French seaweed is characterized by the fact that nearly all the biomass is sampled directly from natural populations mainly growing on and off the shores of Brittany. French regulations classify these marine plants into three categories depending on access to the resource:
- Deep water seaweed which grows at sea and can only be sampled by boat or by foot during very low tides: Laminaria digitata and hyperborea, Saccharina latissima.
- Shore seaweed which grows on the shore, is exposed during all low tides and can be collected by foot: Ascophyllum nodosum, Fucus vesiculosus et spiralis, Himanthalia elongata, Pelvetia caniculata, Chrondrus crispus, Mastocarpus stellatus, Palmaria palmata, Porphyra umbilicalis et Codium
- Stranded seaweed which detaches from algae fields at sea and is found floating or stranded on the shore: all types of seaweed and particularly Ulva species in spring.
It is difficult to estimate the total amount of this natural resource on the French coasts. However, the total amount of this biomass sampled each year reaches 45 000 to 65 000 tons of wet seaweed (grouping all types of seaweed).
Cultivated biomass: aquaculture
Seaweed aquaculture techniques are strongly dependent on reproduction strategies of the seaweed. Some species multiply by simple vegetative propagation (green algae) which makes culture quick and easy to proceed, generally done in on-land tanks. Other species which depend on sexual reproduction cycles (brown and red algae) are more difficult to cultivate, for a deep knowledge and control of the reproduction cycle is necessary beforehand. On-land hatcheries are used for producing seaweed seeds which are then fixed to lines and later put out to sea for biomass growth. Today 90% of the seaweed world production originates from aquaculture. In France, not even 0.1% of its production comes from aquaculture. Indeed, only very few companies cultivate seaweed in France (approximately 10) which produce a total amount of 50 tons per year, mainly Undaria pinnatifida, an introduced Japanese specie.
Seaweed processing industries (for hydrocolloids) depend on natural population harvesting which is undertaken at specific times of the year. Outside harvesting periods these industries import biomass from other countries. Between 16 000 and 20 000 tons of dry seaweed are imported in France per year (2009-2011 data from FranceAgriMer) mainly from Chili (Lessonia nigrescens and trabeculata) and the Philippines (Kappaphycus).