Abstract
Examination of the allometric scaling of light absorption (a
cell
) and scattering (b
cell
) by 28 phytoplankton species showed that light absorption is scaled to the cross-sectional area of the cells (log a
cell
(square micrometres per cell) = −1.06 + 2.32 log d (micrometres)) whereas light scattering is scaled to their volume (log b
cell
(square micrometres per cell) = −1.09 + 3.45 log d (micrometres)). The scaling of light absorption to the cross-sectional area of algal cells is explained by a decrease in intracellular chlorophyll a concentration as cell size increases, thereby avoiding inefficient light capture by photosynthetic pigments. The scaling of light scattering to cell volume conforms to the general theory for large particles (Mie theory). Light absorption by phytoplankton cells, unlike light scattering, deviates from that of nonliving particles because of the covariation between pigment content and cell size that help prevent self-shading.