Field studies on zooplankton‐cyanobacteria interactions

Abstract

Correlative field evidence suggests that large grazers such as Daphnia pulex promote the growth of colonial cyanobacteria by selectively eating competitive phytoplankton. This is supported by experimental evidence that (1) in eutrophic lakes dominated by cyanobacteria grazing by zooplankton on small particles is often > 100% day ‐1 , and (2) colonial cyanobacteria are generally not grazed as rapidly as smaller phytoplankton. Cyanobacteria generally have deleterious effects on grazing zooplankton. Filamentous cyanobacteria such as Anabaena and Oscillatoria can inhibit filtering by cladocerans, reducing growth and reproduction. Detrimental effects on zooplankton via nutritional deficiencies and toxins of cyanobacteria have been demonstrated in the laboratory but not in the field. Grazing on colonial cyanobacteria by zooplankton appears to be an important trophic link in tropical lakes. Generally, calanoid copepods seem best adapted to utilising large cyanobacteria. The generalisation that, with increasing eutrophication, zoo‐plankton communities tend to shift from a dominance of calanoid copepods to cladocerans, does not apply to lakes in New Zealand.