Consumption of cyanobacteria by freshwater zooplankton: Implications for the success of 'top-down' control of cyanobacterial blooms in Australia

Two main approaches have been mooted for the management of fresh waters to prevent or control cyanobacterial blooms: a 'bottom-up' approach in which the supply of essential nutrients is restricted, and a 'top-down' or 'biomanipulation' approach in which attempts are made to restructure the food web to maximize consumption of noxious cyanobacteria by herbivorous zooplankton. In this review, the published literature is examined to gauge whether the common zooplankton of Australian fresh waters have the capacity to control cyanobacterial blooms, especially of toxic forms, and thus whether the biomanipulation approach might be applied successfully in Australia. As zooplankton assemblages in Australian inland waters are quite different in composition from those of the Northern Hemisphere, they are unlikely to respond to manipulations of trophic structure in a similar way. The most common zooplankters in Australian inland waters, calanoid copepods and rotifers, have less potential for controlling cyanobacterial blooms than do large cladocerans. The latter are common in the Northern Hemisphere and are considered requisite for the control of cyanobacterial blooms. Toxic cyanobacteria, which cause the most severe environmental problems, have well documented detrimental effects on zooplankton. The few reports of zooplankton grazing on cyanobacteria in Australian fresh waters do not indicate that native zooplankton can consume noxious cyanobacteria at the rates required for control of algal blooms. There may, therefore, be grounds for strong reservations about the likely success of programmes proposed to control cyanobacterial blooms by the manipulation of trophic structure in Australian fresh waters.