EFFECT OF NITROGEN AND PHOSPHORUS SUPPLY ON GROWTH AND TISSUE COMPOSITION OF ULVA-FENESTRATA AND ENTEROMORPHA-INTESTINALIS (ULVALES, CHLOROPHYTA)

The chlorophyte macroalgae Ulva fenestrata (Postels and Ruprecht) and Enteromorpha intestinalis (Linnaeus) Link. were grown under various nutrient regimens in indoor semi-continuous and batch cultures. Tissue nitrogen contents ranged from 1.3-5.4% N (dry wt), whereas tissue P ranged from 0.21-0.56% P (dry wt). Growth in low nitrogen medium resulted in N:P ratios of 5-8, whereas growth in high nitrogen medium resulted in N:P ratios of 21-44. For U. fenestrata, tissue N:P < 16 was indicative of N-limitation. Tissue N:P 16-24 was optimal for growth and tissue N:P > 24 was indicative of P-limitation. Growth of U. fenestrata was hyperbolically related to tissue N but linearly related to tissue P. Phosphorus-limited. U. fenestrata maintained high levels of tissue N, but N-limited algae became depleted of P. For E. intestinalis, tissue N remained at maximum levels during P-limitation whereas tissue P decreased to about 85% of maximal levels during N-limitation. Growth rates for U. fenestrata decreased faster during P-limitation than during N-limitation. Simultaneously, tissue P was depleted faster than tissue N. Our results suggest that comparing tissue N and P of macroalgae grown in batch cultures is useful for monitoring the nutritional status of macroalgae.