Bloom formation and stratification by a planktonic blue-green alga in an experimental water column

Abstract

The growth and buoyancy of the planktonic blue-green alga Anabaena flos-aquae Breb. was studied under different nutrient conditions in small batch cultures and in a thermally stratified water column. When conditions permitted the development of high algal concentrations, the diffusion of C02 into the culture limited the photosynthetically driven buoyancy-regulating response and the filaments became buoyant. Under similar conditions in the water column C02 again became limiting and the alga floated up to form a waterbloom at the surface, even though the incident light intensity there was 10 klx (200 fiE s"1 m 2). When growth of the alga in culture was limited by reducing the concentration of K2EfP04 the alga sank, even when the light intensity was only 1-7 klx. The alga no longer formed a surface water bloom in the column when the K2HP04 concentration was reduced to 10 jum, but instead it stratified at a depth of about 1 m, where the light intensity was about 1 -2 klx. The behaviour of the alga in the column is reminiscent of that shown by certain planktonic blue-green algae in natural lakes. © 1981 Taylor & Francis Group, LLC.