Environmental tolerances in culture and agar content of Gracilaria verrucosa (Hudson) Papenfuss (Rhodophyta, Gigartinales) from Saldanha Bay

Culture studies have been carried out on a local population of the agar-producing red seaweed Gracilaria verrucosa to ascertain the optimum range of environmental factors for growth, with a view to potential mariculture. The plants grew well at 15 – 25°C, poorly at cooler temperatures, and did not survive 30°C. Despite little salinity variation in the natural habitat, the population was shown to be euryhaline, with reasonable growth from 9 to 45‰ salinity, although plants grew maximally around the salinity of full seawater. An irradiance of 80 μmol m− 2 s− 1 was sufficient for maximal growth, and growth was not severely reduced at 850 μmol m− 2 s− 1 (the highest experimental irradiance). Agar content was 32 – 34% of the dry weight, and this level was not significantly affected by 4 weeks’ growth at various temperatures. Kultuurstudies is uitgevoer op ’n inheemse populasie van die agar-produserende rooi seewier Gracilaria verrucosa om die optimale bereik te bepaal van omgewingsfaktore wat die groei beïnvloed, met die oog op moontlike marikultuur. Plante groei goed tussen 15 en 25°C, swak by laer temperature, en hulle oorleef nie 30°C nie. Ondanks min skommelinge in die soutgehalte van die natuurlike omgewing, blyk die populasie eurihalien te wees, met ’n redelike groei tussen 9 en 45‰ soutgehalte, alhoewel plante maksimaal gegroei het by ’n soutgehalte rondom dié van normale seewater. ’n Beligting van 80 μmol m− 2 s− 1 is voldoende om optimale groei te bewerkstellig, terwyl groei nie ernstig afgeneem het by 250 μmol m− 2 s− 1 (die hoogste eksperimenteel toegepaste beligting) nie. Die agargehalte bedra 32 – 34% van die droë gewig, en hierdie waarde is nie beduidend beïnvloed deur vier weke se groei by verskillende temperature nie.