Calanoid copepods feeding on algae and filamentous cyanobacteria: rates of ingestion, defaecation and effects on trichome length

The relative abilities of freshwater calanoid copepods to graze algae and filamentous cyanobacteria were examined in three species of Boeckella (B.triarticulata, B.hamata, B.dilatata) fed Cydotella, Cryptomonas and two species of Nostoc and Anabaena. Although rates of ingestion were highest on Cryptomonas, all the Boeckella species consumed cyanobacteria, some species at similar rates to Cyclolella. Faecal production on the foods was highest on Cydotella and, in B.triarticulata, higher on A.flos-aquae and Nostoc sp. 2 than on Cryptomonas. At 1 mg l−1 of these cyanobacteria, female B.triarticulata voided 70% by volume of the material they ingested as compact faecal pellets. By their grazing they also decreased dramatically the trichome lengths of A.flos-aquae, A.oscillarioides and Nostoc sp. 2, thereby possibly altering the potential susceptibility of these filamentous cyanobacteria to grazing by other zooplankton.