Grazing on filamentous cyanobacteria by Daphnia pulicaria

I conducted short-term grazer-gradient experiments to assess direct mortality effects of Daphnia pulicaria on phytoplankton species in natural lake phytoplankton assemblages that contained 20-80% filamentous cyanobacteria by biovolume. Filamentous cyanobacteria often interfere with feeding by large cladoceran zooplankton such as D. pulicaria and can limit their distribution, yet some D. pulicaria populations coexist with filamentous cyanobacteria. In my trials, D. pulicaria from Oneida Lake and Cazenovia Lake, New York, consumed three species of filamentous cyanobacteria (Aphanizomenon flos-aquae, Anabaena flos-aquae, Anabaena wisconsinense) but avoided three other species of Anabaena. Despite high filament concentrations, Daphnia consumed diatoms, flagellates, and chlorococcales and reduced overall phytoplankton abundance. Coexistence of Daphnia and filamentous cyanobacteria in these lakes apparently is facilitated by undeterred consumption of some species and avoidance of others, without substantial interference.