Journal of Plankton Research Vol.24 no.7 pp.723-728, 2002
© Oxford University Press 2002
Minimal algal food requirements in the presence of protozoan prey for the rotifer Brachionus calyciflorus
Leibniz—institute Of Freshwater Ecology And Inland Fisheries, Müggelseedamm 301, D-12587 Berlin, Germany
* silvia.mohr{at}mba.de
1 Present Address: Federal Environmental Agency, Department Ii 1.5, Schichauweg 58, D-14191 Berlin, Germany
2 Present Address: Potsdam Institute For Climate Impact Research, Department Of Global Change And Natural Systems, Telegrafenberg C4, D-14412 Potsdam, Germany
As recent experiments demonstrated that protozoans support reproduction of the rotifer Brachionus calyciflorus only in the presence of algal prey, we addressed the question of minimal algal food requirements in a mixed diet of algae and protozoans to ensure positive growth of B. calyciflorus. In numerical response experiments, we determined the algal threshold concentration for zero population growth of B. calyciflorus when feeding on a pure algal diet of Monoraphidium minutum, and on a mixed diet of M. minutum plus the ciliate Coleps sp. Under pure algal and under mixed food conditions, a minimum amount of 0.3 µg carbon (C) ml-1 M. minutum was needed to ensure zero population growth of B. calyciflorus. At lower algal concentrations, Coleps sp. was of low nutritional value. However, when offered in conjunction with a concentration of 0.8 µg C ml-1 M. minutum, Coleps sp. contributed equally to the reproductive success of B. calyciflorus as compared to a sole M. minutum diet. Overall, Coleps sp. can be an adequate supplement in the diet of B. calyciflorus if a sufficient amount of algal prey is available. However, at times of low phytoplankton biomass, consumption of ciliates does not necessarily confer a reproductive advantage for this rotifer.