Mesozooplankton in the Kola Transect (Barents Sea): Autumn and winter structure

The spatial distribution of mesozooplankton was investigated in relation to environmental conditions along the Kola Transect (69 degrees 30'-79 degrees 00'N, 33 degrees 30'E) during autumn (September 2011) and early winter (mid-November 2012). Mesozooplankton abundance averaged 964 and 740 individuals m(-3) and biomass averaged 55 and 32 mg dry mass m(-3) in 2011 and 2012, respectively. Cluster analysis showed good accordance of the mesozooplankton assemblages with the three main types of water masses present in the region. The first assemblage, dominated by Calanus fitunarchicus and Oithona sitnilis, but including neritic taxa, was associated with Murmansk Coastal Water. The second assemblage, with Calanus spp. contributing the majority of the total mesozooplankton biomass, was connected with Atlantic waters. The third assemblage, dominated by Calanus glacialis, was associated with cold Arctic waters. Redundancy analysis revealed that the explanatory factors significantly influencing the community structure of mesozooplankton were surface and bottom temperature, and depth of the sampling layer. Almost 64% of the total mesozooplankton fluctuations could be explained by changes in these environmental variables. Inter-seasonal changes in the structure of mesozooplankton were associated with higher abundances of Calanus hyperboreus, Copepoda nauplii, Microsetella norvegica, Aglantha digitale, Oikopleura vanhoeffenni, and Mertensia ovum and lower numbers of Oithona atlantica and young stages of Paraeuchaeta spp. in September 2011. Regional and seasonal comparisons of the total mesozooplankton biomass observed in the present study with sample data from the summer of 2003-2012 suggest that the mean values were higher in autumn season of 2011 due to differences in sampling layers.