Abstract
The maximum density that algal cells can reach in culture varies as the -1.27 power of the cell volume. This size-dependent density boundary results in a size-dependent biomass boundary, with the maximum biomass changing as the -0.32 power of cell volumes. The existence of size-dependent maximum biomass and density appears to be the consequence of algal self-shading, the efficiency of light absorption being dependent on cell size. The size-dependent density and biomass boundaries are comparable to the qualitatively similary boundary described by the -3/2 power for higher plants.