Zooplankton Feeding Selectivity for Unicellular and Colonial Microcystis Aeruginosa

Feeding selectivity experiments were conducted with a variety of herbivore taxa using the blue-green alga Microcystis aeruginosa in both a unicellular and a colonial morphology. The rotifer Brachionus calyciflorus and the cladoceran Bosmina longirostris fed nonselectively in mixtures of colonial M. aeruginosa and the nutritious green alga Chlamydomonas reinhardi. Other cladocerans selected against the colonial strain, but did not avoid unicellular M. aeruginosa, indicating that their selectivity was based primarily on colony size. Copepods strongly avoided consumption of M. aeruginosa of either morphology, probably in response to chemosensory stimuli. Zooplankton selectivity in algal mixtures including the unicellular strain was not accurately predicted by filtering rates in unialgal experiments, because of inhibitory effects of unicellular M. aeruginosa on filtering rates. Prior acclimation to M. aeruginosa did not influence selectivity, but apparently did inhibit filtering rates.