Short‐Term Variations in Phytoplankton Chlorophyll and Their Significance1

Abstract

Diurnal fluctuations were observed in the chlorophyll a content of natural phytoplankton populations, with the highest concentrations during the morning and afternoon, low values at midday and at night. This periodicity is similar to the daily rhythm of photosynthesis with which it appears closely related. The rate of synthesis of chlorophyll at optimal light intensity is dependent upon its previous rate of synthesis and concentration in the organisms, All of these factors strongly influence the capacity for photosynthesis at optimal light intensity and are probably the basis for the photosynthetic daily periodicity reported elsewhere.