Freshwater cyanobacteria perform a substantial part of the primary productivity of various aquatic systems worldwide. However these cyanobacteria can form blooms which can be toxic. In recent decades there has been an ongoing global increase in harmful cyanobacterial blooms. It is predicted that cyanobacterial dominance will intensify in the future. These blooms received substantial scientific and public attention due to their significant effect on the aquatic ecosystems they invade and on water quality. Both phages (viruses of bacteria) and eukaryotic grazers play a significant role in the top-down control of cyanobacteria, but the selection pressures they apply are different. ​