Calanus spp. grazing affects egg production and vertical carbon flux (the marginal ice zone and open Barents Sea)

Concentration of faecal pellets of Calanus finmarchicus, Calanus glacialis, and Calanus hyperboreus, as well as eggs and nauplii of the first two species in the upper 0–100 m layer, were estimated during 24-h stations in the marginal ice zone and the open Barents Sea in March, May, and July. The importance of Calanus spp. as major contributors to suspended matter and vertical flux was confirmed, as the proportion of their faecal pellets was high and rather stable in the upper 100 m layer throughout the study period, varying between 48% and 95% of total suspended pellet carbon (maximum dimension >50 μm) and comprising more than 50% of sediment matter. Feeding activity of calanoid copepods was not correlated with the seasonal changes in total phytoplankton carbon, but with assumed preferred food. Egg production was correlated with feeding activity depending on the temporal scales of the study (monthly, daily, hourly). A significant positive correlation between egg and faecal pellet concentration on a monthly scale, a weak significant (C. finmarchicus), or, insignificant (C. glacialis) positive correlation between daily egg and faecal pellet production, and a significant negative correlation between hourly egg and faecal pellet production (C. finmarchicus) were obtained. Significant correlations between indices of current feeding activity (or, available food), egg production and nauplii concentration obtained in the field suggest that current feeding, not lipid reserves, played a major role in supplying the energy for reproduction of C. finmarchicus and C. glacialis.