AME 62:25-38 (2011)  -  DOI: https://doi.org/10.3354/ame01455

ABSTRACT: We studied the prey selection and feeding physiology of a non-symbiotic-containing ciliate Mesodinium pulex (Class Litostomatea). In an experiment to test feeding and growth with a variety of prey, M. pulex ingested all 5 species of cryptophytes and the autotrophic dinoflagellate Heterocapsa rotundata offered as food. Despite this, it only grew on the cryptophytes Teleaulax sp. and Guillardia theta and the dinoflagellate, because ingestion rates of the other prey cells, even at very high prey concentrations, were too low to support growth. The numerical and functional responses of M. pulex fed H. rotundata were investigated in the laboratory in the light (100 µmol photons m^–2 s^–1) and in the dark. In the light, the growth rate was significantly higher than in the dark at all prey concentrations. Active photosynthesis was measured in M. pulex but our rates could not explain the increased growth rates in the light, which, instead, were mainly explained by elevated ingestion rates. We also studied the starvation response at irradiances of 100 and 50 µmol photons m^–2 s^–1 and in the dark. M. pulex survived for up to 2 wk without food, but mortality rates in the light were higher than in the dark.

KEY WORDS: Mesodinium pulex · Growth · Ingestion · Ciliate