Wax-ester mobilization by female Calanus finmarchicus (Gunnerus) during spring ascendance and advection to the Faroe Shelf

Time of ascendance and initiation of reproduction in Calanus finmarchicus is closely correlated with the phytoplankton spring bloom. However, significant egg production can take place before the bloom, fuelled by mobilizing stored wax-ester lipids. Calanus finmarchicus from stations on the Faroe Shelf were compared with specimens collected off the shelf. Biological parameters such as gut contents, egg production, developmental stage, and lipid content were determined and correlated with phytoplankton concentration and spatial distribution along two transects in late April 2003 across the shelf northeast and southwest of the Faroe Islands. Grazing by C. finmarchicus on phytoplankton was significantly lower northeast of the Faroe plateau. However, the egg production was generally high for a pre-bloom situation, with significantly higher rates of egg production on the shelf than off it, along both transects. Wax-ester content of female C. finmarchicus was significantly higher and more variable at off-shelf stations than on the shelf (<2 µg female⁻¹). From this, we suggest that off-shelf C. finmarchicus had recently emerged from overwintering depths, in contrast to individuals from stations on the shelf, which had been in the upper water masses for some time. Females (from off-shelf stations) most likely supported the initial egg production from their wax-ester reserves.