Feeding and reproduction of Calanus finmarchicus during non-bloom conditions in the Irminger Sea

Simultaneous ingestion and egg production experiments were conducted with female Calanus finmarchicus in April/May and July/August 2002 in the Irminger Sea. Experimental animals were provided with natural microplankton food assemblages and incubated under in situ conditions for 24 h. The quantity of food consumed was significantly related to the concentration of prey cells, with total daily ingestion rates ranging from 0.6 to 8.1 μg of carbon female ^-1 day^-1, corresponding to carbon-specific rates of 0.6-4.7% day^-1. Egg production rates (EPRs) remained relatively low (0.3-11 eggs female^-1 day^-1) during both periods of investigation and were not influenced by food availability. The data were used to construct energetic budgets in which the microplankton carbon ingested, including ciliates, was compared with the carbon utilized for egg production and respiration. These budgets showed that ingestion alone could not provide the necessary carbon to sustain the observed demands for growth and metabolism. Although ciliates constituted >80% of the total material ingested at times, they were not sufficient to provide the metabolic shortfall. Indeed, the females were typically lacking ∼5 μg of carbon each day, ∼5% of their carbon biomass. Our study results highlight the possible importance of internal reserves in sustaining reproduction in C. finmarchicus during periods of food scarcity.