The effects of temperature, salinity and irradiance upon the growth of Sargassum polycystum C. Agardh (Phaeophyceae)

Abstract

Sargassum polycystum C. Agardh, a brown alga that is widely distributed in tropical areas, has significant economic value by virtue of its use as food, traditional medicine, animal fodder, and chemical products in Asian countries. In order to explore suitable conditions for the aquaculture of this alga, we used 9–10 cm long branches of S. polycystum to assess the effects of various environmental factors, including temperature, salinity, and irradiance upon the relative growth rate (RGR), photosynthetic pigment content, and chlorophyll fluorescence characteristics of this species. Data showed that S. polycystum exhibited a relatively broad tolerance to various environmental conditions, and grew well in different conditions of temperature, salinity, and irradiance, ranging from 15 to 25 °C, 20–40 PSU, and 10–80 μmol photons·m−2·s−1. The maximum RGR of S. polycystum occurred at 23 °C, 32 PSU, and 20–80 μmol photons·m−2·s−1 (P < 0.05). Temperature had a significant effect (P < 0.05) upon RGR and the chlorophyll fluorescence characteristics of S. polycystum, and lower temperature (10 °C) led to rapid reductions in the maximal photochemical quantum yield of photosystem II (F v/F m) and non-photochemical quenching (NPQ) values. Salinity exhibited a relatively weak effect upon the growth of S. polycystum, and the plant was able to survive at salinities from 16 to 40 PSU; during a two-week cultivation period, significant differences in RGR were not observed among different salinity conditions until 2 weeks of cultivation. Chlorophyll a and carotenoid content of S. polycystum decreased as irradiance increased (P 80 μmol photons·m−2·s−1). These physiological data provide valuable data related to the successful cultivation of S. polycystum under controlled conditions.