Circadian photosynthetic activity of natural marine phytoplankton isolated in a tank

Abstract

A large (1200 1) seawater sample from the Gulf of Maine was kept under constant temperature and light conditions for a period of 72 h. Circadian variations were observed in the photosynthetic capacity (PBmax) and efficiency (αB); these occurred in phase, and were not related to changes in chlorophyll α concentrations. Such observations are consistent with the hypothesis that oscillations in photosynthetic characteristics of natural phytoplankton are mediated by an endogenous circadian rhythm.