Role of light, carbon dioxide and nitrogen in regulation of buoyancy, growth and bloom formation of Anabaena flos-aquae

The availability of light, CO2 and NH4-N interacted to control buoyancy and growth of the gas vacuolate blue-green alga, Anabaena flos-aquae. At high light intensities algal growth rates were high; however, the alga was non-buoyant regardless of the availability of CO2 or NH4-N. The mechanism for buoyancy loss involved increased cell turgor pressures at higher light intensities which resulted in collapse of gas vacuoles. At lower light intensities algal growth rates and cell turgor pressures were reduced and buoyancy was controlled by the availability of CO2 and inorganic nitrogen. Carbon dioxide limitation increased buoyancy, while reduced inorganic nitrogen availability reduced buoyancy. Mechanisms for buoyancy regulation at low light intensities involved changes in cellular C/N ratios which appeared to affect the rate of synthesis and accumulation of protein-rich gas vacuoles. Algal specific growth rates were combined with buoyancy data to form a single index (μbloom) to the rate of surface bloom formation of A.flos-aquae as a function of the availability of light, CO2 and NH4-N. The bloom formation index was enhanced with decreased availability of light and CO2, and increased availability of NH4-N.