POTENTIAL HARVESTABLE BIOMASS OF 4 CARRAGEENAN-PRODUCING SEAWEEDS OF THE SOUTHWESTERN CAPE, SOUTH-AFRICA

Four species of carrageenophytes were surveyed to. determine the harvestable biomass of populations in the South-Western Cape, South Africa. Three species, Aeodes orbitosa, Gigartina polycarpa and Sarcothalia stiriata occur in sufficient quantities to be harvested, with summer fresh mass standing stocks of 193,5, 154 and 104 tons respectively. The summer standing stock of Mazzaella capensis (33,5 tons) was too low to warrant exploitation, as was the winter standing stock (10 tons) of Aeodes orbitosa. Biomass of C. polycarpa and S. stiriata fluctuated seasonally being maximum (2,9 and 3,0 kg . m(-2) respectively) in summer and minimum (0,8 and 1,2 kg . m(-2) respectively) in winter. The low biomass of these two species limits, economically, their harvesting potential during that season. The mean carrageenan content of G. polycarpa and S. stiriata was 44-49% (gametophytes) and 39-41% (tetrasporophytes). The expected carrageenan yield from a combined summer harvest of A. orbitosa, C, polycarpa and S, stiriata would be approximately 29,3 tons.