In situ measurement of state transition in cyanobacterial blooms:kinetics and extent of the state change in relation to underwater light and vertical mixing

Abstract

ABSTRACT. Measurements of spectral scalar irradiance were made in a shallow estuarine system during a phytoplankton bloom in summer 1994. High concentrations of dissolved organic matter (DOM) and pigments resulted in strong attenuation of light within the upper 1 m of the water column. Spectral analysis showed an increase in the ratio of far-red p 7 0 0 nm) irradiance to total photosynthetically available radiation (PAR) as depth increased. Under these conditions it is expected that state transition may occur, as far-red light is preferentially absorbed by Photosystem 1 (PSI). Measurements of fluorescence emission at 77K from natural phytoplankton samples as well as from laboratory-grown unialgal cultures showed that redistribution of excitation energy between the photosystems occurred in response to changes in the spectral light environment. Exposure to the far-red-enriched lower euphotic zone induced State 1 (whereby more light energy was directed towards Photosystem 2, PS2), whereas algae reverted to State 2 (redirection of light energy away from PS2) at the surface or after exposure to near-dark conditions at the bottom of the euphotic zone. Differences in the kinetics of state transition between green algae and cyanobacteria together with estimation of the wind-induced mixing time of the water column are discussed with respect to photoacclimation. For both natural phytoplankton and laboratory cultures, state transition occurred on a time scale equal to or faster than the time required for 1 vertical mixing cycle. The faster response of cyanobacteria to changes in spectral irradiance in the water column may be an important factor contributing to cyanobacterial dominance in hypertrophic waters under light-limited conditions.

Predicting Light Acclimation in Cyanobacteria from Nonphotochemical Quenching of Photosystem II Fluorescence, Which Reflects State Transitions in These Organisms

“…In variable light environments (Schubert et al, 1995a(Schubert et al, , 1995b, cyanobacteria experience large and rapid change in irradiance, and the light level to which they acclimate may prove to be a complex function of severa1 environmental and physiological factors. The generality of the pattern suggests that mixed populations will prove amenable to the prediction.…”

Phytoplankton diversity and photosynthetic acclimation along a longitudinal transect through a shallow estuary in summer

“…Although responses of the phytoplankton community to selected levels of variability (spectral shift, UV exposition) were investigated in experimental systems and at selected locations (Schubert et al 1995, the different levels of variability usually prevent a simple inspection of phytoplankton irradiance acclimation along the longitudinal transect. In the present approach, some significant sources of variability were reduced by the selection of the sampling period and sampling scheme.…”

“…Under bloom conditions, sophisticated irradiance acclimation mechanisms can be detected in situ (e.g. Schubert et al 1995). This suggests that a low diversity of higher phytoplankton taxa may facilitate the detection of general acclimation patterns in an entire estuary.…”

Phytoplankton pigments in relation to carbon content in phytoplankton communities

“…The cellular increase in photosynthetic active pigments at the beginning of the experimental period could, however, not compensate for the severe reduction in light intensity. The photosynthetic pigments absorb poorly in green light (Johnsen et al 1992, Schubert et al 1995, which prevailed in this enclosure, and the low light intensity of a poor quality probably caused the observed extinction of the phytoplankton in the DL enclosure (Fig. 1).…”