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.

Phytoplankton photoadaptation to vertical excursion as estimated by an in vivo fluorescence ratio

“…They found significant relationships between this ratio and the parameters of the photosynthesis-irradiance curves (estimated according to the model of Platt et al 1980) which are often used to characterize physiological adaptations of phytoplankton to their light environment (e. g. Talling 1957, Yentsch & Lee 1966, Platt et al 1980. In light of their results, Demers et al (1985) suggested that their fluorescence ratio, which can be continuously measured in situ, could be used as a useful tool in deriving models such as the one proposed by Lewis e t al. (1984a) to study the effects of vertical mixing on phytoplankton photoadaptation.…”

“…Using this setup, Demers et al (1985) measured the in vivo fluorescence of laboratory cultures and observed a typical relationship between the ratio F,/Fb and the time of exposure to bright light. A plateau was reached after about 15 to 20 s of exposure, and the relative level of this plateau depended on the light intensity at which the cultures were grown (see Figs.…”

“…Measurement and significance of the in vivo fluorescence ratio of Demers et al (1985). The expenmental setup used by Demers et al (1985) to measure the fluorescence ratio consists of 2 intercalibrated Turner Designs fluorometers separated by a length of transparent tubing exposed to bright light (2250 pEin m-2 S -I ), through which water is circuIated.…”

“…The expenmental setup used by Demers et al (1985) to measure the fluorescence ratio consists of 2 intercalibrated Turner Designs fluorometers separated by a length of transparent tubing exposed to bright light (2250 pEin m-2 S -I ), through which water is circuIated. The length of tubing and the circulation speed determine exposure time.…”

“…Fluorescence is an example of such a property (Lewis et al 1984a, b, Cullen & Lewis 1988. Demers et al (1985) have suggested the measure of an instantaneous in vivo fluorescence ratio for characterizing the photoadaptation status of phytoplankton in the laboratory and in the natural environment. They found significant relationships between this ratio and the parameters of the photosynthesis-irradiance curves (estimated according to the model of Platt et al 1980) which are often used to characterize physiological adaptations of phytoplankton to their light environment (e. g. Talling 1957, Yentsch & Lee 1966, Platt et al 1980.…”