Response of lake phytoplankton communities to in situ manipulations of light intensity and colour

Abstract

Phytoplankton preferences for light intensity and colour were determined in field experiments using coloured plexiglass cubes suspended at different depths in Heney Lake, Québec. Diatoms and green algae favoured intensities greater than 1% I_o (surface irradiance) contrary to dinoflagellates and other flagellates that preferred lower intensity. Red radiation usually increased the relative proportion of blue-greens, diatoms and green algae, whereas it reduced that of dinoflageilates. We propose that differential utilization of the light gradient allows certain phytoplankton taxa to partition the water column, thereby reducing potential competition. This is supported by the general agreement between our findings and the known depth distribution of algae in lakes.