To determine the mechanism underlying this pattern, we observed the interactions between fluorescently stained zoospores and six microorganisms used in experiment 5: two that had the weakest impact on zoospore viability (Dileptus anser and S. coeruleus), two that had the greatest impact (P. caudatum and Notommatidae spp., experiment 6), and the two species isolated from Pyrenean sites (P. aurelia and L. stichaea). Our observations suggest that the process through which viability is affected is due at least in part to ingestion of zoospores.