Feeding, reproduction and seasonal development of Calanus finmarchicus in relation to water masses and phytoplankton in the southern Norwegian Sea

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In the southern Norwegian Sea, two different water masses dominate in the upper layers: cold water from the East Icelandic Current in the western part and warmer Atlantic water in the eastern and southernmost part. In spring the stratification is stronger in the cold East Icelandic Current Water (EICW) than in the Atlantic Water (AW) and the phytoplankton biomass usually increases earlier in spring in the EICW than in the AW. In both water masses the copepod Calanus finmarchicus is the dominant secondary producer. The paper describes horizontal, interannual, and seasonal variability in C. finmarchicus in relation to hydrography and phytoplankton in the AW and EICW. Abundance, maturity, reproduction and ingestion rates of C. finmarchicus in spring and seasonal development of the copepod in these two water masses are described and related to phytoplankton and hydrography. The reproduction of C. finmarchicus starts significantly earlier in spring in the AW than in the EICW, and 2 generations are produced in the AW while only on is produced in the EICW. Measurements in May 2002 have showed that in despite of high phytoplankton concentrations in the EICW, the phytoplankton mean ingestion rate was in average 1.7 times higher in the AW. Also the mean proportion of mature females was 1.7 times higher and the mean egg production rate was 1.8 times higher in the warm AW than in the cold EICW.