Feeding of Calanus finmarchicus nauplii in the Irminger Sea

Recent studies have shown that the passage from nauplius to copepodite is a key event in the population dynamics of Calanus finmarchicus. As a first step towards understanding if and how trophic interactions influence this event, we investigated the feeding of C. finmarchicus nauplii IV-VI in the Irminger Sea during spring and summer in a series of incubation experiments, Generally, feeding efficiencies were highest on large cells, whereas small flagellates were ingested at very low rates. Colonies of Phaeocystissp. were not ingested. Among the larger cells, the diatoms Chaetoceros pelagicus and Tropodineis sp. and the ciliate Strombidium sp. were the main food sources. We observed a negative relationship between the percentage of diatoms in the food environment and the filtration rate on Strombidium sp. We therefore suggest that the combination of low feeding efficiency on small cells and the generally low concentrations of cillates in oceanic waters explains why C. finmarchicus relies on phytoplankton blooms for recruitment from nauplius to the first copepodite stage.