A theory based on the performance of an electrical analogue circuit for balanced ecosystems relates respiration to the storage of labile organic matter during daytime photosynthesis. A very small storage capacitance and time constant may be introduced into the circuit to simulate a nannoplanktonic sygtem. It is found that respiration approaches photosynthesis during the day and almost ceases at night. Consequently, the usual carbon14 measurements of net production, and the conventional light-and-dark-bottle oxygen measurements of net production and nighttime respiration greatly underestimate gross photosy~thesis of tropical seas. An example of this phenomenon is shown in a planktonic brine microcosm.