An in vivo fluorescence method for the continuous in situ estimation of phytoplankton photosynthetic characteristics

Abstract

This study proposes a simple method to continuously measure, in situ, an in vivo fluorescence characteristic of a natural phytoplankton population, using 2 flow-through fluorometers and a strong light source. By this method, phytoplankton fluorescence before (F,) and after (F,) strong illumination (2250 ~ E i n m-2 S-') was measured simultaneously with parameters of the photosynthesis vs irradiance curves. Data from 3 depths in the mixed layer, at 3 stations in the St. Lawrence Estuary, showed a strong relation between the ratio FA/FB and the photosynthetic parameters aB, Pi,,, I, and I,. The relation was particularly good with I, and I,, 2 possible indices of physiological adaptation. These results suggest that the ratio F,/FB can be used as an instantaneous in vivo index of photosynthetic characteristics. This simple measurement might prove useful for continuous spatio-temporal investigations of phytoplankton responses to their light environment in the water column.