Meta-analysis of cyanobacterial effects on zooplankton population growth rate: species-specifi c responses

We analyzed a large data set of laboratory experiments to examine the effects of cyanobacteria containing or lacking intracellular toxic metabolites and of different morphology on zooplankton population growth rates across multiple genera and species of cladocerans, rotifers and cyanobacteria. Twenty-one of the 29 zooplankton species maintained positive growth rates when fed a diet containing cyanobacteria even though cyanobacteria were a poor food source for half of the zooplankton species tested relative to a diet containing only green algae and/or fl agellates. Differences among zooplankton species could not be explained by grazer species body lengths, even when experiments were restricted to those that used only fi lamentous cyanobacteria. Single-celled cyanobacteria were more detrimental to a larger number of zooplankton species compared to fi lamentous or chroococcoid colonial cyanobacteria. We also found no clear effect of putative cyanobacterial toxins on the growth of seven zooplankton species but we did detect a negative effect for the largest cladoceran species, Daphnia magna. Among the cyanobacterial genera, Microcystis had the largest negative effect on zooplankton population growth and there was no consistent difference between M. aeruginosa strains that produced microcystins and those that did not. Our results highlight the large variation in species-specifi c responses of zooplankton to cyanobacteria. Although cyanobacterial toxicity and mechanical interference may be important drivers in particular cyanobacteria-zooplankton interactions, we did not fi nd general support for these mechanisms through the use of this meta-analysis.