EXPERIMENTAL INVESTIGATIONS FOR THE MARICULTURE OF GRACILARIA IN SALDANHA BAY, SOUTH-AFRICA

Rope rafts were used to evaluate the growth of local Gracilaria gracil is at Saldanha Bay, on the west coast of South Africa, over four years . The plants were grown on horizontally-suspended ropes or netting lin es. Relative Growth Rates (RGR) of plants on ropes with low stocking w eights often exceeded 10% d(-1) in (austral) summer, and fell to betwe en 6 and 7.5% d(-1) in winter. Commercial-style lines of plastic netti ng stocked at 400 g m(-1) and placed 0.75 m apart yielded a mean of ab out 2 kg m(-2) 30 d(-1), with a mean RGR of about 5% d(-1) over a two- year period. Various methods of improving yields were tested, includin g attaching floats to individual lines and optimising stocking weight. In Saldanha Bay in late summer, warm, oligotrophic water can severely reduce growth. Growth was optimised by growing the plants as close as possible to the surface (0.2 m), where water motion, and by implicati on, nutrient uptake, are higher. Agar content and gel strength general ly remained high all year round. The potential for commercial producti on is evaluated in the light of these results.