Nutritional suitability of the dinoflagellate Ceratium furcoides for four copepod species

Abstract

The nutritional suitability of Ceratium furcoides for Eudiaptomus gracilis, Mesocyclops leuckarti, Thermocyclops oithonoides and Cyclops abyssorum was studied by observing ingestion and assimilation. The dinoflagellate was ingested by female adults of all species. The calanoid copepod E.gracilis could not utilize Ceratium; mortality was high and no egg production was observed when Ceratium was the only food source. Mortality was low for the adult cyclopoids on this food and reproduction indicated that Ceratium was assimilated. The first two copepodite instars of M.leuckarti were not able to handle Ceratium, while older stages preyed on them. The dinoflagellate was not ingested by female M.leuckarti when its densities were low. Advanced copepodite stages of C.abyssorum developed into adults on a diet of Ceratium only. Mesocyclops leuckarti females ingested Ceratium when offered a mixed food source of Ceratium and the rotifer Brachionus rubens, but the rotifer was positively selected, even if its density was low. The results show that Ceratium provides a suitable food source for advanced copepodite instars and adult cyclopoid copepods, although it is not a preferred food source.