Regulation of blue-green algal buoyancy and bloom formation by light, inorganic nitrogen, CO2, and trophic level interactions

Studies conducted in highly eutrophic ponds showed that buoyancy and surface bloom formation of Anabaenopsis elenkinii (a gas-vacuolate cyanobacterium) were markedly enhanced by increased light intensity and, to a lesser extent, by decreased availability of carbon dioxide and increased availability of inorganic nitrogen. It was also observed that the spring and early summer blooms of diatoms and green algae reduced light penetration in the ponds, and enhanced the buoyancy and subsequent bloom formation of blue-green algae. In pond 1, which contained no fish, grazing by large cladocerans limited the growth of diatoms and green algae, light penetration remained good, and there was no A. elenkinii bloom. In pond 3, which supported dense populations of planktivorous fish, cladoceran densities were low throughout spring and summer, and the resultant development of diatom and green algal blooms favoured the subsequent occurrence of dense surface blooms of cyanobacteria.