Effects of colonial morphology on zooplankton utilization of algal resources during blue‐green algal (Microcystis aeruginosa) blooms1

Abstract

Experiments were conducted to test the following proposed mechanisms whereby blooms of colonial blue‐green algae (Microcystis aeruginosa) may more negatively affect large‐bodied cladocerans than other zooplankton taxa: that colonial morphology most strongly interferes with the feeding of larger cladocerans, and that larger cladocerans more readily ingest toxic or nonnutritious colonial blue‐greens. Experiments were conducted with both colonial and unicellular M. aeruginosa, in order to distinguish the effects of coloniality from chemical inhibitory factors associated with blue‐green algae. Experiments with colonial M. aeruginosa provided some support for both mechanisms, particularly with the cladoceran Diaphanosoma brachyurum. However, some small‐bodied species associated with blue‐green algal blooms did not conform to the proposed mechanisms, showing relatively strong reductions in clearance rates in the presence of colonial M. aeruginosa (Bosmina longirostris, Ceriodaphnia quadrangula) or relatively high consumption of colonial M. aeruginosa (Brachionus calyciflorus, B. longirostris). Our results indicate that, contrary to earlier proposals, neither body size, taxonomic position, nor association with blue‐green algal blooms are good predictors of the response to colonial M. aeruginosa.