Effect of Controlled Environmental Conditions on Starch and Agar Contents of Gracilaria Sp. (Rhodophyceae)1

The red marine alga Gracilaria sp. (collected on Israel's Mediterranean shore) was grown in the laboratory under controlled conditions. The effects of the medium (natural seawater or enriched seawater) and of irradiance on the following parameters were studied: growth rate, dry weight, content of pigments, CO2 fixation rate, starch content, and the quality and quantity of agar. The total agar content was higher in algae grown in natural seawater than in those grown in enriched seawater and decreased only slightly with increasing irradiance. The agar composition was also different in algae grown in the two media. The starch content was higher in algae grown in natural seawater than in algae grown in enriched seawater, and in algae in both media it increased with increasing irradiance. Since the starch content in Gracilaria can reach 21% on a dry weight basis, it is important to correct for in when determining the agar content.