Diel variations in marine phytoplankton
Date
1972
Authors
Drinnan, R. W. (Robert Warren)
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Abstract
Diel variations in chlorophyll α concentration, photosynthetic potential and total particulate volume were followed in several marine environments. In an inshore location, all three measurements showed a diel variation at the surface, with maximum values during the day and minimum values in the dark period, but only the photosynthetic potential measurements continued to show a diel rhythm after correction for biomass changes. At 30 meters, there was no apparent diel variation in chlorophyll α concentration or total particulate volume but a slight rhythm, similar in phase to the surface rhythms, existed for photosynthetic potential. This rhythm continued when corrected for biomass changes, although the amplitude was much less than at the surface.
A similar diel rhythm for photosynthetic potential (with a maximum during the day and a minimum at night), was found to occur in two locations in the open ocean. Laboratory experiments on natural phytoplankton populations, showed identical rhythms in photosynthetic potential as measured in situ. The rhythms were found to continue during an extended dark period, and the timing of the maxima and minima could be altered by changing the light-dark cycle.
The rhythms in photosynthetic potential were not caused by changes in cellular chlorophyll α. In addition, temperature, salinity, nitrate concentration and the daily variations in light intensity were not believed to be directly responsible for the observed rhythms.