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Effects of Nitrogen and Phosphorus on the Growth and Fatty Acid Composition of Ulva pertusa Kjellman (Chlorophyta)

The effects of nutrient levels, of nitrogen (0, 0.01, 1.5, and 15 mM as nitrate) and phosphorus (0, 1, 75, and 750 μΜ as phosphate) on the growth and qualitative fatty acid composition of the green seaweed, Uha pertusa were studied in a completely randomized laboratory experiment using an artificial seawater medium. Nutrient (nitrogen and phosphorus) starvation resulted in loss of biomass and negative specific growth rates on the 4th day of culture. Nitrogen starvation and very high levels of nitrogen (15mM) increased crude lipid content (as a percentage of dry weight). Increasing the level of nitrogen decreased the proportions of the major polyunsaturated fatty acids 16:4n-3 and 18:4n-3; and increased the proportions of 16:0, 18 : 1 n-7 and 18:2n-6. Nitrogen levels tested gave no significant effects on the other major fatty acids, 18:3n-3 and 18:4n-l . Phosphorus starvation decreased the proportions of 16 : 0 and increased that of 16 : 4n-3. Varying levels of phosphorus did not produce observable changes in the crude lipid content of the seaweed. Chlorosis was observed in nitrogen-starved cultures but not in phosphorus-starved seaweed.