Observations were made on the vertical distribution of colonies of
Aphanizomenon flos-aquae for 9 d at a drift-station east of Bornholm
Island in the Baltic Sea. The buoyant colonies were dispersed in the upper
layers of the
water column during periods of wind-induced mixing but floated up during
calm periods. From measurements
of the vertical light extinction, surface irradiance and the photosynthesis
versus irradiance curve, calculations were
made of the changes in the daily integral of photosynthesis with respect to
time and depth throughout the water
column. From these calculations it is demonstrated that net photosynthesis
by the population of Aphanizomenon
flos-aquae increased nearly threefold by floating up after a deep
mixing event. It is estimated that, averaged over
alternating periods of calm and mixing, the buoyancy provided by gas
vesicles in this organism will result in a
nearly twofold increase in photosynthesis. A quantitative analysis has been
made of the relationship of the daily
integral of photosynthesis by the Aphanizomenon population with the
mean depth of the population in the water
column and the daily insolation. The analysis shows that the integral
decreases linearly with respect to mean depth.