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

Investigation of light conditions suitable for cultivation of Gelidium pulc hellum (Turner) Kurtz was performed under controlled laboratory conditions at 20 degrees C and in the range of irradiance of 10-430 mu mol photons m(- 2) s(-1). Growth, measured as fresh weight increment, increased with irradi ance up to 130 mu mol m(-2) s(-1) and no significant photoinhibition was ob served up to 430 mu mol m(-2) s(-1). Maximum growth rate (10.0% day(-1)) wa s obtained at 130-240 mu mol m(-2) s(-1) under continuous light and aeratio n. The effect of irradiance on agar yield and quality was assessed. Agar yi eld 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 d egrees C increased with increasing irradiance. A similar trend was found fo r sulphate content in both series of extracts, at 95 and 121 degrees C. On the contrary, the molecular weight and the degree of methylation of agar mo lecules in the 95 degrees C extracts decreased with increasing light intens ity. As a consequence of the variations in sulphate content, molecular weig ht and molecular weight distribution, the gel strength was considerably low er at high light intensity. Starch content varied from 0.9 to 7.7% of the a lgal dry weight, and apparently was not related with irradiance.