LIGHT ENVIRONMENT WITHIN DENSE ALGAL POPULATIONS - CELL-SIZE INFLUENCES ON SELF-SHADING

The influence of algal cell size on the light environment within dense phytoplankton populations was analysed in cultures of 11 freshwater algae (mostly Chlorophyta) varying widely in cell size and growing at saturated (220-mu-M m-2 s-1) and limited (11-mu-M m-2 s-1) irradiances. Chlorophyll-a-specific absorbance coefficients did not bear any obvious relationship to cell size and, as expected from previous analyses, were strongly influenced by the light intensity at which the algae were grown. However, biomass (fresh weight)-specific absorbance coefficients decreased as algal cell volume increased regardless of the incoming irradiance. Intracellular chlorophyll a concentration (c(i)), which decreased as algal cell size increased, explained a substantial fraction of the variance in biomass (fresh weight)-specific absorbance coefficients. Thus, this study supports the notion that reduced self-shading allows large algae to support greater maximal biomass than smaller algae.