Seasonal and spatial changes in biomass, structure, and development progress of the zooplankton community in the Barents Sea

During three cruises, in March and May 1998 and July 1999, seasonal and regional variations in biomass and vertical distribution of mesozooplankton as well as cohort development in Calanus spp. were investigated along a transect across the central Barents Sea and marginal ice zone. There were no considerable changes in zooplankton biomass between the seasons. Throughout the investigation, the average biomass for the entire region approximated to ca. 5 g dry weight (DW) m−2 while station-to-station variation ranged with an order of magnitude (1–14 g DW m−2). Biomass of nauplii and small copepods (200–500 μm in body length) obtained from water bottles samples exceeded that from WP-2 net samples 1.5–6.6 times. The maximum abundance of this group reached 16×105 ind. m−2 in the upper 100-m layer, suggesting a significant grazing pressure on phytoplankton. Spatial distribution of Calanus species and some selected species suggests that the zooplankton community composition was primarily affected by water mass circulation and bottom topography. Both the depth distribution of mesozooplankton and cohort progress in Calanus finmarchicus and Calanus glacialis revealed two waves of spring events. The first started in the southernmost area of the Barents Sea and the second nearby the Polar Front. Both developed towards the north.