Seaweed - Definition and Overview

Seaweed covered rocks in the UK

Phycologists consider seaweed to refer any of a large number of marine benthic algae that are multicellular, macrothallic (large-bodied), and thus differentiated from most algae that tend towards microscopic size (Smith, 1944). Seaweeds are found among the green, red, and brown algae. Some cyanobacteria may also be counted as seaweeds. Seaweeds are named after terrestrial "weeds", and are not to be confused with things like seagrass which are vascular plants and not algae.

Structure

Seaweeds may have an appearance that resembles non-arboreal terrestrial plants.

• thallus: the algal body
  • blade: a flattened structure that is somewhat leaf-like
    • sorus: spore cluster
    • on Fucus -- Air bladders: float-assist organ (on blade)
    • on kelp -- floats: float-assist organ (in between blade and stipe)
  • stipe: a stem-like structure
  • holdfast: specialized basal structure providing attachment to the bottom

Uses

Seaweeds are used extensively as food by coastal peoples, most particularly in Japan but also in Korea, in Peru and in the Canadian Maritimes. For example, nori is a dried red alga, formed into sheets, and used to wrap sushi. Irish moss is another red alga used in producing various food additives. Other seaweeds may be used as seaweed fertiliser.

Seaweed is used traditionally in the Welsh diet and still eaten widely across Wales in the form of 'laverballs' and 'laverbread'. The welsh word for seaweed is 'gwynon'. A good place to buy laverballs, for visitors to Wales, is from the fish stall in the covered market on St. Mary Street in Cardiff. Laverbread can be sampled at the Celtic Cauldron opposite Cardiff Castle.

Seaweed is also used for the production of Alginate, a versatile product that is used for a whole range of applications. These include the production of Agar which is used very widely in microbiology as a substrate for culturing organisms. Alginates are also used in the prudction of foodstuffs to improve texture and mouth-feel. Typical products are ice-cream and a range or proprietary desserts (see Carrageenan).

References

• Smith, G.M. 1944. Marine Algae of the Monterey Peninsula, California. Stanford Univ., 2nd Edition.

External link

• The Seaweed Site (http://www.seaweed.ie/), information on all aspects of seaweeds and marine algal biology