It has been shown (Riley, 1946, 1947) that seasonal changes in total phytoplankton populations can be depicted with a reasonable degree of accuracy by a simple theoretical construction in which the rate of change of the population is described in terms of physiological processes that increase or decrease its organic content (photosynthesis, respiration, grazing), and in which the rates of the individual processes are quantitatively predictable by reference to a few environmental factors....