Seaweeds are found throughout the world's oceans and seas and none is known to be poisonous. Many are actually nice to eat and even considered a great delicacy in asian countries. They are used in many maritime countries for industrial applications and as a fertiliser. The major direct use of these plants as food is in Japan, China and Korea, where seaweed cultivation has become a major industry. The main food species grown by aquaculture in these countries are Nori or Zicai (Porphyra, a red alga), Kombu, Kunbu or Haidai (Laminaria or Saccharina: brown algae) and Wakame (Undaria, also a brown alga). In Japan alone, the total annual production value of nori amounts to >US$2 billion, one of the most valuable crops produced by aquaculture in the world. In most western countries food and animal consumption is relatively restricted and there has not been any great pressure to develop mass cultivation techniques. On this site, seaweed aquaculture, including nori, a Japanese red seaweed, is described in detail.
Industrial utilisation of seaweed is mostly centered on the extraction of phycocolloids and, to a much lesser extent, certain fine biochemicals. Fermentation and pyrolysis and the use of seaweed as biofuels are not an option on an industrial scale at present but are possible options for the future, particularly as conventional fossil fuels run out. Seaweeds are being used in cosmetics, as fertilizer. They have the potential to be used as a source of long- and short-chained biochemical with medicinal and industrial uses. Marine algae may also be used as energy-collectors and potentially useful substances may be extracted by fermentation and pyrolysis. Seaweed extracts appear in the oddest of places: you almost certainly have eaten some sort of seaweed extract in the last 24 hrs as many processed foods such as chocolate milk, yoghurts, health drinks, and even high-quality German beers contain seaweed polysaccharides such as agars, carrageenans and alginates! Seaweed baths have been popular in Ireland and Britain since Edwardian times. A recent innovation is the apparent incorporation of seaweed into a fibre, which breaths well and is claimed to absorb what your skin excretes. However, an article in the New York Times casts doubt on some manufacturers' claims: 'Seaweed' Clothing Has None, Tests Show.