Growth Rate Responses of Five Commercial Strains of Gracilaria (Rhodophyta, Gracilariales) to Temperature and Light

Abstract Growth rate responses of five strains of four economically important species of Gracilaria from South America, Africa and Asia were studied under several temperature and light combinations, in experiments lasting from one to four weeks. Gracilaria tenuistipitata var. liui from the People's Republic of China was the most eurythermic of the species studied, growing at temperatures from 13.5 to 33.1 C, and all photon flux densities (15–91 μmol-photons/m² per sec). Gracilaria caudata from Brazil did not survive at 13.5 C and G. chilensis did not survive at 30.2 C, while G. gracilis from Namibia and Argentina survived up to 33.1 C. No strain survived at 35.8 C or higher. In general, there was a trend to an increase in growth rate with temperature, but this varied with the irradiance and the duration of the experiments. There was a clear interaction between temperature and photon flux density, and the duration of the experimental period interfered significantly in the growth responses. All strains tested, including G. chilensis from Chile and G. gracilis from Argentina and Namibia, could be cultivated under ambient conditions of temperature and photon flux density on the southern coast of Brazil.