Saage, Andrea (2006) A comparison of phytoplankton and ciliate feeding by marine calanoid copepods. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, 73 pp.

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Abstract

The feeding behaviour of the marine calanoid copepods Calanus finmarchicus and Centropages hamatus was studied in several laboratory experiments, and the trophic position of C. finmarchicus in the Trondheim Fjord in 2004 was determined through stable isotope analyses. Calanus finmarchicus showed a feeding threshold on algal prey (dinoflagellates) at a concentration of ~60 μg C l-1 (stage CV), whereas ciliates (oligotrichs) were ingested irrespective of ciliate concentration (adult females). The ingestion rate as a function of ciliate concentration could be described by a Holling type III functional response with beginning saturation at ~150 μg C l-1. At prey concentrations >120 μg C l-1 ingestion of algae was higher than that of ciliates, but did not follow typical saturation kinetics. Due to missing data no maximum ingestion could be identified, and at high concentrations ingestion of algal prey declined, probably due to aggregation of cells. Furthermore, C. finmarchicus (adult females) seemed to prefer larger cells out of a mixture, regardless of species specific or total concentration, and to avoid cells <9 μm when larger cells were available. The trophic position of C. finmarchicus in the Trondheim Fjord in 2004 was trophic level 2.2, thus indicating a moderate degree of omnivory under natural conditions. Centropages hamatus (adult males and females) started feeding on algal (flagellates, diatoms) and ciliate prey (oligotrichs) at concentrations of ~5 μg C l-1, and the ingestion rate as a function of prey concentration could be described by a Holling type III functional response. In general, ingestion of ciliates was higher than ingestion of algae, and adult males showed lower feeding rates than adult females at prey concentrations >50 μg C l-1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as soon as those contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching.

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