
/or mussels adjacent to fish farms can reduce the amount of organic nutrients
being dispersed from the fish pens. The cultured seaweed/mussels utilises
the nutrients in the waters surrounding the sea pens, and also provides the
fish farmer with an additional cash crop. Trials are also being undertaken
to farm sea urchins adjacent to salmon farms, it is thought these grazers
will “clean up” the seabed whilst providing an additional commercial
species for the farmer.
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