The effect of light on growth and agar content of Gelidium pulchellum (Gelidiaceae, Rhodophyta) in culture

Abstract

Investigation of light conditions suitable for cultivation of Gelidium pulchellum (Turner) Kurtz was performed under controlled laboratory conditions at 20 °C and in the range of irradiance of 10-430 μmol photons m-2 s-1. Growth, measured as fresh weight increment, increased with irradiance up to 130 μmol m-2 s-1 and no significant photoinhibition was observed up to 430 μmol m-2 s-1. Maximum growth rate (10.0% day-1) was obtained at 130-240 μmol m-2 s-1 under continuous light and aeration. The effect of irradiance on agar yield and quality was assessed. Agar yield varied from 31 to 38.6% of the algal dry weight, and variation was not related to irradiance. However, the yield of agar molecules soluble at 95 °C increased with increasing irradiance. A similar trend was found for sulphate content in both series of extracts, at 95 and 121 °C. On the contrary, the molecular weight and the degree of methylation of agar molecules in the 95 °C extracts decreased with increasing light intensity. As a consequence of the variations in sulphate content, molecular weight and molecular weight distribution, the gel strength was considerably lower at high light intensity. Starch content varied from 0.9 to 7.7% of the algal dry weight, and apparently was not related with irradiance.