Living conditions, abundance and biomass of under-ice fauna in the Storfjord area (western Barents Sea, Arctic) in late winter (March 2003)

The under-ice habitat and fauna were studied during a typical winter situation at three stations in the western Barents Sea. Dense pack ice (7-10/10) prevailed and ice thickness ranged over < 0.1-1.6 m covered by < 0.1-0.6 m of snow. Air temperatures ranged between -1.8 and -27.5 degrees C. The ice undersides were level, white and smooth. Temperature and salinity profiles in the under-ice water (0-5 m depth) were not stratified (T= -1.9 to -2.0 degrees C and S= 34.2-34.7). Concentrations of inorganic nutrients were high and concentrations of algal pigments were very low (0.02 mu g chlorophyll a 1(-1)), indicating the state of biological winter. Contents of particulate organic carbon and nitrogen ranged over 84.2-241.3 and 5.3-16.4 mu g 1(-1), respectively, the C/N ratio over 11.2-15.5 pointing to the dominance of detritus in the under-ice water. Abundances of amphipods at the ice underside were lower than in other seasons: 0-1.8 ind. m(-2) for Apherusa glacialis, 0-0.7 ind. m(-2) for Onisimus spp., and 0-0.8 ind. m(-2) for Gammarus wilkitzkii. A total of 22 metazoan taxa were found in the under-ice water, with copepods as the most diverse and numerous group. Total abundances ranged over 181-2,487 ind. m(-3) (biomass: 70-2,439 mu g C m(-3)), showing lower values than in spring, summer and autumn. The dominant species was the calanoid copepod Pseudocalanus minutus (34-1,485 ind. m(-3)), contributing 19-65% to total abundances, followed by copepod nauplii (85-548 ind. m(-3)) and the cyclopoid copepod Oithona similis (44-262 ind. m(-3)). Sympagic (ice-associated) organisms occurred only rarely in the under-ice water layer.