Studies on carrageenans and effects of seawater phosphorus concentration on carrageenan content and growth ofAgardhiella subulata (C. Agardh) Kraft and Wynne (Rhodophyceae,Solieriaceae)

Gas liquid chromatography, chemical analyses, and infrared and¹³C-NMR spectroscopies indicated that phycocolloids extracted fromAgardhiella subulata had a dominant ι-carrageenan feature with less deviant ι-carrageenan and υ-carrageenan. The presence of methylated galactose and a small contamination by xylose were registered. Unattached plants were cultivated for 4 weeks in tanks receiving seawater enriched with 53.5 µM nitrate and 0 to 20 µM phosphate (P_i) week^?1. The growth was phosphorus (P)-limited up to a tissue P content of 0.14 ± 0.03% dry weight. Maximal specific growth rate and carrageenan content were observed with enrichments of 6 µM P_i and 3 µM P_i, respectively. Hence carrageenan production was promoted in the range of 3–6 µM P_i. Further P_i enrichment was useless. This phenomenon, observed with P nutrition, is comparable to the ‘Neish effect’ in nitrogen nutrition studies.