Spatial variations in reproductive characteristics of the small copepod Oithona similis in the Barents Sea

In the Barents Sea during late summer 2006 and 2007 we investigated spatial variations in the biomass, abundance, reproductive characteristics and production of Oithona similis (copepodite stages IV to V and adults), the most abundant small copepod. The species contributed 0.1 to 15.3% of the total mesozooplankton biomass. Adults were the most abundant stage in 2006 while younger copepodites prevailed in 2007. Prosome length of all stages was negatively and significantly correlated with water temperature. The mean ( SE) relative abundance of ovigerous females and mean ( SE) clutch size were 31 +/- 1 and 38 +/- 2%; and 22 +/- 0 and 21 +/- 0 eggs per sac in 2006 and 2007, respectively. Egg diameter (D) varied from 45 (in the south) to 70 mu m (in the north). Egg production rates (EPR) varied from 0.2 to 1.8 eggs female(-1) d(-1) in both periods. Specific egg production rates (SEPR) were 0.005 to 0.029 and 0.008 to 0.04 d(-1) in 2006 and 2007, respectively, The total secondary production of O. similis varied between stations and between years from 12 to 2714 mu gC m(-2) d(-1). Copepodites V contributed the main part of the total secondary production (47 +/- 2 in 2006 and 52 +/- 3% in 2007). Multiple regression analysis showed that temperature and salinity explained 50 to 92 and 63 to 93% of the total variations in the log(10)-transformed D, EPR and SEPR in 2006 and 2007, respectively. Although 4 regions were separated on the basis of water temperature and salinity, 3 populations of O. similis were delineated by cluster analysis based on the species mean reproductive characteristics. This corresponds with our data based on the analysis of morphological parameters of O. similis in the Barents Sea (Dvoretsky & Dvoretsky 2009; Mar Ecol Prog Ser 385:165-178).