ESTIMATING CARBON, NITROGEN, PROTEIN, AND CHLOROPHYLL-A FROM VOLUME IN MARINE-PHYTOPLANKTON

The size of 30 small (2-60 mum) phytoplankton species was examined wit h a microscope and a Coulter Counter before and after fixation. Acid L ugol's iodine caused cells to shrink immediately. The shrinkage effect was constant for concentrations of 1-10% Lugol's iodine (in seawater) . For optically measured cells fixed in 2% Lugol's iodine, volume of l ive cells = 1.33 x (volume of fixed cells). Coulter Counter and optica lly measured volumes did not agree. For live cells, optical cell volum e = 1.24-2.04 x (Coulter Counter determined volume); this difference i s likely due to inaccurate volume measurements of nonspherical cells b y the Coulter Counter and by inaccurate microscopy resulting from opti cal distortions (errors of <0.5 mum in cell dimensions). Cell quota es timates were presented following the relation y = ax(b), where x = opt ically measured cell volume (mum3), y = any cell constituent (pg cell- 1), and a and b are constants. The constants a and b were 0.109 and 0. 991 for carbon, 0.0172 and 1.023 for nitrogen, 0.043 and 1.058 for pro tein, and 0.00428 and 0.917 for Chl a. Our relation of carbon to volum e differs from other literature values, in which there is no consensus . Our data can be used to determine carbon, nitrogen, protein, and Chl a estimates from field material that has been fixed with Lugol's iodi ne, observed live, optically measured, or Coulter Counter measured; ho wever, the variability in published data suggests that any of these es timates will have a large potential error.