A large fraction of planet Earth’s photosynthesis is carried out by planktonic single-celled algae in the seas. Observation and delineation of regional and seasonal changes in plankton are major concerns of biological oceanography. Historically, the problem has been focused on mapping these changes in the framework of seasonal and spatial change of ocean climatology. Early natural historians made elaborate drawings from astute observations of plankton. Recently, a major advance has come from the measurement of ocean color using Earth-orbiting satellites. The scientific basis for equating photosynthetic biology with ocean color is that the color change is due to the absorption of visible light by photosynthetic pigments of planktonic algae.