Abstract

Variations in growth rate, thickness of the internal cortical and medullary cell walls, and carrageenan yield of the red alga Tichocarpus crinitus grown under differing irradiances were studied from June to October, when the algae were present in the non-reproductive sterile form. Growth rates were related to irradiance and seasonal patterns in water temperature. The highest growth rate (2.42% d⁻¹) was found in the temperature range 20–24 °C in August. Optimal irradiance was found to be in the range of 10−15% of the incident PAR, i. e. approximately 150−160 μE m⁻² s⁻¹ at midday. Irradiance of approximately 90% of the incident PAR induced a large decrease in growth rate plus bleaching and tissue necrosis. The thickness of the cortical cell walls showed large variations between light treatments with high values being found at low irradiances. In contrast, medullary cell walls showed little change in thickness. Phycocolloid yield had the highest value (35.5% DM) in August and the lowest value (11% DM) in October, and was positively related to the growth rate of the algae during the main growing season. Data from ¹³C-NMR and FTIR spectroscopy indicated that the polysaccharides extracted from the sterile form of T. crinitus were predominantly κ/β bhybrid with λ-type carrageenans. They are localized in the internal cortical tissue of the T. crinitus thalli and their accumulation is negatively correlated with photon irradiance, which leads to non-gelling polysaccharides predominating at low irradiances.