BIOSYNTHESIS OF MACROMOLECULAR AND LIPID CLASSES BY PHYTOPLANKTON IN THE NORTHEAST WATER POLYNYA

The patterns and environmental correlates of macromolecular synthesis were investigated during 1993 in the Northeast Water Polynya, a region of variable ice cover and hydrodynamic regime on the continental shel f of northeast Greenland (77 degrees to 81 degrees N). Allocation of p hotosynthate to major macromolecular classes (protein, Lipid, and poly saccharides), like phytoplankton biomass and primary production, showe d strong spatio-temporal variability. Time series observations in the central part of the polynya and correlational analysis over all statio ns provided physiological evidence of nutrient deficiency in surface p opulations as nitrate and silicate were depleted. Lipid, rather than p olysaccharide, synthesis was favoured as nutrient concentrations decre ased, and C/N assimilation ratios inferred from protein labelling reac hed very high values (>15 by weight). C/N composition ratios increased in parallel but remained lower (<10) than the assimilation ratios. Li pid synthesis shifted towards neutral lipids and glycolipids, and away from phospholipids, as nutrient concentrations declined to their obse rved minimum. At stations with a dominance of large (mainly diatom) ph ytoplankton more of the lipid synthesis was directed to glycolipids an d less to phospholipids and neutral lipids than at those dominated by small (mainly flagellate) phytoplankton, but relative allocation to to tal lipids and other macromolecular classes was not significantly diff erent between the 2 types of stations. Although both nitrate and silic ate became depleted, changes in silicate were most closely related to the physiological changes observed, consistent with a predominance of diatoms at the more productive stations.